J.F. Wu

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.

Research on the change of mixture compositions in mixed-refrigerant Joule-Thomson cryocoolers

An experimental system is developed to investigate the dynamic characteristics of the mixture composition variations in the closed throttling refrigeration cycle. The experimental results show that the mixture compositions vary at different operating periods of the cycle. The maximum change of the compositions is up to 6% for different operating periods. The unevenness of the mixture compositions at different positions of the system may be up to 12%, or even more. The experimental results will be helpful in the modification of the existing simulation model of the mixture refrigeration cycle as well as the fabrication of mixture coolers.

Thermodynamic design principle of mixed-gases Kleemenko refrigeration cycles

Mixed-gases throttling refrigeration cycles are recuperative cycles. The refrigeration system has at least one heat exchanger and from zero to three or more phase separators. Detailed discussions are made in this paper on the thermodynamic performance of several cycles, including extensive simulations and optimizations of mixtures, operating parameters of pressures, and flow configurations. The results show that the mixed refrigerant is the most important design parameter that influences the performance of the system. From a thermodynamic point of view, the configurations that were studied can all achieve about the same efficiency with an appropriate selection of the mixture and operating pressures.

Study of a Vortex Tube by Analogy with a Heat Exchanger

Based on the models of Scheper, Lewins, and Bejan, a new model has been established to study the influence of the cold mass flow fraction on the temperature separation effect in a vortex tube. The model is based on making an analogy between the vortex tube and a counterflow heat exchanger. The results show the model can accurately explain the correlation of cold mass flow fraction to the temperature separation effect.

Thermodynamic Analysis of a Mixed-Refrigerant Auto-Cascade J-T Cryocooler with Distributed Heat Loads

In this paper, an effort is made to go further into the thermodynamic process of the Auto-Cascade refrigeration cycle using multicomponent zeotropic mixtures as working fluids. The exergy method is employed to analyze the thermodynamic characteristics of components and the whole refrigeration cycle. Specially, the condition that there are extra-distributed heat loads along the heat exchangers is considered. Extensive comparison is made between the single stage J-T cycle and a typical Auto-Cascade cycle at the same condition. At the calculation conditions presented in this paper, the total exergy gained in the MARC is 6.6% better than the single stage cycle, and 9.5% better in the situation with distributing heat loads. The results show that using appropriate Auto-Cascade cycle can improve the performance of the refrigerator.

Thermodynamic Prediction of the Vortex Tube Applied to a Mixed-Refrigerant Auto-Cascade J-T Cycle

A new hybrid refrigeration cycle of the Mixed-refrigerant Auto-Cascade J-T cycle combined with a vortex tube is introduced. This cycle, which holds the advantage of a mixed refrigerant Auto-Cascade J-T cycle and the vortex tube, is expected to achieve a temperature lower than 65 K. A thermodynamic model is used to investigate the vortex tube energy separation. The exergy method is applied to analyze the thermodynamic performance of each unit and the whole refrigeration cycle. A comparison is made between the Auto-Cascade J-T cycle and the new hybrid refrigeration cycle for the same conditions. The total exergy efficiency achieved in the new hybrid refrigeration cycle is 78.9% better than the Auto-Cascade J-T cycle. The results show that using the new type of compound refrigeration cycle can improve exergy efficiency of the whole cycle. It is completely possible to achieve a temperature lower than 65 K.

Further Development of the Mixture Refrigeration Cycle with a Dephlegmation Separator

Mixed gas refrigeration cycles with phase separators provide a wealth of configuration options for the design of the cycle. This paper focuses on the development of the cycle with a simplified dephlegmation separator. Both theoretical analysis and experimental investigation were carried out to optimize the refrigeration cycle configuration, including the arrangement of the heat exchangers, phase separator, mixer, etc. Particular attention is placed on the position of the mixer. Experimental results confirm the conclusions drawn from the thermodynamic analysis of the configuration of the dephlegmation cycle. A Carnot efficiency of 11.7% was achieved in an experimental test at 125 K with the cycle driven by an air-conditioning compressor with a nominal input power of 1.1 kW.

Research on Adiabatic Capillary Tube Expansion Devices in Mixed-Refrigerant J-T Cryocoolers

This paper presents a study of capillary tubes used as expansion devices in mixed-refrigerant J-T cryocoolers. A numerical model is presented for predicting capillary tube performance with multicomponent refrigerants, and the results are compared with experimental data. Because of the multicomponent refrigerant used in the system, the flow characteristic is different from that in a household refrigerator or freezer. The experimental results are discussed, and the performance of the capillary is analyzed.

External acoustic load on the performance of a travelling-wave thermoacoustic engine

In this paper, external acoustic loads on the performances of a quarter-wavelength traveling-wave thermoacoustic pressure generator are analyzed. First, we derived the maximal frequency and the critical temperature gradient of the thermoacoustic systems by analyzing the conversion between passive network and active network. Then, we considered the effect of the external loads on operating frequency and obtain some qualitative results.