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U.2 W(III. K) IS auutu to 0.UZ II dlalIcter pipe. TIHE ZAJMIsulating Iaterial wiuI K heat transfer coefficient on the outer surface is 6.6 W/(m2.K ). Find the critical radius of 2k ins. insulation. Will the heat loss increase or decrease. Q2.(B) Show that the critical radius of a sphere is r. =

U.2 W(III. K) IS auutu to 0.UZ II dlalIcter pipe. TIHE ZAJMIsulating Iaterial wiuI K heat transfer coefficient on the outer surface is 6.6 W/(m2.K ). Find the critical radius of 2k ins. insulation. Will the heat loss increase or decrease. Q2.(B) Show that the critical radius of a sphere is r. =

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
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.
Chapter7: Forced Convection Inside Tubes And Ducts
Section: Chapter Questions
Problem 7.29P
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heat transfer coefficient on the outer surface is 6.6 W/(m².K ). Find the critical radius of insulation. Will the heat loss increase or decrease. 2k, Q2.(B) Show that the critical radius of a sphere is r. = h ins. Q 3. Choose (A) or (B) (A) A plane wall is 1.25 cm thick and has on surface (x=0) maintained at a constant temperature of 82°C while the other surface (x-L) is at 92 C. The thermal conductivity of the wall is 52.4 W/(m. K) and a uniform heat generation per unit volume of 88.78x10° W/m exists throughout the wall. Determine the temperature distribution and the temperature at center of the wall. (B) A sphere made of aluminum has a mass of 7 Kg and initially at a temperature of 250 C is suddenly placed in a controlled environment in which the temperature is maintained at 15 °C. The convection heat transfer coefficient is 90 W/(m². C ). Calculate the time required to cool the sphere to 100 °C. Take p=2707 kg/m³ and C=896 J/kg C. Use Lumped system analysis. Q4. The cooling system of an electronic package has to dissipate 0.153 kW from the surface of an aluminum plate 100 mm ×150 mm. It is proposed to use eight fins, each at 150mm long and Imm thick. The temperature difference between the plate and the surroundings is 50k, the thermal conductivity of the plate and fins is 0.15kW/(mK) and the heat transfer coefficient is 0.04 kW/m°K. Calculate the height of fins required. Assume the heat loss from the tip of fins may be neglected.
Transcribed Image Text:heat transfer coefficient on the outer surface is 6.6 W/(m².K ). Find the critical radius of insulation. Will the heat loss increase or decrease. 2k, Q2.(B) Show that the critical radius of a sphere is r. = h ins. Q 3. Choose (A) or (B) (A) A plane wall is 1.25 cm thick and has on surface (x=0) maintained at a constant temperature of 82°C while the other surface (x-L) is at 92 C. The thermal conductivity of the wall is 52.4 W/(m. K) and a uniform heat generation per unit volume of 88.78x10° W/m exists throughout the wall. Determine the temperature distribution and the temperature at center of the wall. (B) A sphere made of aluminum has a mass of 7 Kg and initially at a temperature of 250 C is suddenly placed in a controlled environment in which the temperature is maintained at 15 °C. The convection heat transfer coefficient is 90 W/(m². C ). Calculate the time required to cool the sphere to 100 °C. Take p=2707 kg/m³ and C=896 J/kg C. Use Lumped system analysis. Q4. The cooling system of an electronic package has to dissipate 0.153 kW from the surface of an aluminum plate 100 mm ×150 mm. It is proposed to use eight fins, each at 150mm long and Imm thick. The temperature difference between the plate and the surroundings is 50k, the thermal conductivity of the plate and fins is 0.15kW/(mK) and the heat transfer coefficient is 0.04 kW/m°K. Calculate the height of fins required. Assume the heat loss from the tip of fins may be neglected.
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