Foundational Design Rules for Solid-Liquid Phase Change Material - Heat Exchanger (PCM-HX)

The use of phase change materials (PCMs) based Latent Heat Energy Storage Systems (LHESS) is an area of increased research/commercial interests; offering solutions to the problem of conflicting time-dependency of the availability and demand of energy as well as temperature management. Such a technology will play a bigger role with today's push for increased renewable/sustainable energy production in our society's energy mix, for example: solar domestic hot water systems, cold storage from night time excess energy for air conditioning and refrigeration needs, PCMs in buildings enhancing overall energy efficiency, thermal storage in energy production systems, and PCM-LHESS used for temperature control of various electronic devices. At the heart of a large variety of LHESS is a fluid-to-PCM heat exchanger (HX) to move the energy in/out of the storage system; composed of pipes, or channels, fins, baffles, etc.; similar to HX used for more traditional fluid-to-fluid heat exchange with the exception that now, PCM fills one side of the heat exchanger. Traditional HX have well defined and accurate design rules (e-NTU, LMTD, design handbooks) based on decades of experimental work to guide in design selection. However, no design rules exist for PCM-HX. Numerical modeling still cannot be used for the complete characterization of a real complex 3D LHESS, so new design must be tested experimentally, by varying geometrical, material and operational parameters, resulting in a long and costly process, with no guarantee that an economical and functional design will ultimately be found. This explains why very few LHESS are commercially available today! Therefore, the determination of design rules for PCM-HX systems is the single most important advancement required in the field of thermal storage with PCMs, and through enabling faster designs of LHESS, leading to proof of concepts and technological adoptions, will also greatly help the economic case to be made for such systems. The main goal of my research program is to answer the relevant conceptual questions required to comparatively characterize different PCM-HX and use the comparative figures to determine foundational design rules for PCM-HX used for LHESS. To achieve this goal, five different PCM-HX geometries will be studied and characterized using a benchtop experimental setup already built in the applicant's lab. Data related to the heat transfer rates, temperatures in the system, flow rates and pressure drops will be measured. With all the experimental results, work will be done on determining the right parameters to be used to compare the performance of each PCM-HX, and from this, develop novel rules and theory to assist in the design and selection of PCM-HX for given applications. The determination of design rules will serve as a foundation for the area of PCM-HX systems, enabling faster and more economical designs and applications. This will have a transformational impact in the industry.