The Structure Design And Heat Transfer Enhancement Mechanism Of Heat Storage Exchanger Containing Phase Change Material (PCM)

The shell-and-tube heat exchanger and plate heat exchanger with phase change materials are quite popular in the field of thermal energy storage. However, to date the studies on the heat transfer enhancement mechanism of the two types of thermal energy storage exchangers (TESE) have been insufficient, which are reflected in the too simplified working conditions of TESE during charging and discharging process, and the absence of non-dimensional studies of m-PCMs.As disscussed above, the effect of heat exchanger structure, m-PCMs and heat transfer condition on the heat transfer were numerically studied in this dissertation. Besies, due to the high mechanical strength and easy disassembly of shell-and-tube heat exchanger, a new type shell-and-tube heat exchanger was designed to recycle the waste heat of diesel engine.Mathematical model and definite conditions were carefully selected to simulate plate TESE in zigzag configuration containing multi-phase-change-materials (m-PCMs), from which the simulation outcomes were compared with the experimental results for verification. The effect of surface topography of zigzag plate on the heat storage was studied, and the heat transfer was enhanced by optimized combination of m-PCMs. Besides, the effect of the phase change temperature difference was studied. The concept of energy percentage was proposed, and the charging and discharging processes of the zigzag plate with m-PCMs were studied with dimensional analysis. A new work condition of inlet power was defined to correlate the inlet velocity and temperature. The synergistic effect of the inlet temperature and velocity on the charging and discharging processes of zigzag plate-TESE was studied under the given inlet power conditions. When the inlet velocity or temperature changes periodically, the effects of period and amplitude sizes on the charging and discharging processes of zigzag plate TESE were studied, showing the exchanger has perfect "filtering effect".Mathematical model and definite conditions were used to simulate shell-and-tube-TESE, and a reasonable mathematical model was selected by comparing the simulation and experimental results. The effect of tube arrangement on the heat transfer was studied and the heat recovery was improved by using three shell-and-tube-TESE with different PCMs. Under the given power conditions, the synergistic effect of the inlet temperature and velocity on the charging and discharging processes of shell-and-tube-TESE with different PCMs was studied. Besides, the effect of period and amplitude sizes on the charging and discharging process of shell-and-tube-TESE with different PCMs were studied when the inlet velocity or temperature changes periodically in the given inlet power conditions. It was found that the shell-and-tube-TESE with different PCMs would have good "filtering effect".An experimental platform was built to recover the waste heat based on a diesel engine and a new type of shell-and-tube was designed. In order to increase the heat recovery rate of diesel fume, two shell-and-tube heat exchangers with high or low temperature phase change materials were used. The temperature behavior of TESE was studied in the charging and discharging processes and the reason of which was analyzed. Besieds, the heat recovery performance was discussed by first law of thermodynamics and entransy theory respectively. It was found that the effect of tube on the energy storage should not be neglected.