最新刊期
卷 45 ， 期 1 ， 2024
- 摘要：Auto-cascade refrigeration technology has broad application prospects in refrigeration and cryogenic refrigeration owing to its wide operating temperature range, simplicity, and reliability. The construction of new refrigeration cycles and the diversification of mixtures have been extensively studied. The active regulation of mixture concentrations in auto-cascade refrigeration systems to improve performance has been a technical bottleneck and research challenge. This study first reviews the state-of-the-art auto-cascade refrigeration systems and describes the history of refrigeration cycles. Research on the component separation and migration characteristics of zeotropic mixtures, which affect system efficiency, is also summarized. Research on component separation is discussed in terms of refrigeration cycle improvement and the separation performance of the key component – the gas-liquid separator. The causes of component migration, the current status of research on component migration characteristics, and theoretical models of phase accumulation are summarized. Based on this, existing research methods for the regulation of zeotropic mixture components in auto-cascade refrigeration systems are presented. This study summarizes the current status and research directions of component optimization and control as a reference for further performance improvement of auto-cascade refrigeration systems.关键词：auto-cascade refrigeration;mixtures;component separation;component migration;component regulation1750|1193|0发布时间：2024-07-18
- 摘要：With increasing environmental awareness, natural refrigerants have regained prominence. An air-cycle refrigeration system is an effective alternative because air is harmless and environmentally friendly. The expander-compressor system is the core component of an air-cycle refrigeration system, where the compressor input power varies with the expander performance curve. To design a centrifugal compressor that can operate efficiently with an expander, modifications to traditional design methods are required. By combining the conservation of mass, momentum, and energy with the jet wake flow pattern and extending the relevant parameters of the traditional centrifugal compressor to a lower pressure range, a design method for matching the geometric parameters of a centrifugal compressor with an expander is proposed. This method was applied to design a centrifugal compressor corresponding to an existing expander, which was validated using a centrifugal compressor model previously analyzed by other researchers. Computational fluid dynamics (CFD) was employed to simulate and assess the operational performance of the expander-compressor under variable operating conditions, including the utilization efficiency of the expansion power. A centrifugal compressor designed using this method achieved more than 92% and 88% utilization efficiency under the nominal operating condition and variable operating condition, respectively. The expander functioned smoothly within the designed mass flow rate range.关键词：air compression refrigeration;turbo compressor;centrifugal compressor design;expansion power utilization efficiency1379|958|0发布时间：2024-07-18
- 摘要：To explore the characteristics of pressure pulsation in a twin-screw refrigeration compressor, transient pressures during the suction, compression, and discharge phases were measured, and the pressure pulsation characteristics were subsequently analyzed. The study investigated the effects of operating speed and condensing temperature on pressure pulsation and compared pressure pulsation, noise levels, and the coefficient of performance (COP) in twin-screw refrigeration compressors with slide valve control (SVC) and variable-speed control (VSC) at the same volumetric flow rate. The results indicated that pressure pulsation in a twin-screw refrigeration compressor originates from the periodic fluctuation of pressure and mass flow rate. As the rotation speed increased, pressure pulsation gradually increased from 58.6 kPa at 1 380 r/min to 141.0 kPa at 4 200 r/min. With an increase in condensing temperature from 34 ℃ to 57 ℃, pressure pulsation also increased from 132.0 kPa to 314.0 kPa. In comparison to SVC, VSC demonstrated significant advantages, featuring more than 54.6% reduction in pressure pulsation, more than 2.9 dB(A) reduction in noise, and more than 5.5% improvement in COP.关键词：twin-screw refrigeration compressor;pressure pulsation;noise;variable-speed control1366|662|0发布时间：2024-07-18
- 摘要：The miniaturization and performance improvement of components continuously increase the power of electronic devices. Superior heat-dissipation performance is important for the reliability of electronic devices. In this study, an experimental pump-driven refrigerant two-phase cold-plate-cooling system was developed. Four two-phase cold plates with different materials (Cu and Al) and channel heights (10 mm and 15 mm) were designed and processed. The heat-transfer performance of the cold plates, together with their flow resistance characteristics, pump power under different heat fluxes (4.4–22.2 W/cm2), refrigerant cooling capacities (3–11 kW), and heat source positions were studied. The results indicated that the heat-transfer performance of the two-phase cold plate was superior. The maximum heat transfer coefficient was 26 kW/(m2?℃) when dealing with a concentrated heat source with a heat dissipation of 1 000 W and a heat flux of 22.2 W/cm2. The temperature difference between the heat source surface and the refrigerant was less than 15 ℃ when the total pressure drop of the system was less than 20 kPa and the power consumption of the refrigerant pump was less than 20 W. A natural cold source can be used for heat dissipation to achieve energy savings. The heat transfer characteristics of the two-phase cold plate can be described by the fin efficiency correlation and the Kandlikar heat transfer correlation. The deviation between the temperature difference calculated by the theoretical formula and the measured value was less than 1 ℃. The results of this study can guide the design of cold-plate channels.1396|649|0发布时间：2024-07-18
