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exam-mid-solution

# exam-mid-solution - 1 Saturated water vapor leaves a steam...

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1. Saturated water vapor leaves a steam turbine at a flow rate of 1.5 kg/s and a pressure of 0.51 bar. The vapor is to be completely condensed to saturated liquid in a shell-and-tube heat exchanger that uses city water as the cold fluid. For saturated liquid at 310 K, C p = 4.178 kJ/kg K; at 0.51 bar, T sat = 355 K and h fg = 2304 kJ/kg. (1) The city water enters the thin-walled tubes at 17ºC and is to leave at 57ºC. Assuming an overall heat transfer coefficient of 2000 W/m 2 K, determine the required heat exchanger surface area and the water flow rate. (2) After extended operation, fouling causes the overall heat transfer coefficient to decrease to 1000 W/m 2 K. In order to completely condense the vapor, there must be an attendant reduction in the vapor flow rate. For the same water inlet temperature and flow rate, what is the new vapor flow rate required for complete condensation? (1) Required heat transfer rate: 6 3 10 456 . 3 ) 10 2304 )( 5 . 1 ( fg h h m q W From ) ( 1 2 c c c T T C q , 86400 ) 17 57 /( 10 456 . 3 6 c C W/K

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