*4.2.4 Heat pipe exchanger*

These special heat exchangers are generally formed of a number of heat pipes usually made of copper, where several fins (the fin stack) have been mounted in the condensation zone.

As shown in **Figure 23**, each pipe is bent in a U form, slightly flattened where contact is made with the mounting base plate (hot area), and filled with a heat transfer fluid. When the copper pipes are going to be directly in contact with the environment, protection against corrosion could be obtained by nickel plating.

Each heat pipe acts actually as a *heat mover* from the area where heat is generated (the base plate) to the cooling area (fin stack) where air movement carries the heat away.

Rules of thumb


**Figure 23.** *Fixing the fin stack to the base plate.*

3.The bend radius of the heat pipes is to be fixed with care in order not to alter the integrity of the pipes.

4.The minimum *bend radius* should be *three times the diameter of the heat pipe*.

Note that the heat pipes can be directly fixed on the electronic component to be cooled. **Figure 24** shows a heat exchanger made of six copper heat pipes that are directly fixed on a central processing unit (CPU) to convey heat to a 13 fin stacks. The advantage is a direct contact between the component and the heat pipes, thus reducing the thermal resistance of the base plate.

A more elaborated version is the U-shaped vapor chamber design where a U-shaped heat plate replaces the heat pipes, the heat plate operating in the same way as flattened pipes. **Figure 25** shows a heat exchanger formed from a vapor chamber bent to offer a large copper base to be in direct contact with the power electronic component. This design offers the advantage of a large direct contact area, which translates into a better performance: more than 20% better than the design of the pipe.

**Figure 24.** *Heat pipe heatsink to cool a CPU.*

**Figure 25.** *U bent vapor chamber with a fin stack. (a) Complete vapor chamber and (b) showing inside the chamber.*

*Heat Exchangers for Electronic Equipment Cooling DOI: http://dx.doi.org/10.5772/intechopen.100732*
