A micro machined micro jet impingement cooling device

A MICRO-MACHINED MICRO JET IMPINGEMENT COOLING DEVICE LWIN LWIN OO NATIONAL UNIVERSITY OF SINGAPORE 2004 A MICRO-MACHINED MICRO JET IMPINGEMENT COOLING DEVICE LWIN LWIN OO (B.E, M. ENG, Yangon Technological University) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF MECHANICAL AND PRODUCTION ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgement ACKNOWLEDGEMENTS The author wishes to express her profound gratitude and sincere appreciation to her supervisors Associate Professor Simon S. Ang and Professor Andrew Tay, who guided the project and contributed much time, thought and encouragement. They have been very patient and understanding, especially when the project was interrupted for some time due to unforeseen circumstances. Special thanks to Thermo Process Lab Technologist Ms.Roslina Bte Abdullah for her assistance, much guidance and loving kindness. I would also like to express some gratitude to Mr.Lim Ping, for his assistance for the FLUENT software and GAMBIT. Thanks are due to Mr.Kong Yen Peng and Mr.Chan Mei Ma from the Institute of Materials Research and Engineering for their time and help in the use of their equipment. The financial assistance provided by the National University of Singapore of research scholarship is thankfully acknowledged. Finally, the author is also indebted to her father, her beloved husband and all her friends for their support and encouragement throughout her studies. i TABLE OF CONTENTS Page Acknowledgements i Table of Contents ii Summary vii List of Figures ix List of Tables xi Nomenclature xii Chapter Introduction 1.1 General Views 1.2 Objectives 1.3 Scope Literature Review 2.1 Introduction 2.2 Jet Impingement Cooling 2.3 Definition and Analytical Work 2.4 Numerical Studies of Impinging Jets Chapter 2.4.1 Effects of jet-to-plate distance on heat and flow characteristics 2.4.2 Effects of Turbulent Model on heat and flow characteristics 2.5 Experimental Studies of Impinging Jets 11 13 ii Chapter 2.5.1 Air jets Impingement Cooling 13 2.5.2 Mist Spray Impingement Cooing 19 Numerical Simulation of Air Slot Jet impingement 26 3.1 Introduction 26 3.2 Slot Jet Impingement in Micro-Channel 26 3.3 Modelling of a Slot Jet Impingement in Micro-Channel 28 3.3.1 3.3.2 Computational Geometry Model of Slot Jet Impingement 29 3.3.1 (a) Single Micro-Channel 29 3.3.2 (b) Multi Micro-Channel 30 Grid/Mesh Generation of Slot Jet Impingement in Micro-Channel 31 3.3.3 Boundary Conditions for Slot Jet Impingement in a Micro-Channel 3.4 33 Solution Procedure in Fluent for Slot Jet Impingement 33 3.4.1 Select the Fluent Solver of Slot Jet Impingement 34 3.4.2 Physical Model of Slot Jet Impingement 34 3.4.3 Define Properties of the Material for Slot Jet Impingement 3.5 39 3.4.4 Boundary Conductions 40 Solution Accuracy and Convergence Criterion 41 iii Chapter Experimental Set Up and Measurements 43 4.1 Introduction 43 4.2 Test Chip for Micro Channel Cooling Experiments 43 4.3 Test Section for Air Slot Jet Impingement Cooling 45 4.4 Design Considerations 48 4.5 Set Up of Air Slot Jet Impingement Cooling Experiment 49 4.5.1 50 Air Flow system 4.6 Procedure of Air Slot Jet Impingement Cooling Experiment 51 4.7 Set Up of Mist Spray Cooling Experiment 52 4.7.1 Air Atomization Nozzle 53 4.7.2 Liquid Flow System 55 4.8 Procedure of Mist Spray Cooling Experiment 58 4.9 Calibration of Thermocouples 59 4.10 Ultrasonic Cleaning 60 4.11 Anodic Bonding 60 4.12 Test Heater 61 4.13 Power Supply 63 Results and Discussion 64 5.1 Introduction 64 5.2 Numerical Simulation Results 64 5.2.1 Slot-Jet Impingement in a Single Micro-Channel 64 5.2.2 Slot-Jet Impingement in Multi Micro-Channel 66 Chapter iv 5.2.3 Observations and Computational Effort 5.3 76 Comparison between Simulation and Experiment Results