Ercang Luo

A Heat-driven thermoacoustic cooler capable of reaching liquid nitrogen temperature

This article introduces a heat-driven thermoacoustic cooler capable of reaching liquid nitrogen temperature with no moving parts. The thermoacoustic cooler consists of a traveling wave thermoacoustic prime mover and a pulse tube cooler. By using a tapered resonance tube, the prime mover can provide a pressure ratio higher than 1.26. By using a long thin tube, a reservoir is no longer needed in the pulse tube cooler. After preliminary optimizations, the lowest temperature reaches 68.8 K. This result shows the potential to achieve cryogenic temperatures lower than 70 K by applying thermoacoustic technology, which is simply realized through combinations of tubes and solid materials without the need of any moving parts.

Study of nonlinear processes of a large experimental thermoacoustic-Stirling heat engine by using computational fluid dynamics

This article focuses on using computational fluid dynamics (CFD) method to study several important nonlinear phenomenon and processes of a large experimental thermoacoustic-Stirling heat engine. First, the simulated physical model was introduced, and the suitable numerical scheme and algorithm for the time-dependent compressible thermoacoustic system was determined through extensive numerical tests. Then, the simulation results of the entire evolution process of self-excited thermoacoustic oscillation and the acoustical characteristics of pressure and velocity waves were presented and analyzed. Especially, the onset temperature and the saturation process of dynamic pressure were captured by the CFD simulation. In addition, another important nonlinear phenomenon accompanying the acoustic wave, which is the steady mass flow through the traveling-wave loop inside the thermoacoustic engine, was studied. To suppress the steady mass flow numerically, a fan model was adopted in the simulation. Finally, the multi...

Detailed study of a traveling wave thermoacoustic refrigerator driven by a traveling wave thermoacoustic engine

Thermoacoustic systems have very attractive features and possible wide applications in many areas, especially for cooling purposes. Inventions of traveling wave thermoacoustic engines and traveling wave thermoacoustic refrigerators with work recovery capability have greatly improved the thermodynamic efficiencies of the thermoacoustic systems. To fully utilize the advantages of traveling wave systems, a traveling wave work-recoverable thermoacoustic refrigerator has been designed and built that is driven by a traveling wave thermoacoustic engine, which is aimed at domestic refrigeration purposes. So far, the lowest temperature of −64.4°C and 250W cooling power at −22.1°C are obtained by the system with 3.0MPa helium gas and 57.7Hz working frequency. Heat input into the system is 2.2kW. Simulations based on linear thermoacoustic theory have also been done for comparison with experimental results, which shows reasonable agreement within a certain pressure wave amplitude range and cold end temperature range....

Thermoacoustically driven refrigerator with double thermoacoustic-Stirling cycles

Recently, considerable research efforts have been made to search substitution technologies for chlorofluorocarbon-based vapor compression cycles due to the concern over environmental issues. This letter introduces a helium-based thermoacoustic refrigeration system, which is a thermoacoustic-Stirling refrigerator driven by a thermoacoustic-Stirling heat engine, for domestic refrigeration purpose. In the regenerators of both the refrigerator and the prime mover, helium gas experiences near to reversible high efficiency Stirling process. At the operating point with 3.0MPa mean pressure, 57.7Hz frequency, and 2.2kW heat input, the experimental cooler provides a lowest temperature of −64.4°C and 250W cooling power at −22.1°C. These results show good potential of the system to be an alternative in near future for domestic refrigeration with advantages of environment-friendliness, no moving parts, and heat driven mechanism.

300Hz thermoacoustically driven pulse tube cooler for temperature below 100K

This letter introduces a thermoacoustically driven pulse tube cooler system working at around 300Hz. In the system, a thermoacoustic standing-wave engine is used to drive a Stirling-type pulse tube cooler. Besides the design considerations for key components in each subsystem, the benefits of using the acoustic amplifier tube to couple the engine and the cooler have been analyzed through both calculations and experiments. So far, a lowest no-load temperature of 95K has been obtained on the system with the acoustic amplifier tube being used. Since high frequency operation of the system could lead to a much reduced system size, the result shows the potential of using the system in small-scale cryogenic applications.

