最新刊期
- 摘要：Refrigerant leakage from a refrigeration system not only degrades the system performance and increases energy consumption but also aggravates environmental hazards and safety risks because of the high global warming potential or flammability of many refrigerants. Therefore， fast and accurate methods are required to detect and rectify refrigerant leaks. This study focused on a domestic air-conditioning refrigeration system with a cooling capacity of 3.5 kW. Using simulation methods， the dynamic evolution laws of the key node parameters of each component and the system performance parameters under different leakage rates were analyzed quantitatively. Based on the findings， a refrigerant inventory prediction model was developed for the key components. This model， integrated with the operational data， provides a new leakage detection and diagnosis method based on system modeling. This method aims to evaluate the severity of leakage using a small amount of leakage data. The developed refrigerant charge inventory prediction equation maintains the prediction error within ±5% when the leakage rate is below 12%.关键词：refrigerant leakage;refrigerant inventory;refrigeration system;leakage detection7|22|0更新时间：2026-05-06
- 摘要：An experimental setup that uses R290 as the working fluid for the dedicated mechanical subcooling of a transcritical CO₂ heat pump system （DMS） was developed and evaluated in this study. The results were compared with those of the conventional baseline CO2 heat pump system （base）. The results revealed that there is an optimal discharge pressure and subcooling degree for the system. Under the operating conditions of an evaporation temperature of 5 ℃ and supply/return water temperature of 50/30 ℃， the DMS system achieved the maximum coefficient of performance（COP） of 3.89， with the corresponding optimal discharge pressure and subcooling degree being 8.4 MPa and 17.3 ℃， respectively. With an increase in the supply/return water temperature， the maximum COP values of both the DMS and base systems exhibited a gradually decreasing trend. Further， the relative COP improvement rate of the DMS system with respect to the base system increased progressively， and the corresponding optimal discharge pressure increased gradually for both systems. The COP of the DMS system remained consistently higher than that of the base system， whereas the optimal discharge pressure was consistently lower than that of the base system. As the supply/return water temperature was increased from 50/30 ℃ to 58/38 ℃， the COP improvement rate increased from 9.6% to 16.7%. Additionally， the power consumption ratio of the R290 compressor to that of the CO2 compressor exhibited an increasing trend， rising from 21.0% to 27.7%. This study provides an experimental reference for enhancing the energy efficiency of CO2 heat pump systems.关键词：transcritical CO2;heat pump;Dedicated mechanical subcooling;R29010|13|0更新时间：2026-05-06
- 摘要：The drying of agricultural products is a core aspect of post-harvest agricultural processing. Traditional drying techniques suffer from certain limitations， such as a low efficiency， high energy consumption， and poor quality， which make them difficult to adapt to the needs of green agricultural development and the "dual carbon" goals. Air-source heat pump drying technology， which recovers waste heat through the reverse Carnot cycle， offers advantages such as a high energy utilization efficiency， precise control over temperature and humidity， and superior product quality， which render it an ideal alternative to traditional drying methods. This article outlines the latest research progress of air-source heat pumps in the field of agricultural product drying， focusing on analyzing research outcomes in terms of the operating principles of the heat pump drying system， system structure optimization， integrated multi-technology drying， low-GWP（Global Warming Potential） refrigerant substitution， and intelligent operational control strategies. The aim is to provide a reference for the large-scale promotion and application of this technology.关键词：air-source heat pump;drying;multi-technology integration;agricultural products7|22|0更新时间：2026-05-06
