- Batty, J.C. and Folkman, S.L. 1983. Food Engineering Fundamentals. Wiley, New York.Google Scholar
- Earle, R.L. 1983. Unit Operations in Food Processing. Pergamon Press, OxfordGoogle Scholar
- Fellows, P. 1988. Food Processing Technology: Principles and Practice. E. Horwood, Chichester.Google Scholar
- Fellows, P.J. 1990. Food Processing Technology: Principles and Practice. Prentice-Hall, Englewood Cliffs, NJ.Google Scholar
- Giese, J. 1993. On-line sensors for food processing. Food Technol}. 47(5), 88, 90–95.Google Scholar
- Hall, C.W., Farrall, A.W., and Rippen, A.L. 1986. Encyclopedia of Food Engineering. 2nd ed. AVI Publishing Co., Westport, CT.Google Scholar
- Hayes, G.D. 1987. Food Engineering Data Handbook. Wiley, New York.Google Scholar
- Heldman, D.R. and Lund, D.B. 1992. Handbook of Food Engineering. Marcel Dekker, New York.Google Scholar
- Karmas, E. and Harris, R.S. 1988. Nutritional Evaluation of Food Processing. Chapman & Hall, London, New York.CrossRefGoogle Scholar
- Knorr, D. 1993. Effects of high-hydrostatic-pressure processes on food safety and quality. Food Technol. 47(6), 156, 158–161.Google Scholar
- LeMaguer, M. and Jelen, P. 1986. Food Engineering and Process Applications. Elsevier Applied Science Publishers, London.Google Scholar
- McLellan, M.R. 1985. Introduction to computer-based process control in a food engineering course. Food Technol. 39(4), 96–97.Google Scholar
- Mertens, B. and Deplace, G. 1993. Engineering aspects of high-pressure technology in the food industry. Food Technol. 47(6), 164–169.Google Scholar
- Paine, F.A. 1987. Modern Processing, Packaging and Distribution Systems for Food. Chapman & Hall, London, New York.Google Scholar
- Parrott, D.L. 1992. Use of ohmic heating for aseptic processing of food particulates. Food Technol. 46(12):68–72.Google Scholar
- Rizvi, S.S.H. 1986. Engineering Properties of Foods. Marcel Dekker, New York.Google Scholar
- Rizvi, S.S.H. and Mittal, G.S. 1992. Experimental Methods in Food Engineering. Chapman & Hall, London, New York.Google Scholar
- Singh, R.P. and Wirakartakusumah, M.A. 1992. Advances in Food Engineering. CRC Press, Boca Raton, FL.Google Scholar
- Toledo, R. (Editor). ed. 1991. Fundamentals of Food Process Engineering. 2nd ed. Chapman & Hall, London, New York.CrossRefGoogle Scholar
- United National Economic Commission for Europe, Geneva. 1991. Food-Processing Machinery, United Nations, New York.Google Scholar
- Watson, E.L., Harper, J.C., and Harper, J.C. 1988. Elements of Food Engineering. Chapman & Hall, London, New York.Google Scholar
<ul><li><p>UNIT OPERATIONS IN FOOD PROCESSING</p><p>Contents > Heat-Transfer Applications > Introduction, Heat Exchangers this page</p><p>HomeContentsAbout the bookIntroductionMaterial and energybalancesFluid-flow theoryFluid-flow applicationsHeat-transfer theoryHeat-transferapplicationsDryingEvaporationContact-equilibriumseparation processesMechanicalseparationsSize reductionMixingAppendicesIndex to FiguresIndex to ExamplesReferencesBibliographyUseful linksFeedback (email link)</p><p>CHAPTER 6HEAT TRANSFER APPLICATIONS</p><p>Heat exchangersContinuous-flow Heat ExchangersJacketed PansHeating Coils Immersed in LiquidsScraped Surface Heat ExchangersPlate Heat Exchangers</p><p>The principles of heat transfer are widely used in food processing in many itemsof equipment. It seems appropriate to discuss these under the variousapplications that are commonly encountered in nearly every food factory.</p><p>HEAT EXCHANGERSIn a heat exchanger, heat energy is transferred from one body or fluid stream toanother. In the design of heat exchange equipment, heat transfer equations areapplied to calculate this transfer of energy so as to carry it out efficiently andunder controlled conditions. The equipment goes under many names, such asboilers, pasteurizers, jacketed pans, freezers, air heaters, cookers, ovens and soon. The range is too great to list completely. Heat exchangers are found widelyscattered throughout the food process industry.