UNIT OPERATIONS IN FOOD PROCESSING R L EARLE with M.D EARLE An introduction to the principles of food process engineering This is the free web edition of a popular textbook known for its simple approach to the diversity and complexity of food processing First published in 1966 but still relevant today, Unit Operations in Food Processing explains the principles of operations and illustrates them by individual processes Each Chapter contains unworked examples to help the student food technologist or process engineer gain a grasp of the subject Now in electronic form, fully searchable and cross-linked, this online resource will also be a useful quick reference for technical workers in the food industry The author, Dick Earle (owner of the copyright) gives permission to download and print any part or all of the text for any nonprofit purposes Content can be printed by individual page, or as complete Chapters Funding, publication and hosting for the book is provided by the New Zealand Institute of Food Science & Technology (NZIFST) This web edition of Unit Operations in Food Processing is given by Dick and Mary Earle, with the support of the NZIFST, as a service to education in food technology, and to the wider food industry Unit Operations in Food Processing - the Web Edition http://www.nzifst.org.nz/unitoperations Unit Operations in Food Processing Copyright © 1983, R L Earle :: Published by NZIFST (Inc.) ABOUT THE BOOK The Web Edition Process engineering is a major contributor to food technology, and provides important and useful tools for the food technologist to apply in designing, developing and controlling food processes Process engineering principles are the basis for food processing, but only some of them are important and commonly encountered in the food industry This book aims to select these important principles and show how they can be quantitatively applied in the food industry It explains, develops and illustrates them at a level of understanding which covers most of the needs of the food technologist in industry and of the student working to become one It can also be used as an introduction to food engineering When this book was first published in 1966, there were almost no books available in food process engineering This book met an extensive need at its modest standard and cost It was widely distributed and used, all over the world Subsequently other textbooks have emerged and the available literature and data have grown enormously In particular there are excellent books covering advanced food engineering and also specialist areas of food processing However there still seems to be a need for an introductory, less specialised book at an accessible level With the hard copy book in English having been out of print for some time, it seemed appropriate to make the book widely available through a free Web site So what is largely the text of the 2nd Edition with corrections and only minor changes has been converted to a user-friendly computer-based learning source on the World Wide Web Here it will be freely available for consultation or copying, indeed for any use save commercial reproduction It is contributed as a service to the food industry It can be used not only as an interactive learning text for the student, but also as a quick reference for people in industry who from time to time have a specific need for a method of calculation The contents are interlinked so that specific information, examples and figures can easily be found The book is intended to introduce technological ideas and engineering concepts, and to illustrate their use Data, including properties and charts, are provided, but for definitive design details may need to be independently checked to ensure requisite precision Every effort has been made to provide clear explanations and to avoid errors, but errors may occur including in the translation to the Web Also greater precision and clarity may well be achievable So feedback from users will be most welcome, and should be directed to The Editor Obviously this book is the product of much more than just