الفهرس | Only 14 pages are availabe for public view |
Abstract One of the goals engineers pursue in the energy production and recovery field is to design a heat exchanger that can store a large amount of thermal energy in a shorter time. Thermal energy storage systems can be incorporated in the solar applications to conserve the solar heat energy and to store the waste heat from industrial processes such as oil, cement, ceramic, steel, and glass industries, which are considered major waste heat sources. The present work practically tests the performance attributes of a latent heat thermal energy storage system in a vertical shell-and-tube heat exchanger configuration, seven different arrangements of the heat exchanger are studied over various operating conditions. Water (heat transfer fluid) flows in the straight tubes that are arranged as circular layers at certain radii in the shell, which is occupied by organic paraffin phase change material (RT60). The experiments consider the effects of the tubes area ratio, layer radius ratio, number of layers, and distribution of the tubes (inline/staggered), besides incorporating semi-circular tubes instead of complete circular ones. These experiments are conducted by employing heating water (65C to 75C) corresponds to Stefan number range (0.096 to 0.233) during the charging process and cooling water (25C) corresponds to Stefan number of 0.452 during the discharging process, in addition the water volume flow rate of 15 LPM in the opposite direction of gravity. Effects of the different heat exchanger arrangements besides the operating conditions on the PCM total melting/solidification time, time at which the melting/solidification begins, melted/solidified mass fraction, stored/recovered heat energy and charging/discharging effectiveness are studied.The key findings from this work are that increasing the radius ratio from 1/3 to 2/3, employing semicircular tubes instead of complete ones, increasing the area ratio from 2.4% to 4.3%, and distributing the same number of tubes in two layers rather than one layer provide reductions in the charging time of 7.2%, 7.3%, 17.6%, and 11%, respectively. The corresponding augmentations in the charging/discharging effectiveness are 8.1%/2.6%, 7.4%/3.3%, 19.7%/5.7%, and 8%/4.5%, respectively. Moreover, by applying a staggered distribution of the tubes instead of an inline one, the charging effectiveness is amplified by 5.3%. Furthermore, increasing the inlet HTF charging temperature from 65C to 75C decreases the charging time and boosts the charging effectiveness by 4.3% and 5.4%, respectively. Finally, a set of experimental correlations is developed to predict the charging effectiveness of the LHTES system as a function of the investigated parameters. |