in Air Slot-Jet Impingement Cooling 77 Experimental of Mist Spray Cooling Results 80 5.4.1 Experimental Run 81 5.4.2 Experimental Run 83 5.4.3 Experimental Run 86 5.5 Comparison of Air Impinging Jet and Mist Cooling Results 88 5.6 General Discussions 89 Conclusion and Recommendations 93 6.1 Conclusion 93 6.2 Recommendations 94 6.2.1 Simulation 94 6.2.2 Heater 95 6.2.3 Others 95 5.4 Chapter References 97 Appendices 105 A. Design and Test Fixtures 105 1. Design of Teflon Block 105 2. Detail Drawing of Test Section 106 A) Front View 106 B) Side View 107 v C) Top View B. C. 108 Calculations 109 B-1 Calculation of Heat Losses 109 B-2 Local of Heat transfer Coefficient 109 B-3 Average Heat transfer Coefficient 110 B-4 Uncertainty Analysis 110 Properties of Materials 113 C-1 Physical Properties of Air 113 C-2 Physical Properties of Liquid Water 113 C-3 Physical Properties of Silicon 114 vi Summary SUMMARY Nowadays, micro-jet impingement has been increasingly applied to cooling of electronics. The objective of this study is to numerically and experimentally investigate the cooling performance of air impingement and mist cooling on micro-channels fabricated on the back of a silicon chip. In mist cooling, an air-water mist is used as the cooling medium. In the first part of this study, numerical simulations of flow and heat transfer in a microchannel with air-jet impingement was carried out using a commercial CFD (Computational Fluid Dynamics) software called FLUENT. The effect of various parameters on the heat transfer and flow was simulated and studied. Air at 300 K was used as a coolant fluid. The maximum limiting wall temperature was maintained at 373 K on the chip surface when doing the simulation as a higher temperature will cause deterioration of the system’s performance and may cause hardware failure in some cases. In this simulation, micro-channel was considered as a single channel and the flow was assumed to be turbulent. The nozzle to plate distance was found to be quite important in this study. The channel depth was varied from 100 µm to 400 µm while the channel width was fixed at 100 µm. The air inlet velocity was varied from 100 m/s to 300 m/s. From this numerical analysis, it was found that the heat flux was increased when the channel depth or the air inlet velocity was increased. A rig was designed and fabricated for the experimental study. The test section consists of a 21mm x 21mm square silicon die with micro-channels etched on its surface, which was covered with a glass plate to confine the flow through the micro-channels. A slot was vii Summary machined across the glass cover plate to admit air from an inlet manifold. In this experimental study the depth of the air inlet manifold, the slot width and the inlet velocity of the coolant were varied. The depth and width of the micro-channels were not varied due to difficulties in obtaining silicon dies with micro channels machined on the surface. The performance of an air-water mist spray cooling system was also studied experimentally. It was found that an air-water mist spray cooling system could give a higher cooling rate than air-only impingement cooling. For the same heat dissipation, it was found that the air-water mist spray cooling system required a much smaller flow rate of air. viii References [12] Estes, Kurt A., and Mudawar Issam, (1995). Comparison of two-phase electronic cooling using free jets and sprays, Journal of Electronic Packaging, Vol. 117, pp.323-331. [13] Gardon, R., and Cobonpue, J., (1963). Heat transfer between a flat plate and jets of air impinging on it, International Heat transfer Conference 2nd Boulder Colo. and Westminster, London, England, International Developments in Heat Transfer Proceeding, New York, pp. 454-460. [14] Gardon, R., and Akfirat, J.C., (1965). The role of turbulence in determining the heat transfer characteristics of impinging jets, International Journal of Heat Mass Transfer, Vol. 8, pp. 1261-1272. [15] Garimella, S. V., and Nenaydykh, B., (1996). Nozzle-geometry effects in liquid jet impingement heat transfer, International Journal of Heat Mass Transfer, Vol.39, pp.29152923. 