Page 436 - Design and Operation of Heat Exchangers and their Networks

Experimental methods for thermal performance of heat exchangers 419

0.25

B = 0
0.20 −
τ = 0
Pe = 0

0.15
θ− θ Pe = ∞ 1
0.10 2

5
0.05 10
20

0.00
0 2 4 6 8 10
NTU
Fig. 8.7 The effect of the axial dispersion on the initial rise of the outlet fluid
temperature to a unit step change in the inlet fluid temperature (K w ¼0).

1.0 1.0
0.9 NTU = 1 0.9 NTU= 1
0.8 Pe = 0 0.8 Pe = 5
0.7 0.7
0.6 0.6
q 0.5 q 0.5
0.4 0.4
0.3 0.3
B= 5
0.2 4 0.2
3 B= 0 B= 6 B= 0
0.1 2 0.1 5 4 3 0.5
1 0.5 2 1
0.0 0.0
–5 –4 –3 –2 –1 0 1 2 3 4 5 –5 –4 –3 –2 –1 0 1 2 3 4 5
(A) t –B (C) t –B
1.0 1.0
0.9 NTU = 1 0.9 NTU = 1
0.8 Pe = 1 0.8 Pe = 20
0.7 0.7
0.6 0.6 B = 6
5
q 0.5 q 0.5 4
0.4 0.4 3
2
0.3 0.3 1
B = 5
0.2 0.2 0.5
4
3 B= 0 0
0.1 2 1 0.5 0.1
0.0 0.0
–5 –4 –3 –2 –1 0 1 2 3 4 5 –5 –4 –3 –2 –1 0 1 2 3 4 5
(B) t –B (D) t –B
Fig. 8.8 The effect of the fluid thermal capacity on the outlet fluid temperature
responses to a unit step change in the inlet fluid temperature (NTU¼1, K w ¼0).
(A) Pe¼0. (B) Pe¼1. (C) Pe¼5. (D) Pe¼20.