| A thermoacoustic engine, which converts heat energy to acoustic work, occupies advantages of structure simplicity, reliability, heat-driven mechanism, environmental friendliness and so on. Due to no moving components from ambient to cryogenic temperatures, the novel technology of thermoacoustically driven pulse tube refrigerator has a bright prospect of application. In order to enhance the performance of the thermoacoustic engine and to decrease the refrigerating temperature, the theoretical and experimental work of this dissertation focuses on the following sections:1. Numerical Simulation and Experimental Investigation on A Thermoacoustic Engine with Tapered Resonance Tube A symmetrical standing-wave thermoacoustic engine with tapered resonance tube has been numerically simulated with liner thermoacoustics. The simulation shows that using tapered resonance tube in thermoacoustic engine could decrease the velocity amplitude and lower the total acoustic power loss in the resonance tube. The experimental results indicate that the harmonic was suppressed effectively by using the tapered resonance tube, and the pressure ratio was improved.2. Acoustics Principle Analysis, Numerical Simulation and Experimental Investigation on an Acoustic Pressure Amplifier Based on acoustics principle, for an ideal one quarter wavelength acoustic pressure amplifier with one end open and the other closed, a much bigger pressure ratio could be obtained at the closed end. The amplification effect of the acoustic pressure amplifier has been validated by numerical simulation with linear thermoacoustics and experiments. Taking the dissipation in the acoustic pressure amplifier into account, the length of the acoustic pressure amplifier for the maximal pressure ratio is less than one quarter wavelength.3. Numerical Simulation and Experimental Investigation on Thermoacoustically driven RC load The standing-wave thermoacoustic engine connected with an RC (resistance and compliance) load has been numerically simulated with linear thermoacoustics. According to the computed results, the influence of the impedance of RC load on the parameters at RC load inlet and at the hot end of the stack has been analyzed. The influence of impedance of RC load and mean pressure on the performance of thermoacoustically driven RC load have been experimentally carried out. Numerical simulation and experimental investigation on thermoacoustically driven RC load with an acoustic pressure amplifier has been performed. The coupling relation of the thermoacoustic engine with an acoustic pressure amplifier and the RC load has been discussed. The acoustic pressure amplifier length plays an important role in the system. Reversed pressure oscillation may occur at the inlet of the acoustic pressure amplifier with different acoustic pressure amplifier length. When a maximal acoustic power is delivered to the RC load, the phase difference is no longer of -45°between pressure and velocity oscillation at the load inlet.4. Experimental Investigation on thermoacoustically driven pulse tube refrigerator with an acoustic pressure amplifier Incorporating with an acoustic pressure amplifier in a standing-wave thermoacoustically driven pulse tube refrigerator system is propitious to further decrease the cooling temperature. With 1.4 kW heating power, a copper tube of 3.3 m in length and 8 mm in inner diameter as the acoustic pressure amplifier, a pressure amplitude of 0.181 MPa, a pressure ratio of 1.152 have been obtained at the inlet of the pulse tube refrigerator. A cooling temperature of 79.7 K (decreased from 88.6 K) and a cooling power of 2.436 W at 120 K were reached. Modifications of the hot end heat exchanger, the water cooler and the hot buffer of the thermoacoustic engine were carried out to improve the performance. Coupling a newly designed U-shaped pulse tube refrigerator with an acoustic pressure amplifier of 3.4 m in length and 8 mm in inner diameter, 1.8 kW heating power, the pressure amplitude of 0.214 MPa and pressure ratio of 1.179 have been obtained. As a result, a cooling temperature as low as 56.4 K was obtained, which is the lowest so far achieved by a standing-wave thermoacoustically driven pulse tube refrigerator.
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