最新刊期
卷 45 ， 期 6 ， 2024
- 摘要：Sub-Kelvin refrigeration technology (<1 K) is a critical supporting technology for cutting-edge physics research and quantum technology. Currently, it mainly includes adsorption refrigeration, dilution refrigeration, and adiabatic demagnetization refrigeration. Adsorption refrigeration is limited by its evaporative cooling principle, with the lowest temperature higher than 200 mK. Dilution refrigeration and adiabatic demagnetization refrigeration can achieve temperatures below 10 mK. The former can provide a larger continuous cooling capacity between 20 mK and 100 mK, while the latter, based on solid-state refrigeration, can operate efficiently under a microgravity environment. This article briefly introduces the principles, development history, and technical prospects of these three technologies.关键词：sub-Kelvin refrigeration technology;adsorption;dilution;adiabatic demagnetization226|66|0发布时间：2024-12-13
- 摘要：Electrocaloric cooling is a solid-state cooling technique based on the manipulation of electric fields. This technology utilizes the temperature variations induced in electrocaloric materials under the influence of an electric field to achieve refrigeration effects. Owing to its advantages, such as zero direct carbon emissions and high efficiency, it has garnered widespread attention, particularly in the context of global warming and carbon reduction objectives. Since the discovery of the giant electrocaloric effect in 2006, electrocaloric cooling technology has undergone rapid development, particularly in improvements in electrocaloric materials and devices. This article provides an analysis and discussion focused on electrocaloric cooling device research, electrocaloric polymer nanocomposite materials, and high-entropy optimization of electrocaloric materials. It commences by introducing the fundamental principles of the electrocaloric effect and current advancements in active regenerative electrocaloriccooling devices. Subsequently, it summarizes the progress in electrocaloric polymer nanocomposite materials, along with strategies for high-entropy optimization and interface polarization enhancement. Finally, it provides insights into future research directions for electrocaloric cooling within the fields of working substances and systems.关键词：electrocaloric cooling technology;composite materials;flexible refrigeration devices;thermodynamic cycles;zero-carbon refrigeration and heat pumps149|33|0发布时间：2024-12-13
- 摘要：The proportion of high-heat-flux servers has gradually increased with the increasing number and scale of data centers. Traditional air cooling cannot handle the heat dissipation and energy saving needs. In this regard, the liquid cooling technology with a large latent heat and high heat transfer coefficient has emerged. Research on liquid cooling systems primarily focuses on system efficiency enhancement, system comparison, and overall thermal management. Among them, the working fluid, as an important medium for heat exchange, is crucial for the liquid system performance. In this paper, selection principles of phase-change working fluid are proposed. The investigations and application progress of six types of phase-change working fluid (natural working medium, HFCs, HFOs, PFCs, HFEs, mixed working medium) are reviewed, summarized, and analyzed according to the contact modes (direct and indirect). The prospects for future research on phase-change liquid cooling fluids are presented.关键词：data center;heat flux;liquid cooling;phase-change working fluid103|53|0发布时间：2024-12-13
- 摘要：Absorption thermal storage, as a type of thermal storage technology with a high energy storage density and long thermal storage period, is the key to storing solar thermal energy and solving the mismatch between solar thermal energy supply and demand during different seasons. Traditional absorption systems avoid crystallization by limiting the solution concentration, which assures reliability and safety but causes a limited energy storage density of the system. In this study, a closed three-phase absorption heat storage system is designed and tested. Through filtering and high-level inlet by the filters, crystal fusion by the heating rods, and flushing of the solution circulation lines, the system can operate normally after the solution crystallization, increase the concentration glide, and improve the energy storage density. Testing shows that the energy storage density of the system can reach 220 kW·h/m3 upon heat supply, which is an 114% increase compared to traditional two-phase absorption heat storage systems. Hence, the three-phase absorption heat storage technology with the utilization of crystallization is expected to realize high-density long-term solar energy thermal storage.关键词：Absorption thermal storage;energy storage density;Crystallization;prototype design;solar energy81|37|0发布时间：2024-12-13