</p><p>Continuous-flow Heat ExchangersIt is very often convenient to use heat exchangers in which one or both of the materials that are exchanging heatare fluids, flowing continuously through the equipment and acquiring or giving up heat in passing.One of the fluids is usually passed through pipes or tubes, and the other fluid stream is passed round or acrossthese. At any point in the equipment, the local temperature differences and the heat transfer coefficients controlthe rate of heat exchange.The fluids can flow in the same direction through the equipment, this is called parallel flow; they can flow inopposite directions, called counter flow; they can flow at right angles to each other, called cross flow. Variouscombinations of these directions of flow can occur in different parts of the exchanger. Most actual heatexchangers of this type have a mixed flow pattern, but it is often possible to treat them from the point of view ofthe predominant flow pattern. Examples of these exchangers are illustrated in Figure 6.1.</p><p>Unit Operations in Food Processing - R. L. Earle http://www.nzifst.org.nz/unitoperations/httrapps1.htm</p><p>1 dari 7 12/10/2015 14:42</p></li><li><p>Figure 6.1 Heat exchangers</p><p>In parallel flow, at the entry to the heat exchanger, there is the maximum temperature difference between thecoldest and the hottest stream, but at the exit the two streams can only approach each other's temperature. In acounter flow exchanger, leaving streams can approach the temperatures of the entering stream of the othercomponent and so counter flow exchangers are often preferred.Applying the basic overall heat-transfer equation for the the heat exchanger heat transfer:</p><p>q = UA DTuncertainty at once arises as to the value to be chosen for DT, even knowing the temperatures in the enteringand leaving streams.Consider a heat exchanger in which one fluid is effectively at a constant temperature, Tb as illustrated in Fig.6.1(d). Constant temperature in one component can result either from a very high flow rate of this componentcompared with the other component, or from the component being a vapour such as steam or ammoniacondensing at a high rate, or from a boiling liquid. The heat-transfer coefficients are assumed to be independentof temperature.</p><p>The rate of mass flow of the fluid that is changing temperature is G kg s-1, its specific heat is cp J kg-1 C-1. Overa small length of path of area dA, the mean temperature of the fluid is T and the temperature drop is dT. Theconstant temperature fluid has a temperature Tb. The overall heat transfer coefficient is U J m-2 s-1 C-1.</p><p>Therefore the heat balance over the short length is: cpGdT = U(T - Tb)dA</p><p> Therefore U/)cpG) dA = dT/(T Tb)</p><p>If this is integrated over the length of the tube in which the area changes from A = 0 to A = A, and T changesfrom T1 to T2, we have:</p><p> U/(cpG) A = ln[(T1 Tb)/(T2 - Tb)] (where ln = loge) = ln (DT1/ DT2) in which DT1 = (T1 Tb) and DT2 = (T2 - Tb)</p><p>Unit Operations in Food Processing - R. L. Earle http://www.nzifst.org.nz/unitoperations/httrapps1.htm</p><p>2 dari 7 12/10/2015 14:42</p></li><li><p>therefore cpG = UA/ ln (DT1/ DT2)From the overall equation, the total heat transferred per unit time is given by</p><p> q = UADTmwhere DTm is the mean temperature difference, but the total heat transferred per unit is also: q = cpG(T1 T2)</p><p> so q = UADTm = cpG(T1 T2) = UA/ ln (DT1/ DT2)] x (T1 T2)but (T1 T2) can be written (T1 Tb) - (T2 - Tb)</p><p> so (T1 T2) = (DT1 - DT2)therefore UADTm = UA(DT1 - DT2) / ln (DT1/ DT2) (6.1)so that DTm = (DT1 - DT2) / ln (DT1/ DT2) (6.2)</p><p>where DTm is called the log mean temperature difference.In other words, the rate of heat transfer can be calculated using the heat transfer coefficient, the total area, andthe log mean temperature difference. This same result can be shown to hold for parallel flow and counter flowheat exchangers in which both fluids change their temperatures.The analysis of cross-flow heat exchangers is not so simple, but for these also the use of the log meantemperature difference gives a good approximation to the actual conditions if one stream does not change verymuch in temperature.