Numerical Simulation And Experimental Investigation Of Steam Ejector Driven By Marine Waste Heat

As the energy crisis and climate change is becoming more and more serious, how to improve ship’s energy efficiency had become a research hotspot around the world. The advantages of the steam ejector includes utilizing low-grade thermal energy, using water, an environmentally friendly material, as the working medium, simplicity in construction, reliability in operation and low capital cost. These advantages caused the steam ejector to be widely applied in the refrigeration system, Rankine cycle power plant and seawater desalination system. In this thesis, experimental investigation and numerical simulation of steam ejector have been conducted. The principal research works are listed as follows:Firstly, a steam ejector has been designed and fabricated based on the constant pressure model, to explore the performance of steam ejector with the generating temperature below 100℃ and spread its applied fields. The effects of the operating condition, the structure of nozzles, the diameter of the constant area section and the nozzle exist position (NXP) on the performance of steam ejector have been investigated when the generating temperature ranging of 40～70℃ and evaporating temperature ranging of 10～25℃. It was found that the system COP can reach 2.6 when the generating temperature is 40℃ and evaporating temperature is 25℃.Secondly, a steam ejector numerical simulation model has been developed, according to the structure of the experimental steam ejector as mentioned above, to investigate the effect of the turbulence model on the simulation results. This investigation could verify the paradoxical conclusions obtained by different researchers. Five turbulence models, such as k-ε STD, k-ε RNG, k-ε Realizable, k-ω STD and k-ω SST, were used to calculate the entrainment ratio and critical condensing pressure at different operating conditions and structure parameters. Compared with the experimental results, the optimum turbulence model was obtained with different generating temperature conditions.Moreover, the flow field characteristics in the steam ejector, such as pressure, velocity, temperature, density along the axial line and streamlines of the steam ejector, and the effects of the length of the constant area section and NXP on the performance of steam ejector had been investigated to optimize the structure of the steam ejector using the optimum turbulence model had obtained, when the generating temperature of 130℃ and the evaporating temperature of 10℃. It was found that the entrainment ratio will increase at first and then decrease with the length of constant section increasing and the length is range of 25-75 mm for the best performance.In addition, the entrainment ratio will increase at first and then decrease as the NXP increasing and the best position is NXP=55 mm.