Heat transfer engineering an international journal, tập 31, số 9, 2010

Heat Transfer Engineering, 31(9):707–710, 2010 Copyright C Taylor and Francis Group, LLC ISSN: 0145-7632 print / 1521-0537 online DOI: 10.1080/01457630903500809 editorial Heat Transfer in Industrial Applications—PRES 2008 ˇ I´ KLEMESˇ and PETR STEHLIK ´ JIR Centre for Process Integration and Intensification (CPI2 ), Faculty of IT, University of Pannonia, Veszpr´em, Hungary Institute of Process and Environmental Engineering, Brno University of Technology, Brno, Czech Republic This editorial provides an overview of a special issue dedicated to the 11th Conference on Process Integration, Modeling, and Optimization for Energy Saving and Pollution Reduction—PRES 2008 Nine papers have been selected and peer-reviewed covering important subjects of heat transfer engineering They focus on recent development of various features of heat transfer equipment design and optimization This issue of Heat Transfer Engineering is the sixth special journal issue dedicated to selected papers from PRES conferences [1–5] INTRODUCTION Issues of global warming and greenhouse gas emissions, together with other pollution and effluents, are increasingly one of the major technological and also important societal and political challenges Because of the increasing urgency, various conferences are being held to encourage closer collaboration among people of many nations about the problems, and progress in meeting these challenges A very important contribution to successfully deal with those problems can be offered by heat transfer engineering The series of conferences on Process Integration, Modeling, and Optimization for Energy Saving and Pollution Reduction (PRES) is one such opportunity for cross-fertilization, running now into its second decade It was established originally to address issues relevant to process energy integration in connection with the efficient heat transfer issues The organisers of the PRES conferences are proud to continuously attract delegates from numerous countries worldwide, providing a friendly and highly collaborative platform for fast and efficient spreading of novel ideas, processes, procedures, and energy-saving policies PRES conferences have a comprehensive publication strategy: Address correspondence to Prof Jiˇr´ı Klemeˇs, Centre for Process Integration and Intensification (CPI2 ), Research Institute of Chemical Technology and Process Engineering, FIT, University of Pannonia, Egyetem u 10, 8200 Veszpr´em, Hungary E-mail: klemes@cpi.uni-pannon.hu see refs [1] to [8] This special issue is already the sixth special issue of Heat Transfer Engineering dedicated to selected contributions from PRES conferences PRES 2008 was held, as it has been traditionally every second year, in collaboration with the 18th International Congress CHISA 2008 in the heart of Europe—in Prague, the capital of the Czech Republic, 24–28 August 2008 This Central European capital, known as a city of a thousand spires, welcomed delegates from more than 55 countries; 987 authors submitted 345 contributions They represented, beside traditional European countries, Asia, Africa, Australia, and North and South America SELECTED CONTRIBUTIONS For this special issue of Heat Transfer Engineering, nine papers dealing with various aspects of heat transfer engineering and related inputs are included They tackle various aspects and levels of industrial implementations from two-phase flow, through compact heat exchangers and microwaves to total sites The first paper presents a keynote lecture, “Importance of Non-Boiling Two-Phase Flow Heat Transfer in Pipes for Industrial Applications,” authored by Afshin J Ghajar and Clement C Tang from School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma, USA 707 708 J KLEMESˇ AND P STEHL´IK They present extensive results of the recent developments in the non-boiling two-phase heat transfer in air–water flow in horizontal and inclined pipes conducted at their two-phase flow heat transfer laboratory The validity and limitations of the numerous two-phase non-boiling heat transfer correlations that have been published in the literature over the past 50 years are discussed Practical heat transfer correlations for a variety of gas–liquid flow patterns and pipe inclination angles are recommended The application of these correlations in engineering practice, and how they can influence the equipment design and consequently the process design are discussed in detail In their future plans they stated that the overall objective of their research has been to develop a heat transfer correlation that is robust enough to span all or most of the fluid combinations, flow patterns, flow regimes, and pipe orientations (vertical, inclined, and horizontal) They made a lot of progress toward this goal However, to fully accomplish their research objectives, a much better understanding of the heat transfer mechanism in each flow pattern is needed They plan to perform systematic heat transfer measurements to capture the effect of several parameters that influence the heat transfer results They also plan to complement these measurements with extensive flow visualizations They claim that the systematic measurements would allow them to develop a complete database for the development of their “general” two-phase heat transfer correlation The second paper presents a novel extension of heat integration methodology stressing an enhanced heat transfer It is titled “Total Sites Integrating Renewables With Extended Heat Transfer and Recovery,” authored by Petar Varbanov and Jiˇr´ı Klemeˇs from the Centre for Process Integration and Intensification (CPI2 ), Research Institute of Chemical Technology and Process Engineering, Faculty of Information Technology University of Pannonia, Veszpr´em, Hungary The challenge of increasing the share of renewables in the primary energy mix could be met by integrating solar, wind, and biomass as well as some types of waste with the fossil fuels Their work analyzed some of the most common heat transfer application at total sites The energy demands, the local generation capacities, and the efficient integration of renewables into the corresponding total sites CHP (combined heat and power generation) energy systems, based on efficient heat transfer, are optimized minimizing heat waste and carbon footprint, and maximizing economic viability The inclusion of renewables with their changing availability requires extensions of the traditional heat integration approach The problem becomes more complicated and has several more dimensions Revisiting some previously developed process integration tools and their further development enables solving this extended problem Their contribution has been a step in this direction, summarizing the problem and suggesting some options for its solution A demonstration case study illustrated the heat-saving potential of integrating various users and using heat storage Their future work progresses to developing advanced software tools based on the suggested methodology heat transfer engineering “Alternative Design Approach for Plate and Frame Heat Exchangers Using Parameter Plots” by Mart´ın Pic´on-N´un˜ ez, Graham Thomas Polley, and Dionicio Jantes-Jaramillo, from the Department of Chemical Engineering, University of Guanajuato, in Mexico, follows their previous paper published within the PRES Conference series [9] and analyzes the simultaneous design and specification of heat exchangers of the plate and frame type They used a pictorial representation of the design space to guide the designer toward selection of the geometry that best meets the heat duty within the limitations of pressure drop The design space was represented by a bar plot where the number of thermal plates is plotted for three conditions: (i) for fully meeting the required heat load, (ii) for fully absorbing the allowable pressure drop in the cold stream, and (iii) for fully absorbing the allowable pressure drop in the hot stream This type of plot is suitable for representing the design space, given the discrete nature of the plate geometrical characteristics, such as effective plate length and plate width The authors also presented applications of the use of bypasses as a design strategy The fourth contribution, “Heat Transfer of Supercritical CO2 Flow in Natural Convection Circulation System,” comes from Hideki Tokanai, Yu Ohtomo, Hiro Horiguchi, Eiji Harada, and Masafumi Kuriyama from the Department of Chemistry and Chemical Engineering, Yamagata University, in Japan, and presents measurements of heat transfer to supercritical CO2 flow in a natural convection circulation system that consists of a closed-loop circular pipe Systematic data of heat transfer coefficients are given for various pressures and pipe diameters They found that heat transfer coefficients of supercritical CO2 flow were very much higher compared to those of usually encountered fluid flow and expressed them by a nondimensional correlation equation proposed in their work They also presented numerical model calculations of the velocity and temperature distributions in supercritical CO2 flow to elucidate the exceedingly high value of heat