</p><p>EXAMPLE 6.1. Cooling of milk in a pipe heat exchangerMilk is flowing into a pipe cooler and passes through a tube of 2.5 cm internal diameter at a rate of 0.4 kg s-1. Itsinitial temperature is 49C and it is wished to cool it to 18C using a stirred bath of constant 10C water round thepipe. What length of pipe would be required? Assume an overall coefficient of heat transfer from the bath to themilk of 900 J m-2 s-1 C-1, and that the specific heat of milk is 3890 J kg-1 C-1.</p><p>Now q = cpG (T1 T2) = 3890 x 0.4 x (49 - 18) = 48,240 J s-1</p><p>Also q = UADTm DTm = [(49 - 10) - (18 10)] / ln[(49 -10)1(18 - 10)] = 19.6C.Therefore 48,240 = 900 x A x l9.6 A = 2.73 m2 but A = pDLwhere L is the length of pipe of diameter D Now D = 0.025 m. L = 2.73/(p x 0.025) = 34.8 m</p><p>This can be extended to the situation where there are two fluids flowing, one the cooled fluid and the other theheated fluid. Working from the mass flow rates (kg s-1) and the specific heats of the two fluids, the terminaltemperatures can normally be calculated and these can then be used to determine DTm and so, from theheat-transfer coefficients, the necessary heat-transfer surface.</p><p>Unit Operations in Food Processing - R. L. Earle http://www.nzifst.org.nz/unitoperations/httrapps1.htm</p><p>3 dari 7 12/10/2015 14:42</p></li><li><p>EXAMPLE 6.2. Water chilling in a counter flow heat exchangerIn a counter flow heat exchanger, water is being chilled by a sodium chloride brine. If the rate of flow of the brineis 1.8 kg s-1 and that of the water is 1.05 kg s-1, estimate the temperature to which the water is cooled if the brineenters at -8C and leaves at 10C, and if the water enters the exchanger at 32C. If the area of the heat-transfersurface of this exchanger is 55 m2, what is the overall heat-transfer coefficient? Take the specific heats to be3.38 and 4.18 kJ kg-1 C-1 for the brine and the water respectively.With heat exchangers a small sketch is often helpful:</p><p>Figure 6.2. Diagrammatic heat exchanger</p><p>Figure 6.2 shows three temperatures are known and the fourth Tw2 (= T'2 say on Fig 6.2) can be found from theheat balance:By heat balance, heat loss in brine = heat gain in water</p><p>1.8 x 3.38 x [10 - (-8)] = 1.05 x 4.18 x (32 - Tw2) Therefore Tw2 = 7C.And for counterflow</p><p> DT1 = [32 - 10] = 22C and DT2 = [7 - (-8)] = 15C. Therefore DTm = (22 - 15)/ln(22/15) = 7/0.382 = 18.3C.For the heat exchanger q = heat exchanged between fluids = heat lost by brine = heat gain to water = heat passed across heat transfer surface = UADTmTherefore 3.38 x 1.8 x 18 = U x 55 x 18.3 U = 0.11 kJ m-2 C-1 = 110 J m-2 C-1</p><p>Parallel flow situations can be worked out similarly, making appropriate adjustments.In some cases, heat-exchanger problems cannot be solved so easily; for example, if the heat transfercoefficients have to be calculated from the basic equations of heat transfer which depend on flow rates andtemperatures of the fluids, and the temperatures themselves depend on the heat-transfer coefficients. Theeasiest way to proceed then is to make sensible estimates and to go through the calculations. If the final resultsare coherent, then the estimates were reasonable. If not, then make better estimates, on the basis of the results,and go through a new set of calculations; and if necessary repeat again until consistent results are obtained. Forthose with multiple heat exchangers to design, computer programmes are available.</p><p>Jacketed PansIn a jacketed pan, the liquid to be heated is contained in a vessel, which may also be provided with an agitator tokeep the liquid on the move across the heat-transfer surface, as shown in Fig. 6.3(a).