A 1 kW-class multi-stage heat-driven thermoacoustic cryocooler system operating at liquefied natural gas temperature range

This article introduces a multi-stage heat-driven thermoacoustic cryocooler capable of reaching cooling capacity about 1 kW at liquefied natural gas temperature range without any moving mechanical parts. The cooling system consists of an acoustically resonant double-acing traveling wave thermoacoustic heat engine and three identical pulse tube coolers. Unlike other traditional traveling wave thermoacoustic heat engines, the acoustically resonant double-acting thermoacoustic heat engine is a closed-loop configuration consists of three identical thermoacoustic conversion units. Each pulse tube cooler is bypass driven by one thermoacoustic heat engine unit. The device is acoustically completely symmetric and therefore “self-matching” for efficient traveling-wave thermoacoustic conversion. In the experiments, with 7 MPa helium gas as working gas, when the heating temperature reaches 918 K, total cooling capacity of 0.88 kW at 110 K is obtained with a resonant frequency of about 55 Hz. When the heating tempera...

Heat-driven thermoacoustic cryocooler operating at liquid hydrogen temperature with a unique coupler

A heat-driven thermoacoustic cryocooler is constructed. A unique coupler composed of a tube, reservoir, and elastic diaphragm is introduced to couple a traveling-wave thermoacoustic engine (TE) and two-stage pulse tube refrigerator (PTR). The amplitude of the pressure wave generated in the engine is first amplified in the coupler and the wave then passes into the refrigerator to pump heat. The TE uses nitrogen as its working gas and the PTR still uses helium as its working gas. With this coupler, the efficiency of the system is doubled. The engine and coupler match at a much lower operating frequency, which is of great benefit for the PTR to obtain a lower cooling temperature. The coupling place between the coupler and engine is also optimized. The onset problem is effectively solved. With these improvements, the heat-driven thermoacoustic cryocooler reaches a lowest temperature of 18.1K, which is the demonstration of heat-driven thermoacoustic refrigeration technology used for cooling at liquid hydrogen ...

A novel coupling configuration for thermoacoustically-driven pulse tube coolers: Acoustic amplifier

Thermoacoustically-driven pulse tube cooler can provide cryogenic cooling power with no moving components. Up to now, pulse tube cooler is directly coupled with the thermoacoustic engine and obtainable pressure ratio for the pulse tube cooler is limited by the capability of the thermoacoustic engine. The authors propose here the concept of acoustic amplifier, which is actually a long tube connecting the engine with the pulse tube cooler. Theoretical calculation shows that suitable length and diameter of the tube can lead to a pressure wave amplification effect which means that pressure wave amplitude coming from the thermoacoustic engine can be much amplified to drive the pulse tube cooler. Based on this, a 2.8 m long copper tube with 8 mm inner diameter is used as the acoustic amplifier in experiments. The experimental results show that due to the amplification effect, pressure wave amplitude at the inlet of the pulse tube cooler is over 2.5 times of that at the engine outlet. Typically, with 1.67 kW heating power, the pressure ratio provided by the engine is 1.11 while at the inlet of the pulse tube cooler the pressure ratio is 1.32, which leads to a lowest no-load temperature of 65.7 K.

On the temperature distribution in the counter flow heat exchanger with multicomponent non-azeotropic mixtures

Abstract The influence of mixture composition on the temperature distribution in the counter flow heat exchanger used in mixture Joule–Thomson refrigerators is investigated in this paper. A perfect heat capacity matching between the supply and the return streams can be achieved by optimizing the mixture composition. The deeper reason is that in two-phase state the latent heat makes a very important contribution in the overall heat capacity for multicomponent non-azeotropic mixtures. The theoretical results are compared with experimental data; both theoretical and experimental results agree well with each other. The results show that the temperature profile as well as the locations of the pinch points is determined by the mixture compositions. Therefore, it is possible to get a perfect temperature distribution using optimal mixture. This becomes another criterion of the optimization of mixture composition.

A high efficiency hybrid stirling-pulse tube cryocooler

This article presented a hybrid cryocooler which combines the room temperature displacers and the pulse tube in one system. Compared with a traditional pulse tube cryocooler, the system uses the rod-less ambient displacer to recover the expansion work from the pulse tube cold end to improve the efficiency while still keeps the advantage of the pulse tube cryocooler with no moving parts at the cold region. In the meantime, dual-opposed configurations for both the compression pistons and displacers reduce the cooler vibration to a very low level. In the experiments, a lowest no-load temperature of 38.5 K has been obtained and the cooling power at 80K was 26.4 W with an input electric power of 290 W. This leads to an efficiency of 24.2% of Carnot, marginally higher than that of an ordinary pulse tube cryocooler. The hybrid configuration herein provides a very competitive option when a high efficiency, high-reliability and robust cryocooler is desired.