Numerical And Experimental Study Of Geometric Parameters Of Resonantor On The Performance Of The Two-stage Traveling-wave Thermoacoustic Heat Engine

Thermoacoustic heat engine,using inertia gases as working substances and without moving parts,is a new type of energy conversion machine,with the outstanding characteristics of simple structure,high reliability and environment friendliness.By changing cross-section of flow channel to reduce the local speed of the regenerator to maintain the acoustic impedance unchanged,a travelling-wave heat engine with multiple thermoacousric units can create more acoustic power at a low working temperature,which would be a very potential technology to utilize the low-grade energy effectively.However,the more thermoacoustic units not only brings structural complexity of system,but increases the manufacturing cost and the energy loss of acoustic power in the transmission.Besides,multiple thermoacousric units need more heat sources and this decentralized heating mode might against the utilization of heat energy.Taking into account the system performance and the external factors of the contradiction for the mid temperature-driven traveling-wave thermoacoustic heat engine,a travelling-wave thermoacoustic system with two thermoacoustic units was studied numerically and experimentally.The main contents of this thesis are as follows:1.Based on the linear thermoacoustic software DeltaEC,a computational model of two-stage traveling wave thermoacoustic engine was constructed and the influence of geometrical parameters of resonantor on the performance of thermoacoustic engine was studied.It was found the change in the length and diameter of the resonantor and the reducer tube will affect the amplitude and phase of the pressure fluctuation and volumetric flow rate at the regenerator.There is a specific length for a different length of the resonant tube making the system produce the maximum of acoustic power and pressure ratio separately.Using the longer resonant tube can improve the thermal efficiency of the system,but will reduce the frequency of the system to reduce the acoustic power density.For a different length of the resonant tube there is a certain diameter of the reducer tube so that the system produces the maximum of acoustic power and pressure ratio.When the length of the reducer is increased,the acoustic power and pressure ratio of the system decrease,but it makes little difference on the thermal efficiency of the system.2.A two-stage traveling wave thermoacoustic engine was designed and fabricated.Experiments were carried out by using two kinds of working fluid,nitrogen and helium.The effect of the inflatable pressure and the opening of the ball valve on the onset and stabilizing performance of the system were studied.It is found that when the gas working fluid is nitrogen,the onset temperature of the system is lower,the pressure amplitude and pressure ratio are larger and the working frequency is lower,but the system produce more acoustic power when the working fluid is helium.Increasing the inflation pressure can reduce the onset temperature,increase the pressure amplitude and thermoacoustic conversion efficiency,making the system produce more sound power,but will reduce the system pressure ratio.When the ball valve is used to reduce the local cross-sectional area of the resonant tube,the onset temperature of the system can be significantly reduced.For the system's pressure amplitude,pressure ratio and sound power,there is an optimal ball valve opening value to maximize their respective values.Besides,the problems in the experiment were analyzed and the suggestions for improvement were put forward.