Q5. The roof of a house consists of a 15-cm-thick concrete slab (k = 2 W/m C) that is 15 mwide and 20 m long. The convection heat transfer coefficients on the inner and outer surfaces ofthe roof are 5 and 12 W/m² C, respectively. On a clear winter night, the ambient air is reportedto be at 10 °C, while the night sky temperature is 100 K. The house and the interior surfaces ofthe wall are maintained at a constant temperature of 20 °C. The emissivity of both surfaces of theconcrete roof is 0.9. Considering both radiation and convection heat transfers, determine the rateof heat transfer through the roof, and the inner surface temperature of the roofAns: Q-37,440 W.-7.3 C, and 7 out--2.1°CQ6: Compare the heat loss from an insulated and an un-insulated copper pipe (k = 400W/m K) has an internal diameter of 10 cm and an external diameter of 12 cm. Saturated steamflows inside the pipe at 110°C (hci = 10,000 W/m² K). The pipe is located in a space at 30°Cand the heat transfer coefficient on its outer surface is estimated to be 15 W/m² K. Theinsulation available to reduce heat losses is 5 cm thick and its thermal conductivity is 0.20W/mKAns For the un-insulated pipe.For the insulated pipe.Ans:Q7: A spherical tank, 1m in diameter, is maintained at a temperature of 120 °C and exposed to aconvection environment. With h=25 W/m² ° C and T 15 °C, what thickness of urethanefoam should be added to ensure that the outer temperature of the insulation does not exceed 40°C. What percentage reduction in heat loss results from installing this insulation.q/L = 452 W/mq/L = 138 W/mt = 0.023 mq( W/ ins) = 1982

To Find :The rate of heat transfer through the roof and inner surface temperature of the roof Given…

Q5. The roof of a house consists of a 15-cm-thick concrete slab (k = 2 W/m C) that is 15 m wide and 20 m long. The convection heat transfer coefficients on the inner and outer surfaces of the roof are 5 and 12 W/m² C, respectively. On a clear winter night, the ambient air is reported to be at 10 °C, while the night sky temperature is 100 K. The house and the interior surfaces of the wall are maintained at a constant temperature of 20 °C. The emissivity of both surfaces of the concrete roof is 0.9. Considering both radiation and convection heat transfers, determine the rate of heat transfer through the roof, and the inner surface temperature of the roof Ans: Q-37,440 W.-7.3°C, and 7,-2.1°C

Q5. The roof of a house consists of a 15-cm-thick concrete slab (k = 2 W/m C) that is 15 m wide and 20 m long. The convection heat transfer coefficients on the inner and outer surfaces of the roof are 5 and 12 W/m² C, respectively. On a clear winter night, the ambient air is reported to be at 10 °C, while the night sky temperature is 100 K. The house and the interior surfaces of the wall are maintained at a constant temperature of 20 °C. The emissivity of both surfaces of the concrete roof is 0.9. Considering both radiation and convection heat transfers, determine the rate of heat transfer through the roof, and the inner surface temperature of the roof Ans: Q-37,440 W.-7.3°C, and 7,-2.1°C

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.9P

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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.
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