A theoretical and experimental investigation of jet-pump refrigeration system
This thesis describes a theoretical and experimental investigation of the jet-pump refrigerator, and the application of Computational Fluid Dynamics (CFD) to improve the performance of the jet-pump, which lies at its heart. Within this thesis a number of new studies aimed at improving the COP of jet-pump refrigerators are carried out. These include an investigation of a novel jet-pump design methodology, (the Constant Rate of Momentum Change method), the application of CFD in the design of jet-pumps, the experimental testing of two new refrigerant fluids and finally, a comparative experimental investigation of performance benefits resulting from two cycle improvements that had not been tested before - these are the introduction of (i) a pre-heater (or recuperator) between the jet-pump and condenser, to preheat the liquid flow to the vapour generator, and (ii) a pre-cooler (or economiser) in the suction line between the evaporator and jet-pump, in order to sub-cool the liquid refrigerant in the line between the condenser and evaporator. Literature studies of jet-pump refrigerator technology and jet-pump design methodology are reviewed and discussed. A CFD model has been developed, assessed and validated against given experimental data. Simulations of a jet-pump that is part of a jet-pump refrigerator cycle was carried out to investigate the refrigerant flow structure and to assess the dominant influence of operating conditions and geometry. The validated CFD code was then used to optimize the design of the jet-pump for two new refrigerants (R236fa and R245fa). The resulting optimized jet-pumps were manufactured and tested experimentally over a wide range of operating conditions, using an adaptable test rig that was purpose-developed as part of this research work. Detailed experimental studies were carried out. All the experimentally determined results were compared to the CFD predicted values, and these showed good agreement for all the jet-pumps tested. These results showed that CFD has the potential to be an effective and powerful tool for simulating and optimising jet-pumps. The results also show that the jet-pump refrigerator should be considered if sources of low-grade heat are available.