最新刊期
卷 45 ， 期 4 ， 2024
- 摘要：With the adoption and implementation of the Kigali Amendment in China, the R134a refrigerant has gradually reduced and could be eliminated in China′s mobile air conditioning （MAC）. Currently, the most important alternative refrigerants for MAC are R1234yf, CO2, and R290; however, China has no criteria for the selection of these three refrigerants. Recently, Germany and five other countries have proposed regulations to restrict PFASs, and R1234yf has also been included in the restricted list; therefore, the prospect of R1234yf is not optimistic. In this context, this study compares R1234yf, CO2, and R290 in terms of environmental protection, safety, economy, and system performance. Relevant research results and conclusions are summarized, and the latest PFAS substance restriction proposal involving MAC was organized and analyzed. These efforts provide direction for the research of alternative refrigerants in the field of MAC in China, which may be used as a basis for the selection of alternative refrigerants for MAC in the future.关键词：automotive air conditioning;alternative refrigerants;CO2;R1234yf;R290105|56|0发布时间：2024-09-02
- 摘要：Refrigerant substitution in household air conditioning has become a common concern in the global refrigeration and air conditioning industries. This study analyzes the specific clauses of the Kigali Amendment. Based on the GWP value of the R410A refrigerant, different equivalent factors were selected to calculate the regulatory limits of different countries and regions in different years. Under the restrictions of different national laws and regulations, three available refrigerants from R410A, R32, R454B, R161, and R290, have been selected to represent different usage scenarios. The refrigerant replacement process of HFCs was predicted and analyzed following Kigali′s revised Global Warming Potential(GWP) limit, and the influence of refrigerant charge reduction was discussed. The results show that to satisfy the Kigali Amendment, the proportion of R290 in Europe must exceed 30% and become the mainstream refrigerant in 2024, whereas the United States can realize the possibility of not using R290 by reducing the charge of R454B. China can meet the GWP limit by using either R290 or R161and there is no need to switch to both two refrigerants simultaneously.关键词：Kigali Amendment;refrigerant substitution;household air conditioner68|61|0发布时间：2024-09-02
- 摘要：Heat pump technology can be used to upgrade and enhance the quality of low-grade waste heat in production and daily life. Zeotropic mixtures can achieve temperature matching during the heat exchange process of heat pump cycles, which realizes in-depth utilization of waste heat resources. This study conducts an experimental analysis of CO2/R1234yf, CO2/R290, CO2/R600a, and CO2/R32 zeotropic mixtures using a water-source heat pump experimental system. The performances of heat pumps with evaporators and condensers that simultaneously satisfy high-temperature differences were investigated using the zeotropic mixture. Results show that the amount of charge in the zeotropic mixture primarily affects the degree of cycle subcooling, thereby influencing the coefficient of performance (COP) of the system. When the mass composition of CO2/R1234yf is 15%/85%, an optimal refrigerant charge, which corresponds to a COP of 7.66 under the experimental condition (heat source inlet water temperature at 25 ℃, outlet at 5 ℃; heat sink inlet water temperature at 15 ℃, outlet at 45 ℃) is obtained. Furthermore, compared with pure R290, the CO2/R290 working pair exhibits an enhancement of 75.2% in the optimal COP, with a corresponding increase of 107.7% in the volumetric heating capacity (qv). Similarly, the CO2/R1234yf working pair demonstrates an improvement of 27.7% in the optimal COP and an increase of 92.0% in qv. The CO2/R32 working pair exhibits a 15.0% increase in the optimal COP. However, the CO2/R600a working pair exhibited only a 1.7% enhancement in the optimal COP, indicating a relatively low application potential.关键词：heat pump;waste heat recovery;zeotrope;temperature glide47|35|0发布时间：2024-09-02
- 摘要：This study experimentally investigates the impact of flow resistance in risers and downcomers on the heat transfer performance of two-phase thermosyphon loops (TPTLs) with CO2, R134a, and R410A refrigerants. Variations in the heat transfer limit and thermal resistance of the TPTLs were analyzed. The results show that the three TPTLs respond differently to changes in flow resistance. For the CO2 TPTL, the effects of the riser and condenser resistances on thermal performance are similar. When the opening angle of the riser or condenser valve decreases from 90° to 30°, the heat transfer limit of the CO2 TPTL decreases from 1 200 W to 700 W. For the R134a and R410A TPTLs, when the opening angle of the riser valve decreases from 90° to 30°, the heat transfer limit of the R410A TPTL decreases from 1 300 W to 700 W, and the R134a TPTL does not reach normal operating conditions, resulting in substantial superheating and subcooling inside the pipes and a substantial increase in thermal resistance for both types. An increase in the condenser resistance has little effect on the thermal performances of the R134a and R410A TPTLs. For practical design considerations, the same or similar diameters should be used for the riser and downcomer of a CO2 TPTL. However, for R134a and R410A TPTLs, the riser diameter should be significantly larger than the downcomer diameter to achieve material cost savings.关键词：two-phase thermosyphon loop;refrigerant;flow resistance;heat transfer limit;thermal resistance34|24|0发布时间：2024-09-02
