Chapter 1 Basics of Heat Transfer1-38A 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.. Assumptions1 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, . 3Constant 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. ΔΔkepe≅≅0Properties The gas constant of air is R = 0.287 kPa.m3/kg.K (Table A-1). Also, Cp= 1.007 kJ/kg·K for air at room temperature (Table A-15) and Cv= Cp– 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.