... can be specified by (2) To calculate the maximum theoretical performance, assume that the outlet temperature of the shell-side gas is equal to the saturation temperature of the tube-side fluid (~120 K). If the exhaust pressure and temperature of the nitrogen gas is 3 bar, and 270 K respectively, then the maximum enthalpy at the tube-side exit of the economizer, hmax, is 140 kJ/kg, corresponding to a temperature of 155 K. This equates to over 47 kW of steady state heat transfer at the maximum mass flow of 300 g/s, and is 35 K above the saturation temperature of the tube-side fluid. This calculation provides the figure of merit for the performance of the economizer, the heat transfer effectiveness: (3) where h1 is -18 kJ/kg and ?hmax is 158 kJ/kg. If more than 50% of maximum performance can be attained (i.e.: ?econ> 0.5), then this should allow the ambient-air heat exchanger to be ...

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