- 摘要：The use of high-temperature heat pumps to recover industrial waste heat has a high potential for energy conservation. High-temperature heat pumps require high critical temperatures, and the majority of the available working fluids are dry. However, when the dry working fluid is compressed from the saturated vapor phase, the compression process enters the two-phase region, resulting in a risk of liquid slugging that is detrimental to the operation of the compressor and high-temperature heat pump. Two improved vapor injection heat pump cycles (Cycle A and Cycle B) using isohexane, R1336mzz (Z), and R1233zd (E) as working fluids are proposed. The effects of compressor isentropic efficiency, evaporating temperature, and condensing temperature on the minimum superheating degree and heat pump performance are analyzed. The results indicate that, for cycle B, the evaporation temperature increases from 50 ℃ to 80 ℃. For R1336mzz(Z), the maximum COP(coefficient of performance) can be increased by 2.56%, and the maximum volumetric heating capacity (VHC) can be increased by 3.18%. For R1233zd(E), the maximum COP can be increased by 0.44%, and the maximum VHC can be increased by 0.54%. Cycle A has good adaptability to the isentropic efficiency. For cycle B, when the isentropic efficiency is higher than 0.6, isohexane is not suitable as a working fluid. When the isentropic efficiency is higher than 0.95, R1336mzz (Z) is also not suitable.关键词：high-temperature heat pump;dry working fluid;vapor injection;minimum superheating degree93|46|0发布时间：2024-12-13
- 摘要：Pulse tube refrigerators are widely used in space detection and quantum computing due to their low vibration output at the cold end and high reliability. Dual-temperature-zone pulse tube refrigerators can simultaneously achieve dual cooling temperatures. However, in the actual application scenario, the cooling performance is largely affected by the ambient temperature zones, which limits applications in complex environments. In this study, based on the dual-temperature-zone pulse tube refrigerator with an active acoustic power recovery phase shifter, the influence characteristics of the ambient temperature on the gas spring of the phase shifter, inlet acoustic power of the cold finger, and dual-temperature cooling capacities are investigated. Unlike the conventional piston-type phase shifter, which has only an expansion chamber, the acoustic power recovery phase shifter has an acoustic power recovery chamber at the back end of the piston, which can recover the expansion acoustic power from the hot end of the pulse tube. Compared to the traditional piston-type phase regulator containing only an expansion chamber, when the ambient temperature increases from 253 K to 333 K, the maximum change in the total gas spring stiffness of the piston in the acoustic power recovery phase shifter is only 2 630 kg/s2, and the level of impact could be reduced by 86.1%, which shows that the acoustic power recovery phase shifter has a higher adaptability to the ambient temperature. The experiment shows active control of cooling capacities in dual-temperature zones by adjusting the piston motion of the phase shifter at ambient temperatures of 253 K and 333 K.关键词：pulse tube refrigerator;Acoustic power recovery;active phase shifting;ambient temperature;cryogenic technology48|35|0发布时间：2024-12-13
- 摘要：A large-scale scientific facility uses constant-temperature air conditioning (CTAC) to control the air temperature fluctuation at an ultrahigh precision, i.e., ≤±0.1 ℃, which implies that the temperature of the chiller water must also be maintained at an ultrahigh precision level. Traditional CTACs depend on electric heating to maintain the chilled water temperature. However, such methods usually fail to address the issue of high-frequency oscillations and typically are not applied to ultrahigh-precision control. In this study, by conducting a reduced-scale experiment, we first validated the feasibility of two water chillers, one using a plate heat exchanger and another using a mixed water pump, to provide chilled water at an ultrahigh precision. Simulations using Modelica models based on these two approaches were established and experimentally verified. Finally, the steady-state and dynamic performances of these two systems were compared. Both approaches can achieve ±0.1 ℃ temperature fluctuation control when the hardware meets specific criteria, with the plate heat exchanger approach exhibiting superior steady-state performance. Under both schemes the root mean square error (RMSE) for the entire time period is below 0.1 ℃. The settling times for the plate heat exchanger and mixed water pump approaches are 5 000 s and 600 s, respectively. The mixed water pump approach exhibits better dynamic performance. Both plate heat exchanger and mixed water pump approaches are capable of actively dampening high-frequency oscillations in the water supply temperature, with damping coefficients of 0.07 and 0.4, respectively.关键词：constant temperature air conditioning;chilled water system;Automatic control;system simulation52|42|0发布时间：2024-12-13
- 摘要：The power usage limit becomes lower with the green development of data centers. The small liquid cooling device is emerging as a new cooling option for small data centers with high energy density, which helps recover the waste heat. In this paper, the energy efficiency characteristics of three types of water-source heat pump systems under different surplus heat conditions are compared and analyzed in the surplus heat load range of small data centers. The energy efficiency of the water-source heat pump system is distributed at 5-7, 5-6, and 4.5-6.5 on the source side, transmission and distribution side, and user side, respectively. When the user-side heat load is retained at 0 kW to 1 750 kW and 2 500 kW to 3 200 kW, the energy efficiency of the source-side enhanced water-source heat pump system is highest. When the user-side heating load demand is 1 750 kW to 25 00 kW, the energy efficiency of the source-side enhanced water-source heat pump system is near that of the transmission and distribution-side enhanced water-source heat pump system. Finally, the coupling matching formula QN=kQS is obtained between the user-side heat load demand and data center surplus heat load, in which k ranges from 1.196 2 to 1.364 2.关键词：data center;waste heat utilization;water-source heat pump;energy efficiency;coupling formula59|42|0发布时间：2024-12-13
