Thermodynamics HW Solutions 62

Thermodynamics HW Solutions 62 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-122 The duct of an air heating system of a house passes through an unheated space in the attic. The rate of heat loss from the air in the duct to the attic and its cost under steady conditions 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 Steady operating conditions exist since there is no change with time at any point and thus Δ Δ mE CV CV and = = 00 . 3 The kinetic and potential energy changes are negligible, ΔΔ ke pe 0 . 4 Constant specific heats at room temperature can be used for air. This assumption results in negligible error in heating and air-conditioning applications. Properties The gas constant of air is R = 0.287 kJ/kg.K (Table A-1). The specific heat of air at room temperature is C p = 1.007 kJ/kg· ° C (Table A-15). Analysis We take the heating duct as the system. This is a control volume since mass crosses the system boundary during the process. There is only one inlet and one exit and thus
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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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