Chapter 1 Basics of Heat Transfer1-42EAir gains heat as it flows through the duct of an air-conditioning system. The velocity of the air at the duct inlet and the temperature of the air at the exit 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 -222°F and 548 psia. 2 The kinetic and potential energy changes are negligible, . 3Constant specific heats at room temperature can be used for air, CΔΔkepe≅≅0p= 0.2404 and Cv= 0.1719 Btu/lbm·R. This assumption results in negligible error in heating and air-conditioning applications. Properties The gas constant of air is R = 0.3704 psia.ft3/lbm.R (Table A-1). Also, Cp= 0.2404 Btu/lbm·Rfor air at room temperature (Table A-15E). AnalysisWe take the air-conditioning duct as the system. This is a control volumesince mass crosses the system boundary during the process. We observethat this is a steady-flow process since there is no change with time at any point and thus ΔΔmECVCVand ==00&, there is only one inlet and one exit and thus
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