Thermodynamics HW Solutions 10

Thermodynamics HW Solutions 10 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-29 A resistance heater is to raise the air temperature in the room from 7 to 25°C within 20 min. The required power rating of the resistance heater is 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. 4 Heat losses from the room are negligible. 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). Analysis We observe that the pressure in the room remains constant during this process. Therefore, some
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