| High-performance expansion refrigeration equipment under high pressure is needed for natural gas's expansion refrigeration.Jet-oscillation refrigerator is a new type of gas expansion refrigerator,in which self-induced jet oscillator is used to generate oscillation jet's periodical injection into oscillation tube with one-closed end.In the oscillation tube,gas waves are produced owing to interaction between the injected gas and the intrinsic gas. Energy is rapidly transferred from the injected gas to the intrinsic gas by means of propagation of those gas waves,which results in temperature increase of the latter and then heat dissipation to environment across the oscillation tube wall.The refrigeration of the injected gas is obtained due to its energy loss.The jet-oscillation refrigerator has no moving part and its seal is simple.Hence,its use is not confined under the condition of high pressure.Yet,the refrigeration efficiency of the jet-oscillation refrigerator is at a low level presently,and could not satisfy requirement of natural gas's industrial production. Performance and mechanism of the jet-oscillation refrigerator are investigated by experiment and numerical simulation in the current dissertation supported by Chinese 863 National Program Foundation "Study on new technology of combined utilization of natural gas's pressure energy"(No.2006AA05Z216).(1) The self-induced jet oscillator is a key component of the jet-oscillation refrigerator and it is developed based on jet's wall-attaching effect which is also called Coanda effect.The gas in the jet-oscillation refrigerator usually flows at transonic speed.Firstly,the current dissertation studies properties of the transonic wall-attaching jet by numerical simulation. Flow characteristics of the wall-attaching jet are analyzed.Effects of structural parameters and operating parameters on geometrical properties and pressure distribution are investigated。The results show that the deflection degree and attachment distance of the wall-attaching jet are determined by both the jet's flow parameters and the pressure distribution which is influenced by the element's geometrical sizes and the operating conditions.(2) The jet-oscillation refrigerator works on the basis of the jet's steady oscillation.Either the frequency modulation of the jet's oscillation or decrease of total pressure loss of the jet passing the oscillator is important approach to improve performance of the refrigerator.In the present dissertation,sonic oscillator is adopted and its oscillation properties and total pressure loss together with their influencing factors are investigated by experiments and numerical simulations. 1) Effects of width of the nozzle's throat,wall offset,wedge distance,length and width of the controlling tube,the pressure ratio,the pressure value and properties of the working media on oscillation properties are all studied.Mechanisms of the jet's oscillation and those factors's affecting the jet's oscillation are explaned by means of analyzing flow parameters during the jet oscillating.2) Numerical analysis of the jet's total pressure loss reveals that at a certain position downstream of the jet,the total pressure begins to decay sharply due to turbulent dissipation.The total pressure loss of the jet passing the sonic oscillator is caused mainly by turbulent dissipation under the condition of low pressure ratio(the pressure ratio is less than 2.5).Under the condition of high pressure ratio(the pressure ratio is more than 2.5),the total pressure loss is moreover produced by gas waves in the jet among which shock wave could lead to the total pressure's violent decrease.Additionally,effects of the geometrical sizes on the total pressure loss are studied and the mechanisms are analyzed.(3) The current dissertation numerically simulates effects of configurations and geometrical sizes between the sonic oscillator and the oscillation tube on flow field in the jet-oscillation refrigerator with two oscillation tube.The results exhibit that width and configuration of the gas outlet port together with the wall offset all have great effect on flow field in the refrigerator.During the jet striking the open end of the oscillation tube,the injected mass and energy flow rate decreases with widening of the gas outlet port.However,gas couldn't be discharged freely while the gas outlet port is too narrow,which would lead to high pressure in the refrigerator.As a result,only low-intensity gas waves could be produced and the temperature of the gas in the oscillation tube stays low.With too wide gas outlet port,most of the energy would be discharged directively through the gas outlet port while the jet striking the open end of the oscillation tube.Flow fields with three types of gas outlet port are calculated and it is founded out that eddy in the gas outlet port would hind directive discharging of the gas.Therefore,the configuration in which eddy could be produced is advantageous to improvement of the refrigerator's performance.With descend of the wall offset,during the jet attaching to one wall,the jet's oscillating amplitude decreases which results in uniform variation of energy flow rate with time.(4) Performances of the jet-oscillation refrigerator with two oscillation tube driven by sonic oscillator are investigated by experiments.Isoentropy efficiency is introduced to characterize performance of the refrigerator.The isoentropy efficiency and pressure wave in the refrigerator in addition to temperature distribution along the oscillation tube wall are tested.1) Based on the numerical results about total pressure loss,a new type of jet-oscillation refrigerator is introduced on the idea of decreasing distance from outport of the nozzle to inlet port of the oscillation tube.The experimental results reveal that the isoentropy efficiency increases by more than 10%under the same operating conditions as a result of descend of the distance.2) Effects of length of the controlling tube,width and configuration of the gas outlet port, configuration and size of the wedge and the wall offset on isoentropy efficiency of the refrigerator are studied.The following conclusions are drawn.The isoentropy efficiency varies undulately with rise of the controlling tube's length.There exists optimal width which corresponds to the greatest isoentropy efficiency and it is revealed that the optimal width is affected by the pressure ratio.The efficiency ascends with decrease of the wall offset.The configuration of the gas outlet port and the wedge's configuration and size all have great effects on the isoentropy efficiency.Effect mechanisms of all the influencing factors on performance of the refrigerator are analyzed based on the tested data and the numerical results.
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