Refrigerant 134a enters a condenser operating at steady state at 70 lbf/in.2, 16

Question

Refrigerant 134a enters a condenser operating at steady state at 70 lbf/in.2, 160F and is condensed to saturated liquid at 60 lbf/in2 on the outside of tubes through which cooling water flows. In passing through the tubes, the cooling water increases in temperature by 20F and experiences no significant pressure drop. Cooling water can be modeled as incompressible with v = 0.0161 ft3/lb and c = 1 Btu/lbR. The mass flow rate of the refrigerant is 3100 lb/h. Neglecting kinetic and potential energy effects and ignoring heat transfer from the outside of the condenser, determine

(a) the volumetric flow rate of the entering cooling water, in gal/min.

(b) the rate of heat transfer, in Btu/h, to the cooling water from the condensing refrigerant.

Explanation / Answer

enthalpy of R134a at 70psi and 160 F is 198 btu/lb
enthalpy at 60 psi 91.85 btu/lb

energy transfer = 3100*(198-91.85) = 329065 btu/hr

mc(t2-t1) = 329065
m * 1 * 20 = 329065
m = 16453.25 lb/hr
v = 0.0161*16453.25 ft^3/hr
= 264.89 ft^3/hr

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