- 摘要：R404A is widely used in light commercial equipment. However, the Kigali Amendment currently specifies the refrigerant replacement process. R454C and R290, owing to their low global warming potential values, have become promising refrigerants for use in commercial refrigerators. To compare the performances of these three refrigerants in commercial refrigerators, this study uses a climatic chamber to test four commercial refrigerators of different sizes. Four key parameters, namely the refrigerant charge, energy consumption, material cost, and carbon emissions, of the R404A, R454C, and R290 systems were compared. The results indicated that replacing R404A with R454C resulted in energy savings of approximately 5% and a reduction of approximately 15% in carbon emissions. When using R290, the charge was only 20.6%-34.3% of that of R404A, remaining within a safe range. Additionally, the charging cost was only half that of R404A. Furthermore, the system satisfied the performance requirements with this charge amount, leading to a reduction in energy consumption and carbon emissions within the ranges of 15%-35% and 25.3%-43.7%, respectively.关键词：R290;commercial refrigerator;refrigeration performance test;CO2 emission52|52|0发布时间：2024-09-02
- 摘要：To reduce greenhouse gas emissions and improve the performance of space heating systems, a transcritical CO2 heat-pump heating system using an ejector and integrated mechanical subcooling (EJ-IMS) is proposed. A thermodynamic model of the system is developed with the coefficient of performance (COP) as the objective function, and the subcooling degree and discharge pressure are optimized. The winter heating performance of the system located in cities located in different climate zones was evaluated. The results show that the EJ-IMS system has a maximum COP, corresponding to the optimum subcooling degree and the optimum discharge pressure. The optimum subcooling degree is 26.44%-39.21% lower than that of the integrated mechanical subcooling system, and the optimum discharge pressure of the EJ-IMS system is 0.27%-9.37% lower than that of the baseline system and ejector system. The COP and exergetic efficiency of the EJ-IMS system are 6.09%-37.74% and 6.75%-46.02% higher than those of the three conventional systems, respectively. The heating seasonal performance factor of the EJ-IMS system is 6.89%-29.61% higher than those of the three systems, indicating that the EJ-IMS system is suitable in cold regions. This study provides a theoretical reference for the construction of efficient CO2 space-heating systems.关键词：integrated mechanical subcooling;ejector;transcritical CO2;heat pump;space heating36|19|0发布时间：2024-09-02
- 摘要：This study investigates the flow boiling characteristics of R134a and its alternative refrigerant R513A in a microchannel tube. The effects of vapor quality, saturation temperature, heat flux, and mass flux on the heat transfer coefficient and pressure gradients were explored. Additionally, a comparative analysis of R134a and R513A was conducted. The test conditions covered vapor quality from 0 to 1, inlet saturation temperature from 10 ℃ to 30 ℃, heat flux from 2 kW/m2 to 8 kW/m2, and mass flux from 100 kg/(m2·s) to 200 kg/(m2·s). Results show that saturation temperature has almost no effect on the heat transfer coefficient of R134a but slightly influences that of R513A. At high saturation temperatures, the pressure gradient of R513A is low. Heat flux significantly affects the heat transfer coefficients of both refrigerants, and the peak heat transfer coefficient increases by more than 30%. Moreover, under low vapor quality, the heat transfer coefficient increases by more than 80%; however, its effect on pressure gradients is negligible. Mass flux significantly affects the heat transfer coefficient under intermediate vapor quality, and doubling its value causes the heat transfer coefficient to increase by more than 50%. In addition, mass flux significantly affects the pressure gradient. A comparison of the flow boiling characteristics of R134a and R513A under the same test conditions shows that R513A has higher heat transfer coefficients and lower pressure gradients than R134a.关键词：low GWP refrigerant;flow boiling;microchannel43|32|0发布时间：2024-09-02
