Unformatted text preview: e the entropy generated during
this process, in kJ/K.
7–159 A hot-water pipe at 80°C is losing heat to the surrounding air at 5°C at a rate of 2200 W. Determine the rate of
entropy generation in the surrounding air, in W/K.
7–160 In large steam power plants, the feedwater is frequently heated in closed feedwater heaters, which are basically
heat exchangers, by steam extracted from the turbine at some
stage. Steam enters the feedwater heater at 1 MPa and 200°C
and leaves as saturated liquid at the same pressure. Feedwater
enters the heater at 2.5 MPa and 50°C and leaves 10°C below
the exit temperature of the steam. Neglecting any heat losses
from the outer surfaces of the heater, determine (a) the ratio of
the mass flow rates of the extracted steam and the feedwater
heater and (b) the total entropy change for this process per unit
mass of the feedwater.
7–161 Reconsider Prob. 7–160. Using EES (or other)
software, investigate the effect of the state of the
steam at the inlet to the feedwater heater. Assume the entropy cen54261_ch07.qxd 11/18/03 9:58 AM Page 347...
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