- 摘要：The homogenous distribution of liquid and vapor over a plate surface is a key factor affecting the performance of brazed-plate heat exchangers in refrigeration and air-conditioning units. The two-phase flow and distribution over the plate surface were investigated with R410A fluid using computational fluid dynamics (CFD) simulation software. The distributions of pressure, velocity, and liquid volumetric fraction were comparatively analyzed. It was observed that the pressure, velocity, and liquid phase were distributed comparatively evenly for the herringbone plate. The velocity and liquid volumetric fraction along the plate centerline were slightly higher than those along the edges. However, for the dimpled plate, the velocities in the proximal zone were significantly higher than those in the distal zone, which is opposite to the distribution of liquid volumetric fraction. New methods called the mean two-phase flow deviation (MTFD) and mean liquid flow deviation (MLFD) at the nominal section were proposed to evaluate the maldistribution of fluid flow over the plate surface. The results indicated that the distribution and sideways flow were better for the herringbone plate than for the dimple plate. The MTFD values were 14.2% and 39.6%, and the MLFD values were 15.6% and 41.3% for the herringbone and dimple plates, respectively. It was determined that the bypass section existed in the flow direction for the round dimple plate, which led to poor sideways flow and earlier separation between the vapor and liquid. The proposed boomerang dimple plate pattern, similar to fish skin, can improve the two-phase flow distribution over the plate surface because it can reduce the size of the bypass section and generate vortices under a concave shape. The new geometry can enhance turbulence and promote the two-phase fluid to move sideways effectively. The MTFD and MLFD values were 7.6% and 8.9%, respectively.关键词：even distribution;numerical simulation;plate heat exchanger;evaporator;refrigerant1430|614|0发布时间：2024-07-18
- 摘要：Currently, the precise linear cooling of microfluidics remains a challenge in the development and application of microfluidic technology in medicine and life sciences. To realize the linear cooling of the target area on a microfluidic chip, a thermoelectric refrigeration-based temperature control system for microfluidic chips was designed, and linear coupling between the current, cooling capacity, and microfluidic temperature was achieved through numerical simulation and experimental tests. When the thermoelectric cooler was driven by a constant current, the linearity of the cooling process of the microfluidic sample cell was only 0.598. The use of a single-function transient current significantly improved the linearity of microfluidic cooling; however, cold surpluses and inadequacies still existed, which did not meet the accuracy requirements of linear cooling. Finally, a transient current mechanism to realize the linear cooling in microfluidic thermoelectric cooler devices was obtained by coupling a variety of current waveforms. Linear cooling of microfluidic between -19–26 °C and 24–42 °C/min was realized, and the linearity was above 0.9981. The linear cooling mechanism of the thermoelectric cooler for microfluidic devices was successfully verified by experimental tests.关键词：thermoelectric cooling;microfluidics;linear cooling;cooling rate;transient current1283|639|0发布时间：2024-07-18
- 摘要：To alleviate the problem of crop yield reduction and extinction arising from high temperatures in summer greenhouses, a radiative cooling film for greenhouses operated in summer was investigated. The sky radiative cooling effect of a film can be strengthened by integrating a transparent radiation layer with conventional near-infrared reflective materials. The optical properties of films at different wavelengths were determined experimentally, revealing a photosynthetically effective transmissivity of 65.9%, a near-infrared transmissivity of 20.9%, and a mid-infrared reflectivity of 88.1%. A greenhouse environment model was used to compare the greenhouse temperature and energy consumption for cooling with different covering materials. The simulation results showed that the radiative film can reduce the internal temperature of a closed greenhouse in Shanghai by 11.4 ℃, and the cooling contributions of the selective near-infrared reflector and the transparent radiative layer were 6.8 ℃ and 4.6 ℃, respectively. Using this film, the energy consumption of heat pumps in an active-cooling greenhouse can be reduced by 26.9%. This film offers a promising solution for achieving energy-efficient and high-yield agriculture during the hot summer.关键词：radiative cooling;numerical simulation;spectral selectivity;infrared radiation1253|780|0发布时间：2024-07-18
