## How to Calculate Heat Loads for Liquid Cooling Systems

A series of calculations can be used to find the thermal loads in common liquid cooling systems. Calculations of this nature are needed to predict the performance of liquid cooling systems, which are effective but complex thermal management solutions. Several equations must be calculated to fully understand the behavior of a liquid cooled system, and ATS is providing these to engineers via personal instruction and in a paper available free from the company’s website, Qats.com.

IIn the paper, which appears in the company’s e-magazine, ATS considers a liquid cooling system as a closed loop system with three major components: cold plate, heat exchanger and pump. The cold plate is typically made from aluminum or copper, and is attached to the device being cooled. The plate usually has internal fins which transfer heat to the coolant flowing through them. This fluid moves from the cold plate to a heat exchanger where its heat is transferred to the ambient air via forced convection. The final part of the cooling loop is the pump, which drives the fluid through the loop.

A series of equations is provided to predict the final temperature of the device being cooled. The first of these equates the surface temperature of this device with the product of the power dissipated by the device times the thermal resistance of the cold plate (and its thermal interface material), added to the temperature of the water entering the cold plate.

The sequence of calculations factors in specifications from the cold plate, heat exchanger and pump. The result is a solution for the device temperature as a function of cold plate resistance. In the example cited by ATS, a cold plate thermal resistance of less than 18 degrees C/W is required to cool an Intel Xeon 5492 processor in a 25C temperature environment.

Liquid cooling is an important and expanding practice in the electronics industry. It is important to understand the impact on performance of all three major parts of liquid cooling loops (cold plate, heat exchanger and pump) to ensure an acceptable level of performance at the lowest cost.

Instructions for calculating load for liquid cooling systems are available on Qats.com in the pages of Qpedia, the thermal management emagazine from ATS. More information is also available by calling 1-781-949-2522.