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To solve the shortcomings of small cooling capacity of the current Joule-Thomson (J-T) cryocooler, a multi-layer microchannel J-T cryocooler is designed and fabricated by printed circuit board technology. The characteristic of the cryocooler is that there exists heat transfer while throttling. The coupling effect of heat transfer and throttling affects the overall performance of cryocooler. Therefore, the steady-state model was established for each part of the cryocooler. The P-h diagram of N 2 was calculated by the model. Considering the variation of J-T coefficient ( μ jt ) in the process, the coupling performance of heat transfer and throttling in the J-T cryocooler were analyzed. A new parameter, J-T efficiency ( η jt ), was proposed to evaluate the J-T effect. Additionally, according to the dependence of μ jt with temperature and pressure, the refrigeration performance of the cryocooler under different working conditions was simulated. The results show that the heat transfer in the throttle can enhance the throttling effect. When the inlet temperature is 285.0K and the inlet pressure increases to 18.00MPa, the N 2 temperature at the cold end reaches 116.3K, and the gross cooling capacity is 4.55W. When the inlet pressure is 6.00MPa and the inlet temperature reduces to 195.0K, the temperature at the cold end can reach to the saturated temperature of 103.2K, and the maximum gross cooling capacity is 7.68W. For the two groups of working conditions, the heat transfer in the throttle can enhance the J-T effect. η jt reaches 95.87% and 94.76%, the proportion of temperature drop caused by J-T effect is 56.10% and 68.03% of the total temperature drops, respectively. Finally, the variation laws of inlet temperature and η jt are analyzed when N 2 reaches saturated temperature under different pressures to guide the selection of inlet parameters.

The heat transfer performances of a pulsating heat pipe (PHP) with ethanol–water, ethanol–methanol and ethanol–acetone are investigated experimentally. The mixing ratios (MRs) of the ethanol-based mixed working fluids are 2:1 and 4:1, the volume filling ratios (FRs) range from 45% to 90% and the heat input ranges from 10 W to 100 W. The experimental results are as follows: When the mixing ratio is 2:1, the heat transfer performance of PHP with ethanol–water is better than other working fluids at a filling ratio of 45% because of the phase-change inhibition in ethanol–water; at a filling ratio of 55%, PHP with ethanol–acetone shows better performance among those with mixed working fluids. Acetone with a relatively high value of ( dp / dT ) sat (saturation pressure gradient versus temperature) and relatively lower dynamic viscosity can lead to relatively high velocity in the PHP, which can decrease the temperature difference between the evaporation section and condensation section. When the mixing ratio is 4:1, the thermal resistance of PHP with ethanol–water that is close to being dried out under a filling ratio of 45% rises faster than that at a mixing ratio of 2:1 due to the presence of less deionized water (DI water); the heat transfer performance of PHP with ethanol–acetone is excellent at a filling ratio of 55% among the ethanol-based mixed working fluids because the thermal resistance is relatively small and the maximum heat input that PHP can endure is highest. When the volume filling ratio reaches 62%, 70% and 90%, the heat transfer performance of PHP with pure working fluids is better than that with ethanol-based mixed working fluids. This may be partially attributed to the offset of flow driving force caused by the mass transfer due to the concentration difference between the liquid and the vapour phase of mixtures. The filling ratio of 62% shows a marginal leading in terms of lower thermal resistance.

As noted in this investigation, there are only eight sensors commonly installed in factory chillers. However, the fault detection and diagnosis (FDD) models of chillers are now mostly based on laboratory data. In the laboratory, the unit is equipped with more sensors than commercial machines are. The FDD results obtained by this method does not match the data from the factory chillers and cannot be applied in practice. Based on the ASHRAE RP-1043 data, this paper extracts information from three of the factory-installed (FI) sensors, along with information from all eight of the FI sensors, in order to establish the support vector machine (SVM)-3 and SVM-8 diagnostic models based on grid search and cross validation parameter optimization for the seven typical faults. These models are compared to the SVM-64 model, which is based on the 64 parameters from the ASHRAE data. The overall accuracy of SVM-8 model is 97.68%, which meets the needs of field operation diagnosis. In addition, based on the eight factory-installed sensors, if the pressure of oil feed and temperature of oil feed sensors are added together to diagnose the fault, the normal detection rate and the diagnostic performance for condenser fouling and excess oil faults improve, and the overall fault diagnosis is more effective.

Data-driven diagnostic models for refrigeration systems are often used exclusively for a dedicated object. For other types of chillers, a new model must be trained using normal and faulty data, which is both time consuming and heavily data dependent, and accordingly, curbs its application. In this study, the technology for handling imbalanced data is introduced and combined with support vector machine (SVM) to probe the possibility of transferring the FDD (fault detection and diagnosis) knowledge of a centrifugal chiller to a screw chiller by using just a small amount of new data. Principal component analysis (PCA) and the synthetic minority oversampling technique (SMOTE) were used to oversample the faulty sample set with an imbalance ratio of 5%, and a support vector machine (SVM) was employed for fault diagnosis. The experimental results indicate that by using PCA-SMOET-SVM technology, the overall diagnostic performance of the screw chiller with much less data/information is improved with the aid of the prior knowledge transferred from the centrifugal chiller. By investigating the oversampling ratios between 100% and 400%, it was found that the ratio of 100% was the best with the average diagnostic accuracy reaching 96.70% for the faults of the screw chiller.

With the increasing miniaturization of high-powered electronic components, technologies for rapid cooling in small spaces have received more and more attention. Joule-Thomson (J-T) refrigeration is an effective means for rapid cooling. It is widely used in military and medical refrigeration, electronic equipment cooling and many other fields. This paper describes the structural development of J-T refrigerators of the traditional Hampson type, etched microchannel type and others. It reviews experimental studies on refrigeration components and the charge composition of the mixtures in the J-T cryogenic system. It also introduces the main applications of the J-T cryogenic system. Finally, it summarizes the above research and puts forward developmental prospects, hoping to provide reference for future experimental design and research.