- 摘要：Accurately balancing numerical stability and resolution remains a major challenge in compressible multiphase flows where shocks， contact discontinuities， and phase interfaces coexist. To address this issue， a nonlinear local entropy-viscosity-based adaptive interface-capturing algorithm is proposed. By constructing a generalized entropy function that incorporates the physical characteristics of phase interfaces and coupling it with a multi-channel discontinuity sensing mechanism， the proposed method achieves unified identification and classification of shocks， contact discontinuities， and phase interfaces. Furthermore， a nonlinear adaptive allocation strategy of local entropy viscosity is introduced， in conjunction with directional interface compression， an energy-consistent surface tension-phase change coupling model， and a dynamic adaptive parameter adjustment technique. This framework significantly enhances interface resolution while maintaining numerical robustness. A transcritical CO2 ejector flow is selected as a representative test case， in which numerical simulations involving phase change， shock/interface interactions， and nonequilibrium thermodynamic processes are performed. The results demonstrate that the proposed algorithm can clearly capture multiscale flow structures， with the interface thickness consistently maintained within 2-3 grid cells. The mass and energy conservation errors are both below 1%， indicating superior accuracy and reliability in complex multiphase flow fields characterized by strong gradients and multi-physics coupling. The proposed method therefore provides a generally applicable high-resolution numerical tool for multiphase flow simulations in practical engineering applications.关键词：compressible multiphase flow;computational fluid dynamics;interface capturing;entropy viscosity;ejector5|21|0更新时间：2026-05-06
- 摘要：In this study， potassium aluminum sulfate dodecahydrate （KAl（SO4）2·12H2O， PASD） was selected as the thermal storage material to achieve efficient thermal storage in medium-to-low temperature ranges. To overcome its drawbacks， such as its high phase transition temperature， significant supercooling， and poor thermal conductivity， a synergistic modification strategy of "eutectic modification-nucleation temperature adjustment-thermal conductivity enhancement" was employed to successfully obtain a high-performance composite phase-change material. Seven potential eutectic components were screened， and potassium nitrate （KNO3） was found to form a stable eutectic system with PASD. At a KNO3 mass fraction of 16%， the phase transition temperature decreased from 92.5 to 77.4 ℃， whereas the latent heat value remained at 248.9 J/g， and the supercooling was reduced to 6.03 ℃. Mechanistic studies revealed that the introduction of K⁺ effectively lowered the energy barrier for crystal melting by weakening the hydration of ［Al（H₂O）₆］³⁺ complex ions. Furthermore， the addition of magnesium sulfate heptahydrate （MSH） at 2% mass fraction as a lattice-matched nucleating agent induced heterogeneous nucleation owing to the similar orthorhombic crystal structures of MSH and PASD， nearly eliminating supercooling （i.e.， supercooling approached 0 ℃） and fine-tuning the phase transition temperature to 75.8 ℃. Finally， 200-mesh graphite powder （GP200） was used at 5% mass fraction as a thermal conductivity-enhancing phase to construct an efficient thermal network， increasing the thermal conductivity of the composite to 1.215 W/（m·K）， achieving 217% improvement over that of the base material， while maintaining a high latent heat of 219.0 J/g. This study provides a theoretical basis for the modification and preparation of high-performance hydrated inorganic salt-based phase-change materials， demonstrating their broad application prospects in solar thermal utilization and industrial waste heat recovery.关键词：potassium aluminum sulfate dodecahydrate;eutectic phase change material;inhibited subcooling;heat conduction enhancement;thermal energy storage7|17|0更新时间：2026-05-06
- 摘要：ObjectiveTo address the demand for high-efficiency heat dissipation in railway transportation and aerospace equipment under variable gravity environments， we systematically investigated the flow boiling heat transfer characteristics of water-glycol mixtures in microchannels and developed data-driven predictive models. Although microchannel flow boiling offers a compact cooling solution， its characteristics under variable gravity are not well understood， and traditional empirical correlations lack prediction accuracy. In this study， we aimed to fill this gap and provide a theoretical basis for optimizing cooling systems for both railway and aerospace applications.MethodsBoth experimental and machine-learning approaches were employed to evaluate flow boiling heat transfer performance. A variable gravity experimental platform based on a centrifugal rotating table was established， capable of simulating gravity environments from 1.00g to 3.16g. The experimental system featured closed-loop circulation with a 200 mm-long， 2 mm-inner-diameter copper microchannel test section. Experiments were conducted across mass fluxes of 50-500 kg/（m2·s）， heat fluxes of 100-800 kW/m2， system pressures of 0.1-0.3 MPa， and inlet subcoolings of 10-30 ℃. T-type thermocouples with ±0.1 ℃ accuracy were used for temperature measurements， while pressure transducers and differential pressure sensors monitored system pressures. Three machine learning