the efforts of the author whose name appears on the title The ideas developed have been built up over the years by a multitude of researchers, inventors, scientists, engineers and technologists, far too numerous to list Some have been identified in the text and references, and some of these have made individual contributions; the material they made available has provided the essence of the book, the facts and figures and diagrams It is hoped that they have been accurately quoted and nowhere misinterpreted Pergamon Press first published the book giving it clear layout and wide distribution at a reasonable price A number of colleagues helped with improvements for the second edition More extensive acknowledgement of these contributors has been made in the Prefaces and elsewhere in the earlier editions The thanks and gratitude of the author to all who have provided material remain undiminished Prof Buncha Ooraikul and Prof Paul Jelen encouraged putting it onto the Web, as it was still being used by their students Editions even for the Web not come without cost So particular mention for this Web edition must be made of the New Zealand Institute of Food Science and Technology which contributed finance and hosting, and of Chris Newey who converted it to the new form Chris found that translation of printed text carrying many tables, equations, superscripts and subscripts into Web format moved well beyond the capacity of the optical character recognition, and it gave him a great deal of work before final emergence in the convenient html and swf forms I am very grateful to him for his extensive and very worthwhile contribution As in the earlier editions, even more so in this, appearance would never have occurred without the cheerful, unstinting, and technically invaluable help of my wife Mary We will all be rewarded by this site being both useful, and well and widely used Richard L.Earle Palmerston North, New Zealand 2003 About the Author R L Earle, Emeritus Professor, Massey University, Palmerston North, New Zealand Dick Earle trained as a chemical engineer, and in research in food technology, before entering the New Zealand meat industry His interests were particularly in refrigeration and energy usage, heat transfer and freezing, and byproduct and waste processing Dick joined Massey University in 1965, initially in food technology, and later founding the biotechnology discipline, which had special interests in the processing of biologically-based materials He has published several books jointly with his wife (Dr) Mary Earle on product development and reaction technology, and many technical papers and reports He is a Distinguished Fellow of the Institution of Professional Engineers New Zealand (IPENZ) Dick and Mary Earle have recently established a scholarship for the support and encouragement of postgraduate research into aspects of technology in New Zealand universities The Print Editions This book is now out of print It was originally published by Pergamon Press: First edition 1966 Second edition 1983 British Library Cataloguing in Publication Data Earle, R L Unit operations in food processing - 2nd ed - (Pergamon Commonwealth and International Library) Food industry and trade - Quality control I Title 664 '.07 TP372.5 ISBN 0-08-025537-X Hardcover ISBN 0-08-025536-1 Flexicover Copyright Copyright © 1983-2004 R L Earle All Rights Reserved Copyright remains with the author, however, the author gives permission to The New Zealand Institute of Food Science & Technology (Inc.) (NZIFST) for free use and display of this material on the internet, and permission to all site visitors for the free use and copying of all or part of the text for non-commercial purposes, subject to acknowledgement of the source (which is, unless otherwise indicated): Unit Operations in Food Processing, Web Edition, 2004 Publisher: The New Zealand Institute of Food Science & Technology (Inc.) Authors: R.L Earle with M.D Earle CONTENTS ABOUT THE BOOK The history of Unit Operations in Food Processing, and how it came to be published on the web CHAPTER INTRODUCTION