Key Thermal Considerations During Liquid Cold Plate Design
Cold Plate Thermal Specifications
In addition to four types of cold plate technologies, there are also four scenarios of thermal requirements, which are listed below:
- Uniform Heat Flux, Fixed Flow Rate, 1 Maximum Pressure Drop, 1 Maximum Surface Temperature - With thermal scenario one, there is uniform input heat flux, a fixed flow rate, one specified maximum pressure drop that is limited at a fixed flow rate, and one specified maximum surface temperature where the surface temperature does not need to be uniform.
- Same as 1, but Non-Uniform Heat Flux - Thermal scenario two has the same specifications as scenario one, but heat loads vary instead of being uniform. The heat loads are concentrated in several locations under components or under specific areas.
- Same as 1, but Surface Temperature Maximum Varies - Thermal scenario three also has the same specifications as scenario one, but thermal scenario three has specified maximum surface temperatures that vary across the cold plate, usually at the individual components.
- Same as 1, 2, or 3, but Surface Temperature Uniformity Required - With thermal scenario four, the thermal specifications may be the same as with thermal scenarios one, two, or three, but with the additional requirement that the maximum surface temperature must be uniform across the entire cold plate or under specific components. For example, if there are two types of components mounted on the cold plate, each component type may require temperature uniformity of the common components, but the two types may have different maximum surface temperatures.
Cold plate scenarios 2 and 3 are the ones most commonly encountered in custom cold plate design. Scenarios 1 through 4 are listed in order of increasing complexity and cost.
When designing custom cold plates to any specification, the logical steps most thermal experts take are defining the thermal map, generating the liquid circuiting concept, calculating temperature rise and pressure drop, and rerouting the liquid circuit if necessary.
Defining the Thermal Map
With several possible thermal scenarios, step one in custom cold plate design is to define the thermal map in detail. To create a thermal map, an engineer needs the dimensions, locations, and heat loads of the components to be cooled. The maximum allowable cold plate surface temperature(s); the coolant composition, its flow rate, and inlet temperature; and available pressure drop are needed as well. Also, heat flux must be calculated for each component which includes thermal spreading, if necessary.