- 摘要：To address the issues of the high-energy consumption of traditional air conditioners in communication cabinets, disordered airflow organization in cabinets, and poor temperature control effect of the baseband unit (BBU), this study integrates air-conditioning with heat pipes for communication cabinets using a temperature control system with heat pipe cooling as the primary cold source and vapor compression air conditioners as the supplementary cold source. Floor ventilation with air return from the ceiling is adopted with high wind speed and internal circulation. The unit was applied to a communication base station in Zhengzhou, and field testing results showed that under the short-term high-temperature condition during the transition season, the average working temperature of the BBU in operation mode 1 was 38.2 ℃, and the maximum outlet temperature was 46.5 ℃. Moreover, under the normal working conditions of the transition season, the average working temperature of the BBU regulated by operating mode 2 was 29.5 ℃, and the maximum air temperature was 41.3 ℃, which met the temperature control requirements of relevant standards and ensured the safe operation of BBU. Compared with those of the traditional air conditioner of the communication cabinet, the compressor operation ratio of the air-conditioning heat pipe integrated equipment in operation modes 1 and 2 was 24.9% and 0; the energy saving rate was 57.3% and 71.9%; the power usage efficiency (PUE) was 1.43 and 1.19, respectively. The comprehensive energy saving in the transition season was 71.3%, and the PUE was 1.20.关键词：Communication cabinet;heat pipe;air conditioning;energy saving76|51|0发布时间：2024-12-13
- 摘要：R516A is one of the new substitutes for R134a refrigerant in water-cooled chillers. The COP (coefficient of performance) and discharge temperatures of R516A and R134a are compared through a single-stage vapor compression cycle. Under nominal and variable operating conditions, the performances of a small water-cooled chiller charged with R134a and R516A are tested and compared. The cost changes of replacing R134a with R516A in the water-cooled chiller are discussed. The conclusions indicate that, in the theoretical cycle, the COP of R516A is 1.5% lower than that of R134a, and the discharge temperature is 4.9-6.0 ℃ lower than that of R134a. Under nominal operating conditions, there is a certain performance gap between the R516A chiller and the R134a chiller, with a COP difference of 4.9%-7.2%. Under variable operating conditions, the performance of the R516A chiller is basically equivalent to that of the R134a chiller, and the COP gap is reduced to 0.5%-2.3%. Owing to the mild flammability of R516A, the cost of the R516A chiller is 10%-15% higher than that of the R134a chiller.关键词：performance comparison;R516A;water-cooled chiller;refrigerant replacement52|39|0发布时间：2024-12-13
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COSMO-RS Method for Screening Absorption Refrigerant Working Pairs Using Ionic Liquids as Absorbents
摘要：In this work, absorption refrigerant working pairs consisting of four HFO refrigerants, R1234ze(E), R1234yf, R1233zd, and R1243zf, and ionic liquids were studied. The different ionic liquids contained 20 cations and 16 anions. The Henry′s law constant and solubility data of working pairs were simulated by the COSMO-RS method. The differences in Henry′s law constant and solubility between the different working pairs are discussed from the perspective of polarized charge density on the molecular surface. The polarized surface charge density curve of the R1234ze(E) refrigerant has a peak in the negative region. It is compatible with anions with a peak in the positive region. However, the compatibility with the peak in the negative region is poor. Ionic liquids with low Henry′s law constants and high solubilities were screened out when they were paired with HFO refrigerants.关键词：COSMO-RS;ionic liquids;HFO refrigerants;absorption refrigeration31|37|0发布时间：2024-12-13 - 摘要：The vehicle-mounted cold storage plate is an important part of a refrigerated vehicle. Charging time reduction of the cold storage plate has an important role in improving the efficiency of cold chain logistics. A heat pipe integrated cold storage plate was proposed, and the cooling and freezing processes of the cold storage plate were simulated and studied. The reliability of the theoretical model was verified through experiments. The influences of the heat pipe diameter, pipe spacing, refrigerant flow rate in the channel, and Reynolds number on the cooling performance of the cold storage plate were studied using the orthogonal experimental method. Under the condition of a conventional cold storage plate with a single-layer thickness of approximately 50 mm, a pipe diameter of 7 mm, pipe spacing of 39 mm, refrigerant flow rate of 1.2 m/s in the channel, and Reynolds number of 3.89 (optimal parameter), the average freezing time and complete freezing time are 45 min and 78 min, respectively. Compared to the results reported in the literature, the cooling time of the heat pipe integrated cold storage plate under the optimal parameters is significantly reduced.关键词：Heat pipe heat transfer;Cold storage plate;Freezing performance;Orthogonal experiments34|27|0发布时间：2024-12-13
