HEAT TRANSFER ENHANCEMENT IN PCM THERMAL ENERGY STORAGE VIA THE TRIPLEX TUBE HEAT EXCHANGER
A major challenge in the utilization of renewable-energy, especially solar, is irregularity in the availability.
A way of overcoming this, is to apply Phase Change Materials (PCMs), for thermal energy storage. However, the primary drawback, is the low thermal conductivity of PCMs, which critically limits the energy storage capability. Thus, melting/solidification rates are grossly reduced, making the system response time to be undesirably long. Enhancement techniques have been studied for overcoming this problem. These
include, insertion of fins together with the heat exchanger, application of heat pipes, and dispersion of highly conductive nanoparticles. There is also, the use of efficient performing heat exchanger along with these techniques. The triplex-tube heat exchanger applied in this study, compared to the regular double-pipe heat exchanger is such that the PCM is in the annular space between the inner tube and the middle tube, while the heat transfer fluid (HTF), flows in the inner tube and the outer tube. Thus, it provides a larger heat transfer area between the PCM and the HTF. This paper presents a summary of some studies using the triplex tube heat exchanger that the authors are involved in, the background of which they have ongoing further studies involving application of fins, metal foams, nanoparticles and cascaded techniques. Results so far, indicate remarkable enhancement in heat transfer and reduction in the thermal energy storage and recovery times.