| Current chilled water systems require vast amounts of water and pumping power to meet increasing cooling demands. Existing cooling and heating distribution systems have an inherent thermal capacity limitation that is often neglected when adding new buildings to military, industrial, or commercial facilities, resulting in higher equipment and infrastructure costs. Through the use of an advanced material concept, namely Microencapsulated Phase Change Materials (MPCM), performance enhancement of an improved heat transfer fluid is being pursued. MPCMs have the unique characteristics that can increase the thermal capacity of heat transfer fluids by providing latent heat capacity at a temperature different than the melting point of the carrier fluid. In order to successfully use MPCM slurries in typical applications, the MPCMs thermal and fluid properties and their effectiveness in transferring heat have to be fully characterized and understood.; The research consists of a variety of experimental investigations relevant to MPCM. Initial quantitative characterization of MPCM material properties, including latent heat of fusion, melting and freezing points, and temperature- and concentration-dependent viscosity data, are presented. State-of-the-art equipment was used to characterize the MPCM slurry, including a differential scanning calorimeter, a temperature-controlled concentric viscometer, and a well-calibrated heat transfer loop. Results indicate that the use of an effective nucleating agent is necessary to prevent a large amount of supercooling of the phase change material. Other experimental results indicate that MPCM slurry's heat transfer coefficient and apparent specific heat are affected significantly by the phase change process and the slurry mass fraction. The study also examines the impact of the combination of enhanced surface tubing and MPCM slurry under constant heat flux and turbulent conditions. |