- 摘要：Gravity heat pipes garner attention owing to their high thermal conductivities. In this study, the variable saturation temperature and variable physical properties of the working medium were added to the VOF model. The start-up process of a U-shaped gravity heat pipe was studied, and the evolutions of pressure and temperature during the start-up process were thoroughly discussed. The improved model could be better validated by the experimental data. The average deviation was only 5 K, which shows a high accuracy. Based on the simulation results, three stages can be divided: initial, equilibrium, and variation stages. In the initial stage, the temperature increase for the adiabatic and condensation section was hysteretic compared to that of the evaporation section, and small fluctuations of pressure difference between the evaporation and condensation sections could be observed (the average fluctuation was 81.5 Pa). In the equilibrium stage, the temperature increase for the condensation section was obtained. There were more obvious fluctuations in the pressure difference between the evaporation and condensation sections (the average fluctuation was 230.2 Pa), in which geyser boiling could be observed. In the variation stage, both temperature and pressure exhibited fluctuations. The pressure fluctuation was more obvious.关键词：gravity heat pipe;VOF model;start-up process;pressure;temperature;thermal conductivity45|56|0发布时间：2024-12-13
- 摘要：The two-phase distribution uniformity of a refrigerant is an important factor affecting the heat exchanger performance. To address the poor uniformity of the liquid phase in the vertical header of the microchannel heat exchanger, a design scheme of a two-stage distribution header is proposed. The gas and liquid flow ratios of each branch under different dryness and total mass flow rates are compared by two-phase refrigerant distribution testing. The top branch of the empty header does not have a sufficient amount of liquid, while the bottom has excess liquid. The relative standard deviation (RSD) of the liquid phase for each branch is larger than 95%. The multiflow header uses the bottom inlet cavity to distribute the liquid, and then the liquid flows upward in the multiflow channel and enters the annular cavity through the side outlet hole. The liquid RSD of each branch is larger than 60%. When the core flow-regulated cavity and top distribution cavity are added into the multiflow header, the distribution performance is satisfactory, with RSDs of liquid and gas phases below 5% and 15%, respectively.关键词：microchannel heat exchangers;Vertical header;refrigerant distribution;Two-phase55|39|0发布时间：2024-12-13
- 摘要：Under the background of "double carbon", heat pipe heat exchangers are widely used in fresh air systems to reduce the energy consumption of air conditioning systems in buildings. In this study, combined with the actual operating conditions of an air conditioning and fresh air integrated machine, a new type of high-efficiency energy recovery device based on a three-dimensional distorted tube is developed. The energy recovery effects of different parameters are calculated and simulated to determine the optimal parameters, and the indoor air distributions before and after the retrofit are simulated. During the summer season, the three-dimensional distorted tube with a pitch of 60 mm and a long axis to short axis ratio of 1.3 is used, along with a square opening for the air inlet and outlet of the energy recovery device, resulting in the highest energy recovery rate of 77.11%. Under the premise of achieving the same refrigeration effect, compared to the baseline air conditioners, remarkably, it saves nearly 35% of the power consumption. In addition, after the addition of the energy recovery device, the indoor temperature fluctuation becomes small, and the thermal comfort is improved.关键词：air-conditioning;energy recovery;heat transfer enhancement;fresh air;summer working condition35|34|0发布时间：2024-12-13
- 摘要：The central air conditioning system has been of interest for peak load regulation in the power grid due to its high energy consumption and overlapping with the peak load of the power grid. To study and explore the potential of peak load regulation in central air conditioning systems, a self-storage method for central air conditioning systems is proposed. This method achieves storage and release of cold energy by adjusting the chilled water temperature of the user-side pipeline network, transferring peak air conditioning energy consumption, and achieving the goal of peak shaving and valley filling. The central air conditioning system of a certain actual building is used as a research object. A model of the central air conditioning system is developed, and simulations are conducted to study the operating characteristics of the system under different air conditioning load rates and cold storage capacity. The peak shaving potential and operational economy of the building′s self-storage energy are evaluated. The energy efficiency ratio for a cold storage capacity of 100% at an air conditioning load ratio of 40% is 4.2, and 27 min are required. Under an air conditioning load ratio of 100%, cold storage capacity of 100%, and cooling end water temperature of 12 ℃, the peak shaving electricity consumption after 60 min of cooling is 745 kW·h, and the peak shaving ratio is 23.9%. The use of self-storage energy during a typical day during the cooling season with a maximum cooling load of 11 673 kW can reduce the peak electricity consumption of the air conditioning system by 3.9% and peak electricity consumption by 19.8%, resulting in a daily saving of 3.0% in the operating electricity cost of the air conditioning system.