Page 466 - Advanced thermodynamics for engineers

19.4 HEAT TRANSFER NETWORK WITH A PINCH POINT 457

Hot streams
310 245 280
3 5 7 Steam

72.0 210.8
MJ/h MJ/h 34.0 MJ/h
1 95 H 205
511.7
MJ/h 6.7 MJ/h 220
40
2
Cold streams 4 150 408.7 205
MJ/h

MJ/h
MJ/h
6 65 408.7 354.0 140

205 95 65
FIGURE 19.13
Diagram showing minimum number of heat exchangers to achieve heat transfer.

Table 19.3 Characteristics of Streams
Process Stream Heat
Supply Target Capacity Heat Load
Temperature, Temperature Flowrate, jmC(T S -T T )j

Number Type T S /( C) T T /( C) mC/(MJ/hK) /(MJ/h)
1 Cold 50 110 2.0 120
2 Hot 130 70 3.0 180
3 Cold 80 115 4.0 140
4 Hot 120 55 1.5 97.5

19.4 HEAT TRANSFER NETWORK WITH A PINCH POINT
Consider there are four streams of fluid with the characteristics given in Table 19.3. Assume that the
minimum temperature difference between any streams to obtain acceptable heat transfer is 5 C, i.e.

dT min ¼ 5 C. This value of dT min is referred to as the pinch point because it is the closest that the

temperatures of the streams are allowed to come. The temperatures of the streams can be ordered in a
manner similar to the first case, and the results of this are shown in Table 19.4.