Phase Change Material (PCM) heat sinks can be used for a wide variety of applications where thermal storage is required. PCM’s are ideal because the latent heat associated with melting and freezing is capable of storing much more heat than sensible thermal storage alone. When the heat generating component is on, the PCM will maintain the component at a certain temperature while passively storing the heat. Once the heat generating component is shut-off the PCM will begin to solidify by releasing the stored energy. The most common applications that benefit from PCM include those with known duty cycles. Other applications include those where time shifting the dissipation of heat is advantageous, possibly to a time when the sink is colder (at night) or more readily available.
The thermal storage applications that will be discussed range from mJ to MJ in size, and include the following:
- Storage for one-time use applications
- Protection from momentary cooling failure or a reduction in cooling capacity
- Dampening of heat loads in pulsed mode operation
- Thermal Storage to increase cooling capacity during hot days, using the colder air at night to recharge the thermal storage
ACT has conducted innovative thermal storage related R&D, on storage scales ranging from milli-Joule to Mega-Joule:
- On-Chip PCM for Pulsed Power Placing PCM within several µm of the gates on high power pulsed GaN chips can reduce temperatures and/or increase maximum power without overheating.
- Electronics Heat Sinks (One Time Use, Loss of Coolant, Dampening) are used for electronics cooling for both pulsed power operations, and when the existing heat sink is inadequate.
- PCM Vapor Chamber (Increase in Cooling Capacity)
- PCM Heat Exchangers for Pulsed Power (Dampening) can improve the Size, Weight, and Power (SWaP) for Directed Energy Weapons (DEW), by allowing the overall system to be designed for the average power, instead of the peak power.
- HVAC Energy Savings (Increase in Cooling Capacity)
- Power Plant Cooling (Increase in Cooling Capacity) Dry Cooling Power Plants reject megawatts of heat to condense low temperature, low pressure steam, without consuming fresh water. However, the power producing capacity of dry cooling systems must be reduced when the ambient air temperature is high, since less steam can be condensed. ACT is developing a Cool Storage System that uses Phase Change Material (PCM) and Thermosyphons to increase the cooling capacity during the daytime, by melting the PCM.
- Thermal Storage with Venting Most thermal storage systems are designed to store heat by melting a Phase Change Material (PCM), and can operate over a very large number of cycles. When only a few cycles must be handled, Thermal Storage with Venting should be considered, since it can result in lighter and/or more compact systems.
- Single Use Vapor Venting Systems for Thermal Storage (One to a Few Cycles) When heated, liquid held in a porous structure boils, vaporizes, and then the vapor is vented.
- Hydride Thermal Storage Systems use metal hydrides, which desorb hydrogen when heated.
- Single Use Hydride Venting Systems for Thermal Storage (One to a Few Cycles) offer a potential volume reduction of 90 percent or more, when compared with PCM systems.
- Hydride Thermal Storage for Multiple Cycles (Dampening)