algorithms—Random Forest （RF）， Support Vector Machine （SVM）， and Extreme Gradient Boosting （XGBoost）—were developed using 80% training and 20% testing data splits with 5-fold cross-validation for hyperparameter optimization.Results and DiscussionsThe results demonstrate significant gravity-induced enhancement of flow boiling heat transfer. As gravity increased from 1.00g to 3.16g， the heat transfer coefficient （HTC） improved by 60%-80%， while the critical heat flux （CHF） increased by 20%-35%. In the region of low vapor quality （x<0.3）， gravity enhancement reduced bubble departure diameter according to the relationship Db ∝ g-0.5， leading to increased departure frequency and enhanced microlayer evaporation. In the medium quality region （0.3<x<0.7）， gravity intensification resulted in thinner and more uniform liquid films， with peak HTC values reaching 23 000 W/（m2·K） at 3.16g compared to 14 100 W/（m2·K） at 1.00g. In the high-quality region （x>0.7）， hypergravity delayed the onset from x=0.75 to x=0.8. A comparison with ten classical correlations showed that traditional models exhibit large prediction errors under variable gravity， with the best-performing Fang model achieving only a 9.6% mean absolute error （MAE）. In contrast， the XGBoost model achieves an MAE of 3.1% across all gravity conditions， with particularly superior performance at 3.16g （MAE=3.35%） compared to the Fang model （MAE=18.61%）.ConclusionsThis study confirms that gravity is a critical factor in flow boiling heat transfer， significantly enhancing both HTC and CHF through mechanisms such as bubble dynamic optimization and liquid film redistribution. The XGBoost machine-learning model demonstrates superior accuracy in predicting heat transfer performance under variable gravity compared to traditional methods. These findings provide a crucial theoretical basis for the optimal design of cooling systems for railway-vehicle-mounted aerospace airborne equipment that operate in complex gravitational environments.关键词：variable gravity environment;micro-channels;boiling heat transfer;critical heat flux;machine learning29|67|0更新时间：2026-04-28
- 摘要：We investigated the quality changes of ready-to-eat pomegranate arils during storage at 5， 15， 25， and 35 ℃. The kinetic parameters of each quality index were fitted using quality degradation kinetic equations， and a shelf life prediction model was developed by integrating the fitting results with the Arrhenius equation. The results demonstrated that the anthocyanin content exhibited an optimal fit with the first-order kinetic model， exhibiting the highest fitting accuracy. A first-order kinetic model with anthocyanin content as the characteristic index was subsequently combined with the Arrhenius equation to construct a shelf-life prediction model. Validation experiments revealed that the mean absolute error between the predicted and actual values was less than 10%， confirming the high accuracy and reliability of the model. This model can effectively predict the shelf life of pomegranate arils over the temperature range of 5-35 ℃， providing theoretical support and methodological guidance for quality maintenance during the circulation and marketing of the product.关键词：ready-to-eat;pomegranate arils;shelf temperatures;shelf life prediction model11|53|0更新时间：2026-04-27
- 摘要：Against the backdrop of the "dual carbon" goals， in this study we aimed to achieve efficient recovery and reuse of low-grade waste heat generated by high-voltage direct current （HVDC） converter valves. Using R515b as the system refrigerant， thermodynamic models and economic models were established. Through experimental testing， the thermodynamic performance variations and economic analysis of evaporative compression heat pumps versus ejector compression heat pumps were compared at different evaporation and condensation temperatures. The results indicate that the COP of the injection compression heat pump was， on average， 8.75% higher than that of the vapor compression heat pump， with the compressor power consumption reduced by 4.78% and the system heating capacity increased by 3.50%. The total friction losses in the injection compression heat pump were primarily concentrated in the condenser and injector， accounting for 32.6% and 27%， respectively. Economically， the net present value of the injection compression heat pump system increased by approximately 10.9% compared to traditional systems， with a dynamic payback period of 4.08 years. The results show that injection compression heat pumps effectively recover expansion losses， enhance the system energy efficiency and economic performance， and provide an efficient and economical solution for recovering waste heat from inverter valves.关键词：converter valve;waste heat utilization;ejector compression heat pump;heating system14|55|0更新时间：2026-04-27
