Theoretical Analysis And Experimental Investigation Of A Highly Efficient Ejector Refrigeration

Ejector refrigeration can utilize thermal energy with a relatively low temperature ranging from100℃to200℃such as solar energy or industrial waste heat, to power the system and use the most environmentally friendly substance-water as the working fluid. The ejector refrigeration system has a number of other unique features such as simplicity in construction, high reliability and low cost. However, the ejector refrigeration system is labeled as low coefficient of performance (COP) and low cooling capacity which restricts its applications. In the current dissertation, theoretical analysis and experimental investigation have been carried out to improve the thermal performance of the ejector refrigeration. The main works in this dissertation are summarized as follows:1. The mathematical model of the ejector was investigated based on the thermodynamic analysis and compressible fluid flow. Considering the flow characteristics of the working fluid in the nozzle, mixing chamber and diffuser, an efficiency was defined. Using this new defined efficiency a mathematical model has been redeveloped. The effect of the generation temperature and evaporation temperature on the performance and structure of the ejector refrigeration system, which can provide theoretical basis for the design of the ejector. In addition, results were compared with available experimental data in the literature and it shows that the model developed herein can result in a better prediction.2. The effects of the working conditions, ejector structure and nozzle exit position (NXP) on the ejector refrigeration performance have been conducted. A novel steam ejector refrigeration system was developed which could adjust the nozzle position, modify the mixing chamber, and change diffuser. In addition, the pressure distribution along the ejector could be readily measured. Experimental results show that the effects of generation temperature, evaporation temperature, condensing pressure and the structure of mixing chamber, diffuser and nozzle on the performance of the steam ejector refrigeration system could be readily obtained. Using this system, the optimal nozzle exit position (NXP) at a given working condition could be found.3. A highly efficient ejector system requires an extra-high efficient evaporator. In order to develop this highly efficient evaporator for the ejector system, a mathematical model was developed to determine heat transfer through both the thin film and bulk regions of a liquid in a rectangular micro groove. An analytical solution of the temperature distribution within the meniscus bulk region, where the interface is dominated by surface tension was found via a coordinate transformation and the Galerkin Method. The model includes the effect of contact angle and wall superheat on heat transfer and total heat transfer coefficient through both regions and the ratio of heat transfer in thin film region to total heat transfer. A thin film evaporation test setup has been built with rectangular micro groove surface to investigate the heat flux, superheat and thermal resistance of the thin film evaporator under different evaporating temperature.