- 摘要：Solar radiation is a significant factor affecting indoor air-conditioning loads. When sunlight directly reaches the human body, it impacts the heat exchange between the body and the surrounding environment, consequently affecting thermal sensation. The change in temperature of an environment in which a body is in thermal neutrality is related to the energy consumption of the air-conditioning system and human thermal comfort. In this study, a winter experiment was conducted in an artificial climate chamber using a solar radiation simulation device to control the intensity of the solar radiation. The subjects wore typical clothing and performed sitting and walking tasks (at speeds of 3.2 km/h and 5 km/h). Physiological parameters and thermal sensation questionnaires were analyzed to determine the heat exchange characteristics between the bodies and the surrounding environment under the combined effects of solar radiation and different activity levels. Furthermore, the displacement law of the thermal comfort zone was examined. The results showed that, compared with the case of solar radiation, as the activity level increased, the proportion of evaporation heat exchange increased, the proportions of convective heat exchange and radiant heat exchange decreased, the thermal comfort zone shifted downward, and the environmental temperature required to maintain a comfortable state in winter decreased. This study provides a reference for design parameters to improve the efficiency of air-conditioning systems.关键词：solar radiation;activity level;heat transfer characteristics;thermal comfort zone;thermal sensation1298|715|0发布时间：2024-07-18
- 摘要：A solar-driven closed-wheel desiccant air-conditioning system is proposed to efficiently recycle the sensible heat and latent heat of regenerative exhaust air to solve the problem of exhaust air energy waste in traditional open-wheel desiccant air-conditioning systems. The system was modeled using TRNSYS software. Simulations were conducted to assess the influence of the cold-water flow rate ratio and fresh-air ratio on system performance and dynamic behavior. Additionally, an experimental device was built to verify the accuracy of the simulation model. The maximum relative error between the simulation results and the experimental results was ±9.8%. The optimal cold-water flow rate ratio of the system was determined to be 1:5:4. During the entire refrigeration season (1st June to 30th September) in Guangzhou, the average power COPe was 2.4, the average thermal COPth was 2.1, the harvesting water capacity was 25.66 t, and the heat recovery capacity was 9.70 MW. Compared with the solar-driven open-wheel desiccant air-conditioning system, the average COPe and COPth of the solar-driven closed-wheel desiccant system increased by 42.1% and 69.2%, respectively, and the carbon dioxide emission was reduced by 29.3%.关键词：air conditioning;desiccant wheel;solar energy;heat recovery;TRNSYS simulation909|498|0发布时间：2024-07-18
- 摘要：A new system based on rotary dehumidification is proposed using evaporative supercooled water to create ice slurry. Rotary dehumidification is employed to reduce the steam partial pressure, generating supercooled water droplets outside heat transfer tubes. This design circumvents the high energy consumption associated with the traditional vacuum method. Additionally, when compared with the solution dehumidification method, this system is simple and has better dehumidification performance. A high degree of supercooling of the water droplets was realized, and the regeneration load of the desiccant wheel was supplemented by the condensation heat from the refrigeration system. A complete ice-making system was constructed, and component models for the desiccant wheel, carbon dioxide heat pump, and evaporative ice-making process were established. The feasibility and efficiency of the system were preliminarily verified by simulation, and the influence of the main operating parameters on the system performance was studied. Under optimal operating conditions, the coefficient of ice production performance for this new system exceeded that of the traditional supercooling water method by 25.9%, and the ice-making capacity in a single cycle increased by 4.3 times.关键词：evaporation;desiccant wheel;ice slurry;carbon dioxide heat pump;ice-production performance coefficient547|599|0发布时间：2024-07-18
- 摘要：To maintain a suitable working temperature range for power batteries and ensure their safe and efficient operation in various application scenarios, a cold plate and a submerged cooling system were designed for a standard box power-battery pack. The structure was optimized, and the cooling performance of the cold plate and the submerged cooling system was compared and examined. After structure optimization, the outlet pressure drop of the battery pack cooled by the cold plate was 30 Pa, with a maximum surface temperature of the battery at 31.65 ℃ and a maximum surface temperature difference of the battery being 6.51 ℃. The battery pack with immersion cooling was surrounded by a 2 mm electrical insulating fluid around the battery. The fluid filling capacity of the standard box was 10.93 L. The outlet pressure drop was 22 Pa. The maximum temperature of the battery surface was 28.49 ℃, and the maximum temperature difference on the battery surface was 2.39 ℃. Comparing the simulation and test results, the deviation for each data was within 2%, indicating high accuracy in the simulation model. The cooling effect of the optimized immersion cooling system was better than that of the original cold plate cooling system, and the inlet flow rate was reduced from 4 L/min to 2 L/min, which further reduced the pumping power of the working fluid. Furthermore, the maximum temperature difference on the battery surface was reduced by 4.12 ℃, enhancing temperature uniformity across the battery surface. This study shows that compared with cold plate cooling, immersion cooling has a more obvious effect on reducing the average surface temperature, maximum temperature, and surface temperature difference of a battery.关键词：power battery;cooling plate;immersion cooling;electrical insulating fluid;temperature uniformity623|605|0发布时间：2024-07-18
