Phase Change Material (PCM) Heat Sinks

ACT is a leading provider of Phase Change Material (PCM) heat sinks for military, aerospace and industrial thermal management applications. PCM Heat Sinks can absorb thermal energy (heat) with minimal temperature rise during the solid to liquid phase transition. During this phase transition, the latent heat (J/kg) is at least one (1) to two (2) orders of magnitude higher than the sensible energy that can be stored by the specific heat of a material in its solid or liquid phase. Figure 1 illustrates this phenomena by plotting the temperature rise of a PCM over time with a steady state energy input.

Figure 1. Temperature Rise vs Time. Temperature is maintained during, phase transition.

Figure 1. Temperature Rise vs Time. Temperature is maintained during, phase transition.

In practice, a PCM is contained in a hermetically sealed enclosure and used to maintain the temperatures of critical heat generating components over a given period of time. Applications such as missiles which have finite mission life can utilize PCM energy storage to replace complex active thermal management solutions. PCM Modules are also used in systems having pulse mode operations by storing the heat during the “on” cycle and dissipating the heat (as the PCM refreezes) during the “off” cycle.

Although the concept of storing heat by melting a phase change material is fairly simple, there are numerous practical challenges that must be addressed to obtain a volume or mass optimized, fully functional and highly reliable PCM heat sink design. ACT has the expertise in all areas from initial evaluation, through prototyping to full volume production.

  • PCM Selection
  • Heat Sink Design
  • Performance Predictions
  • Manufacturing

PCM Selection

A Phase Change Material, in a broad sense, is any material that can change phase from solid to liquid or vice versa while being heated or cooled. Below is a list of typical PCMs that have been used in thermal management applications:

  • Paraffin Waxes
  • Hydrated Salts
  • Low Temperature Solders
Multi-Chamber PCM Heat Sink

Figure 2. Multi-Chamber PCM Heat Sink

The first consideration when designing a PCM heat sink should be the PCM’s melt temperature. Typically, the PCM is selected to provide a melting temperature that is several degrees lower than the maximum component temperature throughout the mission. Paraffin waxes are common, because they are available with a wide range of melt temperatures. The second consideration is the energy that must be stored and the duration. The combination of these two factors, along with the thermal properties of the PCM, will ultimately determine the amount of PCM required in heat sink. For more information on PCM Selection, click here PCM Selection (Coming Soon)

Heat Sink Design Considerations

The challenge with many PCM Heat Sink Designs is the poor thermal conductivity of the PCM. For example, paraffin waxes typically have thermal conductivities of less than 1 W/m-K. This is remedied by adding internal features to increase the overall effective thermal conductivity of the enclosure. ACT is experienced with fins, heat pipes and metal foams as options for these internal structures. Click here for an Internal Fin Structure Design Study (Coming Soon)

Thermal Simulations

ACT has expertise in analyzing PCM systems and accurately predicting transient response. In-house analytical tools in combination with computational fluid dynamics (CFD) software are leveraged for thermal simulations involving PCM. In most cases, a dynamic specific heat is created to capture effects during multiple stages. Click here for an example of analyzing PCM melt front. (Coming Soon)  

Manufacturing

ACT has developed necessary manufacturing technologies required to produce high quality, high reliability PCM heat sinks. Some of these manufacturing technologies include brazing of complex structures, precision charging of PCM , and safe and reliable sealing of the assembly. From initial evaluation and detailed design to prototyping and production, ACT is the ideal choice for your PCM needs! View PCM Heat Sink Examples (Coming Soon)

 

 

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