Heat pipes and vapor chambers are not typically used on their own to move heat from point A to Point B. To remove heat to ambient temperatures, they are typically embedded into heat sinks, the chassis or the system enclosure.
Baknor will meet your toughest challenges by designing, modeling and manufacturing custom phase change cooling assemblies using heat pipes and vapor chambers. It may be determined that using standard heat sink materials, (aluminum or copper) are insufficient or may be too bulky to meet the design objectives, the next step is to include heat pipes or vapor chambers in the design.
Heat pipes can be attached by epoxy, press-fit, and soldering. When attaching heat pipes and fins, they are typically soldered together or the fins are press fit on to the heat pipes. The fins have holes that are just a bit smaller than the diameter of the heat pipe. Pressure is used to attached the fins which creates a tight fit assembly. This allows the heat to move from a high-powered component in a tightly constrained area, to the more conductive fin array.
When modeling the assembly, three-dimensional simulation becomes important. The evaporation and condensation process are complex, which makes it difficult to simulate the physical process directly. Therefore, the heat pipe is modeled as a super conductor with highly effective thermal conductivity. (The longer the heat pipe, the higher the effective of thermal conductivity). This can be corrected once prototypes are measured for thermal performance.
Heat pipes can also be embedded in the base of a heat sink. The spreading resistances in the base of the heat sink often limits the performance of the design. By embedding a heat pipe in the base, the spreading capability will greatly improve the performance of the heat sink.
Tubular heat pipes (1.2mm to 38mm) and planar heat pipes (also called vapor chambers) can be assembled using standard sizes. Custom sizes can also be made to ensure the assembly meets the customer’s requirements. Specialized bending methods are available to achieve extremely tight bend radii for shapes that may be more complex. The more complex the shape, the lower the maximum amount of heat that can be carried. Baknor’s engineers can ensure the right trade-offs are made during the design of the assembly.
Vapor chambers offer some advantages over heat pipes. Vapor chambers can be in direct contact with the heat source and is able to spread heat uniformly in all directions. Like heat pipes, vapor chambers can be added to the base of an extruded heat sink or can be part of an assembly of fins with mechanical attachments. Vapor chambers can also be integrated in to a stack of fins directly. They are also able to accept higher heat fluxes than an aluminum or copper surface. System packaging can take advantage of the smaller size and less weight in addition to quieter operation through less air flow. Vapor chambers are able to operate in any orientation. They will pass shock and vibration testing, and freeze thaw thermal cycling.
The combination of copper and water are most commonly used. But it is important to select the correct fluid for the customer application. The freezing point of the fluid selected must be lower than the freezing point of the application. When the temperature is above the vapor condensation point of the working fluid, the vapor will not condense back to liquid phase. If the working fluid freezes and cannot circulate, the assembly cannot transfer heat or cool sensitive equipment.
Different wicks will have different capillary limits (the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. Based on wick selection and gravity orientation, the performance of the two-phase cooling will be impacted.
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