Method of studying food process engineering Basic principles of food process engineering Conservation of mass and energy Overall view of an engineering process Dimensions and units Dimensions symbols Units Dimensional consistency Unit consistency and unit conversion Dimensionless ratios specific gravity Precision of measurement Summary Problems CHAPTER MATERIAL AND ENERGY BALANCES Basic principles Material balances Basis and units total mass and composition concentrations Types of Process situations continuous processes blending Layout Energy balances Heat balances enthalpy latent heat sensible heat freezing drying canning Other forms of energy mechanical energy electrical energy Summary Problems CHAPTER FLUID-FLOW THEORY Introduction Fluid statics fluid pressure absolute pressures gauge pressures head Fluid dynamics Mass balance continuity equation Energy balance Potential energy Kinetic energy Pressure energy Friction loss Mechanical energy Other effects Bernouilli's equation flow from a nozzle Viscosity shear forces viscous forces Newtonian and Non-Newtonian Fluids power law equation Streamline and turbulent flow dimensionless ratios Reynolds number Energy losses in flow Friction in Pipes Fanning equation Hagen Poiseuille equation Blasius equation pipe roughness Moody graph Energy Losses in Bends and Fittings Pressure Drop through Equipment Equivalent Lengths of Pipe Compressibility Effects for Gases Calculation of Pressure Drops in Flow Systems Summary Problems CHAPTER FLUID-FLOW APPLICATIONS Introduction Measurement of pressure in a fluid manometer tube Bourdon tube Measurement of velocity in a fluid Pitot tube Pitot-static tube Venturi meter orifice meter Pumps and fans Positive Displacement Pumps Jet pumps Air-lift Pumps Propeller Pumps and Fan Centrifugal Pumps and Fans pump characteristics fan laws Summary Problems CHAPTER HEAT-TRANSFER THEORY Introduction Heat Conduction thermal conductance thermal conductivity Thermal Conductivity Conduction through a Slab Fourier equation Heat Conductances Heat Conductances in Series Heat Conductances in Parallel Surface-Heat Transfer Newton's Law of Cooling Unsteady-State Heat Transfer Biot Number Fourier Number charts Radiation-Heat Transfer Stefan-Boltzmann Law black body emissivity grey body absorbtivity reflectivity Radiation between Two Bodies Radiation to a Small Body from its Surroundings Convection-Heat Transfer Natural Convection Nusselt Number Prandtl Number Grashof Number Natural Convection Equations vertical cylinders and planes horizontal cylinders horizontal planes Forced Convection Forced-convection Equations inside tubes over plane surfaces outside tubes Overall Heat-Transfer Coefficients controlling terms Heat Transfer from Condensing Vapours vertical tubes or plane surfaces horizontal tubes Heat Transfer to Boiling Liquids Summary Problems CHAPTER HEAT-TRANSFER APPLICATIONS Introduction Heat Exchangers Continuous-flow Heat Exchangers parallel flow counter flow cross flow heat exchanger heat transfer log mean temperature difference Jacketed Pans Heating Coils Immersed in Liquids Scraped Surface Heat Exchangers Plate Heat Exchangers Thermal Processing Thermal Death Time F values Equivalent Killing Power at Other Temperatures z value sterilization integration time/temperature curves Pasteurization milk pasteurization High Temperature Short Time HTST Refrigeration, Chilling and Freezing Refrigeration Cycle temperature/enthalphy chart evaporator condenser adiabatic compression coefficient of performance ton of refrigeration Performance Characteristics Refrigerants ammonia refrigerant 134A Mechanical Equipment Refrigeration Evaporator Heat transfer coefficient fins Chilling Freezing Plank's equation freezing time shape factors Cold Storage Summary Problems CHAPTER DRYING Basic Drying Theory Three States of Water phase diagram for water vapour pressure/temperature curve for water Heat Requirements for Vaporization Heat Transfer in Drying Dryer Efficiencies Mass Transfer in Drying mass transfer coefficient Psychrometry absolute humidity relative humidity dew point humid