Background
Phase change materials have been used for a number of years for solar energy storage and for space applications involving pulsed power loads. Such materials have a large latent heat, allowing absorption of large thermal loads during transient periods; the thermal energy can later be released to the environment over an extended time. A number of different materials have been employed for such applications, depending upon the phase change temperature range of interest. Recently, such materials have also become available in micro-encapsulated form, where the phase change material (e.g. paraffin for near room temperature applications) is contained within small polymer spheres. The resulting powders of such materials can be incorporated in a variety of end use applications. The use of PCMs for electronics cooling appears to be a promising solution for handling transient heat loads.
Approach
- Develop a computational model to investigation of the applicability of PCMs for passive thermal control. The geometric configuration consists of a SEM-E type module used in avionics applications. The power dissipation is considered uniform within regions occupied by multichip modules (MCMs) in the SEM-E cards.
- Analyze the coupled heat conduction and melting/ solidification effects, using the enthalpy method for the phase change heat transfer.
- Evaluate different configurations, including application of a PCM laminate and the possibility of convective motion of the molten material.
- Compare performance due to the use of PCMs to the baseline computations without phase change.
- Develop a test plan is for experimental validation of the computations.
Work Accomplished
A computational model has been developed to predict the temperature distribution in SEM-E type modules cooled by PCM. The model considers the transient temperature response following a sudden loss of forced liquid internal cooling. The model can handle the melting and natural convection motion of the PCM. The model has been validated against benchmark problems. Two different types of PCM have been examined. The first is n- Eicosene, an organic paraffin, and the second is a eutectic alloy of Bi/Pb/Sn/In. Three configurations were analyzed. In the first, PCM laminate was placed on top of the MCM; in the other, PCM laminate was placed under the substrate in the primary heat flow path. When natural convection effects are considered, the SEM-E module is oriented vertically. Time-wise variations of maximum temperature in the MCM have been obtained for selected power dissipation levels and for different laminate thicknesses. The model has also been modified to include the effects of microencapsulated PCM. Computations have been performed with the microencapsulated PCM over and surrounding the MCM. An experiment has been designed to evaluate the thermal performance of modules cooled with microencapsulated PCM.
