(a) Explanation Write the expression for the mass balance for each fluid stream in the heat exchanger which acts as a system. m ˙ in − m ˙ out = Δ m ˙ system (I) Here, mass flow rate of the fluid entering the system is m ˙ in , mass flow rate of the fluid leaving the system is m ˙ out and change in mass flow rate of the system is Δ m ˙ system . For steady state, the change in mass flow rate of the system is zero. Δ m ˙ system = 0 Substitute 0 for Δ m ˙ system in Equation (II). m ˙ in − m ˙ out = 0 m ˙ in = m ˙ out m ˙ 1 = m ˙ 2 = m ˙ s m ˙ 3 = m ˙ 4 = m ˙ fw Here, mass flow rate of the steam is m ˙ s , mass flow rate of the feed water is m ˙ fw and subscripts 1, 2, 3 and 4 represent states. Write the expression for the energy balance equation for the closed system. E ˙ in − E ˙ out = Δ E ˙ system (II) Here, rate of net energy transfer in to the control volume is E ˙ in , rate of net energy transfer exit from the control volume is E ˙ out and rate of change in internal, kinetic and potential energies of system is Δ E ˙ system . For steady state, the rate of change in internal, kinetic and potential energies of the system is zero. Δ E ˙ system = 0 Substitute 0 for Δ E ˙ system in Equation (II). E ˙ in − E ˙ out = 0 E ˙ in = E ˙ out m ˙ 1 h 1 + m ˙ 3 h 3 = m ˙ 2 h 2 + m ˙ 4 h 4 m ˙ s h 1 + m ˙ fw h 3 = m ˙ s h 2 + m ˙ fw h 4 m ˙ s ( h 2 − h 1 ) = m ˙ fw ( h 3 − h 4 ) m ˙ s m ˙ fw = h 3 − h 4 h 2 − h 1 (III) Here, enthalpies of the steam at state 1 and 2 are h 1 and h 2 respectively and enthalpies of the feed water at state 3 and 4 are h 3 and h 4 respectively (b) To determine The reversible work per unit mass of the feed water during the process.

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 8.8, Problem 109RP

(a)

To determine

The ratio of mass flow rates of the steam and feed water.

(b)

To determine

The reversible work per unit mass of the feed water during the process.

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Chapter 8.8, Problem 108RP

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The ratio of mass flow rates of the steam and feed water.

Solution Summary: The author calculates the mass balance for each fluid stream in the heat exchanger which acts as a system.

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The ratio of mass flow rates of the steam and feed water.

The reversible work per unit mass of the feed water during the process.

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Chapter 8 Solutions