| Since pulse tube refrigerators have a number of advantages such as simple in construction with few moving parts (therefore a longer lifetime and better reliability) and being environmentally benign (i.e., no CFC problem), they provide attractive applications ranging from the cooling of the infrared sensors, semiconductor, superconducting magnets at cryogenic temperatures to the cooling of other civilian applications at higher temperatures.; Existing analyses have not been able to provide a clear explanation on what is the refrigeration mechanism in these devices and why an orifice pulse tube refrigerator has a better performance than that of a basic pulse tube refrigerator. In order to provide a clearer picture of the physical process occurring in these machines for the improvement of their efficiencies, we have carried out a perturbation analysis to study a compressible flow oscillating at high frequencies in a closed tube at a cycle steady condition. Unlike the previous analyses, we consider the global conservation of mass, momentum, and energy by integrating the governing equations with respect to time and cross-sectional area. The analytical solution clearly shows that there is the so-called “mass streaming”, “momentum streaming” and “energy streaming” in these devices. It is found that (1) there is a non-vanishing mean velocity in the compressible oscillating flow caused by the mass streaming due to the fluctuation of the density, (2) the cycle-averaged pressure gradient is responsible for the momentum streaming and friction effect, (3) the refrigeration effect is essentially caused by the non-vanishing mean velocity, and (4) the increase of the refrigeration capacity in the orifice pulse tube refrigerator is owing to the large pressure drop across the throttling construction. This analysis can also used to explain successfully why there is an optimal opening of the throttling construction. Such a fundamental investigation provides a full and clear explanation of the refrigeration mechanism in these pulse tube refrigerators and thermoacoustic machines.; An experimental rig of a pulse tube refrigerator, consisting of a compressor, controlling valves, a regenerator, a pulse tube and heat exchangers, was constructed. The system was insulated at a vacuum environment to minimize the convection and heat conduction losses. The effects of different parameters on the performance have been experimentally investigated to verify the analytical and numerical results. The optimum refrigeration temperature of our single-stage G-M type double-inlet pulse tube refrigerator was below 60°K(−213.15°C). By measuring the pressure waves in the system, it is found that the cycle-averaged pressures are varying with respect to the axial locations, which confirm that the cycle-averaged pressure is responsible for the momentum streaming and cycle-averaged friction force.; A 1-D transient numerical simulator has been developed in order to reveal the nonlinear characteristics and dynamical performance of a basic pulse tube refrigerator, an orifice pulse tube refrigerator, and a double-inlet pulse tube refrigerator operating at low oscillating frequencies. In this simulator, governing equations, consisting of state equation, continuity equation, momentum equation, the energy equations for the fluid and the solid, which are spatially and temporally conjugated, were numerically solved. The unrealistic assumption that the refrigeration temperature is kept constant in the existing simulations was relaxed in our simulator. Numerical results of the double-inlet pulse tube refrigerator are shown to be in good agreements with experimental data. This numerical model can be used to optimize the design of the three types of pulse tube refrigerators. |