- 摘要：Condensers， a critical component in refrigeration and heat pump systems， require rapid and accurate performance prediction， which is crucial for system selection and design optimization. Conventional condenser performance evaluation methods， such as computational fluid dynamics simulations and experimental testing， suffer from computational inefficiency and prolonged cycle times. To address their technical limitations， this study developed a synergistic optimization framework integrating genetic algorithms with the simulation modes of the condenser. This approach refined the heat transfer correlations in the single-phase region to enhance the predictive accuracy of the model. The results show that under this optimization method， the average absolute errors in the degree of under subcooling for the plate and finned tube condensers are 1.83 ℃ and 2.23 ℃， respectively. In addition， validation results based on 32 sets of experimental data covering a wide range of operating conditions showed that the average relative errors for both the heat transfer capacity and outlet temperature of the refrigerant were maintained within 5%. This method improved the prediction accuracy of simulation models to some extent， providing effective technical support for the rapid simulation and engineering applications of refrigeration systems.关键词：condenser;thermodynamic model;genetic algorithm;fast prediction12|142|0更新时间：2026-04-24
- 摘要：To investigate the heating performance characteristics of R290 refrigerants in electric vehicle compressors under low-temperature conditions， a comprehensive performance testing system for electric vehicle air-conditioning compressors was established. The variation patterns of power consumption， heating capacity， isentropic/volumetric efficiency， COP， oil circulation rate， and discharge temperature of R290 compressors under low-temperature operating conditions were investigated. The results demonstrate that power consumption and heating capacity increase linearly with rotational speed， with heating capacity decreasing by 13.6%-15.3% for every 5 ℃ reduction in evaporation temperature； isentropic efficiency decreases by 6.2%-9.3% with increasing speed and is more significantly affected by evaporation temperature than by condensing temperature； volumetric efficiency initially increases and then decreases， dropping by 3.5%-4.9% for every 10 ℃ decrease in evaporation temperature and only 0.4%-1.2% for every 10 ℃ increase in condensing temperature； COP decreases with rotational speed， with reductions of approximately 0.15-0.40 and 0.25-0.45 every 5 ℃ decrease in evaporation temperature and every 10 ℃ increase in condensing temperature， respectively； oil circulation rate increases monotonically with speed， being significantly influenced by evaporation temperature while being less affected by condensing temperature； and discharge temperature rises with increasing speed， although the temperature rise induced by speed variation is considerably smaller than that caused by thermal operating condition changes. In this study， we demonstrate that R290 compressors maintain satisfactory heating performance under low-temperature conditions， while validating the feasibility of R290 as an environmentally friendly refrigerant for electric-vehicle air conditioning systems.关键词：R290;compressor;worst cold case;heating performance9|66|0更新时间：2026-04-24
- 摘要：In this study， we analyzed the flow-boiling heat transfer behavior of a copper microchannel heat sink with a high geometric aspect ratio of 18. An experimental platform was established to systematically evaluate the thermohydraulic response and heat dissipation capability under two heating regimes： continuous and intermittent. In the continuous mode with a heat flux of 300 W/cm² and in the intermittent mode with 750 W/cm² for 90 s， the heat sink successfully maintained the heat-source surface temperature below 75 ℃， while the inlet-outlet pressure drop remained around 18 kPa， indicating excellent two-phase thermal and hydraulic performance. In addition， the flow rate and microchannel pressure drop exhibited a strong positive correlation.关键词：thermal management;heating modes;high aspect ratio microchannels;flow boiling heat transfer13|59|0更新时间：2026-04-24
