Question 3.1: Compute the enthalpy of saturated air at 60 F and standard a......
Compute the enthalpy of saturated air at 60 F and standard atmospheric pressure.
Equation 3-20a will be used to compute enthalpy; however, the humidity ratio W_s must first be determined from Eq. 3-14b:
i = 0.240t + W (1061.2 + 0.444t) Btu/lbma (3-20a)
W = \frac{18.015}{28.965} \frac{p_{\text{v}}}{p_{a}} = 0.6219 \frac{p_{\text{v}}}{p_{a}} (3-14b)
W_{s} = 0.6219 \frac{p_{s}}{p_{a}} = 0.6219 \frac{p_{s}}{P – p_{s}}
From Table A-1a, p_{s} = 0.2563 psia and
W_{s} = 0.6219 \frac{0.2563}{14.696 – 0.2563} = 0.01104 Ibmv/Ibma
i_{s} = (0.24) 60 + 0.01104 [1061.2 + (0.444) 60] = 26.41 Btu/Ibma
The enthalpy calculated using ideal gas relations is about 0.25 percent low but quite satisfactory for engineering calculations.