Description
A Master of Science thesis in Mechanical Engineering by Akram Mohamed Gadalla entitled, “Optimization of Vapor Compression Refrigeration Cycles with Clathrate Hydrates Thermal Energy Storage”, submitted in December 2021. Thesis advisor is Dr. Mohamed Omar Abdelgawad. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
This thesis presents detailed modelling and analysis of different refrigeration systems as well as cold thermal energy storage systems (CTES) using clathrate hydrates. The Engineering Equation Solver (EES) was used to model various refrigeration systems including liquid line-suction line, dedicated mechanical subcooling, a two-stage with a flash chamber and two evaporators, and with a flash tank and intercooling. The refrigerants used in the modelling analyses include three different categories namely hydrofluorocarbon (HFC) (R134a, R404A, R410A), hydrochlorofluorocarbon (HCFC) (R22, R123, R141b), and chlorofluorocarbon (CFC) (R114, R11, and R12). Performance indicators including energetic and exergetic coefficient of performances (COPs), refrigeration efficiency, compressor power per ton refrigeration, and the exergetic destruction ratio were calculated and compared among proposed refrigeration systems under different operating conditions. Results indicate that R134a had the best performance. It was found that the energetic and exergetic COPs of liquid-line suction line system at the operating evaporator and condenser temperatures of 4ºC and 40ºC are about 5.0 and 0.29, respectively. At the same operating conditions, the refrigeration efficiency, and the input power per ton refrigeration of R134a were found to be 66% and 0.7 kW/ton, respectively. Results of the two-stage with a flash chamber and two evaporators had greatest performance with COP = 7.4 and kW/ton = 0.47. The effect of additives in a high-pressure tube was studied using constant temperature baths to identify the fastest clathrate formation time. Indirect and direct contact CTES using clathrate hydrate was evaluated experimentally with single stage and two stage systems. Numerous closed loop cooling cycles using clathrate hydrates of R134a have been evaluated at different operating conditions such as refrigerant flow rate, compressor speed, and water/refrigerant mass ratio to determine the COP, and the clathrate hydrates behaviour during the charging mode. Experimental results indicate that at higher water/refrigerant mass ratios in the storage tank (evaporator; crystallizer) the COP decreases due to increases in charging time and compressor power input. Finally, experimental results conclude that COPs of CTES systems are higher than COPs of the conventional refrigeration systems used in modelling.