- 摘要：Transcritical CO2 thermal systems have emerged as leading solutions to addressing challenges such as "range anxiety in winter" and pronounced greenhouse effects associated with the working fluid in electric vehicle thermal systems. Nevertheless, the intricate interplay of transcritical cycles in the varied scenarios of electric vehicles introduces complexity, with performance and operational stability intricately linked to the refrigerant charge. This study conducts simulations to investigate the variability in refrigerant charging requirements for transcritical CO2 thermal management systems under diverse operating conditions. We specifically examined the impact of three critical factors, namely ambient temperature, indoor airflow rate, and outdoor air velocity, on refrigerant requirements in different modes and their underlying mechanisms. In the heat pump mode, the demand for refrigerant charge increases with ambient temperatures and wind speed and decreases with cabinet air flow rate, with changes of 18.6%, 18.9%, and 6.16%, respectively. In the cooling mode, the refrigerant charge requirement decreases with ambient temperatures and cabinet air flow rate and increases with outdoor wind speeds, with changes of 7.03%, 7.85%, and 2.27%, respectively. In situations of nonoptimal charging, potential alterations in the interaction between system control variables and target variables contribute to system instability. This necessitates adjustments to refrigerant distribution to mitigate instability under specific operating conditions. The research outcomes hold substantial reference value for the optimization of electric vehicle air-conditioning accumulator designs, enhancement of energy efficiency, and improvement of overall thermal comfort.关键词：electric vehicle;CO2 thermal management system;refrigerant charge demand;system instability42|31|0发布时间：2024-09-02
Refrigerant Substitution Technology
- 摘要：The electrocaloric effect is a novel solid-state refrigeration technology that is considered an option to replace traditional vapor compression refrigeration owing to its advantages, such as low cost, high coefficient of performance (COP), and miniaturization. Currently, the main limitation that hinders the application of electrocaloric refrigeration devices is the insufficient temperature change in materials exhibiting the single-chip electrocaloric effect. In device design, the use of a regenerative or series structure can increase the system temperature span to the level of engineering applications. This study introduces the concept, performance indicators, and current research achievements of thermal switch devices in a series of electrocaloric refrigeration devices. Using the principle of the electrocaloric effect, the adaptability of different types of thermal switches in electrocaloric refrigeration devices was analyzed, and the research results of regenerative and a series of electrocaloric refrigeration prototype devices were presented. Simulations and analyses of the impact of thermal switching devices on the performance of refrigeration devices were conducted using a series of electrocaloric refrigerators. We believe that the series structure is theoretically suitable for electrocaloric refrigeration devices. The use of the fast response speed and high thermal resistance of thermal switch devices driven by an electric field to drive the fluid medium can assist a series of electrocaloric refrigeration devices to address the current technological limitation and thus unleash the technical potential of electrocaloric refrigeration technology in various refrigeration systems.关键词：thermal switch;electrocaloric effect;solid-state refrigeration technology;thermal management technology49|49|0发布时间：2024-09-02
- 摘要：The rapid development of the electronic industry has led to a sharp increase in the heat flux of electronic equipment. The search for efficient cooling methods can significantly reduce the operating temperature of devices, improve their performance, and extend their lifespan. To further reduce the maximum operating temperature of chips, this study proposes a thermal control method for an electronic chip using the elastocaloric effect in shape memory alloys. The cold energy generated during unloading was transferred through the fluid to the microchannel heat sink thermal control system of the electronic chip with good heat dissipation performance. The temperature variation characteristics of the system under three-dimensional conditions were analyzed using FLUENT software. The results showed that the heat transfer fluid after refrigeration could reduce the highest temperature of the chip by 5.5 K, and the performance of the microchannel heat sink was improved by approximately 10.7%. Parametric analysis shows that an increase in the cycle frequency and accumulated flow rate of cooling liquid can significantly improve the cooling capacity of the refrigeration system, with cycle frequencies of 0.25 Hz and 0.33 Hz improving the cooling power by 68% and 92%, respectively.关键词：heat dissipation;elastocaloric effect;microchannel heat sink;refrigerating system;cooling power41|31|0发布时间：2024-09-02
