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A composite refrigerator wall is composed of 5 cm of corkboard sandwiched between a 1.2-cm-thick layer of oak and a 0.8-mm-thick layer of aluminum lining on the inner surface. The average convection heat transfer coefficients at the interior and exterior wall are 11 and
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Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- 1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1arrow_forwardAn electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.arrow_forward2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.arrow_forward
- A house has a composite wall of wood, fiberglass insulation and plaster board, as indicated in Figure 2.1. The total wall surface area is 300 m2. - Represent the composite wall by a thermal circuit, and label all thecomponents in the circuit. - Determine the total heat transfer rate, ?̇ through the wall and the inner surface temperature of the house.arrow_forwardQ1 A composite house wall is constructed from 1.2 cm layer of fiber insulating board, an 8.0 cm layer of loosely packed asbestos, and 10 cm layer of common brick. Assuming convection heat transfer coefficient of 12 W/m?.C on the both sides of the wall. Calculate the overall heat transfer coefficient for this arrangement. Thermal conductivities for building materials are korick= 0.76 W/m. C, koard-0.025 W/m.°C, and kabestos= 0.032 W/m. C)arrow_forwardA transparent film will be glued onto an upper surface of a solid plate within a heated chamber. For common gluing, the temperature between the glue, a film and the solid board must be kept at 70 °C. The transparent film has a thickness of 1 mm and thermal conductivity 0.05 W/mK, while the solid board is 13 mm thick. thickness and thermal conductivity of 1.2 W / mK. Inside the climate chamber, the convection heat transfer coefficient is 70 W/m²K. The bottom surface of the solid plate is kept at 52 °C, determines the temperature inside the heated chamber and the temperature of the surface of the transparent film. Assume negligible thermal contact resistance.arrow_forward
- A composite wall layer consists of layer A covered by layer B. The thermal resistance of layer A is 0.75 °C/W and the thermal resistance of layer B is 2.50 °C/W. The exposed surface of layer A is at a temperature of 60°C. If the heat transfer per unit area across the composite wall is 30 W/m?, what is the temperature at the interface between layer A and layer B? Express your answer in °C.arrow_forwardAn industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively. Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m2. What does this heat energy represent in terms of the refrigeration system of the cold room?arrow_forwardAn industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively. Without any calculations, how would you expect the internal and external air temperatures to be relative to the wall surface temperatures? Explain your answer.arrow_forward
- An industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively.a) Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m^2. What does this heat energy represent in terms of the refrigeration system of the cold room? b) Without any calculations, how would you expect the internal and external air temperatures to be relative to the wall surface temperatures?c) How do you expect the heat gain calculated in question 1a) above…arrow_forwarda. Consider a 5-m-high, 8-m-long, and 0.20-m-thick wall whose representative cross section is as given in the figure. The thermal conductivities of various materials used, in W/m K, are kA = 2, kB = 8, kc = 15 and kD = 10. Assuming heat transfer through the wall to be one-dimensional, determine the total resistance of the wall using the thermal resistance network analysis. 15 сm 15 cm 1m 10 cm' 5 cm 5 cmarrow_forwardOne vessel having a carbon-steel wall of thickness 5 mm carrying saturated steam and water at 423K. The vessel is insulated with magnesia of thickness 50 mm. If the ambient air temperature is 321 K, determine the heat loss from the vessel. Given: i. thermal conductivity of carbon steel is 52 W/m.K ii. thermal conductivity of magnesia is 0.5 W/m.K iii. surface coefficient of insulation surface is 3 W/m2.Karrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning