Page 140 - Design and Operation of Heat Exchangers and their Networks

128 Design and operation of heat exchangers and their networks

3.5.4.4 Wavy fins
Dong et al. (2007) correlated their own experimental data from 11 wavy fin
geometries and proposed the following correlations:

0:309 0:3703 0:25 0:1152
f ¼ 1:16Re ð s f =h f Þ ð 2a=s f Þ ð l w =l s Þ (3.302)
j ¼ 0:0836Re 0:2309 ð s f =h f Þ 0:1284 ð 2a=s f Þ 0:153 ð l w =l s Þ 0:326 (3.303)
where a is the wave amplitude, l w is the wavelength, and l s is the strip length
of a wavy fin strip.
Based on CFD calculation, Chennu (2016) presented the correlations for
wavy fins as follows:
0:322 2a 0:394 0:603

f ¼ 9:827Re 0:705 h fs l w ð 100 Re 800Þ
s fs s fs 2a
(3.304)

0:264 2a 0:848 1:931
f ¼ 10:628Re 0:359 h fs l w ð 1000 Re 15;000Þ
s fs s fs 2a
(3.305)
0:312 0:192 0:432
2a
j ¼ 2:348Re 0:786 h fs l w ð 100 Re 800Þ
s fs s fs 2a
(3.306)

0:235 2a 0:288 0:553
j ¼ 0:242Re 0:375 h fs l w ð 1000 < Re 15;000Þ
s fs s fs 2a
(3.307)
More correlations based on their CFD simulation were summarized by
Chennu (2018).

3.6 Multistream parallel heat exchangers
The multistream heat exchangers can be classified into two categories: One
is the multichannel heat exchanger in which there is no thermal intercon-
nection between the walls separating the fluids, such as shell-and-tube heat
exchangers and plate heat exchangers. The other is multistream plate-fin
heat exchanger. The mathematical model and its analytical solution for
the thermal performance of parallel multistream plate-fin heat exchangers
were first proposed by Kao (1961). Haseler (1983) defined a bypass efficiency
that describes heat transfer between nonadjacent layers in a plate-fin heat
exchanger to illustrate the bypass effect. For multichannel heat exchangers,
a general solution of the temperature distributions was proposed by