Page 112 - DJJ20063- Thermodynamics 1
P. 112
DJJ20063- Thermodynamics 1
Note that on a p-V diagram, the area under the process line represents the amount of
work transfer. From Figure 3.2.3-5
W = area of the shaded rectangle
= height x width
= p (V2 – V1) (larger volume – smaller volume)
This expression is identical to equation 3.21
Heat transfer:
Applying the non flow energy equation
Q – W = U2 – U1
or Q = (U2 – U1) + W (3.22)
Thus part of the heat supplied is converted into work and the remainder is utilized in
increasing the internal energy of the system.
Substituting for W in equation 3.22
Q = (U2 – U1) + p(V2 – V1)
= U2 – U1 + p2 V2 – p1 V1 (since p2 = p1 )
= (U2 + p2 V2) – (U1 + p1 V1)
Now, we know that h = u + pv or H = U + pV
Hence
Q = H2 – H1 (larger H – smaller H) (3.23)
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