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Developing convective heat transfer in deep rectangular micro-channels, International Journal of Heat and Fluid Flow, Vol.20, pp. 149-157. [22] Huber, A. M., and Viskanta, S.V., (1994). Convective heat transfer to a confined impinging array of air jets with spent air exits, ASME Journal of Heat Transfer, Vol. 41, pp. 570-576. [23] Huber, A. M., and Viskanta, S.V., (1994). Effect of jet - spacing on convective heat transfer to confined, impinging arrays of axisymmetric air jets, International Journal of Heat Mass Transfer, Vol.37, pp. 2859-2869. 100 References [24] Law, H.S., and Masliyah, J.H., (1984). Mass transfer due to a confined laminar impinging two-dimensional jet, International Journal of Heat Mass Transfer, Vol. 27, No.4, pp. 529-539. [25] Lee, S. L., Yang, Z. H., and Hsyun, Y., (1994). Cooling of a heated surface by mist flow, Journal of Heat Transfer, Vol. 116, pp. 167-172. [26] Leland J.E., Pannappan, R., and Klasing, K.S., (1999). Experimental investigation of an air micro jet array impingement cooling device, AIAA 99-0476, 37th AIAA Aerospace Science, Reno, N V. [27] Li, X., Gaddis, J.L., and Wang, T. (2001). Mist /steam heat transfer in confined slot jet impingement, Journal of Turbo Machinery, Vol. 123, pp. 161-167. [28] Li, X., Gaddis, J.L., and Wang, T. (2001). Mist /steam cooling by a row of impinging jets, Proceedings of ASME Turbo Expo, New Orleans, Louisiana. [29] Lin, Z.H., Chou, Y.J., Hung, Y.H., (1997). Heat transfer behaviors of a confined slot jet impingement, International Journal of Heat Mass Transfer, Vol.40, pp. 1095-1107. [30] Lyte, D., Webb, B.W., (1994). Air impingement heat transfer at low nozzle-plate spacing, International Journal of Heat Mass Transfer, Vol.37, pp. 1687-1697. 101 References [31] Mikhail, S., Morcos, S.M., Abou-Ellail, and Ghalay, W.S., (1982). Numerical prediction of flow field and heat transfer from a row of laminar slot jet impinging on a flat plate, Proceeding of the 7th International Heat Transfer Conference, Munich, Germany, Vol.3, pp.377-382. [32] Mode, M., (1979). Critical heat flux in the saturated forced convection boiling on a heated disk with impinging droplets, Journal of Heat Transfer, Japanese Research, Vol.8, pp.54-64. [33] Moffat, R.J., (1985). Using Uncertainty Analysis in the Planning of an Experiment, Journal of Fluids Engineering, Vol.107, pp.173-178. [34] Oh Yian Yian Elisabeth (2002). The experimental investigations of a micro machined micro channel cooling device, Thesis (B.E), Department of Mechanical Engineering, National University of Singapore. [35] Oliphant, K., Webb*, B.W., and Mcquay, M.Q., (1998). An experimental comparison of liquid jet array and spray impingement cooling in the non-boiling regime, Experimental Thermal and Fluid Science, Vol.18, pp.1-10. [36] Oliveira, M. S. A., and Sousa, A.C.M., (2001). Neural network analysis of experimental data for air/water spray cooling, Journal of Material Processing Technology,Vol.113, pp. 439-445. 