heat Wet-bulb Temperatures dry bulb temperature Psychrometric Charts Measurement of Humidity hygrometers Equilibrium Moisture Content Air Drying drying rate curves Calculation of Constant Drying Rates Falling-rate Drying Calculation of Drying Times Conduction Drying Drying Equipment Tray Dryers Tunnel Dryers Roller or Drum Dryers Fluidized Bed Dryers Spray Dryers Pneumatic Dryers Rotary Dryers Trough Dryers Bin Dryers Belt Dryers Vacuum Dryers Freeze Dryers Moisture Loss in Freezers and Chillers Summary Problems Lewis number CHAPTER EVAPORATION The Single-Effect Evaporator Vacuum Evaporation Heat Transfer in Evaporators Condensers Multiple-Effect Evaporation Feeding of Multiple-effect Evaporators Advantages of Multiple-effect Evaporators Vapour Recompression Boiling Point Elevation Raoult's Law Duhring's rule Duhring plot latent heats of vaporization Evaporation of Heat-Sensitive Materials Evaporation Equipment Open Pans Horizontal-tube Evaporators Vertical-tube Evaporators Plate Evaporators Long-tube Evaporators Forced-circulation Evaporators Evaporation for Heat-sensitive Liquids Summary Problems CHAPTER CONTACT-EQUILIBRIUM PROCESSES Introduction contact equilibrium separation phase distribution equilibrium distribution coefficients PART 1: THEORY Concentrations mole fraction partial pressure Avogadro's Law Gas-Liquid Equilibria partial vapour pressure Henry's Law solubility of gases in liquids Solid-Liquid Equiibria solubility in liquids solubility/temperature relationship saturated solution supersaturated solution Equilibrium-Concentration Relationships overflow/underflow equilibrium diagram Operating Conditions contact stages mass balances Calculation of Separation in Contact-Equilibrium Processes combining equilibrium and operating conditions deodorizing/steam stripping McCabe/Thiele diagram PART 2: APPLICATIONS Gas Absorption number of contact stages Rate of Gas Absorption Lewis and Whitman Theory Stage-equilibrium Gas Absorption Gas-absorption Equipment Extraction and Washing equilibrium and operating conditions McCabe Thiele diagram Rate of Extraction Stage-equilibrium Extraction Washing Extraction and Washing Equipment extraction battery Crystallization mother liquor Crystallization Equilibrium growth nucleation metastable region seed crystals heat of crystallization Rate of Crystal Growth Stage-equilibrium Crystallization Crystallization Equipment scraped surface heat exchanger evaporative crystallizer Membrane Separations osmotic pressure ultrafiltration reverse osmosis Rate of Flow Through Membranes Van't Hoff equation Diffusion equations Sherwood number Schmidt number Membrane Equipment Distillation Equilibrium relationships boiling temperature/concentration diagram azeotropes Steam Distillation Vacuum Distillation Batch Distillation Distillation Equipment Summary Problems CHAPTER 10 MECHANICAL SEPARATIONS Introduction The velocity of particles moving in a fluid terminal velocity drag coefficient terminal velocity magnitude Sedimentation Stokes' Law Gravitational Sedimentation of Particles in a Liquid zones velocity of rising fluid sedimentation equipment Flotation Sedimentation of Particles in a Gas Settling Under Combined Forces Cyclones- optimum shape efficiency Impingement separators Classifiers Centrifugal separations centrifugal force particle velocity Liquid Separation radial variation of pressure radius of neutral zone Centrifuge Equipment Filtration rates of filtration filter cake resistance equation for flow through the filter Constant-rate Filtration Constant-pressure Filtration filtration graph Filter-cake Compressibility Filtration Equipment Plate and frame filter press Rotary filters Centrifugal filters Air filters Sieving rates of throughput standard sieve sizes cumulative analyses particle size analysis industrial sieves air classification Summary Problems CHAPTER 11 SIZE REDUCTION Introduction Grinding and cutting Energy Used in Grinding Kick's Law Rittinger's Law Bond's Law Work Index New Surface Formed by Grinding shape factors Grinding equipment Crushers Hammer mills Fixed-head mills Plate mills