Water at 80°F enters a No. 18 BWG 5/8 in. condenser tube made of nickel chromium steel (k = 15 Btu/(h ft² ∞F)) at a rate of 5.43 gpm. The tube is 10 ft long and its outside is heated by steam condensing at 120°F. Under these conditions, the average heat-transfer coefficient on the water side is 1750 Btu/(h ft² °F). The heat transfer coefficient on the steam side may be taken as 2000 Btu/(h ft² °F). On the interior of the tube, however, there is a scale forming with a thermal conductance equivalent to 1000 Btu/(h ft² °F).

(a) Calculate the overall heat transfer coefficient U per square foot of exterior surface area after the scale has formed, and 

(b) Calculate the exit temperature of the water.

GIVEN

• Water flow in nickel chromium steel condenser tube
• Water flow rate (v) = 5.43 gpm = 43.5 ft₃/h
• Tube: 5/8 in, No. 18 BWG
• Inlet water temperature (T_w,in) = 80°F

ASSUMPTIONS

• Negligible scaling on the outside of the tube (R_o = 0)

Transcribed Image Text:

Condencing Steam Water Iw, out -? Tw. In - 80°F L= 10 ft