Numerical Simulation And Optimization Study Of Small-sized Steam Ejector

Recently, with increasing of peoples' consciousness in energy conservation and environmental protection, renewable energy becomes preferable to various facilitates and systems that consume energy as driving power. Under the policy of energy conservation and emission reduction, the solar jet refrigeration system attracts increasing attention of more and more professionals. The ejector is the core part of solar jet refrigeration system, which actualizes the conversion of energy through the jet from the primary flow to the suctioned flow. As ejectors have the advantages of compact structure, low operation costs, easy maintenance, no moving parts and no special limitation to fluid, it has been widely used in refrigeration. However, the energetic efficiency is rather low, which is the very concerned subject by engineers and scientists. So far the design of ejector has been carried out with various semi-experiential formulas based on one-dimensional isentropic hypotheses, the ejector structure being definitely determined by its work conditions. As the interior flow field of ejector is very complicated, the one-dimensional theoretic analysis and experiment can not meet our requirements. On the other hand, thanks to the great development of computer technology and numerical theory, the numerical simulation technology obtained the wide application in various fields. In this paper, we adopted FLUENT, a CFD software, as a working platform. Through the simulation of the interior flow field of the ejector, we learned the connection between the characteristics of ejector and its structure parameters, and obtained some new knowledge in ejector structure, which will play a significant role to ejector design.According to the actual demand, we first carried on the preliminary design for ejector structure sizes, and then simplified the physical model. We used the GAMBIT software to establish the mathematical model and finished the grid partition. After setting up the boundary conditions, the case was read to the FLUENT software. In this step, we checked the grid first, and then we selected the most suitable solver. In this paper, we adopted the Density Based Solver, Explicit Formulation, Axisymmetric Space and Standard k-εTurbulent Model. In order to guarantee the accuracy and the reliability of the model choice, we contrasted the simulated data to experimental data, and found the choice is correct. When observing the ejector interior flow field, we can see the shock wave phenomena clearly. The influence of the injecting pressure, the nozzle exit distance and the mixing section length on entrainment ratio is analyzed. The results show that entrainment ratio will increase with secondary pressure, and there are optimum nozzle position and throat length for a given operation condition.Up to now there are a few articles published whether domestically or internationally on the investigation of small-scale ejectors, which are to be used in solar steam jet refrigeration systems. The results of this study have provided something new of the basic knowledge for the optimal design of such sort of ejectors. Meanwhile, the author has achieved some fruitful explorations in establishment and simplification of such complicated model, grid division, etc.