- 摘要：The centrifugal reverse Brayton cycle (CRBC) is a novel refrigeration cycle that harnesses the conversion of inertial potential energy to pressure energy, enabling efficient compression and expansion processes through centrifugal and centripetal flows of the working fluid within a rotating tube. This offers a promising potential for improving the refrigeration efficiency of conventional gas refrigeration cycles. Building on previous studies, this study employs a thermodynamic model to conduct a parametric analysis of the CRBC to explore the thermodynamic efficiency and loss distributions of the cycle, providing a theoretical foundation for system evaluation and enhancement. Results show that, under the same inlet air temperature, an optimization possibility exists for the heater inlet temperature. The system experiences substantial exergetic losses during the centrifugal isothermal compression flow, adiabatic compression, and centripetal adiabatic expansion flow, each at approximately 20%. Conversely, the exergetic losses during the air-cooling process and the centrifugal adiabatic compression process are comparatively low and demonstrate an inverse relationship with the inlet temperature of the gas heater. The exergetic efficiency of the CRBC reaches 19.2%, which significantly surpasses the values of 8.1% for the CO2 reverse Brayton cycle, 4.9% for the open-air reverse Brayton cycle, and 2.3% for the closed-air reverse Brayton cycle.关键词：reverse Brayton cycle;CO2 refrigeration cycle;super-gravity field;exergy analysis35|20|0发布时间：2024-09-02
- 摘要：To reduce the energy consumption of a CO2 ice-making system and improve system performance, this study proposes a transcritical CO2 two-stage compression ejector expansion direct cooling ice-making system with complete intercooling (TCEIS). The effects of key parameters on system performance were analyzed by developing a thermodynamic model. Using this model, the COPR+HR, annual power consumption, heat recovery capacity, annual operating cost, and heat recovery income of the system applied in different seasons and cities were evaluated and compared with those of a two-stage compression direct cooling ice-making system (TCS), a two-stage compression direct cooling ice-making system with complete intercooling (TCIS), and an ejector expansion direct cooling ice-making system (ES). The results show that TCEIS has the highest COPR+HR considering heat recovery, with the advantages being noticeable in hot seasons and cities. When operating in Guangzhou with cooling loads of 410.989 kW in winter, 542.092 kW in transition seasons, and 701.353 kW in summer, the annual operation cost of TCEIS can be reduced by 107.6 thousand yuan, 397.9 thousand yuan, and 583.1 thousand yuan compared with those of TCIS, TCS, and ES, respectively. This study provides a theoretical reference for the construction and application of CO2 direct-cooling ice-making systems.关键词：direct cooling ice-making;coefficient of performance;economic analysis;two-stage compression;ejector;CO237|27|0发布时间：2024-09-02
- 摘要：In this study, using a direct evaporation indoor CO2 artificial ice rink as the research object, we establish a mathematical model for the stable temperature field of the indoor ice rink to analyze the influence of mass flux, tube spacing, oil content, and other factors on ice surface temperature and ice temperature difference when the evaporating temperature is -13 ℃ in a 12.7 mm diameter copper pipe. Results show that an increase in the lubricating oil content increases the pressure drop in the pipe and the temperature difference between the inlet and outlet of the ice surface. However, because the pipe diameter and mass flux investigated in this study are relatively large, the influence range is small. The temperature distribution on the ice surface is mainly affected by the distance between the cooling pipes and the mass flux. The temperature difference of the ice surface increases with an increase in tube spacing and mass flux. To ensure a temperature difference of the ice surface less than 0.5 ℃, the recommended mass flux should be less than 200 kg/(m2·s), and the tube spacing should be less than 90 mm.关键词：CO2;direct evaporation;artificial ice rink;ice surface temperature29|16|0发布时间：2024-09-02
- 摘要：Because of the limited experimental studies on transcritical CO2 refrigeration systems at low evaporating temperatures, an experimental platform of a two-stage transcritical CO2 compression refrigeration system with an ejector was designed and built. We evaluated the performance of the proposed refrigeration system under the following experimental conditions: evaporating temperature within the range of -33 ℃--29 ℃, gas cooler outlet temperature of 30 ℃-40 ℃, and high pressure of 8.20 MPa-9.70 MPa. The results show that the variation trend of the experimental results is consistent with that of the theoretical thermodynamic calculation results, and the application of the ejector can significantly improve the performance of the two-stage transcritical CO2 compression refrigeration system. The maximum increase rate of the coefficient of performance (COP) of the refrigeration system by the ejector is 29.37%. Under experimental conditions, the optimal high pressure of the two-stage transcritical CO2 compression refrigeration system with an ejector is 8.80 MPa, and the corresponding optimal COP is 1.63. The cooling capacity and COP of the two-stage transcritical CO2 compression refrigeration system with an ejector increase with increasing evaporating temperature, and the gas cooler outlet temperature significantly affected the performance of the refrigeration system. As the gas cooler outlet temperature increases from 30 ℃ to 40 ℃, the COP of the refrigeration system decreases by 61.4%. The research results provide a reference for research on two-stage transcritical CO2 compression refrigeration systems with ejectors.关键词：two-stage transcritical compression;ejector;low evaporating temperature;CO2;refrigeration performance34|24|0发布时间：2024-09-02