102 References [37] Paris, M. R., Chow, L. C., and Mahefkey, E. T., (1992). Surface roughness and its effects on the heat transfer mechanism in spray cooling, ASME Journal of Heat Transfer, Vol.114, pp. 211-219. [38] Selvan, R.Panner, J. Kather, Y.Jung, S.Ang, and A.Elshabini, (2001). Computer modeling to optimize the heat removal capacity of the micro-jet array, Proceeding of the IMAPS, International microelectronic conference. [39] Sehmbey, M. S., Chow, L. C., Paris, M. R., and Mahefkey, T., (1994). High heat flux spray cooling: A review; Heat transfer in high heat flux system ASME, Heat Transfer Device, Vol. 301, pp39-46. [40] Tilton D., Paris M.R., Chow L.C. and Mahefky K.E., (1989). High heat flux, low superheated evaporative spray cooling, 27th Aerospace Science Meeting, Reno, NV. [41] Webb, B. W., and Ma, C. F. (1995). Single-phase liquid jet impingement, Advances in Heat Transfer, Vol.26, pp. 105- 112. [42] Wu, S., Mai‫٭‬, J., Tai, Y. C., Ho‫٭‬, C. M., (2000). Micro heat exchanger by using MEMS impinging jets, Journal of Electrical Engineering, pp.136-93, California Institute of Technology, Pasadena, CA 91125. 103 References [43] Yang Cheng (2001). Cooling of electronic component jet impingement boiling, Thesis (Ph.D), Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore. [44] Yao, S.C and Choi, K.J (1987). Mechanisms of film boiling heat transfer of normally impacting sprays, International Journal of Heat and Mass Transfer, Vol.30 pp. 113-120. [45] Gambit Modeling Guide (1998). Fluent Incorporated Lebanon, pp.3-137. [46] Fluent User’s Guide Volume (1998). Fluent Incorporated Lebanon, pp.18-62. 104 Appendix APPENDIX A Design and Test Fixtures 1. Design of Teflon Block Figure A-1: Teflon (PTFE) Block 105 Appendix 2. Detail Drawing of Test Section (A) Front View AIR IN LET 30 mm 5mm 15mm MANIFOLD PYREXGLASS MICROCHANNEL TEFLON BLOCK THICK FILM HEATER INSULATION WIRE HOLE 25mm AIR OUT LET 35mm AIR OUT LET THERMOCOUPLE PYREXGLASS 80mm FRONT VIEW 106 Appendix (B) Side View AIR IN LET 30 mm 5mm 15mm MANIFOLD MICROCHANNEL TEFLON BLOCK THICK FILM HEATER INSULATION HEATER WIRES 25mm 35mm THERMOCOUPLE PYREXGLASS 80mm SIDE VIEW 107 Appendix (C) Top View 30 mm 16.6 mm 12.7 mm PYREXGLASS TEFLON BLOCK THICK FILM HEATER MICROCHANNELS AIR OUT LET 80 mm 29.8 mm 25.4 mm 21 mm AIR OUT LET WIRE HOLES INSULATION HEATER WIRE GROOVES 21 mm 80 mm TOP VIEW 108 Appendix APPENDIX B Calculations: B-1 Calculation of Heat Losses The bulk of the heat losses occur through the bottom of the resistor through the Teflon block. This heat loss is estimated by measuring the temperature at the top surface of the Teflon block, Ta and that at the bottom surface of the block, Tb, using thermocouples. The Teflon block is 12.5 mm wide and 30mm long. Heat flux (through bottom), qb = k Ta − Tb t Heat loss, Qb = q b × At where thermal conductivity of Teflon, k =0.25 W/m K. Thickness of Teflon, t = 7mm. Area of Teflon, At = 12.5 × 30mm . B-2 Local Heat Transfer Coefficient The local heat transfer coefficient on the heated surface is calculated as follows: h= q , ∆T where q = heat flux (W/m2), and ∆T = Temperature difference between the local surface temperature and the inlet fluid temperature (K). 109 Appendix B-3 Average Heat Transfer Coefficient The average heat transfer coefficient is calculated as follows: h =∫ hdA , A where h = local heat transfer coefficient (W/m2K) A = area of the heated surface (m2) However, Fluent provides the surface integral function that calculates the magnitude of the average heat transfer coefficient on the heated surface. B-4 Uncertainty Analysis An uncertainty analysis is provided to determine the correctness of the experimental results. Uncertainty is an estimation of the difference between the experimental value and the true value of a measured quality by the investigator, with a given confidence interval. All measurement of a variable contains inaccuracies and it is very important to have an understanding of these inaccuracies when the experiments are conducted. An uncertainty analysis is conducted on the average heat transfer coefficient in this study based on the methodology proposed by Moffat [33]. A standard uncertainty analysis showed that the uncertainty at 95% confidence interval could