Page 426 - Mechanical Engineers' Handbook (Volume 4)

3 Thermal Control Techniques 415

700
Pr = 20
t = 0.02
600
H/O = 7
500 15
10
400
Nu D 300 5

200
0.7
100
0
0 20000 40000 60000 80000 100000
Re D
Figure 19 Effect of Reynolds and Prandtl numbers on heat transfer.

1 H/D 0.05 H/D 0.3
6
0.6/ƒ 0.5 0.6/ƒ 0.5 (126)
0.5
and that the second term is not far different from 0.6ƒ . Reexpressing Eq. (126) with these
simplifications, the average heat-transfer coefficient, h, is found to approximately equal
Nu 0.5 0.3 0.35 0.667 0.42
H
D ƒ Re D Pr (127)
This approximation falls within 30% of Eq. (124) throughout the parametric range indicated,
but is within 10% for H/D 3.

200
Pr = 20 t = 0.02
= 10,000
Re D
15
150
10
Nu D 100 5

50
0.7

0
0 2 4 6 8 10 12 14
H/D
Figure 20 Effect of jet aspect ratio on heat transfer.