| With the development of global economy and the increasing energy consumption, energy and environment are becoming hot topics worldwide. In our country, energy consumption is increasing with high speed developing economy. Energy has become one of the main problems that restrict the sustainable development of national economy. Employing advanced energy conservation technology and improving energy efficiency are the most important and urgent issues in energy field. Driven by low grade heat, such as solar energy, geothermal energy and industry waste heat, ejector refrigeration systems gain more and more interests at home and abroad.Ejector is the key part of the ejector refrigeration system. It entrains low pressure fluid by high speed working fluid and realizes energy transfer through the ejection of the working fluid. The ejector is characterized by simple structure, no moving parts, convenience for operation and maintenance, as well as low requirement for the entrained fluid. While the knowledge on the flowing and mixing mechanism of the ejector is not complete and shortcomings exist in present design method which leads to low entrainment ratio and system COP, ultimately restricts the widely application of ejector refrigeration system. Hence, improving system performance has become the main task which needs to enhance the investigations on ejector design theory, geometrical optimization, operation mechanism and optimization of operation parameters to design better ejector and more appropriate operation conditions. With these in mind, this thesis is focused on the following work:(1) A new design method named Constant Mach number Gradient (CMNG) is proposed. It is focused on the design of the profile of nozzle, mixing chamber and diffuser of the ejector, i.e., the wall profile is changing with fluid Ma closely so that the fluid can attach on the wall better and realizes steady variety of fluid velocity, which in turn can reduce vortex at nozzle exit and friction in the mixing section, also avoid shock in the diffuser. Ultimately, the entrainment ratio and the energy transfer efficiency of the mixture from momentum energy to potential energy are improved that is good for the discharging of the mixture and can efficiently improve the performance of the ejector. In addition, the design program based on CMNG method is proposed for convenient design the geometrical parameters of the ejector.(2) Theoretical analysis of ejector performance with different refrigerants has been investigated in detail. Results indicate that R134a is more applicable for ejector refrigeration systems driven by low-grade heat. When condenser temperature is 30℃, evaporator temperature is 5℃with generator temperature between 70-85℃, the entrainment ratio using R134a is 20.5%～71.8% higher than that using R123, 25%～39.7% higher than that using R141b and 6.8%～19.6% higher than that using R152a.(3) The influence of operation parameters on the entrainment ratio and system COP is investigated in detail. Results indicate that the condenser temperature affects the entrainment ratio and system COP most, and then is the generator temperature, the evaporator temperature affects the least. When the condenser temperature changes 1℃, the variety of the entrainment ratio is 2.7%～8.5% and COP 3.7%～8.9%. The variety of the entrainment ratio 1.4%～1.9% and COP 1.4%～2.1% is obtained when the evaporator temperature changes in the same range. While the variety of the entrainment ratio is as low as 0.75%～4.4% and COP 0.59%～4.6% when the generator temperature changes 1℃.(4) The visualization analysis of a CMNG ejector using software package FLUENT indicate that the entrainments of the secondary fluid is caused by the great velocity difference between the working fluid and the entrained fluid, where a discontinuous cross section of velocity is formed and then the secondary fluid is entrained by shearing force, after that, both fluids undergoes the mixing process. Detailing comparisons of the flowing field between the CMNG ejector and traditional ejector have been performed which shows the vortex and boundary layer separation are removed in the CMNG ejector.(5) The influence of geometrical parameters and operation parameters on the performance of an ejector has been analyzed by utilizing gray theory. Results indicates that the main factor that influences the performance of an ejector is area ratio, and then is the expansion ratio and compression ratio, while the nozzle exit position affects the least. A gray predication model has been established for quick forecasting the performance of an ejector.(6) Our country is wide in area with different climates between south and north. Also, the solar duration and solar radiation vary great between cities. Take these in account, a general model to predict the performance of the solar driven ejector refrigeration system has been established. Seven representative cities have been selected to analyze the feasibility and reliability of applying such system in our country. Results indicate that the system COP is between 0.16～0.24, wherein, COP in Lhasa is the highest. Generally speaking, the system COP decreases with lower latitude. In most cities, the system COP is more than 0.18 with solar fraction between 0.32～0.82, which can reduce power consumption of air conditioner 1/3～4/5. It shows the solar driven ejector refrigeration works well in most of our country. Also, the results supply a basis for the popularity of such system.(7) Taking the conditions in Shanghai for instance, an insight analysis and discussion of the dynamic performance of the solar driven ejector refrigeration system offering air conditioning for office buildings has been performed. Results indicate that from 9:00 am to 4:00 pm, the system works with COP between 0.17～0.22, and the average COP and solar fraction are 0.19 and 0.88, respectively.
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