transfer coefficient They concluded that the heat transfer enhancement of supercritical CO2 resulted from the high speed flow near the pipe wall This strong flow shows steep velocity and temperature gradients to enhance the rate of heat transfer in the vicinity of the pipe wall Zdenˇek Jegla, Bohuslav Kilkovsk´y, and Petr Stehl´ık, from the Institute of Process and Environmental Engineering, Brno University of Technology, the Czech Republic, deal with “Calculation Tool for Particulate Fouling Prevention of Tubular Heat Transfer Equipment.” They studied fouling of heat transfer equipment in incineration plants They found that the main process stream in such plants produced a stream of flue gas, and its thermal and physical properties significantly influence operating, maintenance, and investment costs of installed equipment and its service life Their contribution deals with the issue of fouling mechanism at the heat transfer area of tubular heat transfer equipment installed in plants like these They presented a mathematical model developed for fouling tendency prediction and for prevention in design and operation of tubular heat transfer equipment designed for applications in the field of waste vol 31 no 2010 J KLEMESˇ AND P STEHL´IK incineration Obtained results were compared with experimental data published in worldwide available literature and a very good agreement was found Their model is suitable for equipment fouling tendency prediction and for prevention in design and operating of tubular heat transfer equipment designed for applications in waste incinerating plants The application for design of the economizer demonstrates the contribution of a developed extended mathematical model to a complex analysis The results of the developed extended model together with technical and economic analysis can contribute to selecting the most suitable design alternative that can successfully satisfy requirements from several different points of view, such as fouling, design, operation, and economics The sixth paper comes from the University of Ottawa, Canada, and its title is “Effect of High-Temperature Microwave Irradiation on Municipal Thickened Waste Activated Sludge Solubilization.” The authors are Isil Toreci, Kevin J Kennedy, and Ronald L Droste They deal with sludge digestion and stabilization Increasing hydrolysis by implementing pretreatment prior to digestion can increase the digestion efficiency They studied microwave pretreatment (MWP) as an alternative to conventional thermal pretreatment They stated that MWP above the boiling point has not been studied yet for sludge solubilization and digestion Their paper provides preliminary results on the effect of MWP conditions such as high temperature (110–175◦ C), MWP intensity of 1.25 and 3.75◦ C/min, and sludge concentration of and 11.85% on solubilization The next paper deals with “Improvement of a Combustion Unit Based on a Grate Furnace for Granular Dry Solid Biofuels Using CFD Methods.” The authors, Christian Jordan and Michael Harasek, come from the Institute of Chemical Engineering, Vienna University of Technology, in Austria They studied the design and construction of an improved small-scale combustion unit for various biofuels: wood, straw pellets, and especially grain Using computational fluid dynamics (CFD) methods and measurement data from a pilot unit, this study contributes to the continuous enhancement of biomass firing technology by addressing the commonly known problems regarding emissions and ash melting Based on the calculated results, improvements for the existing prototype geometry have been suggested and will be included in the design of a new 1.5-MW pilot-scale grate firing unit that was planned to start operation by the beginning of 2009 Their future work will deal with the detailed design of the prototype Plans for 2009 also included setting up a new grate furnace at a production facility by Polytechnik GmbH and starting continuous operation by mid 2009 Detailed fuel analyses will be carried out to close the mass and energy balances This will be followed by further measurements for longer periods of stable operation and will provide a more reliable foundation for validation of the simulation Additional CFD simulations will be done for other fuels (e.g., grain) The introduction of a soot model, fuel NOx , and a more detailed bed combustion model will be considered heat transfer engineering 709 The eighth paper comes from the State University of New York College at Buffalo, New York, USA The authors, David J Kukulka, Holly Czechowski, and Peter D Kukulka, evaluate the feasibility of using surface coatings on commonly used process surfaces to minimize/delay the effect of fouling They explored stainless steel and copper with AgION and Xylan coatings They placed sample plates vertically in test tanks and then exposed them to untreated lake water for various time periods Their results compare surface roughness over time Additional results show transient deposit weight gain The progressive change in surface appearance with increasing immersion times is also presented and gives a visual representation of the surface at a specific time Their review includes observations on the fouling of coated process surfaces All coated samples showed some deposit accumulation with no change in surface appearance for the periods of immersion considered The authors summarized results of the material coatings for surfaces that are commonly used in designs where fouling may be a concern Fouling rates, transient surface roughness values, and transient photographs of the frontal surfaces of the materials were given for typical conditions The last paper, prepared by Zoe Anxionnaz, Michel Cabassud, Christophe Gourdon, and Patrice Tochon, from Chemical Engineering Laboratory, University of Toulouse/INPT, France, and Atomic Energy Commission–GRETh, Grenoble, France, has the title “Transposition of an Exothermic Reaction From a Batch Reactor to an Intensified Continuous One.” The implementation of chemical syntheses in a batch or semi-batch reactor is generally limited by the removal or the supply of heat A way to enhance thermal performances is to develop multifunctional devices like heat exchanger/reactors The authors analyzed a novel heat exchanger/reactor characterized in terms of residence time, pressure drop, and thermal behavior in order to estimate capacities to perform an exothermic reaction: the oxidation of sodium thiosulfate by hydrogen peroxide Their experimental results highlighted the performances of the heat exchanger/reactor in terms of intensification, which allows the implementation of the oxidation reaction at extreme operating conditions They compared these conditions with a classical batch reactor The studied ShimTec reactor was a good example of intensified unit and sustainable technology By combining reaction and heat transfer, the process became safer, more environment friendly, and cheaper The future work will be aimed at setting up reliable control system, design, scale-up, and optimization procedures and safety studies CONCLUDING REMARKS We believe that the papers in this special issue of Heat Transfer Engineering will be of interest and relevance to a broad range of the scientific community and will bring to their attention the PRES Conference series as well The PRES’09 Conference was held in Italy, in the historical city of Rome vol 31 no 2010 710 J KLEMESˇ AND P STEHL´IK REFERENCES [1] Klemeˇs, J., and Stehlik, P., PRES Conference—Challenges in Complex Process Heat Transfer, Heat Transfer Engineering, vol 23, pp 1–2, 2002 [2] Stehl´ık, P., and Klemeˇs, J., Selected Papers from the PRES 2002 Conference, Heat Transfer Engineering, vol 25, pp 1–3, 2004 [3] Klemeˇs, J., and Stehl´ık, P., Selected Papers from the PRES 2003 Conference, Heat Transfer Engineering, vol 26, pp 1–3, 2005 [4] Stehl´ık, P., and Klemeˇs, J., Recent Advances on Heat Transfer Equipment Design and Optimization—Selected Papers from PRES 2004 Conference, Heat Transfer Engineering, vol 27, pp 1–3, 2006 [5] Stehl´ık, P., and Klemeˇs, J., Achievements in Applied Heat Transfer—PRES 2006, Heat Transfer Engineering, vol 29, pp 503–505, 2008 [6] Klemeˇs, J., and Pierucci, S., Emission Reduction by Process Intensification, Integration, P-Graphs, Micro CHP, Heat Pumps and Advanced Case Studies, Applied Thermal Engineering, vol 28, pp 2005–2010, 2008 [7] Klemeˇs, J., and Huisingh, D., Economic Use of Renewable Resources, LCA, Cleaner Batch Processes and Minimising Emissions and Wastewater, Journal of Cleaner Production, vol 16, pp 159–163, 2008 [8] Bulatov, I., and Klemeˇs, J., Towards Cleaner Technologies: Emissions Reduction, Energy and Waste Minimisation, Industrial Implementation, Clean Technologies and Environmental Policy, vol 11, pp 1–6, 2009 heat transfer engineering [9] Picon-Nunez, M., Canizalez-Davalos, L., and Morales-Fuentes, A., Alternative Design Approach for Spiral Plate Heat Exchangers, PRES’07, ed Jiˇr´ı Klemeˇs, Chemical Engineering Transactions, vol 2, pp 183–188, 2007 Jiˇr´ı Klemeˇs is a P´olya Professor and EC Marie Curie Chair Holder (EXC), Head of the Centre for Process Integration and Intensification (CPI2 ) at the University