Question 10.12: Referring to Example 10-11, a water heater at the end of the......

The enthalpy of vaporization for the steam is about 960 Btu/lbm from Table A-1a. Then

$\dot{m}_{\text{v}}  =  \dot{q}/i_{fg}  =  50,000/960  =  52  lbv/hr  =  \dot{m}_{c}$

Using Fig. 10-46 with a system steam pressure of 5 psig, ∆P/L of 0.2 psi/100 ft, and mass flow rate of 52 lb/hr, the pipe size is between 1 and $1\frac{1}{4}$ in. and the velocity based on 0 psig is 2400 ft/min. The velocity at 0 psig may be converted to the velocity at 5 psig using Fig. 10-47 to obtain 2200 ft/min. This velocity is a little high; therefore, use the 1 $\frac{1}{4}$ in. pipe, which will have a lower velocity and pressure loss. The dry condensate return for this case may be sized by referring to Table 10-6a. With a line slope of $\frac{1}{8}$ in./ft and flow rate of 52 lb/hr, select the nominal $\frac{1}{2}$ in. pipe, which is rated at 54 lb/hr.