7. Determine the heat loss through a ventilated attic under the following conditions: indoor temperature 21°C, outdoor temperature 10°C, roof area 260 m?, ceiling area 200 m?, ceiling U-value = 0.15 W/m?K (include films), roof U-value = 1.7 W/m²K (include films), attic ventilation = 10 L/s. Neglect the air leakage through the ceiling. Determine the attic temperature.

7. Determine the heat loss through a ventilated attic under the following conditions: indoor temperature 21°C, outdoor temperature 10°C, roof area 260 m?, ceiling area 200 m?, ceiling U-value = 0.15 W/m?K (include films), roof U-value = 1.7 W/m²K (include films), attic ventilation = 10 L/s. Neglect the air leakage through the ceiling. Determine the attic temperature.

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 8.40P

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In the United States, energy for household heating is generally sold using English units, e.g., therm, gal, and cord. A house in Wisconsin uses 1200 therms of thermal energy during the heating season. Calculate the cost of fuel if the furnace uses (a) natural gas with an efficiency of 70%; (b) No. 2 fuel oil, efficiency 65%; (c) kerosene, efficiency 99.9% (unvented); and (d) wood with l5% moisture with an efficiency of 50%. Use the data in Tables 2.2, 2.7, and 2.13. The efficiencies are based on the HHV. Assume the cost of natural gas is $8/MBtu, the cost of No. 2 fuel oil is $3/gal, the cost of kerosene is $3.50/gal, and the cost of wood is $100/cord. Assume the bulk density of cord wood is 30 lbm/ft3 .
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The thermal conductivities of human tissues vary greatly. “Fat” and “skin” have conductivities of approximately 0.200 W /m 0K and 0.0200 W /m 0K, respectively, while other “tissues” inside the body have conductivities of approximately 0.500 W /m 0 Assume that between the core region of the body and the skin surface lies a “skin” layer of 1.00mm, a “fat” layer of 0.500 cm., and 3.20 cm. layer of other “tissues”. Find the rate of energy loss when the core temperature is 37.00C and the exterior temperature is 0.000 Assume a body area of 2.00 m2. (Both a protective layer of clothing and an insulating layer of unmoving air are absent).
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SUMMARIZED IN YOUR OWN WORDS THE RELEVANCE OF IST AND SECOND LAW OF THERMODYNAMICS IN YOUR CAREER AS A CIVIL ENGINEER
A 6 kg/s of hot liquid flow continuously without leaking in a 40 mm inside diameter with thickness of 7 mm pipe with temperature of 50℃. Thermal conductivity of pipe is 10W/(m℃) and surface conductance of liquid is 9W/(m^2℃). The outer fluid has temperature of 25℃ and surface conductance of 6W/(m^2℃). Cp of hot liquid = 4.2KJ/(Kg℃). Find the minimum length of pipe in meters just to cool down the hot liquid as much as possible if the maximum heat transfer is the constant heat transfer throughout the pipe.