Thermodynamics HW Solutions 17

Thermodynamics HW Solutions 17 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-38 A room is heated by an electrical resistance heater placed in a short duct in the room in 15 min while the room is losing heat to the outside, and a 200-W fan circulates the air steadily through the heater duct. The power rating of the electric heater and the temperature rise of air in the duct are to be determined. . Assumptions 1 Air is an ideal gas since it is at a high temperature and low pressure relative to its critical point values of -141 ° C and 3.77 MPa. 2 The kinetic and potential energy changes are negligible, . 3 Constant specific heats at room temperature can be used for air. This assumption results in negligible error in heating and air-conditioning applications. 3 Heat loss from the duct is negligible. 4 The house is air-tight and thus no air is leaking in or out of the room. ΔΔ ke pe ≅≅ 0 Properties The gas constant of air is R = 0.287 kPa.m 3 /kg.K (Table A-1). Also, C p = 1.007 kJ/kg·K for air at room temperature (Table A-15) and C v = C p R = 0.720 kJ/kg·K.
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This note was uploaded on 01/14/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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