of Pannonia, Veszpr´em, in Hungary Previously he worked for nearly 20 years in the Department of Process Integration and the Centre for Process Integration at UMIST and after the merge at the University of Manchester, UK, as a senior project officer and honorary reader He has many years of research and industrial experience In 1998 he founded and has been since the President of the International Conference “Process Integration, Mathematical Modeling, and Optimization for Energy Saving and Pollution Reduction—PRES.” Petr Stehl´ık is a professor of process engineering at the Brno University of Technology (UPEI—VUT Brno) and a director of the Institute of Process and Environmental Engineering He is also a member of the Presidium of the Czech Society of Chemical Engineers, and a member of renowned foreign engineering societies He had several years of experience in engineering practice before joining the university His research interests involve applied heat transfer, process design, mathematical modeling, energy saving, and environmental problems He is the author of numerous publications vol 31 no 2010 Heat Transfer Engineering, 31(9):711–732, 2010 Copyright C Taylor and Francis Group, LLC ISSN: 0145-7632 print / 1521-0537 online DOI: 10.1080/01457630903500833 Importance of Non-Boiling Two-Phase Flow Heat Transfer in Pipes for Industrial Applications AFSHIN J GHAJAR and CLEMENT C TANG School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma, USA The validity and limitations of the numerous two-phase non-boiling heat transfer correlations that have been published in the literature over the past 50 years are discussed The extensive results of the recent developments in the non-boiling two-phase heat transfer in air–water flow in horizontal and inclined pipes conducted at Oklahoma State University’s two-phase flow heat transfer laboratory are presented Practical heat transfer correlations for a variety of gas–liquid flow patterns and pipe inclination angles are recommended The application of these correlations in engineering practice and how they can influence the equipment design and consequently the process design are discussed INTRODUCTION In many industrial applications, such as the flow of oil and natural gas in flow lines and well bores, the knowledge of nonboiling two-phase, two-component (liquid and permanent gas) heat transfer is required During the production of two-phase hydrocarbon fluids from an oil reservoir to the surface, the temperature of the hydrocarbon fluids changes due to the difference in temperatures of the oil reservoir and the surface The change in temperature results in heat transfer between the hydrocarbon fluids and the earth surrounding the oil well, and the ability to estimate the flowing temperature profile is necessary to address several design problems in petroleum production engineering [1] In subsea oil and natural gas production, hydrocarbon fluids may leave the reservoir with a temperature of 75◦ C and flow in subsea surrounding of 4◦ C [2] As a result of the temperature This is an extended version of the keynote paper presented at the 11th Conference on Process Integration, Modeling and Optimization for Energy Saving and Pollution Reduction (PRES2008), Prague, Czech Republic, August 24–28, 2008 Generous contributions in equipment and software made by National Instruments are gratefully acknowledged Sincere thanks are offered to Micro Motion for generously donating one of the Coriolis flow meters and providing a substantial discount on the other one Thanks are also due to Martin Mabry for his assistance in procuring these meters Address correspondence to Professor Afshin J Ghajar, School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, USA E-mail: afshin.ghajar@okstate.edu gradient between the reservoir and the surrounding, the knowledge of heat transfer is critical to prevent gas hydrate and wax deposition blockages [3] Wax deposition can result in problems, including reduction of inner pipe diameter causing blockage, increased surface roughness of pipe leading to restricted flow line pressure, decrease in production, and various mechanical problems [4] Some examples of the economical losses caused by the wax deposition blockages include: direct cost of removing the blockage from a subsea pipeline was $5 million, production downtime loss in 40 days was $25 million [5], and the cost of oil platform abandonment by Lasmo Company (UK) was $100 million [6] In situations where low-velocity flow is necessary while high heat transfer rates are desirable, heat transfer enhancement schemes such as the coil-spring wire insert, twisted tape insert, and helical ribs are used to promote turbulence, thus enhancing heat transfer Although these heat transfer enhancement schemes have been proven to be effective, they come with drawbacks, such as fouling, increase in pressure drop, and sometimes even blockage Celata et al [7] presented an alternative approach to enhance heat transfer in pipe flow, by injecting gas into liquid to promote turbulence In the experimental study performed by Celata et al [7], a uniformly heated vertical pipe was internally cooled by water, while heat transfer coefficients with and without air injection were measured The introduction of low air flow rate into the water flow resulted in increase of the heat transfer coefficient up to 20–40% for forced convection, and even larger heat transfer enhancement for mixed convection [7] 711 712 A J GHAJAR AND C C TANG Two-phase flow can also occur in various situations related to ongoing and planned space operations, and the understanding of heat transfer characteristics is important for designing piping systems for space operations limited by size constraints [8] To investigate heat transfer in two-phase slug and annular flows under reduced gravity conditions, Fore et al [8, 9] conducted heat transfer measurements for air–water and air–50% aqueous glycerin aboard NASA’s Zero-G KC-135 aircraft Due to limited studies available in the literature, Wang et al [10] investigated forced convection heat transfer on the shell side of a TEMA-F horizontal heat exchanger using a 60% aqueous glycerin and air mixture Their work resulted in recommendation of correlations for two-phase heat transfer coefficient in stratified, intermittent, and annular flows in shell-and-tube heat exchangers In this article, an overview of our ongoing research on this topic that has been conducted at our heat transfer laboratory over the past several years is presented Our extensive literature search revealed that numerous heat transfer coefficient correlations have been published over the past 50 years We also found several experimental data sets for forced convective heat transfer during gas–liquid two-phase flow in vertical pipes, very limited data for horizontal pipes, and no data for inclined pipes However, the available correlations for two-phase convective heat transfer were developed based on limited experimental data and are only applicable to certain flow patterns and fluid combinations The overall objective of our research has been to develop a heat transfer correlation that is robust enough to span all or most of the fluid combinations, flow patterns, flow regimes, and pipe orientations (vertical, inclined, and horizontal) To this end, we have constructed a state-of-the-art experimental facility for systematic heat transfer data collection in horizontal and inclined positions (up to 7◦ ) The experimental setup is also capable of producing a variety of flow patterns and is equipped with two transparent sections at the inlet and exit of the test section for in-depth flow visualization In this article we present the highlights of our extensive literature search, the development of our proposed heat transfer correlation and its application to experimental data in horizontal, inclined, and vertical pipes, a detailed description of our experimental setup, the flow visualization results for different flow patterns, the experimental results for various flow patterns, and our proposed heat transfer correlation for various flow patterns and pipe orientations comprehensive literature search was carried out and a total of 38 two-phase flow heat transfer correlations were identified The validity of these correlations and their ranges of applicability have been documented by the original authors In most cases, the identified heat transfer correlations were based on a small set of experimental data with a limited range of variables and gas–liquid combinations In order to assess the validity of those correlations, they were compared against seven extensive sets of two-phase flow heat transfer experimental data available from the literature, for vertical and horizontal tubes and different flow patterns and fluids For consistency, the validity of the identified heat transfer correlations were based on the comparison between the predicted and experimental two-phase heat transfer coefficients meeting the ±30% criterion In total, 524 data points from the five available experimental studies [12–16] were used for these comparisons (see Table 1) The experimental data included five different gas–liquid combinations (air–water, air–glycerin, air–silicone, helium–water, Freon 12–water), and covered a wide range of variables, including liquid and gas flow rates and properties, flow patterns, pipe sizes, and pipe inclination Five of these experimental data sets are concerned with a wide variety of flow patterns in vertical pipes and the other two data sets are for limited flow patterns (slug and annular) within horizontal pipes Table shows 20 of the 38 heat transfer correlations [14, 16–35] that were identified and reported by Kim et al [11] Eighteen of the two-phase flow heat transfer correlations were not tested, since the required information for those correlations was not available through the identified experimental studies In assessing the ability of the 20 identified heat transfer correlations, their predictions were compared with the experimental data from the sources listed in Table 1, both with and without considering the restrictions on ReSL and VSG /VSL accompanying the correlations The results from comparing the 20 heat transfer correlations and the experimental data are summarized in Table for major flow patterns in vertical pipes There were no remarkable differences for the recommendations of the heat transfer correlations based on the results with and without the restrictions on ReSL and VSG /VSL , except for the correlations of Chu and Jones [18] and Ravipudi and Godbold [25], as applied to the air–water experimental data of Vijay [12] Details of this discussion can be found in Kim et al [11] Based on the results without the authors’ restrictions on ReSL and VSG /VSL , the correlation of Chu and Jones [18] was Table The experimental data used in Kim et al [11] COMPARISON OF 20 TWO-PHASE HEAT TRANSFER CORRELATIONS WITH SEVEN SETS OF EXPERIMENTAL DATA Numerous heat transfer correlations and experimental data for forced convective heat transfer during gas–liquid two-phase flow in vertical and horizontal pipes have been published over the past 50 years In a study published by Kim et al [11], a heat transfer engineering Source Orientation Fluids Vijay [12] Vijay [12] Rezkallah [13] Aggour [14] Aggour [14] Pletcher [15] King [16] Vertical Vertical Vertical Vertical Vertical Horizontal Horizontal Air–water Air–glycerin Air–silicone Helium–water Freon 12–water Air–water Air–water vol 31 no 2010 Number of data points 139 57 162 53 44 48 21 713 (L) NuTP = 0.029(ReTP ) Groothuis and Hendal [28] 0.17 1/3 (µB /µW ) 0.14 (for air–water) 0.14 P L TP P L L 0.32 Sieder and Tate [35] Vijay et al [34] Ueda and Hanaoka [33] Shah [31] Serizawa et al [29] Rezkallah and Sims [27] Ravipudi and Godbold [25] Oliver and Wright [23] Martin & Sims [21] Kudirka et al [19] Knott et al [17] Source where hL is from Sieder and Tate [35] 1/4 0.33 0.14 (T) NuL = 0.027Re0.8 SL PrL (µB /µW ) NuL = 1.86(ReSL PrL D / L)1/3 (µB /µW )0.14 (L) 0.5 0.33 NuL = 0.0155Re0.83 (T) SL PrL (µB /µW ) NuL = 1.615(ReSL PrL D / L)1/3 (µB /µW )0.14 (L) hTP /hL = ( PTPF / PL )0.451 0.4 NuL = 0.023Re0.8 (T) µB /µW SL PrL PrL 0.6 NuTP = 0.075(ReM ) + 0.035(PrL - 1) 0.14 NuL = 1.86(ReSL PrL D / L)1/3 (µB /µW )0.14 (L) hTP hL = +VSG VSL NuTP = NuL 1.2 0.2 RL R0.36 L 1/3 (QG + QL )ρD PrL D / L NuL = 1.615 (µB /µW )0.14 Aµ VSG 0.3 µG 0.2 µB 0.14 (ReSL )0.6 (PrL )1/3 NuTP = 0.56 VSL µL µW hTP / hL = (1 − α)−0.9 where hL is from Sieder and Tate [35] hTP = + 462X−1.27 where hL is from Sieder and Tate [35] TT hL Tate [35] hTP 1/3 VSG 1/8 µG 0.6 µB 0.14 (ReSL )1/4 (PrL )1/3 VSL µL µW hL = + 0.64 VSG VSL where hL is from Sieder and NuTP = 125 VSG hTP = 1+ hL VSL Heat transfer correlations Note α and RL are taken from the original experimental data ReSL < 2000 implies laminar flow, otherwise turbulent; and for Shah [31], replace 2000 by 170 With regard to the equations given for Shah [31] in this table, the laminar two-phase correlation was used along with the appropriate single-phase correlation, since Shah [31] recommended a graphical turbulent two-phase correlation hTP RL−0.52 = hL + 0.025Re0.5 SG 0.4 NuL = 0.023Re0.8 SL PrL 0.55 0.4 NuTP = 0.26 Re0.2 SG ReSL PrL NuTP = 2.6(ReTP )0.39 (PrL )1/3 (µB /µW )0.14 (for air–(gas–oil)) ˙ L cL 1/3 µB 0.14 m NuTP = 1.75 (RL )−1/2 RL kL L µW (PrL ) 0.87 King [16] (L) (ReTP )0.7 (PrL )1/3 µB µW NuTP = 0.029(ReTP )0.87 (PrL )0.4 0.33 0.14 NuL = 0.0123Re0.9 SL PrL (µB /µW ) hTP / hL = (1 − α)−0.8 (T) hTP / hL = (1 − α) −1/3 NuTP = 0.5 µG µL Khoze et al [32] 0.14 0.5 0.33 NuL = 0.0155Re0.83 (T) SL PrL (µB /µW ) µB 0.14 Pa 0.55 1/3 NuTP = 0.43(ReTP ) (PrL ) µW P 0.28 0.87 DGt x µL NuTP = 0.060 ρL ρG PrL0.4 Elamvaluthi and Srinivas [26] Hughmark [30] (µB /µW ) hTP / hL = (1 − α)−0.83 Turbulent (T) NuL = 1.615(ReSL PrL D/L) 1/3 hTP /hL = (1 − α)−1/3 Laminar (L) Heat transfer correlations 1/4 Dusseau [24] Dorresteijn [22] Davis and David [20] Chu and Jones [18] Aggour [14] Source Table Heat transfer correlations chosen by Kim et al [11] 714 A J GHAJAR AND C C TANG Table Recommended correlations for vertical pipes, Kim et al [11] Air–water Correlations Aggour [14] Chu and Jones [18] Knott et al [17] Kudirka et al [19] Martin and Sims [21] Ravipudi and Godbold [25] Rezkallah and Sims [27] Shah [31] B S √ √ F √ √ √ √ Air–glycerin A √ B S F A √ √ √ √ B S C A Helium–water F B √ √ √ √ √ √ S √ √ √ √ √ Air–silicone √ F Freon 12–water A √ √ F A √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ S √ √ √ √ B √ √ √ √ Air–water A S √ √ √ √ √ √ Note = Recommended correlation with and without restrictions Shaded cells indicate the correlations that best satisfied the ±30% two-phase heat transfer coefficient criterion A = annular, B = bubbly, C = churn, F = froth, S = slug recommended for only annular, bubbly-froth, slug-annular, and froth-annular flow patterns of air–water in vertical pipes While the correlation of Ravipudi and Godbold [25] was recommended for only annular, slug-annular, and froth-annular flow patterns of air–water in vertical pipes However, when considering the ReSL and VSG /VSL restrictions by the authors, the correlation of Chu and Jones [18] was recommended for all vertical pipe air–water flow patterns including transitional flow patterns, except the annular-mist flow pattern While the correlation of Ravipudi and Godbold [25] was recommended for slug, froth, and annular flow patterns and for all of the transitional flow patterns of the vertical air–water experimental data All of the correlations just recommended have the following important parameters in common: ReSL , PrL , µB /µW , and either void fraction (α) or superficial velocity ratio (VSG /VSL ) It appears that void fraction and superficial velocity ratio, although not directly related, may serve the same function in two-phase flow heat transfer correlations From the comprehensive literature search, Kim et al [11] found that there is no single correlation capable of predicting the flow for all fluid combinations in vertical pipes In the following section, the effort of Kim et al [36] in developing a heat transfer correlation that is robust enough to span all or most of the fluid combinations and flow patterns for vertical pipes is highlighted Kim et al [36] developed a correlation that is capable of predicting heat transfer coefficient in two-phase flow regardless of fluid combinations and flow patterns The correlation uses a carefully derived heat transfer model that takes into account the appropriate contributions of both the liquid and gas phases using the respective cross-sectional areas occupied by the two phases A ( = AG + AL ): α= AG AG + AL (1) The actual gas velocity VG can be calculated from VG = ˙G ˙ m mx QG = = AG ρG AG ρG αA (2) Similarly, for the liquid, VL is defined as: VL = ˙L ˙ (1 − x) QL m m = = AL ρL AL ρL (1 − α) A (3) The total gas–liquid two-phase heat transfer coefficient is assumed to be the sum of the individual single-phase heat transfer coefficients of the gas and liquid phases, weighted by the volume of each phase present: hTP = (1 − α) hL + αhG = (1 − α) hL + α 1−α hG hL (4) There are several well-known single-phase heat transfer correlations in the literature In this study the Sieder and Tate [35] equation was chosen as the fundamental single-phase heat transfer correlation because of its practical simplicity and proven applicability Based upon this correlation, the single-phase heat transfer coefficients in Eq (4), hL and hG , can be modeled as functions of Reynolds number, Prandtl number, and the ratio of bulk to wall viscosities Thus, Eq (4) can be expressed as: hTP = (1 − α) hL + α fctn Re, Pr, µB µW − α fctn Re, Pr, µB µW G (5) L or DEVELOPMENT OF THE HEAT TRANSFER CORRELATION FOR VERTICAL PIPES The void fraction (α) is defined as the ratio of the gasflow cross-sectional area (AG ) to the total cross-sectional area, heat transfer engineering hTP = (1 − α)hL + × vol 31 no 2010 α fctn 1−α (µB /µW )G PrG , PrL (µB /µW )L ReG , ReL (6) A J GHAJAR AND C C TANG Substituting the definition of Reynolds number (Re = ρVD/µB ) for the gas (ReG ) and liquid (ReL ) yields hTP α fctn = 1+ (1 − α) hL 1−α ρVD G µB L ρVD L µB G ρG VG DG , ρL VL DL 4/5 (9) kL D 1/3 µB µW 0.14 (12) L For the Reynolds number (ReL ) in Eq (12), the following relationship is used to evaluate the in-situ Reynolds number (liquid phase) rather