Coldplates are designed as part of a liquid cooling system for high heat density
electronic equipment. As heat dissipation levels increase, standard methods of cooling
involving air become inadequate. In order to achieve acceptable levels of performance
at the IC level, liquid cooling systems are being used in increasing number of applications.
Liquid cooling systems will generally include a coldplate (to collect heat from the
heat source), a pump (to circulate the cooling fluid), and a heat exchanger (where
the heat is removed). There are a number of different types of coldplates that are
available depending on the application of interest. Coldplates can be tubed, drilled,
brazed, sintered or other.
Due to increasingly higher heat fluxes generated at the IC level, coldplate designs
are now more advanced and achieve significantly higher heat transfer coefficients
using micro-channels and impingement techniques. The higher thermal performance of
the coldplate is usually accompanied with higher coldplate pressure drop. As a result,
the design of the liquid cooling system must include a pump that is capable of delivering
an adequate amount of cooling fluid at the appropriate pressure drop. Since many
electronics applications require small form factors, the pump must be small in size
while being capable of providing the correct flow and pressure.
TDMG has performed analysis and evaluation for various coldplate types. The following
example demonstrates the performance of a CPU coldplate used for High Performance
Computing application. The application in question required thermal impedance in
the range of 0.2 C/W at an ambient of 40 Deg C for the system. In order to achieve
this, the coldplate was designed with crosscut (diamond shape) fins that yielded
an overall system performance well within specification requirements. The coldplate
pressure drop was limited to 0.125 psi per coldplate, which allowed the pump to provide
up to approximately 1 liter per minute in a dimensional envelope of 1.6” (< 1U height)
when the complete system operating.
Various types of coldplate designs were investigated, and the latter (diamond shape)
was deemed the best design based on performance versus cost implications. Other coldplate
designs investigated included micro-channels. Although these would have provided
an increase in thermal performance at the coldplate level, the significant increase
in pressure drop would have meant that the pumps would not have been capable of providing
the required flow to achieve that thermal performance. In addition, the increased
cost would have been significant and rendered the micro-channel design expensive
by comparison. The choice of coldplate design is application dependent and perhaps
for other applications, a micro-channel design (or other) might have been the correct
choice. In the case of this application a more simplistic design yielded the required
performance at a lower price.