Metal Foams: A Design Guide

228 Metal Foams: A Design Guide
in accordance with:
q/q D ⊲bsi/bhs⊳ 2
⊲17.1⊳
With bsi D 1
2 cm, this requirement results in bhs D 25 cm, causing the overall
system to occupy a large volume. The goal of the case study is to reduce bhs to
3 cm, by using a cellular metallic heat sink, resulting in an order of magnitude
reduction in overall volume.
The power density at the electronics is limited by the temperature reached
at the junction, Tj. For Si electronics, Tj must be less than 120°C toavert
unacceptable degradation. The design of the system and the importance of
the heat transfer coefficient at the sink interrelate through q, q and Tj. The
capacity of the fluid pumping system is another key factor. Such systems are
characterized by an operating curve that connects the back pressure to the
allowable fluid flow rate through the sink (Figure 17.13).
Mesocell
Heat
Sink
;;;;;
;;;;;
;;;;;
Cooling fluid
PCM 2
PCM 1
T s (r)
Cooling fluid
1 Heat spreader
2 Planar micro heat pipe
bA N z q
q=0 hsi r Si Electronics q=0
h A N
h cu
h 1
b si
h 2
b
A N
T b (r)
Figure 17.13 An example of integrated gate bipolar transistor design
q
q
V •
b hs
H
H s