- 摘要：Based on the measured data from a typical ground-source heat pump air conditioning project in Wuxi, Jiangsu Province, with the primary objective of minimizing total energy consumption on the ground-source side, an equipment model for optimizing the operating conditions of the ground-source heat pump is constructed in this study. The optimal control strategy is compared with two traditional control strategies, and recommendations for further optimization are presented. The results showed that the optimal control strategy based on the load had a significantly better energy-saving effect than that of the constant-frequency control strategy. On typical test days in winter and summer, it achieved average energy savings of 28.43% and 21.21%, respectively, resulting in energy savings of 3.61% and 2.21%, respectively, when compared to the 5 ℃ temperature difference frequency conversion strategy. Moreover, it was found that the traditional constant temperature difference control strategy should elevate the temperature difference by 1–5 ℃ from the 5 ℃ baseline, to enhance energy savings when the load ratio exceeded 60%. These findings offer valuable guidance for optimizing the variable-flow strategy of ground-source side water systems in ground-source heat pumps.关键词：ground-source heat pump;buried pipe heat exchanger;variable flow;temperature difference between supply and return water;energy-saving ratio510|518|0发布时间：2024-07-18
- 摘要：Based on the cross-entropy loss function and stochastic gradient descent algorithm, a weight regression fault diagnosis model was established for seven common faults in a chiller. The weighted regression model was slightly more complex than the pure linear regression model; however, the fault diagnosis performance was clearly better, and the minimum performance was improved by 40.50% under different feature sets. When comparing the effects of feature sets from various sources in this model and introducing a new feature set, the accuracy reached 89.83%. Notably, the diagnostic accuracy for local faults exceeded 98%. The explicit model for chiller fault diagnosis is summarized, and by examining the parameter weights in the visual diagnosis model, it was determined that the oil supply pressure, oil supply temperature, and degree of subcooling were the most crucial parameters for diagnosing three types of system faults. Conversely, the refrigerant pressure in the condenser, temperature difference in the condenser, and water flow parameters between the evaporator and condenser were identified as the most important parameters for diagnosing four local faults.关键词：chiller;fault diagnosis;explicit model;cross entropy;stochastic gradient descent547|509|0发布时间：2024-07-18
- 摘要：To examine the influence of different parameters of a 10 kW refrigeration unit on the performance of a refrigerated vehicle, the capacity, coefficient of performance (COP), and pressure performance of the circulation system of a refrigeration unit were tested using experimental and simulation methods. Additionally, changes were made to the refrigerant charge, degree of superheating, and refrigerant type to conduct experimental and simulation studies. The results showed that the capacity and COP of the refrigeration unit exhibited different trends with changes in the refrigerant charge and superheat. The cooling capacity and COP errors between simulation and experiment were 6.4% and 8.5%, respectively, and the error of all results was within 10%. It was confirmed that the performance variation in the refrigeration unit was more sensitive to the variation in the degree of superheating than to the refrigerant charge. The best capacity and COP were achieved when the degree of superheat was 4 ℃ and the refrigerant charge was 7.4 kg. Furthermore, through numerical simulation, it was determined that the COP performance of the refrigerant R449A, used in the refrigeration cycle system, was approximately 4% higher than that of R404A. It was confirmed that the refrigerant R449A can be used instead of R404A.关键词：refrigerated vehicle;refrigeration unit;cooling capacity;degree of superheat;COP;R449A583|563|0发布时间：2024-07-18