Roller mills Miscellaneous milling equipment Cutters Emulsification disperse/continuous phases stability emulsifying agents Preparation of Emulsions shearing homogenization Summary Problems 10 APPENDICES APPENDIX STEAM TABLE - SATURATED STEAM Temperature Pressure(Absolute) (°C) (kPa) Enthalpy (sat vap.) (kJ kg-1) Latent heat Specific volume (kJ kg-1) (m3 kg-1) 2501 2499 2497 2492 2487 2483 2478 2473 2468 2464 2459 2454 2449 2445 2440 2435 2431 2407 2383 2359 2334 2309 2283 2257 2244 2230 2217 2203 2189 2174 2160 2145 2114 2083 206 193 180 157 138 121 106 93.9 82.8 73.3 65.0 57.8 51.4 45.9 40.0 36.6 32.9 19.5 12.0 7.67 5.04 3.41 2.36 1.67 1.42 1.21 1.04 0.892 0.771 0.669 0.582 0.509 0.393 0.307 Temperature Table 10 12 14 16 18 20 22 24 26 28 30 40 50 60 70 80 90 100 105 110 115 120 125 130 135 140 150 160 0.611 0.66 0.71 0.81 0.93 1.07 1.23 1.40 1.60 1.82 2.06 2.34 2.65 2.99 3.36 3.78 4.25 7.38 12.3 19.9 31.2 47.4 70.1 101.4 120.8 143.3 169.1 198.5 232.1 270.1 313.0 361.3 475.8 617.8 2501 2503 2505 2509 2512 2516 2520 2523 2527 2531 2534 2538 2542 2545 2549 2553 2556 2574 2592 2610 2627 2644 2660 2676 2684 2692 2699 2706 2714 2721 2727 2734 2747 2758 300 180 200 1002 1554 2778 2793 2015 1941 0.194 0.127 2485 2479 2473 2468 2464 2460 2452 2445 2433 2424 2406 2393 2358 2319 2274 2258 2251 2244 2238 2232 2227 2221 2216 2211 2207 2202 2182 2164 2148 2134 2121 2109 2057 2015 129 109 93.9 82.8 74.0 67.0 54.3 45.7 34.8 28.2 19.2 14.7 7.65 3.99 2.09 1.69 1.55 1.43 1.33 1.24 1.16 1.09 1.03 0.978 0.929 0.886 0.719 0.606 0.524 0.463 0.414 0.375 0.256 0.194 Pressure Table 7.0 9.7 12.0 14.0 15.8 17.5 21.1 24.1 29.0 32.9 40.3 45.8 60.1 75.9 93.5 99.6 102.3 104.8 107.1 109.3 111.4 113.3 115.2 116.9 118.6 120.2 127.4 133.6 138.9 143.6 147.9 151.6 167.8 179.9 1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 4.0 5.0 7.5 10.0 20.0 40.0 80.0 100 119 120 130 140 150 160 170 180 190 200 250 300 350 400 450 500 750 1000 2514 2519 2523 2527 2531 2534 2540 2546 2554 2562 2575 2585 2610 2637 2666 2676 2680 2684 2687 2690 2694 2696 2699 2702 2704 2707 2717 2725 2732 2739 2744 2749 2766 2778 * Reproduced with permission from J H Keenan et al., Steam Tables - lnternational Edition in Metric Units, John Wiley, New York, 1969 Note Gauge pressure Absolute pressure + 100 kPa 301 APPENDICES APPENDIX (a) PSYCHROMETRIC CHART Normal temperatures 1013.25 millibars 302 APPENDICES APPENDIX (b) PSYCHROMETRIC CHART High temperatures 1013.25 millibars 303 APPENDICES APPENDIX 10 STANDARD SIEVES Aperture -3 (m x 10 ) ISO nominal aperture U.S no Tyler no -3 (m x 10 ) 22.6 7/8 in 0.883 in 16.0 16 5/8 in 0.624 in 11.2 11.2 7/16 in 0.441 in 8.0 8.00 5/16 in 1/2 mesh 5.66 5.66 No.3 1/2 1/2 mesh 4.00 4.00 5 mesh 2.83 2.80 7 mesh 2.00 2.00 10 mesh 1.41 1.41 14 12 mesh 1.00 1.00 18 16 mesh 0.71 0.710 25 24 mesh 0.500 0.500 35 32 mesh 0.354 0.355 45 42 mesh 0.250 0.250 60 60 mesh 0.177 0.180 80 80 mesh 0.125 0.125 120 115 mesh 0.088 0.090 170 170 mesh 0.063 0.063 230 250 mesh 0.044 0.045 325 325 mesh Note 500m = 0.50 m x 10-3 aperture = 35 US No = 32 mesh 304 APPENDICES APPENDIX 11 (a) PRESSURE/ENTHALPY CHARTS FOR REFRIGERANTS (a) Tetrafluoroethane (refrigerant 134a) reference state h = 200.0 kJ/kg; s = 1.00 kJ/(kg-K) for saturated liquid at 0°C Reproduced with permission: The International Institute of Refrigeration (IIR) - Institut International du Froid, Paris, France http://www.iifiir.org/ 305 APPENDICES APPENDIX 11 (b) PRESSURE / ENTHALPY CHARTS FOR REFRIGERANTS (b) Ammonia (refrigerant 717) Reproduced with permission: from Kaltermachinen Regeln, 5th edition, Verlag, C F Muller, Karlsruhe 306 INDEX TO FIGURES CHAPTER INTRODUCTION 1.1 Unit operation CHAPTER MATERIAL AND ENERGY BALANCES 2.1 Mass and energy balance; 2.2 Heat balance 2.3 Casein process CHAPTER FLUID-FLOW THEORY 3.1 Pressure in a fluid 3.2 Pressure conversions 3.3 Mass and energy balance in fluid flow 3.4 Flow from a nozzle 3.5 Viscous forces in a fluid 3.6 Shear stress/shear rate relationships in liquids 3.7 Energy balance over a length of pipe 3.8 Friction factors in pipe flow CHAPTER FLUID-FLOW APPLICATIONS 