Calculate the overall heat transfer coefficient 424

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Calculate the overall heat-transfer coefficient.4.24In a food processing plant,a steel pipe (thermalconductivity517 W/m8C,internal diameter55 cm;thickness53 mm) is being used to transport a liquid food.The inside surface temperature of the pipe is at 958C. A4-cm-thick insulation (thermal conductivity50.03 W/m8C)is wrapped around the pipe. The outside surface temperatureof the insulation is 308C. Calculate the rate of heat transferper unit length of the pipe.4.25A walk-in freezer of 4 m width,6 m length,and 3 m heightis being built. The walls and ceiling contain 1.7-mm-thickstainless steel (k515 W/[m8C]),10-cm-thick foaminsulation (k50.036 W/[m8C]),and some thickness ofcorkboard (k50.043 W/[m8C]) to be established,and1.27 cm-thickness wood siding (k50.104 W/[m8C]). Theinside of the freezer is maintained at2408C. Ambient airoutside the freezer is at 328C. The convective heat-transfercoefficient is 5 W/(m2K) on the wood side of the wall and2 W/(m2K) on the steel side. If the outside air has a dewpoint of 298C,calculate the thickness of corkboardinsulation that would prevent condensation of moisture on402CHAPTER 4Heat Transfer in Food Processing
the outside wall of the freezer. Calculate the rate of heattransfer through the walls and ceiling of this freezer.4.26A liquid food is being conveyed through an uninsulated pipeat 908C. The product flow rate is 0.25 kg/s and has a densityof 1000 kg/m3,specific heat of 4 kJ/(kg K),viscosity of831026Pa s,and thermal conductivity of 0.55 W/(m K).Assume the viscosity correction is negligible. The internalpipe diameter is 20 mm with 3 mm thickness made ofstainless steel (k515 W/[m8C]). The outside temperature is158C. If the outside convective heat-transfer coefficient is18 W/(m2K),calculate the steady-state heat loss from theproduct per unit length of pipe.*4.27A liquid food is being pumped in a 1-cm-thick steel pipe.The inside diameter of the pipe is 5 cm. The bulktemperature of liquid food is 908C. The inside pipe surfacetemperature is 808C. The surface heat-transfer coefficientinside the pipe is 15 W/(m2K). The pipe has a 2-cm-thickinsulation. The outside bulk air temperature is 208C. Thesurface heat-transfer coefficient on the outside of insulationis 3 W/(m2K).a.Calculate the insulation surface temperature exposed tothe outside.b.If the pipe length is doubled,how would it influence theinsulation surface temperature? Discuss.4.28For a metal pipe used to pump tomato paste,the overall heat-transfer coefficient based on internal area is 2 W/(m2K). Theinside diameter of the pipe is 5 cm. The pipe is 2 cm thick.The thermal conductivity of the metal is 20 W/(m K).Calculate the outer convective heat-transfer coefficient. Theinside convective heat-transfer coefficient is 5 W/(m2K).4.29A cold-storage room is maintained at2188C. The internaldimensions of the room are 5 m35 m33 m high. Each wall,ceiling,and floor consists of an inner layer of 2.5 cm thickwood with 7 cm thick insulation and an 11 cm brick layer onthe outside. The thermal conductivities of respective materialsare wood 0.104 W/(m K),glass fiber 0.04 W/(m K),andbrick 0.69 W/(m K). The convective heat-transfer coefficientfor wood to still air is 2.5 W/(m2K),and from moving air*Indicates an advanced level of difficulty in solving.

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Term
Winter
Professor
Mr. Stump
Tags
Heat Transfer, The Land, Heating and Cooling Food Products, Professor R Paul Singh

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