- 摘要：Refrigerant hydrates have potential applications in air-conditioning systems as phase-change cold-storage materials. However， refrigerants are insoluble in water， the nucleation of hydrates in static systems is slow， and the actual cold storage density is low. Surfactants can improve the refrigerant hydrate formation. In this study， fatty acid polyoxyethylene esters （LAE-4 and LAE-9） and fatty alcohol polyoxyethylene ethers （AEO-4 and AEO-9） were used to accelerate the hydrate formation. It was found that the amount of surfactant added affected the hydrate formation. The hydrate-formation induction time with a mass fraction of 2.5% AEO-9 was the shortest （63 min）. Hydrate exhibited the largest cold storage density （246.10 kJ/kg） and its growth rate reached 4.47 kJ/（kg·min） when the mass fraction of AEO-9 added was 2.5%. Surfactants with short hydrophilicities caused the droplets of the emulsion to become large and stratified， whereas surfactants with long hydrophilicities improved the stability of the emulsions. The hydrophobic ester bonds in LAE-9 promoted rapid hydrate formation. Hydrate showed a “memory” effect. There was no evident induction time for hydrate reformation. The stability of emulsions played a pivotal role in hydrate formation. The LAE-9 emulsion system exhibited the best stability in the hydrate formation/dissociation cycle.关键词：hydrate;surfactant;Induction time;cold storage;cycle stability9|55|0更新时间：2026-04-24
- 摘要：For an office building in Zhengzhou， the ground-source heat pump （GSHP） system meets only the heating demand， cannot provide cooling， and its long-term operation leads to soil thermal imbalance and performance degradation. Based on measured data， we first verified the accuracy of the TRNSYS dynamic model， providing a reliable basis for subsequent operational analysis and control strategy research. On this basis， the operation process of a single GSHP system was analyzed， an air-source-ground-source heat pump （ASHP-GSHP） coupling scheme was proposed， and a hybrid PSO-GPS algorithm was used to optimize a dual-threshold control strategy with the goals of system economy and soil thermal balance. The results show that under the temperature control strategy， the annual average system COP remained basically stable at about 3.24 over the 10-year operating period， with a cumulative soil temperature rise of 0.35 °C； under the load control strategy， the annual average system COP remained basically stable at about 3.05， with a cumulative soil temperature rise of 0.38 ℃， and the economic performance was the best， with a payback period of about 4.26 years. Compared with the original heating-only system， in which the COP declined and the soil temperature dropped by 7.47 ℃， the coupling scheme effectively improves system efficiency， maintains soil thermal balance， and reduces CO₂ emissions by approximately 11 000 kg annually. This study provides a reference for the optimal design and efficient operation of cooling and heating cogeneration systems in office buildings located in cold regions.关键词：ASHP–GSHP coupling;combined heating and cooling system;operational control logic;PSO–GPS optimization algorithm20|63|0更新时间：2026-04-24
- 摘要：To promote the development of high-efficiency tubular condensation heat exchangers， we studied R134a flow-condensation heat transfer characteristics in six micro-fin tubes with different structures， evaluated the prediction performance of four correlations （Koyama et al.， Miyara et al.， Cavallini et al.， and Oliver et al.）， and explored the influence mechanisms of experimental conditions and tube structural parameters. The results show that the R134a heat transfer coefficient increases with the increase of mass flux （500~1 100 kg/（m²·s）） and the decrease of condensation temperature （35~45 ℃）； the Koyama et al.'s correlation exhibits the best prediction concentration （deviation range of -43.6% to -27.4%）， the Cavallini et al.'s correlation has the optimal overall prediction performance but poor concentration， the Miyara et al.'s correlation overestimates （deviation range of 21.3%~56.4%）， and the Oliver et al.'s correlation underestimates （deviation range of -31.4% to -52.5%） the heat transfer characteristics. Therefore， based on the prediction performance of the Koyama et al.'s correlation for the flow-condensation heat transfer characteristics in micro-fin tubes， the dimensionless variable characterizing the fluid turbulence in the model was redefined. The obtained model can accurately predict R134a flow-condensation heat transfer characteristics in 1# （14.6%） & 2# （-11.0%） & 3# （4.9%） & 4# （-12.0%） & 5# （8.4%） & 6# （2.7%） micro-fin tubes. The average prediction deviation， which ranges from -12.0% to 14.6%， sufficiently validates practical values provided by the model developed.关键词：R134a;micro-fin tube;flow condensation;heat transfer coefficient;correlation8|57|0更新时间：2026-04-24