than the superficial Reynolds number (ReSL ) as commonly used in the correlations of the available literature [11]: ReL = ρVD µ = L √ ˙L 4m (13) π − αµL D Any other well-known single-phase turbulent heat transfer correlation could have been used in place of the Sieder and Tate [35] correlation The difference resulting from the use of a different single-phase heat transfer correlation will be absorbed during the determination of the values of the leading coefficient and exponents on the different parameters in Eq (11) The values of the void fraction (α) used in Eq (11) either were taken directly from the original experimental data sets (if available) or were calculated based on the equation provided by Chisholm [37], which can be expressed as α PrG x , , , 1−x 1−α PrL µL µG n (11) hL = 0.027ReL PrL Further simplifying Eq (9), combine Eqs (2) and (3) for VG (gas velocity) and VL (liquid velocity) to get the ratio of VG /VL and substitute into Eq (9) to get ì q àG µL (8) PrG µL , PrL µG hTP = (1 − α)hL + fctn p PrG PrL m where C, m, n, p, and q are adjustable constants, and hL comes from the Sieder and Tate [35] correlation for turbulent flow, where the assumption has been made that the bulk viscosity ratio in the Reynolds number term of Eq (7) is exactly canceled by the last term in Eq (7), which includes the same bulk viscosity ratio Substituting Eq (1) for the ratio of gas-to-liquid diameters (DG /DL ) in Eq (8) and based upon practical considerations assuming that the ratio of liquid-to-gas viscosities evaluated at the wall temperature [(µW )L /(µW )G ] is comparable to the ratio of those viscosities evaluated at the bulk temperature (µL /µG ), Eq (8) reduces to √ α hTP α ρG VG , = 1+ fctn √ (1 − α)hL 1−α L VL ì ì (7) PrG (àW )L ì , PrL (àW )G x 1x hTP = (1 − α)hL + C Rearranging yields α hTP fctn = 1+ (1 − α)hL 1−α rameters that appear in Eq (10), then it can be expressed as: , PrG (àB /àW )G ì , PrL (àB /àW )L 715 1/2 ρ α= 1+ 1−x+x L ρG 1−x x ρG ρL −1 (14) (10) Assuming that two-phase heat transfer coefficient can be expressed using a power-law relationship on the individual pa- In the next section the proposed heat transfer correlation, Eq (11), is tested with four extensive sets of vertical two-phase flow heat transfer data available from the literature (see Table 1) Table Results of the predictions for available two-phase heat transfer experimental data using Eq (11), Kim et al [36] Values of constant and exponents Fluids (ReSL > 4000) All 255 data points Air–water [12], 105 data points Air–silicone [13], 56 data points Helium–water [14], 50 data points Freon 12–water [14], 44 data points C m n p 0.27 −0.04 1.21 0.66 q −0.72 RMS Mean Number of deviation deviation data (%) (%) within ±30% ReSL 12.78 2.54 245 12.98 7.77 15.68 13.74 3.53 5.25 −1.66 1.51 98 56 48 43 heat transfer engineering Range of parameters ReSG PrG /PrL µG /µL 4000 to 14 to 9.99 × 10−3 to 3.64 × 10−3 to 127,000 209,000 137 × 10−3 23.7 × 10−3 vol 31 no 2010 D J KUKULKA ET AL [6] and Holah and Thorne [7] also indicate that surface defects were more closely associated with significant increases in bacterial attachment Tests conducted on pipes of different materials have demonstrated that smooth materials (glass and electropolished 316 stainless steel) had 35% less biofilm deposit than a corresponding “as received” 316 stainless steel (Mott [8]) Temperature of a system also plays a critical role on the thickness of a deposit Systems with lower temperatures typically have thinner deposits than systems with higher temperatures Mott [8] shows that by raising the system temperature from 30◦ C to 35◦ C the deposit thickness increases by approximately 80% Muller-Steinhagen and Zhao [9] investigated the development of stainless-steel surfaces with low surface energy created by ion implantation These surfaces reduce fouling accumulation without the use of surface coatings Zhao et al [10] further studied the advantages of ion-implanted stainless-steel surfaces Their experimental results showed that these implanted stainless steels, particularly SiF+ -implanted stainless steel, performed much better than untreated stainless steel in reducing bacterial attachment Rosmaninho et al [11] studied modifying stainlesssteel process surfaces for use in the dairy industry Fouling may be defined as the accumulation of undesired solid material at phase interfaces These deposits will impede the transfer of heat and increase fluid flow resistance Fouling occurs with or without a temperature gradient in a variety of industrial, domestic, and natural processes The growth of these deposits causes the thermal and hydrodynamic performance of heat transfer equipment to decline with time, affecting the performance of the equipment or the contamination of the product that is being produced Recent studies performed by Gogenko et al [12] and Liporace and De Oliveira [13] have accounted for fouling in real time Fouling is a function controlled by a variety of parameters, including geometry of the heat transfer surface, surface properties/material, interface temperature, deposit composition/temperature, free stream velocity, and fluid composition/characteristics Industrial and commercial operations contain many environments where corrosion and fouling processes are potentially troublesome; these include cooling-water systems, storage tanks, water and wastewater systems, filters, piping systems, ship hulls, reverse osmosis membranes, porous media, heat exchangers, and drinking-water systems A recent study by Zettler et al [14] evaluated the surface properties and characteristics of a plate heat exchanger Fouling and corrosion can occur in turbulent flows, laminar flows, or in stagnant waters; on smooth surfaces or in crevices; and on metals or most other surfaces It causes an enormous economic loss since it directly influences the initial cost as well as the operating cost of the equipment The added costs include increased capital expenditure, increased maintenance cost, loss of production, quality control problems, safety problems, and energy losses Rhehman Khan and Zubair [15] present a good discussion on the economics of fouling To compensate for fouling, the heat transfer area of the process surface must be increased Pumps and fans need to be overheat transfer engineering 783 sized, and often duplicate heat exchangers need to be installed Taborek et al [1, 2] described fouling as the major unresolved problem in heat transfer, and today it maintains its importance EXPERIMENTAL DETAILS Six-inch-square plates of glass, copper, and stainless steel were placed in tanks at the Great Lakes Research Center (State University of New York College at Buffalo) for varied amounts of time with water from Lake Erie supplied at 70◦ F (21.1◦ C), with a flow of L/min After the prescribed time, the tank was drained and the samples were dried and weighed All materials are commercially available and have typical finishes Some samples had coatings applied AgION coating was tested on a series of stainless steel samples AgION is an antimicrobial coating that is a polymer-based film coating Xylan coating was applied to a variety of stainless and copper samples Xylan is a fluoropolymer coating designed for use on various materials It provides wear resistance, heat resistance, and nonstick properties and at the same time can also protect the material from corrosion Xylan contains polytetrafluoroethylene (PTFE) and is applied in thin films The operating temperature range for Xylan-coated materials is –120◦ F (–84.4◦ C) to 550◦ F (287.8◦ C) with an applied film thickness less than 0.002 inch (0.05068 mm) Xylan coatings are often used to solve the problems created when the ideal material for use in engineering has the wrong surface properties Coatings were applied to smooth as well as textured surfaces A combination of proper preparation and application techniques were used to apply the coatings All of the coatings exhibited no visual signs of delaminating or damage after exposure Materials Studied The stainless steel materials included: Type 304, satin smooth initial finish Type 304, satin smooth initial finish, AgION coated Type 304, textured rough initial finish Type 304, textured rough initial finish, Xylan coated Electropolished The copper materials were: Textured rough initial finish Textured rough initial finish, Xylan coated Glass was also used Tank Setup Several test tanks were used in the experimental setup with the same flow and temperature conditions Samples were held vol 31 no 2010 784 D J KUKULKA ET AL Table Sample Lake Erie water composition and characteristics Cations Ions (ppm) Ca Mg Na K Fe Cu Ba Sr Al Mn Total CaCO3 (ppm) Anions Ions (ppm) CaCo3 (ppm) 91.45 OH 0.00 38.84 CO3 0.00 117.07 30.35 HCO3 2.71 SO4 38.4 0.27 Cl 22.49 0.01 NO3 0.00 0.02 F 0.00 0.16 Total 0.338 0.000 164.15 Total dissolved solids ppm ions = 240.79 Total dissolved solids ppm CaCO3 = 168.68 Total hardness ppm as CaCO3 = 130.29 Total alkalinity ppm as CaCO3 = 96.00 Fouling index = pH of water = 6.80 0.00 0.0 96.00 39.98 31.71 0.00 0.00 167.69 36.58 9.43 13.92 2.12 0.10 0.01 0.02 0.14 0.061 0.000 Figure Process surface test tank with positioned plates (composition is given in