be utilized. The uncertainty of a measured value can be divided into two parts, the bias limit and precision limit. The bias limit consists of fixed errors such as fossilized error of a thermo physical property table, and calibration errors, which arise from calibrating the measuring instrument to a 110 Appendix known input. The precision limit consists of a combination of process and instrument unsteadiness attributed to randomness. The listing of these components of uncertainty for the heat transfer quantities directly measured in this study is given in Table B1 [34]. The bias limits are determined from the calibration performed or otherwise provided from the instrument manufacturer. The precision limits of the heat transfer quantities are given as two times the standard deviation of a measured value for a set of observations from a steady state experiment. The total uncertainty of a measured value can be determined as follows: U=( B2 +P2)1/2 Table B1 Bias (B) Precision (P) Current, I 0.36% 0.01A Voltage, V 0.025% 0.01V 0.5°C 0.1°C Temperature, °C The heater power, Q = V × I The result Q of an experiment is calculated from measurements of voltage and current. Thus, the uncertainty of heat power Q can be calculated using the following expression: ∂Q ⎧⎪ ∂V =⎨ Q ⎪⎩ V ∂A + A 1/ ⎫⎪ ⎬ ⎪⎭ 111 Appendix The average heat transfer coefficient is defined as, h = Q , where Q is heater As Ts − Tin ( ) power, Tw is the surface wall temperature and Tin is the jet or inlet temperature. Surface wall temperatures are measured by thermocouples embedded directly underneath the length of the chip. Air inlet temperature is also measured by thermocouple at the air supply pipe. The uncertainty of heat transfer coefficient is also calculated from a measured of heat power, Q, the cross-sectional area, As and temperature of difference, ∆T. The cross-sectional area, As is constant so that the uncertainty of heat transfer coefficient is calculated using the following expression: ∂h ⎧⎪ ∂Q ∂T =⎨ + h T ⎪⎩ Q 1/ ⎫⎪ ⎬ ⎪⎭ Table B2 shows the uncertainty of heater power and heat transfer coefficient above the calculations. Table B2 No. Uncertainty U 1. Heater power, Q 0.5% 2. Heat transfer coefficient, h 1.0∼3.5%(All cases) 112 Appendix APPENDIX C Properties of Materials: C-1 Physical Properties of Air Table C-1: Properties of air used in the experiment Density ( ρ) 1.225 kg/m3 Specific heat capacity (Cp) 1.006KJ/kg K Thermal conductivity (K) 0.0242 W/m K Viscosity (µ) 1.7894x10-5 Kg/m s C-2 Physical Properties of Liquid Water Table C-2: Properties of liquid water used in the experiment Density (ρ) 998.2 Kg/m3 Specific heat capacity (Cp) 4.18 KJ/kg K Thermal conductivity (K) 0.6 W/m K Viscosity (µ) 0.001003 kg/m s Latent heat 2263.07 KJ/kg Boiling point 373 K 113 Appendix C-3 Physical Properties of Silicon Table C-3: Properties of silicon used in the experiment Density (ρ) 2330 kg/m3 Specific heat capacity (Cp) 712 J/kg K Thermal conductivity (K) 100 W/m K 114 [...]... flux and the droplet velocity affects the heat transfer The comparison of the two cooling techniques showed that spray cooling could provide the same heat transfer as jet cooling but with a significantly lower liquid mass flux Graham and Ramadhyani [20] made experimental and theoretical studies of mist jet impingement cooling The mist jet was created using a coaxial jet atomizer, and experimental data... studied the heat transfer characteristics of single and dual exit drainage configurations for arrays of liquid jets impinging normal to a heated plate They found that the plate-averaged heat transfer coefficient increased for decreasing jet- to -jet spacing Moreover, the maximum plate-averaged Nusselt number was found at a nozzle-to-plate spacing of four jet diameters Garimella and Nenaydykh [15] conducted... of accelerating