4.1 Pressure measurements in pipes 4.2 Venturi meter 4.3 Liquid pumps 4.4 Characteristic curves for centrifugal pumps CHAPTER HEAT-TRANSFER THEORY 5.1 Heat conduction through a slab 5.2 Heat conductances in series 5.3 Heat conductances in parallel 5.4 Transient heat conduction CHAPTER HEAT-TRANSFER APPLICATIONS 6.1 Heat exchangers 6.2 Diagrammatic heat exchanger 6.3 Heat exchange equipment 6.4 Thermal death time curve for Clostridium botulinum 6.5 Thermal death time/temperature relationships 6.6 Time/Temperature curve for can processing 6.7 Pasteurization curves for milk 6.8 Mechanical refrigeration circuit 6.9 Pressure /enthalpy chart 6.10 Refrigeration evaporators 6.11 Freezing of a slab 6.12 Coefficients in Plank’s Equation CHAPTER DRYING 307 7.1 Phase diagram for water 7.2 Vapour pressure/temperature curve for water 7.3 Psychrometric chart 7.4 Equilibrium moisture contents 7.5 Drying-rate curves 7.6 Drying curve for fish 7.7 Generalized drying curve 7.8 Dryers CHAPTER EVAPORATION 8.1 Evaporator 8.2 Double effect evaporator – forward feed 8.3 Duhring plot for boiling point of sodium chloride solutions 8.4 Evaporators (a) basket type (b) long tube (c) forced circulation CHAPTER CONTACT-EQUILIBRIUM PROCESSES 9.1 Solubility of sodium nitrite in water 9.2 Contact equilibrium stages 9.3 Flows into and out from a stage 9.4 Steam stripping: McCabe-Thiele plot 9.5 Hexane extraction of oil from soya beans: stages 9.6 Hexane extraction of oil from soya beans: McCabe-Thiele plot 9.7 Extraction battery 9.8 Solubility and saturation curves for sucrose in water 9.9 Reverse osmosis systems 9.10 Boiling point/concentration diagram 9.11 Distillation column (a) assembly, (b) bubble-cap trays CHAPTER 10 MECHANICAL SEPARATIONS 10.1 Continuous-sedimentation plant 10.2 Cyclone separator: (a) equipment (b) efficiency of dust collection 10.3 Liquid separation in a centrifuge 10.4 Liquid centrifuge (a) pressure difference (b) neutral zone 10.5 Liquid centrifuges: (a) conical bowl, (b) nozzle 10.6 Liquid/solid centrifuges (a) telescoping bowl, (b) horizontal bowl-scroll discharge 10.7 Filtration Graph 10.8 Filtration equipment: (a) plate and frame press (b) centrifugal filter 10.9 Particle-size analysis CHAPTER 11 SIZE REDUCTION 11.1 Crushers: (a) jaw, (b) gyratory 11.2 Grinders: (a) hammer mill, (b) plate mill CHAPTER 12 MIXING 12.1 Performance of propeller mixers 12.2 Mixers (a) ribbon blender, (b) double-cone mixer 12.3 Kneader 308 INDEX TO EXAMPLES CHAPTER INTRODUCTION 1.1.Dimensions of Velocity; 1.2 Conversion of grams to pounds; 1.3 Velocity of flow of milk in a pipe; 1.4 Viscosity: conversion from fps to SI units; 1.5 Thermal conductivity of aluminium: conversion from fps to SI units CHAPTER MATERIAL AND ENERGY BALANCES 2.1 Constituent balance of milk; 2.2 Concentration of salt in water; 2.3 Air composition; 2.4 Carbonation of a soft drink; 2.5 Materials balance in continuous centrifugation of skim milk and cream; 2.6 Materials balance of yeast fermentation; 2.7 Blending of minced meat; 2.8 Drying yield of potatoes; 2.9 Extraction of oil fom soya beans; 2.10 Heat demand in freezing bread; 2.11 Dryer heat balance for casein drying; 2.12 Heat balance for cooling pea soup after canning; 2.13 Refrigeration load in bread freezing CHAPTER FLUID FLOW THEORY 3.1 Total pressure in a tank of peanut oil 3.2 Head of Water 3.3 Head of mercury 3.4 Velocities of flow 3.5 Pressure in a pipe 3.6 Flow rate of olive oil 3.7 Mass flow rate from a tank 3.8 Pump horsepower 3.9 Flow of milk in a pipe 3.10 Pressure drop in a pipe CHAPTER FLUID FLOW APPLICATIONS 4.1 Pressure in a vacuum evaporator 4.2 Velocity of air in a duct 4.3 Centrifugal pump for raising water CHAPTER HEAT TRANSFER THEORY 5.1 Rate of heat transfer in cork 5.2 Heat transfer in cold store wall of brick, concrete and cork 5.3 Heat transfer in walls of a bakery oven 5.4 Heat transfer in jacketed pan 5.5 Heat transfer in cooking sausages 5.6 Radiation heat transfer to loaf of bread in an oven 5.7 Heat loss from a cooking vessel 5.8 Heat transfer in water flowing over a sausage 309 5.9 Surface heat