Explanation The following figure shows the heat exchanger for applying steady flow energy equation. Figure-(1) Write the expression for steady flow energy equation for energy balance. Q ˙ C V + m 1 ( h 1 − h 2 ) + m 3 ( h 3 − h 4 ) = 0 m ˙ 1 ( h 1 − h 2 ) = m ˙ 3 ( h 4 − h 3 ) − Q ˙ C V m ˙ 1 = m ˙ 3 ( h 4 − h 3 ) − Q ˙ C V ( h 1 − h 2 ) (I) Here, enthalpy at entry for steam is h 1 , enthalpy at exit for steam is h 2 , enthalpy at entry for cooling water is h 3 , enthalpy at exit for cooling water is h 4 , mass flow rate for steam is m ˙ 1 and mass flow rate for cooling water is m ˙ 3 . Write the expression for heat transfer from the heat exchanger to its surrounding. h 1 − h 2 = x 1 h f g (II) Here, dryness fraction at section (1) is x 1 . Write the expression for heat transfer from the heat exchanger to its surrounding. Q ˙ C V = − 0.10 [ m ˙ 3 ( h 4 − h 3 ) ] (III) Here, heat transfer from the heat exchanger is Q ˙ C V . Write the expression for enthalpy difference between state (3) and state (4). h 4 − h 3 = c v ( T 4 − T 3 ) + v ( P 4 − P 3 ) (IV) Here, temperature at state (3) is T 3 , temperature at state (4) is T 4 , pressure at state (3) is P 3 , pressure at state (4) is P 4 , volume at state (3) and (4) is same v , and specific heat at constant volume is c v Conclusion: Refer to table A-3 ,“Properties of saturated water” to obtain the values of specific enthalpy of liquid and vapour mixture at 250 kPa as 2181.5 kJ / kg . Substitute 2181.5 kJ / kg for h f g at pressure 250 kPa and 0

Fundamentals of Engineering Thermodynamics

8th Edition

ISBN: 9781118832318

Author: MORAN

Publisher: WILEY

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Heat Exchangers

Heat exchangers are the types of equipment that are primarily employed to transfer the thermal energy from one fluid to another, provided that one of the fluids should be at a higher thermal energy content than the other fluid.

Heat Exchanger

The heat exchanger is a combination of two words ''Heat'' and ''Exchanger''. It is a mechanical device that is used to exchange heat energy between two fluids.

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Chapter 4.12, Problem 76P

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Fundamentals of Engineering Thermodynamics

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