An ideal Stirling engine with air as the working fluid is considered. The temperature of the source-energy reservoir, the amount of air contained in the engine, and the maximum air pressure during the cycle are to be determined.
Assumptions: Air is an ideal gas with constant specific heats. Properties: The properties of air at room temperature are R = 0.3704 psia·ft3 /lbm.R, cp = 0.240 Btu/lbm·R, cv = 0.171 Btu/lbm·R, and k = 1.4.
From the thermal efficiency relation
"\\eta_{th}=\\frac{W_{net}}{Q_{in}}=1-\\frac{T_L}{T_H}\\implies \\frac{2.5}{6}=1-\\frac{510}{T_H}\\implies T_H=874" R
State 3 may be used to determine the mass of air in the system:
"m=\\frac{P_3V_3}{RT_3}=\\frac{10\\cdot0.5}{0.3704\\cdot510}=0.02647" lbm
The maximum pressure occurs at state 1:
"P_1=\\frac{mRT_1}{V_1}=\\frac{0.02647\\cdot0.3704\\cdot874}{0.06}=143" psia
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