A plane wall is a composite of two materials, A and B. The wall of material A has uniform heat generation qG = 1.5 × 106 W/m3, kA = 75 W/m⋅K, and thickness LA = 50 mm. The wall material B has no generation with kB = 150 W/m⋅K and thickness LB = 20mm. The inner surface of material A is well insulated, while the outer surface of material B is cooled by a water stream with T∞ = 30°C and h = 1000 W/(m2⋅K). a. Sketch the temperature distribution that exists in the composite under steady-state conditions. b. Determine the temperature of the insulated surface and the temperature of the cooled surfac

A plane wall is a composite of two materials, A and B. The wall of material A has uniform heat generation qG = 1.5 × 106 W/m3, kA = 75 W/m⋅K, and thickness LA = 50 mm. The wall material B has no generation with kB = 150 W/m⋅K and thickness LB = 20mm. The inner surface of material A is well insulated, while the outer surface of material B is cooled by a water stream with T∞ = 30°C and h = 1000 W/(m2⋅K). a. Sketch the temperature distribution that exists in the composite under steady-state conditions. b. Determine the temperature of the insulated surface and the temperature of the cooled surfac

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.10P: 1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss...

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2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.
2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)
A steel duct whose internal diameter is 5.0 cm, and external diameter is 7.6 cm and thermal conductivity is: k = 15.0 (W/(m ºC)) is covered with an insulating material whose thickness is 2.0 cm and of thermal conductivity k = 0.2 (W/(m ºC)). A hot gas flows through the interior of the duct at a temperature of 330.0 ºC that generates a heat transfer coefficient by forced convection h=400.0 (W/(m^2 · ºC)). The outer surface of the insulating layer is exposed to air whose temperature is 30.0 ºC with forced convection heat transfer surface h = 60.0 (W/(m^2 · °C)). As a process engineer and in charge of company operations, you have been asked to: i. Determine the heat loss experienced by the pipe along 10.0 m.ii. The temperature drops that are generated in the different thermal resistances of the system. That is, on the air side, the duct wall and on the hot gas side.
A domestic refrigerator with inner dimensions of 0.7 m by 0.7 m at the base and height 1 m was designed to maintain a set temperature of 6 ˚C. The bodies consist of two 10-mm-thick layers of Aluminium (k = 225 W/mK) separated by a 30 mm polyurethane insulation (k=0.028 W/mK). If the average convection heat transfer coefficient at the inner and outer surfaces are 11.6 W/m2K and 14.5 W/m2K respectively, calculate: the steady rate of heat transfer from the interior to maintain the specified temperature in the kitchen at 25 ˚C in W to 2 decimal places.
A domestic refrigerator with inner dimensions of 0.7 m by 0.7 m at the base and height 1 m was designed to maintain a set temperature of 6 ˚C. The bodies consist of two 10-mm-thick layers of Aluminium (k = 225 W/mK) separated by a 30 mm polyurethane insulation (k=0.028 W/mK). If the average convection heat transfer coefficient at the inner and outer surfaces are 11.6 W/m2K and 14.5 W/m2K respectively, calculate: the steady rate of heat transfer from the interior to maintain the specified temperature in the kitchen at 25 ˚C in W to 2 decimal places. thermodynamics
A steel tube with a thermal conductivity of 45 W/m.K carries a fluid at 200°C, with a convection heat transfer coefficient of 210 W/m2./K. The tube has an external diameter of 5 cm, a wall thickness of 1 cm and a length of 2 m. The ambient air and surroundings are at 25°C, with a convection heat transfer coefficient of 25 W/m2.K. Neglecting the effects of radiation, determine: 1) resistance by conduction through the pipe wall 2) the convection resistance inside the tube 3) The total heat transfer rate 4) The temperature of the outer surface of the tube 5) The total resistance considering the effects of radiation only on the outside, with the coefficient hr = 2W/m2.K 6) The new heat transfer rate, considering the effects of radiation, if an additional layer of 15 mm thick foam with a conductivity of 0.03 W/m.K is added to the system. 7) The critical insulation radius of the system after adding this insulating layer.
A steel tube with a thermal conductivity of 45 W/m.K carries a fluid at 200°C, with a convection heat transfer coefficient of 210 W/m2./K. The tube has an external diameter of 5 cm, a wall thickness of 1 cm and a length of 2 m. The ambient air and surroundings are at 25°C, with a convection heat transfer coefficient of 25 W/m2.K. Neglecting the effects of radiation, determine: 1) resistance by conduction through the pipe wall 2) the convection resistance inside the tube 3) The total heat transfer rate 4) The temperature of the outer surface of the tube Upload resolution images, please.
the composite wall of a refrigerator has a thermal conductivity of 0.05 W/m-K and a wall thickness of 50 mm. In a room of 25 °C, the refrigerated cold space inside the refrigerator is maintained at 4 °C. Assume the inner and outer convection heat transfer coefficients are 5 W/m² K and 10 W/m².K, respectively. Neglect radiation heat transfer. Determine the rate of heat leaking into the refrigerator per unit surface area.
Calculate the overall heat transfer coefficient of the steel pipe based on the inner surface. The inner diameter of the pipe is 12.7 cm, and the thickness of the pipe is 2.4 cm. The convection heat transfer coefficient in the pipe is 350 W / (m² ° C), the convective heat transfer coefficient outside the pipe is 25 W / (m² ° C), the thermal conductivity of the steel pipe is 15 W / (m ° C). If the pipe is used to deliver steam at 110 ° C and the ambient temperature is 20 ° C, determine the heat transfer rate of the pipe per meter. q = Watt / m