transfer to vegetable puree 5.10 Heat loss from a cooking vessel 5.11 Effect of air movement on heat transfer in a cold store 5.12 Comparison of heat transfer in brick and aluminium walls 5.13 Condensing ammonia in a refrigeration plant CHAPTER HEAT-TRANSFER APPLICATIONS 6.1 Cooling of milk in a pipe heat exchanger 6.2 Water chilling in a counter flow heat exchanger 6.3 Steam required to heat pea soup in jacketed pan 6.4 Time to heat pea soup in a jacketed pan 6.5 Time/Temperature in a can during sterilisation 6.6 Pasteurisation of milk 6.7 Freezing of fish 6.8 Rate of boiling of refrigerant 6.9 Operation of a compressor in a refrigeration system 6.10 Chilling of fresh apples 6.11 Freezing of a slab of meat 6.12 Freezing of a carton of meat: controllable factors CHAPTER DRYING 7.1 Heat energy in air drying 7.2 Heat energy in vacuum drying 7.3 Heat energy in freeze drying 7.4 Efficiency of a potato dryer 7.5 Partial pressure of water vapour 7.6 Relative humidity 7.7 Relative humidity, enthalpy and specific volume of air 7.8 Relative humidity of heated air 7.9 Water removed in air drying 7.10 Humidity of air leaving a dryer 7.11 Reheating of air in a dryer 7.12 Air conditioning 7.13 Rate of evaporation on drying 7.14 Heat transfer in air drying 7.15 Temperature and RH in air drying of carrots 7.16 Lewis relationship in air drying 7.17 Time for air drying at constant rate 7.18 Time for drying during falling rate 7.19 Moisture content of breakfast food after drum drying CHAPTER EVAPORATION 8.1 Single effect evaporator: steam usage and heat transfer surface 8.2 Water required in a jet condenser for an evaporator 8.3 Heat exchange area for a surface condenser for an evaporator 8.4 Triple effect evaporators: steam usage and heat transfer surface 8.5 Duhring Plot for sodium chloride solutions 8.6 Concentration of tomato juice in a climbing film evaporator CHAPTER CONTACT-EQUILIBRIUM PROCESSES 9.1 Mole fractions of ethanol in water 310 9.2 Mole fractions in air 9.3 Solubility of carbon dioxide in water 9.4 Deodorizing; single stage steam stripping, of taint from cream 9.5 Deodorizing: multiple stage steam stripping of taints from cream 9.6 Counter current extraction of oil from soya beans with hexane 9.7 Washing of casein curd 9.8 Crystallization of sodium chloride 9.9 Heat removal in crystallization cooling of lactose 9.10 Multiple stage sugar crystallisation by evaporation 9.11 Reverse osmosis; concentration of sucrose solution 9.12 Ultrafiltration of whey 9.13 Distillation of alcohol/water mixture CHAPTER 10 MECHANICAL SEPARATIONS 10.1 Settling velocity of dust particles 10.2 Separating of oil and water 10.3 Centrifugal force in a centrifuge 10.4 Centrifugal separation of oil in water 10.5 Centrifugal separation of milk and cream 10.6 Volume of filtrate from a filter press 10.7 Sieve analysis CHAPTER 11 SIZE REDUCTION 11.1 Grinding of sugar 11.2 Surface area of salt crystals CHAPTER 12 MIXING 12.1 Mixing salt and magnesium carbonate 12.2 Mixing of yeast into dough 12.3 Mixing vitamin addition into powdered cereal 12.4 Blending starch and dried vegetables for a soup mix 12.5 Mixing time for bread dough 12.6 Blending vitamin concentrate into molasses 311 REFERENCES ASHRAE Guide and Data Books, American Society of Heating, Refrigerating and Air Conditioning Engineers, New York BIRD, R B., STEWART, W E and LIGHTFOOT, E N (1960) Transport Phenomena, Wiley, New York BOND, F C (1952) Min Engng 4, 484; 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British Library Cataloguing in Publication Data Earle, R L Unit operations in food processing - 2nd ed - (Pergamon Commonwealth and International Library) Food industry and trade - Quality control... so using the data: Toe HkJkg-1 -2 0.6 55.88 Giving C- = Giving C = -1 7.8 15.6 18.3 65.35 203.4 210.4 M M M M 65.35 -5 5.88 20.6 -1 7.8 210.4 -2 03.4 18.3 -1 5.6 = = 3.4 kJkg-10C-1, 2.6 kJkg-1 °e-1 Note... Hg lb-mole-l K- , (b) m3 Pa mole-l K-I, (c) Joules g-mole-l K-I Assume 1atm = 760mm Hg = 1.013x105 Nm-2• Remember joule = INm and in this book, mole is kg mole ((a) 999 ft3mm Hg lb-mole-l K-I (b)