fluid between the nozzle-plate gap as well as a significant increase in local turbulence was found to lead to substantially increased local heat transfer with decreased nozzle-plate spacing A stagnation point minimum surrounded by an inner and outer peak in the local heat transfer was observed for nozzle-plate spacing less than z/d = 0.25 These primary and secondary maxima are explained... at the higher Reynolds numbers With a nine -jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet However, for four -jet arrangement, each jet was found to have stagnation region heat transfer coefficients that were comparable to the corresponding single -jet data, although the average heat transfer coefficient was higher for the jet array Huber and Viskanta... required Although such jets yield very high heat transfer coefficients in the stagnation zone, the cooling performance drops rapidly away from the impingement zone 1.2 Objectives The main objectives of this study are to simulate, fabricate and evaluate a MEMS-based micro- jet impingement cooling device using air and air/water mist spray as the cooling medium for microelectronic and micro system applications... reported that heat transfer rates at the stagnation point were very high, but at a distance of two to three nozzle diameters from the stagnation point, the cooling rate is less than half that of the stagnation value Chatterjee and Deviprasath [7] studied heat transfer in confined laminar axisymmetric impinging jets at small nozzle-plate distances They reported that the occurrence of the off-stagnation point... peak was attained to be due to a transition to a turbulent wall jet They also reported that the large orificetarget spacing (H/d =1,6), an inter jet spacing of 8 resulted in higher local Nusselt numbers than smaller inter jet spacing of 4 and 6 An inter jet spacing of four diameters was found to provide the highest average heat transfer over a given surface area Garrett and Webb [18] experimentally studied... air velocity at any given temperature gave higher heat dissipation A simple analytical model was developed to predict the liquid film thickness and heat transfer rate The predictions found very good agreement with the air/methanol data and reasonable agreement with the air/water data Paris et al [37] investigated surface roughness effects in the air/water mist impingement scheme Their experiment was... target surface With the measurement of jet mean velocity and turbulence intensity distributions at nozzle exit, two jet flow characteristics at nozzle exit; initially laminar and transitional/turbulent regimes were classified As for the investigation of heat transfer behavior on stagnation, local and average Nusselt number, the effect of jet separation distance was not significant; while the heat transfer... of gas, where it was clear that for both types of jets, a lower inlet pressure gave a higher cooling efficiency In jet array cooling, they also reported that the surface temperature distribution was more uniform than single jet cooling This was more evident in the case of nozzle arrays, which was the most efficient arrangement among the four variations Finally, they reported that a micro impinging jet . The main objectives of this study are to simulate, fabricate and evaluate a MEMS-based micro- jet impingement cooling device using air and air/water mist spray as the cooling medium for microelectronic. in a micro- channel with air -jet impingement was carried out using a commercial CFD (Computational Fluid Dynamics) software called FLUENT. The effect of various parameters on the heat transfer. transfer and flow was simulated and studied. Air at 300 K was used as a coolant fluid. The maximum limiting wall temperature was maintained at 373 K on the chip surface when doing the simulation as