- 摘要：Stirling cryocoolers have the advantages of fewer moving parts, oil-free, single-phase heat transfer, a large refrigeration temperature range, convenient and adjustable refrigeration capacity, and high refrigeration efficiency. Therefore, they have broad application prospects in commercial and domestic refrigeration systems. To meet the demands of low-temperature refrigerators, this study developed a multi-temperature zone refrigerator with a vapor compression refrigeration system and a Stirling cryocooler. The performance of the Stirling cryocooler was tested. The designs of the heat dissipation and cooling conduction structures were optimized, and the refrigerator’s overall performance was examined. Moreover, the influences of input power and ambient temperature on the performance of the Stirling cryocooler were investigated. The results showed that the cooling output and coefficient of performance (COP) of the Stirling cryocooler increased with an increase in the cold-end temperature, and increasing the input power provided a higher cooling capacity but decreased the COP. Under an ambient temperature of 43 °C, the cooling capacity of the Stirling cryocooler was 28.97 W with a COP of 0.37 when the cold-end temperature was -60 °C. Heat transfer structures at the cold and hot ends of the Stirling cryocooler based on heat-pipe technology were also proposed, and the simulation showed that the proposed structures for heat dissipation and cooling conduction met the system design requirements. Finally, an experimental test of refrigerator performance was conducted. A no-load experiment at an ambient temperature of 32 °C showed that the pull-down time of the low-temperature room was 28% shorter than that of the freezer room. Under an ambient temperature of 43 °C, the low-temperature room reached an average temperature of -64.5 °C, and the power consumptions of the Stirling cryocooler and refrigerator were 2.33 kW?h/d and 4.13 kW?h/d, respectively.关键词：Stirling cryocooler;refrigerator;low temperature;power consumption600|784|0发布时间：2024-07-18
- 摘要：Temperature failure at the end of cold-chain transportation is common. Based on phase-change technology, a cold energy storage box suited for the end of cold-chain transport below -18 ℃ was developed. The temperature field characteristics and cold-storage performance of the cold-storage box under the influence of the environmental temperature, the thickness of the vacuum insulated panel (VIP), relative positions of the phase-change material (PCM) and VIP, type of PCM, and other parameters were examined. The study revealed that the cold-storage box had strong immunity to variations in the ambient temperature, and the maximum effective cold preservation time can be extended to 29.26 h when assembling the vacuum insulated panels. When the VIPs were placed on the outer layer of the corresponding PCM panels, the effective cold preservation period increased by 54.3%. Four types of organic PCMs with different phase-change temperatures were examined for use in cold-storage boxes. It was determined that 2-octanone with a phase transition temperature of -21.55 ℃ had the optimal performance in terms of cold preservation time, uniformity coefficient, and power consumption. The bottom plate had the greatest impact on the overall cold-storage capacity as evidenced by its 0.454 individual plate factor.关键词：cold storage unit;cold thermal energy storage;phase-change material;coefficient of performance603|602|0发布时间：2024-07-18
- 摘要：In recent years, hydrogels have exhibited considerable advantages in cell and organoids culture as well as cryopreservation, particularly in cell cryopreservation. In this study, the spray method was selected, and ferric iron and calcium were used as cross-linking agents. The hydrogels were prepared using a low-cost and readily available airbrush. Subsequently, calcium alginate and iron alginate hydrogels were prepared, and HEK293T cells and HepG2 cells were encapsulated using this method. The study also investigated the impact of cross-linking solutions on cell viability during encapsulation, revealing that longer crosslinking times led to greater cell damage. Additionally, it was observed that crosslinking with sodium alginate solution reduced cell damage in the crosslinking solution. Furthermore, hydrogels crosslinked with CaCl2 (0.2 mol/L) using sodium alginate solution at various mass concentrations (1%, 1.5%, and 3%) were prepared. HEK293T cells were encapsulated and cultured for 7 d under these conditions, and successful cell culture was observed across all concentrations. Finally, the viability of cell cryopreservation after encapsulation was examined. The results showed that the viability of HEK293T and HepG2 cells, under the precondition of using two different volumetric concentrations of dimethyl sulfoxide as protective agents, was significantly higher than that of the unencapsulated group. Specifically, for HEK293T cells before encapsulation, cell viability was 33.16% ± 2.70% (10% DMSO) and 16.75% ± 2.3% (5% DMSO). After encapsulation, cell viability increased to 76.51% ± 5.32% (10% DMSO) and 60.86% ± 2.41% (5% DMSO). Similarly, for HepG2 cells, cell viability increased from 48.93% ± 3.06% (10% DMSO) and 36.22% ± 2.54% (5% DMSO) to 78.79% ± 4.43% (10% DMSO) and 64.64% ± 3.13% (5% DMSO) after encapsulation. Moreover, when using ethylene glycol (1 mol/L) + propylene glycol (1.5 mol/L) + trehalose (1 mol/L) as a protective agent, the viability of HEK293T cells after vitrification increased from 33.5% ± 0.8% to 79% ± 3.76% after encapsulation. These results strongly indicate that encapsulated cells exhibit significantly higher viability after cryopreservation compared to unencapsulated cells, emphasizing the protective capacity of ionic cross-linked alginate hydrogels during cryopreservation.关键词：alginate;hydrogel;cell;vitrification;cryopreservation575|546|0发布时间：2024-07-18
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