Page 418 - Mechanical Engineers' Handbook (Volume 4)

3 Thermal Control Techniques 407

h A
NTU 0 (104)
Wc p
and the overall passage efficiency is
A ƒ
1 (1 ) (105)
ƒ
0
A
The surfaces to be used in the cold plate are those described by Kays and London 41
where physical, heat-transfer, and friction data are provided.
The detailed design procedure for the double-side-loaded isothermal case is as follows:
1. Design specification
(a) Heat load, q,W
(b) Inlet air temperature, t , C
1
(c) Airflow, W, kg/sec
(d) Allowable pressure loss, cm H O
2
(e) Overall envelope, H, W, D
(f) Cold-plate material thermal conductivity, k , W/m C
m
(g) Allowable surface temperature, T , C
s
2. Select surface 41
(a) Type
(b) Plate spacing, b,m
(c) Fins per meter, fpm
(d) Hydraulic diameter, d ,m
e
(e) Fin thickness, ,m
2
(f) Heat-transfer area/volume, ,m /m 3
(g) Fin surface area/total surface area, A /A,m /m 3
2
f
3. Plot of j and ƒ data 41
ƒ (Re) ƒ
dG
j (St)(Pr) 2/3 e
1 1

where St is the Stanton number
hG
St (106)
c p
and ƒ is the friction factor
ƒ ƒ (Re) ƒ
dG
e
2 2

4. Establish physical data
(a) a (b/H) ,m /m 3
2
(b) r d /4, m
h
e
(c) ar h
(d) A WH,m 2 (frontal area)
fr
(e) A A ,m 2 (flow areas)
fr
c