Examples on Heat Exchangers

Examples: Heat Exchangers

Closed Heat Exchanger

In the condenser of a steam power plant, a mass flow m˙ c = 10 t

saturated liquid-vapor mixture at 35 ◦C, x = 0.9 is isobarically condensed to the saturated liquid state by heat exchange with cooling water. We determine the mass flow m˙ w of cooling water which enters at Tw1 = 20 ◦C and leaves at Tw2 = 30 ◦C.

The cooling water can be described as incompressible liquid with constant specific heat cw = 4.18 kJ . From (9.48) we obtain, with A for the cooling water and B for the condensate,

Adiabatic and Isobaric Mixing

Compressed water at T1 = 20 ◦C is mixed with superheated steam at T2 = 400 ◦C; both streams are at p = 2 bar. We determine the mass flow ratio m˙ 2/m˙ 1 so that the outflow is just saturated liquid at p = 2 bar (state 3), and the entropy generation rate.

Enthalpy and entropy of the three states are

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