</p><p>Unit Operations in Food Processing - R. L. Earle http://www.nzifst.org.nz/unitoperations/httrapps1.htm</p><p>4 dari 7 12/10/2015 14:42</p></li><li><p>Figure 6.3. Heat exchange equipment</p><p>The source of heat is commonly steam condensing in the vessel jacket. Practical considerations of importanceare:1. There is the minimum of air with the steam in the jacket.2. The steam is not superheated as part of the surface must then be used as a de-superheater over which lowgas heat-transfer coefficients apply rather than high condensing coefficients.3. Steam trapping to remove condensate and air is adequate.The action of the agitator and its ability to keep the fluid moved across the heat transfer surface are important.Some overall heat transfer coefficients are shown in Table 6.1. Save for boiling water, which agitates itself,mechanical agitation is assumed. Where there is no agitation, coefficients may be halved.</p><p>TABLE 6.1SOME OVERALL HEAT TRANSFER COEFFICIENTS IN JACKETED PANS</p><p>Condensing fluid Heated fluid Pan material Heat transfer coefficientsJ m-2 s-1 C-1</p><p>Steam Thin liquid Cast-iron 1800Steam Thick liquid Cast-iron 900Steam Paste Stainless steel 300Steam Water, boiling Copper 1800</p><p>EXAMPLE 6.3. Steam required to heat pea soup in jacketed panEstimate the steam requirement as you start to heat 50 kg of pea soup in a jacketed pan, if the initial temperatureof the soup is 18C and the steam used is at 100 kPa gauge. The pan has a heating surface of 1 m2 and theoverall heat transfer coefficient is assumed to be 300 J m-2 s-1 C-1.</p><p>From steam tables (Appendix 8), saturation temperature of steam at 100 kPa gauge = 120C and latent heat = l</p><p>Unit Operations in Food Processing - R. L. Earle http://www.nzifst.org.nz/unitoperations/httrapps1.htm</p><p>5 dari 7 12/10/2015 14:42</p></li><li><p>= 2202 kJ kg-1.</p><p> q = UA DT = 300 x 1 x (120 - 18) = 3.06 x 104 J s-1Therefore amount of steam = q/l = (3.06 x 104)/(2.202 x 106) = 1.4 x 10-2 kg s-1 = 1.4 x 10-2 x 3.6 x 103 = 50 kg h-1.</p><p>This result applies only to the beginning of heating; as the temperature rises less steam will be consumed as DTdecreases.The overall heating process can be considered by using the analysis that led up to eqn. (5.6). A stirred vessel towhich heat enters from a heating surface with a surface heat transfer coefficient which controls the heat flow,follows the same heating or cooling path as does a solid body of high internal heat conductivity with a definedsurface heating area and surface heat transfer coefficient.</p><p>EXAMPLE 6.4. Time to heat pea soup in a jacketed panIn the heating of the pan in Example 6.3, estimate the time needed to bring the stirred pea soup up to atemperature of 90C, assuming the specific heat is 3.95 kJ kg-1 C-1.</p><p> From eqn. (5.6) (T2 - Ta)/(T1 Ta) = exp(-hsAt/crV ) Ta = 120C (temperature of heating medium) T1 = 18C (initial soup temperature) T2 = 90C (soup temperature at end of time t) hs = 300 J m-2 s-1 C-1 A = 1 m2, c = 3.95 kJ kg-1 C-1. rV = 50 kgTherefore t = -3.95 x 103 x 50 x ln (90 - 120) / (18 - 120) 300 x 1 = (-658) x (-1.22) s = 803 s = 13.4 min.</p><p>Heating Coils Immersed in LiquidsIn some food processes, quick heating is required in the pan, for example, in the boiling of jam. In this case, ahelical coil may be fitted inside the pan and steam admitted to the coil as shown in Fig. 6.3(b). This can givegreater heat transfer rates than jacketed pans, because there can be a greater heat transfer surface and also theheat transfer coefficients are higher for coils than for the pan walls. Examples of the overall heat transfercoefficient U are quoted as:</p><p>300-1400 for sugar and molasses solutions heated with steam using a copper coil,1800 for milk in a coil heated with water outside,3600 for a boiling aqueous solution heated with steam in the coil.</p><p>with the units in these coefficients being J m-2 s-1 C-1.</p><p>Scraped Surface Heat ExchangersOne type of heat exchanger, that finds considerable use in the food processing industry particularly for productsof higher viscosity, consists of a jacketed cylinder with an internal cylinder concentric to the first and fitted withscraper blades, as illustrated in Fig. 6.3(c). The blades rotate, ca..</p></li></ul>
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