- 摘要：Efficient recovery of industrial waste heat is crucial for achieving the industrial "dual-carbon" goals. In this study， we addressed the challenges associated to low- and medium-temperature waste heat， such as low utilization rates， demand for high-temperature lift， and temporal mismatch. We focused on recovering continuous waste heat from an air compressor station to meet intermittent high-temperature industrial heat demand. We also researched on the design and performance of a transcritical high-temperature heat pump system based on a zeotropic mixture and cascaded phase-change thermal storage. First， via single-objective optimization， the optimal zeotropic mixture R290/cis-Butene （0.5/0.5） was selected， achieving a coefficient of performance （COP） of 3.31 and a volumetric heating capacity （VHC） of 5 975.63 kJ/m³. Subsequently， the structural parameters of the thermal storage unit were obtained， and the optimized configuration of the cascaded phase-change materials （PCMs） was determined to be a volume ratio of 25∶35 for high-temperature to low-temperature paraffin. Finally， the operational performance of the system was investigated. The results show that the cascaded PCM configuration （Case 1） reduces temperature non-uniformity within the PCM during both charging and discharging processes， maintains a higher average outlet temperature during discharge， and achieves optimal performance with an average COP of 2.88 and the lowest compressor power consumption.关键词：transcritical;high-temperature heat pump;zeotropic mixture;cascade phase change thermal energy storage20|76|0更新时间：2026-04-24
- 摘要：To evaluate the reliability and increase the accuracy of dynamic energy efficiency testing of room air conditioners， uncertainty quantification of the dynamic test is essential. In this study， we categorize the uncertainty sources of dynamic testing into three types： systematic， random， and time-delay errors. The uncertainty resulting from systematic and random errors was evaluated using the GUM and MCM methods， with the error limits set based on the steady-state measurement uncertainty requirements specified in GB 7725—2022 Room Air Conditioners. The time-delay error was modeled and analyzed using a first-order model， with the sensor response time set based on common values. Using an air conditioner with a rated cooling capacity of 3.5 kW as an example， the uncertainty calculation results showed that the relative expanded uncertainty caused by systematic and random errors was 3.8%， and the uncertainty due to the time delay was 1.0%， leading to a total uncertainty of 3.9% in the dynamic energy efficiency. Extending to other air conditioners with various capacities， the total uncertainty should be in the range of 3.2% to 5.4%. Contribution analysis revealed that the uncertainty in capacity measurement caused by systematic error is the primary factor affecting the uncertainty in dynamic energy efficiency testing. Concerning the capacity measurement， the accuracy of the inlet and outlet wet-bulb temperatures of the indoor side makes the most significant contribution.关键词：dynamic testing;uncertainty;room air conditioner;air-enthalpy method;time delay10|25|0更新时间：2026-04-24
- 摘要：To explore the refrigeration performance of the ternary mixed refrigerant R600a/R1150/R50， an experimental setup was established based on the Linde-Hampso cycle refrigeration principle for experimental research， and the refrigeration characteristics of the ternary mixed refrigerant were comparatively analyzed. The experimental results indicate that when the optimal charging amount of the ternary mixed refrigerant （R600a/R1150/R50） is 161.8 g/26.2 g/2.0 g， the throttling temperature after stable operation is -94.6 ℃， the ambient temperature in the box is -87.1 ℃， the cooling capacity is 22 W， and the coefficient of performance （COP） is 0.043. In the ternary mixed working medium， with an increase in the high-temperature working medium （R600a）， the performance of the regenerator is improved， and both the throttling temperature of the system and exhaust temperature gradually decrease. Under the premise of sufficient precooling， when the temperature before throttling does not reach the liquefaction temperature under the corresponding exhaust pressure of R1150， the addition of R1150 can reduce the pressure ratio， throttling temperature， and refrigeration flow rate of the system. Because the liquefaction temperature of R50 is too low under the exhaust pressure of a conventional refrigeration system， the pressure ratio increases and the mass flow rate decreases after adding the system. The experimental results have a certain guiding significance and reference value for the performance analysis of the Linde-Hampso cycle and the selection of mixed refrigerant charge ratios and system commissioning.关键词：Linde-Hampso cycle;low temperature;mixture;R600a/R1150/R5012|176|0更新时间：2026-04-16