Table 1) from Lake Erie, and the water makeup did not vary in vertical positions as shown in Figure In each tank the plates were placed in the same position to maintain consistency throughout the experiment The inlet hose was placed opposite the drain on the bottom of the tank to create a crossflow over the plates All test tanks were monitored during the experiment to ensure the conditions and plates were kept constant Water Temperature and Composition The temperature of incoming lake water averaged approximately 70◦ F (21.1◦ C) Inlet water flow into the test tanks was held at 2.6 ft/s (6 L/min) Water tested was raw surface water Sample Processing and Data Collection After each tank reached its experimental time length, the inlet water to that tank was shut off The drain tube was then removed, allowing the tank to drain in a manner that least disturbed the system Before the plates were removed, they were allowed to completely air dry Care was given not to jostle or handle the plates in excess prior to collecting data The first step after drying was to observe and photograph the surface appearance of each plate Photographs of the plate surfaces were taken at 10 times magnification to capture the characteristics of the deposits on each plate surface The next step was to obtain surface roughness measurements Measurements Table Photographs showing transient surface deposition (frontal view, 10×) for AgION-coated stainless steel when exposed to 70◦ F (21.1◦ C) flowing lake water heat transfer engineering vol 31 no 2010 D J KUKULKA ET AL 785 Table Photographs showing transient surface deposition (frontal view, 10× ) for satin stainless steel when exposed to 70◦ F (21.1◦ C) flowing lake water Table Photographs showing transient surface deposition (frontal view, 10×) for Xylan-coated stainless steel with an initial texture when exposed to 70◦ F (21.1◦ C) flowing lake water Table Photographs showing transient surface deposition (frontal view, 10×) for Xylan-coated stainless steel with an initial smooth finish, when exposed to 70◦ F (21.1◦ C) flowing lake water heat transfer engineering were taken using Pocket Surf I, a portable surface roughness gage with a traverse speed of 0.2 inch (5.08 mm) per second and a probe radius of 0.0004 inch (10 µm) Each sample was tested in three locations on the strip Data were collected so that the Pocket Surf probe traversed across the grain of the metal and also with the grain of the metal The mean of three surface roughness readings was reported Finally, each sample was photographed using an Olympus microscope, model SZX12, which was mounted with a Hitachi digital camera Table Photographs showing transient surface deposition (frontal view, 10×) for Xylan-coated copper with an initial texture when exposed to 70◦ F (21.1◦ C) flowing lake water vol 31 no 2010 786 D J KUKULKA ET AL Figure Amount of fouling (grams) versus time (days) for various surfaces when exposed to flowing, 70◦ F (21.1◦ C) lake water RESULTS AND CONCLUSIONS Materials (copper and stainless steel) with various surface finishes and coatings were tested These materials were placed in tanks at the Great Lakes Research Center for varied amounts of time, with once though water from Lake Erie circulated After the prescribed time, the tank was drained and the samples were dried As each set of plates was removed from the medium, observations about the conditions of each plate was made These obser- vations included visible film, color change, corrosion, deposit characteristics, etc Tables 2–6 show the surfaces of the plates Fouling rate curves are given in Figure Surface roughness measurements can be found for each of the materials in Figure The graphs show the surface roughness measurements versus the time the plate was in the lake water Since three measurements were taken for each plate sample, the data points were averaged surface roughness at a particular time period Trend lines were then drawn between the plotted points Each material showed an increase in the surface roughness from the original sample Figure Surface roughness versus time (days) for various surfaces when exposed to flowing, 70◦ F (21.1◦ C) lake water heat transfer engineering vol 31 no 2010 D J KUKULKA ET AL to the maximum measured time Comparing the surface roughness values over the time period shows a gradual increase in the roughness values with increasing immersion time It is evident from Figures and that coatings delay the onset of fouling Coated, initially textured plates have a slower rate of fouling than uncoated, smooth surfaces Surface roughness results for the coated surfaces are more than 50% less than the values for uncoated surfaces This indicates that coatings can be applied to process surfaces with imperfections or surfaces that show erosion Figure details the transient rate of fouling, showing that smooth plates accumulate deposits 50% more quickly than coated smooth plates Similar surface improvements are also shown for initially textured surfaces Xylan-coated plates accumulate less deposits than glass surfaces for the same time period When compared to glass, AgION-coated plates accumulate deposits at a slightly faster rate, but are still much better than uncoated surfaces In general, coated surfaces accumulated fewer deposits than polished samples; however the long-term (erosion) effects have not thoroughly been examined This study showed that the thickness of the deposit became more visible the longer the plate was in the lake water and is correlated through the use of the surface roughness measurements Not only does the length of time affect the amount of fouling, but surface coating has an equal effect A more detailed examination of other materials/surfaces/coatings, temperatures, and flow rates and an evaluation of coated heat exchangers is also currently being undertaken REFERENCES [1] Taborek, J., Knudsen, J., Aoki, T., Ritter, R B., and Palen, J W., Fouling—The Major Unresolved Problem in Heat Transfer, Part I, Chemical Engineering Progress, vol 68, no 2, pp 59–67, 1972 [2] Taborek, J., Knudsen, J., Aoki, T., Ritter, R B., and Palen, J W., Fouling—The Major Unresolved Problem in Heat Transfer, Part II, Chemical Engineering Progress, vol 68, no 7, pp 69–78, 1972 [3] Turakhia, M H., Characklis, W G., and Zelver, N., Fouling of Heat Exchange Surfaces: Measurement and Diagnosis, Heat Transfer Engineering, vol 5, pp 93–101, 1984 [4] Boulange-Peterman, L., Rault, J., and Bellon-Fontaine, M.N., Adhesion of Streptococcus thermophilus to Stainless Steel with Different Surface Topography and Roughness, Biofouling, vol 11, no 3, pp 201–216, 1997 [5] Frank, J., and Chmielewski, R., Influence of Surface Finish on the Cleanability on Stainless Steel, Food Protein, vol 68, no 8, pp 1178–1182, 2001 [6] Jones, C R., Adams, M R., Zhadan, P A., and Chamberlain, A H L., The Role of Surface Physiochemical Properties in Determining the Distribution of the Autochthonous Microflora in Mineral Water Bottles, Journal of Applied Microbiology, vol 86, pp 917–927, 1999 [7] Holah, J T., and Thorne, R H., Cleanability in Relation to Bacterial Retention on Unused and Abraded Domestic Sink Materials, Journal of Applied Bacteriology, vol 69, pp 599–608, 1990 [8] Mott, I E C., Biofouling and Studies Using Simulated Cooling Water, Ph.D thesis, Univ Birmingham, Birmingham, UK, 1991 heat transfer engineering 787 [9] Muller-Steinhagen, H., and Zhao, O., Investigation of Low Fouling Surface Alloys Made by Ion Implantation Technology, Chemical Engineering Science, vol 52, no 19, pp 3321–3332, 1997 [10] Zhao, Q., Liu, Y., Wang, C., Wang, S., Peng, N., and Jeynes, C , Reduction of Bacterial Adhesion on Ion-Implanted Stainless Steel Surfaces, Medical Engineering and Physics, vol 30, no 3, pp 341–349, April 2008 [11] Rosmaninho, R., Santos, O., Nylander, T., Paulsson, M., Beuf, M., Benezech, T., Yiantsios, S., Andritsos, N., Karabelas, A., Rizzo, G., Muller-Steinhagen, H., and Melo, L F., Modified Stainless Steel Surfaces Targeted to Reduce Fouling—Evaluation of Fouling by Milk Components, Journal of Food Engineering, vol 80, no 4, pp 1176–1187, 2007 [12] Gogenko, A., Anipko O., Arsenyeva, O., and Kapustenko P Accounting for Fouling in Plate Heat Exchanger Design, PRES’07, Ischia, ed Jiri Klemeˇs, Chemical Engineering Transactions, vol 12, 2007, pp 207–212 [13] Liporace, F S., and De Oliveira, S G., Real Time Fouling Diagnosis and Heat Exchanger Performance, Heat Transfer Engineering, vol 28, no 3, pp 193–201, March 2007 [14] Zettler, H U., Wei, M., Zhao, Q., and Muller-Steinhagen, H., Influence of Surface Properties and Characteristics on Fouling in Plate Heat Exchangers, Heat Transfer Engineering, vol 26, no 2, pp 3–17, March 2005 [15] Rehman Khan, J., and Zubair, S M., A Risk-Based Performance Analysis of Plate-andFrame Heat Exchangers Subject to Fouling: Economics of Heat Exchanger Cleaning, Heat Transfer Engineering, vol 25, no 6, pp 87–100, September 2004 David J Kukulka is a professor at the State University of New York College at Buffalo and the coordinator of the Mechanical Engineering Technology Program He received his B.S., M.S., and Ph.D degrees in mechanical engineering from the State University of New York at Buffalo His