Theoretical evaluation and experimental investigation of microencapsulated phase change materials (MPCM) in electronics cooling applications

In many liquid-cooled applications, the bulk temperature of the coolant, rather than the surface heat flux, limits the amount of cooling achieved. In such applications, the coolant flow path is often characterized by significant pressure losses, thus limiting the overall mass flow rate within the system. As a remedy, the idea of increasing the heat capacity of the cooling fluid by adding microencapsulated phase change material (MPCM) to the fluid has been lately explored. Firstly, this increase in the heat capacity comes at the cost of higher pressure-drop due to the increased viscosity of the slurry. Thus, the benefit of adding MPCMs to the coolant can only be realized if the increase in the latent heat capacity due to these materials is substantially more than the heat capacity lost due to the reduction in the mass flow rate. Secondly, it is expected that the conduction of heat through the plastic encapsulate from the coolant to the MPCM might tend to be a limiting factor at high flow rates. As a result, the latent capacity might get under-utilized at higher flow rates if the MPCMs do not completely fuse while the coolant undergoes heat absorption in the system to be cooled. In the present work, a theoretical performance metric is developed to assess the benefit margins obtainable with the use of MPCM slurries. The theoretical predictions on the effective specific heat of the slurry have been assessed against experimental measurements. The figures of merit proposed in this paper serve as design guidelines for liquid-cooled applications employing MPCM slurries.