- 摘要：High-temperature auto-cascade heat pumps exhibit a simple and compact structure and reliable operating performance and can achieve heating at relatively high temperatures. Currently， the research and application of high-temperature auto-cascade heat pumps remain relatively immature， and most studies are still in the theoretical stage. Although their heating capacity and coefficient of performance （COP） are relatively low， they still hold significant promise for development in the field of high-temperature heating. This paper first introduces the research status of auto-cascade technology in the fields of refrigeration and heating and then reviews the research progress of auto-cascade heat pumps from two aspects： research advances in refrigerants and the optimization of system processes. The analysis showed that the replacement of refrigerants with a low global warming potential （GWP） is the current research focus. Refrigerants with high critical temperatures， such as R1233zd（E） and R1224yd（Z）， enable auto-cascade heat pumps to achieve high-temperature heating. R290 and R1234yf are more suitable for heating in areas with low ambient temperatures， whereas R1234ze（Z） and R1234ze（E） exhibit excellent thermodynamic performance. The proportion of mixed refrigerants has a significant impact on the performance of auto-cascade heat-pump systems. Online cycle concentration measurement methods and active control strategies for mixed refrigerants can maintain the system at an optimal proportion at all times. In terms of the optimization of heat-pump system processes， the application of vapor injection technology for increasing enthalpy is the most mature and widespread. Technologies such as multistage evaporation and ejection show potential for development. Multi-system coupling is conducive to improving system performance but may affect the stability of system operation.关键词：high-temperature auto-cascade heat pump;zeotropic mixed working fluid;process optimization;research progress17|118|0更新时间：2026-04-16
- 摘要：Vapor injection technology can effectively enhance the heating performance of heat pump-type multi-unit air conditioning systems （heat pump VRF） under low-temperature conditions. However， complex system configuration and component coupling necessitate a more general steady-state simulation approach for VRF heat pumps. This study proposes an improved graph-theory-based steady-state simulation method for a multiunit air-conditioning system with vapor injection. By abstracting the components into computational units， a graph-theory-based description method guided by the refrigerant flow paths was established. A directed graph of computation units was employed to characterize the adjacency relationships in cooling/heating modes， with mode switching achieved using a four-way valve model. A dual-layer path generation method for system pressure and flow paths is proposed， along with a decoupled iterative algorithm for flow pressure calculation. Validation based on experimental data from a heat pump VRF system with vapor injection （four indoor units） shows that the model prediction error is within ±5% under rated cooling/heating conditions. A steady-state simulation platform with customizable system configurations was developed based on the proposed method， providing a convenient digital tool for the VRF system design.关键词：multi-unit air conditioning systems;heat pump;vapor injection;steady-state simulation;graph theory11|55|0更新时间：2026-04-16
- 摘要：Current evaporative cooling air conditioning systems adopt traditional HVAC design parameters as their design conditions， using extreme weather conditions as design day parameters， which overlooks the coupling between the diversity of evaporative cooling operation modes and meteorological factors. This study considers data centers as the research object and proposes a new method for generating design days based on the operational characteristics of indirect evaporative cooling air-conditioning systems in dry， wet， and mixed modes. First， a TRNSYS model was established for an indirect evaporative cooling air-conditioning system in data centers， with the supply air temperature serving as the criterion for determining the operation mode. The climatic features corresponding to the hourly outdoor dry- and wet-bulb temperatures under the three switching modes were extracted. By combining conventional principal component analysis and the weighted dynamic time warping method， the meteorological days most similar to these characteristic sequences were identified from historical weather data， thereby generating design-day parameters for different operation modes. The results show that， compared with the original design parameters， the peak cooling loads generated by the new method under the three operating modes exhibit relative deviations from the actual design loads of 0.15%， 0.03%， and 0.41%， respectively. The design-day parameters proposed in this study effectively mitigated the design redundancy issues associated with the original parameters， thereby better satisfying the accuracy requirements of the engineering design.关键词：data center;indirect evaporative cooling;supply air temperature;meteorological parameters;energy-saving optimization14|133|0更新时间：2026-04-16
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