| Energy transfer between fluids could be accomplished in pressure oscillating tube by imposing periodic boundary conditions. Gas wave ejector consisting of many pressure oscillating tubes is a direct fluid-fluid contact energy transfer device. Comparing with the traditional turbo machinery, it has many advantages, such as simple structure, low rotation speed, good performance with liquid entrainment, while comparing with the steady flow ejector, it has the advantage of high isentropic efficiency. The research on gas wave ejector is valuable for wave machine development and pressure energy recovery in practice.However, the research of pressure exchange technology has mainly been focused on four-port wave rotor which can enhance the performance of internal combustion engines. The studies on gas wave ejector are far from enough to be dealt with especially at high compression ratio condition, and the research on gas wave ejector has not yet been reported in our country. The aim of this research is to investigate the mechanism of energy transfer, study the unsteady flow behavior inside the pressure oscillating tube, develop the optimal method for structure design and explore the strategies for application of this device in high compression ratio and big expansion ratio conditions. This dissertation presents a detailed account of the theoretical analysis, the numerical simulation and experiments conducted to validate the results, including:(1) The optimal principle wave process to achieve suction was proposed. The theory calculation of the whole energy transfer process was conducted. The theory analysis was used for fast predicting the port size and seeking the limiting conditions for operation.(2) A numerical model was established to investigate the complex flow in pressure oscillating tube and a test rig was set up. The running rules of shock wave, expansion wave and contact surface were obtained and the optimal wave diagram was determined. A three-port gas wave ejector was manufactured. The maximum efficiency of this ejector was about57.5%when the expansion ratio was1.5, while for expansion ratio of2.0, the maximum efficiency was45.6%, which was also much higher than that of the steady flow ejector. Therefore, the performance of gas wave ejector is excellent.(3) The matching relations for optimal port width and position determination were obtained by numerical simulation and experiment. The optimal width and position of each port under different operating conditions were acquired and a design method was proposed. With this method, the optimal port size at any channel length L, drum diameter D and rotation speed n could be gotten. The design method is valuable for gas wave ejector design.(4) The reason for performance deterioration at high compression ratio was revealed after founding the characteristic that the average pressure and temperature of the channel at the pressure equalization region reduced as pm0rising. The improvement strategy, using part of the middle pressure outflow as recirculation flow to pre-compress the low pressure gas inside the channel, was implemented. The isentropic efficiency raised by9.1%and the enthalpy ratio increased by about21.3%.The optimal pre-compression port width and position were obtained.(5) The sliding-mesh method was adopted to describe the gradual open process of the channel to the port. The results indicated that the gradual open loss included vortex loss, mixing loss and shock loss. The gradual open loss reduced as the opening time decreasing and when r,<0.4the gradual open loss could be neglected. The sum of gradual open loss and flow loss was minimal when Ï„t=0.6, thus the optimal width of the channel could be obtained.(6) Supersonic velocity of the outflow was the reason for poor performance at big expansion ratio. Feedback multi-stage series which is simple for engineering and has a small expansion ratio in each stage could solve this problem. The series stage and inter-stage matching scheme was determined according to the thermodynamic model. |
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