关键词：central air conditioning system;variable chilled water temperature operation;self energy storage;peak shaving of the power grid;peak shaving and valley filling56|33|0发布时间：2024-12-13
- 摘要：The regulation of the throttling device has an important impact on the performance of constant-temperature and humidity cabinets. Based on a constant-frequency refrigeration system, the effects of EEV (electronic expansion valve) opening from 10% to 30% on the evaporator superheat, compressor discharge temperature, evaporator fin temperature, and temperature and humidity in the cabinet under different target conditions were experimentally studied. When the opening of the electronic expansion valve is 15%-30%, the superheat (8-15 ℃) and discharge temperature can be guaranteed in safe and reasonable ranges. When the opening of the electronic expansion valve is below 20%, a bypass capillary tube is set for a safe compressor operation with liquid cooling in suction. Under the conditions of low temperature and humidity and high temperature and humidity, the larger opening reduces the temperature and humidity adjustment time by 10-20 min. Under the conditions of a low temperature and high humidity and a high temperature and low humidity, the larger opening causes energy consumption for additional humidity compensation or thermal compensation and prolongs the temperature and humidity adjustment time. Under different target conditions, the relative humidity and dry bulb temperature in the small opening (15%) cabinet are closer to the target temperature and humidity than those for the large opening (25%, 30%), and the temperature and humidity control accuracy is higher.关键词：constant temperature and humidity cabinet;electronic expansion valve;superheat;exhaust temperature49|29|0发布时间：2024-12-13
- 摘要：To reveal the evaporation characteristics of a defrosting retention droplet on a fin surface, the effects of droplet size, fin surface wettability, fin tilt angle, and heating temperature on the droplet evaporation process were studied by a visualization experiment. The experimental results show that the droplet evaporation modes on the bare fin surface are constant contact diameter and mixing modes, and that the pining phenomenon is obvious. Constant contact angle and mixing modes are observed on the hydrophobic fin surface, and there is no spiking phenomenon. Compared to the bare fin, the evaporation time of a droplet on the hydrophobic fin surface is longer. The evaporation time on the bare surface decreases with the increase in the tilt angle. A larger tilt angle leads to an earlier denailing phenomenon. When the initial volume of the droplet is the same, with the increase in heating temperature from 30 ℃ to 40 ℃, the evaporation time decreases by 60%. In addition, a larger initial volume of the droplet leads to a longer evaporation time, but the evaporation mode remains unchanged.关键词：air-source heat pump;fin;defrosting retention droplet;evaporation;pining phenomenon55|42|0发布时间：2024-12-13
- 摘要：An experimental system of an air-source heat pump with multiple outdoor units in parallel was designed and built. The outdoor units were defrosted in turn using hot subcooled liquid for defrosting. The heat pump heating performance variations in the course of frosting and defrosting under different outdoor temperature and humidity conditions were experimentally studied, and the heating performances of the hot liquid subcooling alternate defrosting system and hot gas bypass alternate defrosting system were compared and analyzed. The experimental results show that the hot liquid subcooling alternate defrosting can enable the heat pump to complete the defrosting under the condition of continuous heating and that the defrosting performance is good. When the outdoor air temperature is -10 ℃ and the relative humidity is 90%, the optimal time to start defrosting is 30 min. At this time, the system heating capacity decreases from 9.87 kW when there is no frost to 8.71 kW when the defrosting starts, and the heating COP decreases from 3.73 to 3.36. When the system operates defrosting under different humidity conditions, the minimum values of system heating capacity and heating COP can reach 5.42 kW and 2.28, respectively. Compared to the case of bypassing 20% of discharge gas for defrosting, the average heating capacity of hot liquid subcooling alternate defrosting is 13.8% higher, and the heating COPC is 10.1% higher.关键词：air-source heat pump;hot liquid defrosting;hot gas defrosting;heating performance49|33|0发布时间：2024-12-13
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