Power & packaging requirements have dictated an inevitable acceptance that liquid cooling has obvious advantages over more traditional air cooled systems.
Once these advantages have been accepted the next step is to select from the multiple cold plate types the one most suited to the application and the budget.
In certain high performance systems the simple tube in plate & gun drilled construction has certain limitations on its ability to cool effectively due to tube bending limitation and the straight flow paths in a gun drilled cold plate.
These limitations effectively mean that the flow path cannot get to the location on the cold plate where the cooling is most needed. These inherent limitations can be easily overcome by selecting a Multi-Piece Cold plate design commonly called Vaccum brazed cold plate, FSW Friction Stir Welded cold plate or Dip brazed cold plate.
Multi-Piece Cold Plates
In a Multi-Piece cold plate the flow path can be precisely milled into one half of the cold plate with strategic positioning in the most critical heat transfer areas.
The geometry of the channels can also be designed such that the Reynolds number is optimized to provide the best thermal performance for the required flow rate and pressure drop constraints. Because the flow path is CNC machined, features such as component mounting holes can easily be avoided without sacrificing any cooling performance.
CNC Machined Cold Plates
Cold plates that have CNC machined flow paths are very flexible, often the location of the inlet and outlet are dictated by the end user’s geometry, achieving the very best thermal performance can be quite a challenge.
A simple serpentine path from inlet to outlet even if channel width and depth are optimised would result in a thermal gradient from inlet to outlet, see the upper image below.
Columbia-Staver have developed an optimised counter-flow channel design. This concept can be adapted to a multitude of inlet and outlet positions.
Typically this flow path will result in a much improved range of surface temperatures and a reduction or near total elimination of hotspots.
CFD results
When comparing a traditional Serpentine flow path with the Columbia-Staver optimised counter -flow path, the results shown below would not be uncommon. In this instance with exactly the same parameters the CS counter-flow path eliminated the hot spot making the surface temperature more isothermal by 29%.
The base plate with the CNC machined flow path is then mated to a cover plate or lid completing the cold plate assembly. The joining of these pieces may be vacuum-brazed, dip brazed or Friction Stir Welded (FSW) to create a leak free joint.
In this two-piece construction where access to the flow path is open prior to joining a further enhancement is possible.
The surface area within the flow path can be increased by machining fins into the flow path, or more commonly introducing a folded fin, this internal fin increases surface area for heat transfer as well as creating turbulence, minimizing the fluid boundary layer and further reducing thermal resistance.
The available folded fin designs offer enormous customization possibilities and designs can be precisely engineered to match performance, pressure drop, and dimensional requirements.
Columbia-Staver tailors the internal flow configuration to the application, creating a design that maximises thermal performance and minimises cold plate pressure drop.
Because of the sheer number of potential variations it is highly recommended that a Columbia-Staver design engineer be involved as early in the design stage as possible to ensure the most cost effective solution is developed. All custom cold plate designs are different, but the design process or fundamentals of design remain the same.
The use of advanced thermal analysis software to model the system heat loads and fluid flow will ensure a cold plate design that meets or exceeds the target thermal requirements yet still maintains the pressure drop performance requirements.
Once designed the Columbia-Staver manufacturing engineers ensure that the cold plate is cost-effective to build and is designed for high reliability. Custom cold plates are then manufactured and pressure tested to meet working pressure requirements.
