Study On Heat-driven Thermoacoustic Cryocoolers Operating In The Cryogenic Temperature Range From Liquid Nitrogen To Liquid Hydrogen

Heat-driven thermoacoustic cryocooler is a new kind of cryogenic technology without any moving parts which promises high reliability, long lifetime and low cost. There are great application potentials for it in the place where electricity is insufficient. Now, heat-driven thermoacoustic cryocooler has become a focus of energy and cryogenic engineering field. Although significant progress has been made on it in the past decades, more efforts is still needed to be made to understand its work mechanism and to improve its efficiency. In this paper, progresses are made as follows:1. Further development of Meso-scope thermodynamic theory for cyclic flow engines and refrigerators and systemic summarization of linear thermoacoustic theory.Based on the Meso-scope thermoacoustic theory, the thermodynamic processes and cycles of the parcels in regenerators were analyzed. It was proved that thermal efficiency of an ideal regenerator equals to the Carnot efficiency. And this theory was further expanded to analyze the parcels in heat exchangers and thermal buffer tubes (pulse tubes). Beside this, the linear thermoacoustic theory was summarized and the method of numerical simulation for thermoacoustic prime mover and cryocoolers was presented in this paper.2. Systematic analysis of various phase shifters of pulse tube refrigerators and theoretical and experimental study of newly proposed phase shifters.A new phase shifter composed of inertance tubes without reservoir was presented. It was proved that this new phase shifter can replace the traditional phase shifter which is composed of an inertance tube and a reservoir when the flow is laminar. But when the flow is turbulent, they often can not offer the necessary phase shift for the pulse tube refrigerators. It was also proved that only when the inertance tube doesn't offer the necessary phase shift for the pulse tube refrigerators, can the double-inlet mode improve the performance of the pulse tube refrigerator. Otherwise it will deteriorate the performance. In order to suppress the DC flow induced by double-inlet mode, a DC flow suppressor was introduced. Based on these improvements, a first heat-driven thermoacoustic cryocooler capable of reaching liquid nitrogen temperature was set up.3. Theoretical investigation and experimental verification of newly proposed coupling devices for the heat-driven thermoacoustic cryocoolers.Four configurations of coupling thermoacoustic engines and pulse tube refrigerators are introduced: acoustic transformer, double-gas coupler, acoustic amplifier, double-gas acoustic amplifier. The later two couplers can greatly improve the performance of the heat-driven thermoacoustic cryocoolers. With the acoustic amplifier or the double-gas acoustic amplifier, the refrigerator can obtain a driven pressure ratio of higher than 1.3, the heat consumed by the thermoacoustic prime mover is lowered and the acoustic power utilized by the refrigerator is significantly improved. With the double-gas acoustic amplifier, the working frequency of the thermoacoustic prime mover can even be decreased about by 67%, which will make the prime mover get a better match with the refrigerator.4. Research and development of a first heat-driven thermoacoustic cryocooler working below liquid hydrogen temperature.In this cryocooler, an energy-focused traveling-wave thermoacoustic prime mover is employed to converted heat to acoustic power, a two-stage pulse tube refrigerator is to pump heat and a double-gas acoustic amplifier is to couple the prime mover and refrigerator. The prime mover uses nitrogen as the working gas, meanwhile the refrigerator uses helium as the working gas. So the system can work at a low frequency of about 23.3Hz. With a heating power of about 2600 W, the amplitude of pressure wave can be doubled by the amplifier and the refrigerator obtains a temperature of 18.1K which is the lowest temperature ever obtained by heat-driven thermoacoustic cryocoolers.5. A numerical study for a high-frequency three-stage pulse tube refrigerator working at liquid helium temperature.The thermal properties of some new materials are discussed. A kind of stainless steel mesh electroplated with lead and three kinds of rare-earth metals are respectively employed as the fillings of the second and third stage regenerator. Developed a numerical program for three-stage pulse tube refrigerator and the influences of the dimensions of regenerators, fillings and pulse tubes on the lowest cooling temperature were detailed discussed. After optimization, a three-stage pulse tube refrigerator working at the liquid helium temperature was designed. Its lowest cooling temperature without cooling load reached 3.9K.