Browsing by Subject "MPCM"
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Item Study of Laminar Flow Forced Convection Heat Transfer Behavior of a Phase Change Material Fluid(2010-01-14) Ravi, GurunarayanaThe heat transfer behavior of phase change material fluid under laminar flow conditions in circular tubes and internally longitudinal finned tubes are presented in this study. Two types of boundary conditions, including uniform axial heat flux with constant peripheral temperature and uniform axial and peripheral temperature, were considered in the case of circular tubes. An effective specific heat technique was used to model the phase change process assuming a hydrodynamically fully-developed flow at the entrance of the tube. Results were also obtained for the phase change process under hydro dynamically and thermally fully developed conditions. In case of a smooth circular tube with phase change material (PCM) fluid, results of Nusselt number were obtained by varying the bulk Stefan number. The Nusselt number results were found to be strongly dependent on the Stefan number. In the case of a finned tube two types of boundary conditions were studied. The first boundary condition had a uniform axial heat flux along the axis of the tube with a variable temperature on the peripheral surface of the tube. The second boundary condition had a constant temperature on the outer surface of the tube. The effective specific heat technique was again implemented to analyze the phase change process under both the boundary conditions. The Nusselt number was determined for a tube with two fins with different fin height ratios and fin thermal conductivity values. It was determined that the Nusselt number was strongly dependent on the Stefan number, fin thermal conductivity value, and height of the fins. It was also observed that for a constant heat axial flux boundary condition with peripherally varying temperature, the phase change slurry with the internally finned tube performed better than the one without fins. A similar trend was observed during the phase change process with internal fins under the constant wall temperature boundary condition.Item Thermal Performance of Microencapsulated Phase Material (MPCM) Slurry in a Coaxial Heat Exchanger(2014-05-08) Yu, KunMicroencapsulated phase change material (MPCM) slurries and coil heat exchangers had been recently studied separately as enhancers of convective heat transfer processes. Due to the larger apparent heat related to the phase change process of the phase change material (PCM), MPCMs have shown improved heat capacity when compared with water. It has also shown better performance as heat storage and secondary heat transfer fluid. Coil heat exchangers had been already used in industrial applications due to their high heat transfer performance. This study explores the use of MPCM and coil heat exchanger in terms of heat transfer efficiency and pressure drop when these two enhancers work together. The objective of this study is to understand the effects of microencapsulated phase change material (MPCM) slurries as heat transfer fluid (HTF) on coil heat exchangers. An in depth survey of the literature pertaining to both coil heat exchangers and MPCMs has been conducted in an effort to understand the effect of using MPCMs as HTFs in different heat exchangers. The review covers the basic understanding of heat exchangers under laminar and turbulent flow as well as a more in depth review of helical coil and coaxial heat exchangers and their flow and heat transfer characteristics. Previous research in the field of MPCM's is also presented to help understand the effects of their thermal properties including density, viscosity, thermal conductivity, and specific heat on heat transfer performance. A detailed description of the present experimental setup is given, which includes physical dimensions as well as operating parameters. Steps taken during the data reduction process are included in order to facilitate the analysis of the results. Experiments were conducted using a fully instrumented heat transfer system under laminar and turbulent flow conditions of MPCM slurry at different flow rates and mass fractions. The results are compared to each other as well as to heat transfer correlations from previous studies. Heat exchanger effectiveness calculations and results are also presented. Using these analyses, conclusions have been made on the effects of using MPCM slurry in coaxial coil heat exchangers. Results show that MPCM flows are characterized by high pressure drop, but higher heat transfer rates at a certain mass fraction. Finally, future research directions are proposed based upon the present results.