Module 1 : Classical Thermodynamics

Lecture 9 : Examples of Quality Degradation

Mass balance:

m1 + m2 = m3 = m(say)

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Let,

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By first law of thermodynamics,

m1h1 + m2h2 = (m1 + m2)h3

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or,

xh1 + (1 - x)h2 = h3

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Since,

h = h(T)

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From Eq. (1.240)

xT1 + (1-x)T2 = T3

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where

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By second law of thermodynamics,

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or,

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Let, Ns Entropy generation number =

Now, substituting from Eq. (1.243) in Eq. (1.249), we get

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For, x = 1, Ns = 0 ⇒ m2 = 0, the system is with single stream.

For, , Ns = 0, temperature of both the streams are same.

Rate of exergy loss due to mixing is,

Wlost = I = T0Sgen

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