research interests include thermal/fluid design and surface science studies Many recent projects have been in the area of enhanced heat transfer surface design and studies involving fouling He is a registered professional engineer in the State of New York and is a consultant for many local and national companies Recently he has been involved in new product development for Rigidized Metals Corporation He has published peer-reviewed papers on a variety of topics and has delivered numerous keynote lectures Holly Czechowski is an honors graduate from the State University of New York at Buffalo with a degree in mechanical engineering She currently is involved with corrosion coating research and nanotechnology applications at the State University of New York College at Buffalo and Cameron Compression Peter D Kukulka received his degree from the State University of New York at Buffalo He is currently involved in coatings research and surface science at the State University of New York College at Buffalo He is also a research engineer at Wendel Duchscherer, an engineering firm in Amherst, New York vol 31 no 2010 Heat Transfer Engineering, 31(9):788–797, 2010 Copyright C Taylor and Francis Group, LLC ISSN: 0145-7632 print / 1521-0537 online DOI: 10.1080/01457630903501153 Transposition of an Exothermic Reaction From a Batch Reactor to an Intensified Continuous One ZOE ANXIONNAZ,1 MICHEL CABASSUD,1 CHRISTOPHE GOURDON,1 and PATRICE TOCHON2 Chemical Engineering Laboratory of Toulouse, Univeristy of Toulouse/INPT, France Atomic Energy Commission-GRETh, Grenoble, France The implementation of chemical syntheses in a batch or semi-batch reactor is generally limited by the removal or the supply of heat A way to enhance thermal performances is to develop multifunctional devices like heat exchanger/reactors In this work, a novel heat exchanger/reactor is characterized in terms of residence time, pressure drops, and thermal behavior in order to estimate its capacities to perform an exothermic reaction: the oxidation of sodium thiosulfate by hydrogen peroxide Experimental results highlight the performances of the heat exchanger/reactor in terms of intensification, which allows the implementation of the oxidation reaction at extreme operating conditions These conditions are finally compared to the ones of a classical batch reactor • INTRODUCTION In general, the main barrier of classical chemical reactors is the supply or the removal of the heat, since many chemical reactions are temperature dependent Thus, in continuous apparatuses, thermal intensification between the reaction mixture and the utility stream may be the solution to remove this barrier [1, 2] This is the main characteristic of the continuous heat exchanger/reactor, which consists in combining a reactor and a heat exchanger in the same unit [3–5] In case of an exothermic reaction, for instance, heat is removed more rapidly and more efficiently in such apparatuses than in a batch reactor [6] As a consequence, operating modes to implement chemical syntheses can be redefined: Reactants are quickly mixed (which is equivalent to a perfect batch operation), reaction mixture is less diluted (the solvent as a thermal buffer becomes unnecessary), and operating temperature is more controlled As a result, chemical kinetics will increase and reaction time will thus decrease Heat exchanger/reactors are an important part of process intensification technology Many benefits of using such apparatuses are those of process intensification [7–10]: The authors gratefully acknowledge Mark Wood from Chart Industries for providing the experimental heat exchanger/reactor Address correspondence to Professor Michel Cabassud, Chemical Engineering Laboratory of Toulouse, UMR 5503 CNRS/INPT/UPS, all´ee E Monso, BP 84234, 31432 Toulouse Cedex 4, France E-mail: Michel.Cabassud@ensiacet.fr High selectivity and yields due to enhanced heat and mass transfer and flow structure (plug flow behavior) • Minimized risk of runaway reaction due to enhanced heat transfer and smaller sizes • Diminution of waste of energy and raw materials • Smaller and cheaper plant However, the batch or semi-batch reactor is still the reference process because of its high flexibility and adaptability and its well-known working procedures (startup, data acquisition, reaction supervision, control system, etc.) However, the continuous intensified technology is expected to lead to other substantial improvements First, it offers a significant shortening of the time to market [9], particularly in fine chemical and pharmaceutical industries Then, it allows major improvements in safety and environment fields Indeed, the reduction of the size involves the reduction of the volume of reactants Furthermore the quantity of solvent is reduced since reaction mixture is less diluted Finally, unsteady chemical intermediaries can be produced on-line, which reduces storage and transport of dangerous and flammable products The present work aims at characterizing a novel heat exchanger/reactor: the ShimTec reactor designed and built by Chart Industries [11] The characterization is made in terms of residence time distribution, pressure drop, and thermal behavior Then, from results of the characterization, extreme 788 Z ANXIONNAZ ET AL 789 Figure Internal shims from the ShimTec reactor Figure Experimental setup operating conditions are set up to carry out the oxidation reaction of sodium thiosulfate The comparison with a batch reactor is made considering heat removal performances and reaction parameters Finally, the successful application of the “Reduce” concept (Reduce, Reuse, and Recycle) to the ShimTec reactor (considered as a sustainable technology) is highlighted EXPERIMENTAL SETUP The ShimTec reactor from Chart Industries is an example of a heat exchanger/reactor It is composed of three plates: one process plate sandwiched between two utility plates The utility flow rate (Fu ) varies from to 165 L-h−1 and is measured with an electromagnetic flowmeter The utility line is supplied with raw water inside a temperature range of 13◦ C to 80◦ C Two feed lines are available for the process fluids, one for each reactant; Table Details of the ShimTec reactor Details Number of parallel channels Number of layers of each streams Individual channel width (mm) Individual channel depth (mm) Average flow area per channel (mm2 ) Individual channel length, L (mm) Hydraulic diameter, dh (mm) Total fluid volume, V (mm3 ) Total surface area, A (mm2 ) Thickness of the metal between streams (upper bound), e (mm) Process stream Utility stream 2.0 2.0 4.0 1855 2.0 14,836 29,673 70 1.05 3.0 2.61 125 1.14 45,712 160,209 1.2 heat transfer engineering process lines temperature varies in a range of 20◦ C to 60◦ C The main line flow rate (Fp1 ) varies from to 13 L-h−1 , whereas the secondary line flow rate (Fp2 ) varies from to L-h−1 Process flow rates are also measured with an electromagnetic flowmeter Pressure sensors and temperature sensors (Pt100) are set up on process and utility lines inlets and outlets as shown in Figure All measurements (pressure, flow rate, and temperature) are recorded by an on-line data storage system Geometrical data and characteristic sizes of the heat exchanger/reactor are detailed in Table Figure shows a photograph of the internal shims from the reactor, stacked in the picture to produce a mm deep channel METHODS, RESULTS, AND ANALYSIS Residence Time Distribution Experiments Procedure RTD experiments have been carried out in order to characterize the process hydrodynamics inside the ShimTec reactor [12] A spectrophotometric technique that entails a colored tracer has been used Bromothymol blue (BBT), whose intensity of absorbance depends on the concentration, is the tracer, and the measuring probe is located at the process outlet The operating protocol adopted during residence time distribution experiments is the following: • The reactor is fed with a given flow rate When steady state is reached, a known amount of tracer is instantaneously injected (Dirac pulse) with a syringe through a septum at the inlet of the reactor • The tracer concentration is recorded at the reactor outlet • vol 31 no 2010 790 Z ANXIONNAZ ET AL 0,20 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 (a) - Fp=6.9 L-h-1 water - 20°C Water - 20°C P (bar) 0,15 0,10 0,05 0,5 1,5 2,5 0,00 Relative time variable 50 100 150 200 15 20 Utility flow rate (L/h) 0,5 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 Water - 20°C -1 (b) - Fp=17.6 L-h water - 20°C P (bar) 0,4 0,3 0,2 0,1 0,5 1,5 2,5 Relative time variable 10 Process flow rate (L/h) Figure RTD curves function of the flow rate Figure 20◦ C Evolution of pressure drops as a function of flow rate for water at Pressure Drop Each experiment has been performed at room temperature with a total process flow rate varying from to 17.5 Lh−1 The acquisition time of the spectrophotometer is set at 0.12 second Experimental Results Figure shows the RTD obtained with two different flow rates The curves have been represented using a reduced time variable The aspect of the residence time distribution shows that the behavior of the ShimTec reactor can be compared to the one of a plug flow reactor