Qinguo Hu

Study on the overall heat transfer coefficient for the tube-in-tube heat exchanger used in mixed-gases coolers

In this paper, an experimental set up is established to investigate the behavior of the heat exchanger with multi-components mixtures based on a real mixture refrigeration system. Two tube-in-tube heat exchangers with different configurations are tested extensively with different mixtures operating at three typical temperature ranges, such as 80 K–100 K, 120 K–150 K, and 180 K–200 K temperature ranges. The two heat exchangers are fabricated specially to be able to measure the temperatures and pressures distributions. With the measurement of the mixture compositions, temperatures, and pressures, the thermodynamic and hydraulic behaviors of the two heat exchangers are studied extensively. Finally, the heat transfer characteristics are obtained, which is useful in future design of the mixture refrigeration system.

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.

A new type mixture refrigeration auto-cascade cycle with partial condensation and separation reflux exchanger and its preliminary experimental test

A new type of mixture refrigeration cycle with reflux exchanger is presented in this paper. In this cycle, a new type of L-V separator with inner heat and mass transfer is employed to replace the combination of conventional L-V separator or complicated rectifier and succeeding heat exchanger used in traditional auto-cascade cycle or Kleemenko cycle. A prototype is developed based on this refrigeration cycle. The thermodynamic performance is discussed as well as some other specifications such as cost, reliability, etc. The experimental results show that this prototype can reach 74 W at 135 K and 265 W at 171 K with a nominal input power of 1.5 HP.

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.

Chapter 39 – Development of a cryogenic water-trap based on the recuperative mixture refrigeration cycle*

Publisher Summary This chapter explores the details of a cryogenic water-trap based on the recuperative mixed-refrigerant refrigeration. The cryogenic water-vapor trap is driven by an oil-lubricated single-stage compressor with nominal input power of 500 W. The lowest temperature is 110 K, at which the saturated vapor pressure of water is about 1 e-10 Pa. A comparison is made between a vacuum system with and without the cryogenic water-trap. The overall pumping speed of the system that combined with a turbo molecular pump is ten times higher than that without the cold trap. The result is that the pumping down time with the cryogenic water-trap can be reduced greatly as ten times. Compared with the traditional cryogenic pump, there is no requirement of periodic maintenance. Moreover, this new developed cryogenic water-trap has high reliability, low cost, and easy to be built in large scale based on numerous merits of mixed-refrigerant refrigeration system. When attempting to select the high vacuum pump for any given application, it becomes obvious that there is no universal or ideal pump. The practice is to make serious compromises usually based on cost trade-offs. The proper approach is to utilize the advantages of the most applicable pumps and use a combination of pumps.

Development of a cryogenic water-trap based on the recuperative mixture refrigeration cycle

Publisher Summary This chapter explores the details of a cryogenic water-trap based on the recuperative mixed-refrigerant refrigeration. The cryogenic water-vapor trap is driven by an oil-lubricated single-stage compressor with nominal input power of 500 W. The lowest temperature is 110 K, at which the saturated vapor pressure of water is about 1 e-10 Pa. A comparison is made between a vacuum system with and without the cryogenic water-trap. The overall pumping speed of the system that combined with a turbo molecular pump is ten times higher than that without the cold trap. The result is that the pumping down time with the cryogenic water-trap can be reduced greatly as ten times. Compared with the traditional cryogenic pump, there is no requirement of periodic maintenance. Moreover, this new developed cryogenic water-trap has high reliability, low cost, and easy to be built in large scale based on numerous merits of mixed-refrigerant refrigeration system. When attempting to select the high vacuum pump for any given application, it becomes obvious that there is no universal or ideal pump. The practice is to make serious compromises usually based on cost trade-offs. The proper approach is to utilize the advantages of the most applicable pumps and use a combination of pumps.