Chapter 1 Basics of Heat Transfer1-39The resistance heating element of an electrically heated house is placed in a duct. The air is moved by a fan, and heat is lost through the walls of the duct. The power rating of the electric resistance heater is 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. ΔΔkepe≅≅0Properties The specific heat of air at room temperature is Cp= 1.007 kJ/kg·°C (Table A-15). AnalysisWe take the heating duct as the system. This is a control volumesince mass crosses the system boundary during the process.
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