Moreover, Figure shows that after s, there is no tail The intensity of absorbance is equal to the one before the injection Thus, it seems that the specific design of the ShimTec reactor offers good mixing performances and has no dead zones, recirculations, or stagnant volumes This result is important to implement chemical syntheses Indeed, no dead zones means that there will be no reactants accumulation, which increases the safety of the process by avoiding the development of hot spots Moreover, a good mixing and no stagnant zones will have a positive impact on yields and selectivity Curve (a) presents a longer tail than curve (b); this is due to the influence of the flow rate Indeed, the higher the flow rate is, the better the plug flow behavior is heat transfer engineering Analysis of pressure drop aims at defining a law that links pressure drop to the Reynolds number This law is characteristic of the geometry and of the size of the reactor channels The influence of flow rate on pressure drops for process and utility fluids is presented in Figure Pressure drop of the process fluid is low, under 0.4 bars (± 0.05 bars) for 15 L-h−1 Regarding utility fluid, pressure drop is negligible since it is under 0.15 bars (± 0.05 bars) with a flow rate of 150 L-h−1 As a consequence, no relation will be established concerning the utility side The goal of pressure drop experiments is to determine the correlation between pressure drop and Reynolds number In the literature [13], the general expression is written: P= · L u2 ·ρ· dh with = a · Reb (Darcy coefficient) and Re = ρ · u · dh µ From the experimental results, the correlation between Darcy coefficient ( ) and Reynolds number is established This law is specific to the process channel and its expression is for Reynolds vol 31 no 2010 Z ANXIONNAZ ET AL Darcy coefficient ( ) Darcy coefficient ( ) 3,00 Correlation with singularities (2) Experimental data 2,5 Correlation (1) Smooth duct channel 1,5 0,5 400 600 800 1000 Figure Comparison between experimental Darcy coefficients, correlation (1), correlation with singularities (2), and Darcy coefficient in a smooth duct channel number in the range of 200 to 1200: 257.4 (1) Re However, concerning square-cross-section channels with singularities and laminar regime (Re < 2100), the literature [14] offers the following definition of the Darcy coefficient: = where drops,” lam = lam + K · dh L is the coefficient of friction for “regular pressure 64 57.6 = Re Re and K is the coefficient of singularities From experimental data, the coefficient of singularities, K, has been estimated to 324.4; thus, for a Reynolds number range from 200 to 1200, the Darcy coefficient is written: lam = 0.9 · dh 57.6 + 324.4 · (2) Re L This correlation shows that the coefficient of friction, lam , depends on the Reynolds number, whereas the coefficient of singularities, K, is a constant depending on the geometry of each apparatus Figure compares the experimental data with the correlations (1) and (2) and with the correlation in a smooth duct channel [12]: sing = 57.6 Re Unexpectedly, the correlation of singularities (2) does not fit very well with the experimental data These results could actually reveal that the coefficient of singularities, K, may depend on Reynolds number In order to confirm this hypothesis, a third correlation was established for Reynolds number in the range of 200 to 1200: sin g sing = 57.6 + Re = 182.5 dh + 32 · Re L Correlation with singularities (3) smooth duct channel 2,00 1,50 1,00 0,50 400 (3) heat transfer engineering 600 800 1000 1200 Reynolds number (Re) 1200 Reynolds number (Re) sing Correlation (1) Experimental data 2,50 0,00 200 200 791 Figure Comparison between experimental Darcy coefficients, correlation (1), correlation with singularities (3), and Darcy coefficient in a smooth duct channel Comparison between correlation (3) and experimental results is shown in Figure Correlation (3) highlights the fact that in the ShimTec reactor, the coefficient of singularities, K, does not depend only on the channel geometry but also varies with Reynolds number Therefore, in the case of viscous flow, i.e., low Reynolds numbers, singularities will have a strong impact on pressure drops (about four times more than in theory) As a consequence, a great care has to be taken when designing bends, since their influence on pressure drops is not negligible at all Thermal Characterization Industrial chemical syntheses are exo- or endothermic As a consequence, reactors have to be efficient about heat transfer and fitted with an important heat transfer area The ShimTec reactor has been designed for this objective since its geometry is based on a plate heat exchanger concept Therefore, the thermal study aims at characterizing its performances according to two steps: first, study and check of the thermal performances; and then, estimation of heat transfer coefficients Procedure Thermal study is based on experiments that aim at cooling the process fluid A thermostat has been put on the process line, upstream from the reactor inlet, to heat the process fluid from 20 to 60◦ C Process fluid is distilled water at room temperature or heated with a thermostat, whereas utility fluid is water at about 15◦ C Experiments with water are necessary since they allow the study of thermal performances of the reactor regardless of any other phenomenon (reaction, mass transfer, etc.) As a consequence, thermal study is an important preliminary step before performing chemical reactions For each experiment, the operating protocol was as follows: • First, only process channels are fed, and once steady state is reached, thermal losses can be determined • Then, utility plates are fed with raw water until steady state is reached, and heat exchanged between the two fluids is calculated vol 31 no 2010 792 Z ANXIONNAZ ET AL Table Operating conditions for thermal characterization 10 13 Process temperature (◦ C) Ratio Fu /Fp Utility temperature (◦ C) 40–50 40–50 40–50 5–10 2–5–10–15 2–5–10–15 13 13 13 Fu=27 L-h-1 Fu=0 L-h-1 60 Temperature (°C) Process flow rate (L-h−1 ) Fu=0 L-h-1 50 Tu,in 40 Tp,out Tp,in Tu,out 30 20 10 • Finally, the utility is shut down; when steady state is reached the experiment is stopped During the two last steps, starting and stopping utility fluid will allow the determination of reactor dynamics The operating conditions for thermal experiments are summarized in Table Results and Discussion Thermal losses The reactor is made of stainless steel, which is a highly conductive material As a consequence, even if thermal transfer between process and utility fluid is expected to be very good, there also may be thermal losses between the reactor and the outside These losses have to be estimated in order to decouple heat really transferred by convection from thermal losses with the room To estimate thermal losses, the reactor was fed with process fluid, i.e., with hot water, without any utility fluid At steady state, inlet and outlet temperatures were recorded This protocol was repeated for each operating condition previously detailed From temperature recordings, heat due to thermal losses, Ql,th , can be calculated: in Ql,th = Fp · Cp,water · Tout p − Tp Thermal losses vary from to 13 W in a flow rate range of to 13 L-h−1 Because of uncertainties of measurements related to temperature sensors, thermal losses are low enough to consider that they are negligible against heat transferred by convection Finally, although the reactor is made of stainless steel, which is a highly conductive material, low thermal losses for process stream are observed This phenomenon may be due to the fact that the process plate is sandwiched between two utility plates, which isolate it Global heat transfer coefficient, U Figure shows the evolution of temperature versus time in the ShimTec reactor Experiments highlight the high thermal efficiency of the ShimTec reactor Indeed, for each (utility flow rate Fu )/(process flow rate Fp ) ratio higher than 5, thermal efficiency is higher than 95%, which means that all the heat is exchanged between process and utility fluids, as shown in Table This characteristic of the ShimTec reactor is very interesting and important to carry out highly exothermic reactions As a consequence, calculation of the heat transfer coefficient is only made here for a few experiments whose thermal efficiency does not exceed 95% This restriction will have an heat transfer engineering 5000 10000 15000 20000 Time (s) Figure Temperature recording during a thermal experiment; Fp = 13 Lh−1 , Fu = 27 L-h−1 impact on the following value of the global heat transfer coefficient Indeed, its value will be underestimated since it is calculated only in the case of restricted operating conditions (Fu /Fp < 5) This barrier could be removed by adding temperature sensors along the process and utility channels; this was not possible in the present apparatus The global heat transfer coefficient is written: U= Qp A · Tml with out Qp = Fp · Cpp · Tin p − Tp and Tml = in out out Tin p − Tu − Tp − Tu Ln in (Tin p −Tu ) out (Tout p −Tu ) Table sums up global heat transfer coefficients for experiments without temperature pinch (i.e., thermal efficiency