- 摘要：To investigate the vapor injection performance of a scroll compressor with a short profile, a three-dimensional transient numerical model of a vapor-injection scroll compressor for an electric vehicle with a displacement of 38 cm3/r is established and verified with deviations within 9.5%. We investigated the effects of the pressure and temperature of vapor injection on the performance of the scroll compressor using the model. The results show that under the condition of a constant superheat, with an increase in injection pressure, the discharge temperature of the compressor initially decreases and then gradually increases. Moreover, the heating capacity exhibits an increasing trend, with the maximum increase in heating capacity reaching 20.5% and 17.1% at rotary speeds of 5 000 and 6 000 r/min, respectively. In addition, the heating coefficient of performance (COP) increases during the first stage and then decreases. Moreover, the maximum values of the heating COP with vapor injection at the former speeds were 3.9% and 2.3% higher than those without vapor injection, respectively. The compressor efficiency exhibits the same tendency as the heating COP, and the volumetric efficiency gradually decreases. The compressor discharge temperature increases slightly with constant injection pressure, whereas the compressor power, heating capacity, and heating COP remain almost constant as the injection temperature increases. Compared with the injection temperature, the injection pressure has a significant impact on the scroll compressor.关键词：electric vehicle scroll compressor;enhanced vapor injection (EVI);injection pressure;injection temperature36|44|0发布时间：2024-09-02
- 摘要：Serpentine microchannel heat exchangers have extensive application potential owing to their compact structures and high heat-transfer coefficients. Existing studies on two-phase flow in serpentine channels have mostly used conventionally sized channels and focused on their curved sections. The analysis of the two-phase-flow pressure drop in serpentine microchannels cannot provide a complete theoretical explanation for practical applications. In this study, two-phase pressure drop in a serpentine microchannel with a hydraulic diameter of 0.65 mm and curvature radii of 1.2 mm, 1.8 mm, and 2.4 mm is experimentally investigated. Based on the experimental results, the proportion of pressure drop is calculated when the mass flow rate is 600 kg/(m2·s). The pressure drop changes were analyzed at mass flow rates of 600 kg/(m2·s), 1 200 kg/(m2·s), 1 800 kg/(m2·s), and 2 400 kg/(m2·s). Experimental data were compared with existing empirical two-phase-flow pressure-drop correlations; however, they showed poor agreement.关键词：microchannel;two-phase flow;frictional pressure drop;flow boiling;phase-change heat transfer37|32|0发布时间：2024-09-02
- 摘要：Small-diameter heat exchangers for air conditioning can reduce cost and refrigerant charge, which is of great significance for realizing energy savings and emission reduction. In this study, the plate fins of a 5 mm single-row air-conditioning condenser are optimized to replace a 7 mm single-row air-conditioning condenser. The optimization variables are tube spacing, fin width, and fin spacing, and the objectives are to maximize heat transfer and minimize air-side pressure drop and cost. The Taguchi method was selected for the experimental design and single-objective optimization, and the grey relational analysis and comprehensive performance index method were used for multi-objective optimization. The final optimum tube spacing, fin width, and fin spacing were 16.0 mm, 16 mm, and 1.4 mm, respectively. The heat transfer was the same as that of the 7 mm tube condenser. The pressure drop was reduced by 35%, and the cost was reduced by 26%, validating the effective replacement of the 7 mm condenser.关键词：air conditioning condenser;plate fins;Taguchi method;grey relational analysis;comprehensive performance index method;optimization53|59|0发布时间：2024-09-02
- 摘要：The vacuum sublimation-rehydration thawing (VSRT) method, as an innovative approach for thawing, holds promising prospects in the field. To further understand the mechanism of the new vacuum sublimation-rehydration thawing method and optimize its thawing process, fresh pork tenderloin is selected as the research subject, and the effects of rehydration water volume on thawing time, thawing effect, and energy consumption are experimentally investigated and compared with those of the traditional vacuum steam thawing (VST) method. The results showed that the rehydration water volume had an important effect on heat and mass transfer in the rehydration stage, and the thawing performance varied significantly under different rehydration water volumes. When the rehydration water volume entering the unit-volume vacuum chamber was 0.013 5 mL/cm3, the thawing efficiency, energy consumption, and thawed product quality simultaneously reached the optimal state. Compared with using the VST method, when using the VSRT method, the thawing time could be shortened by 55% and the thawing loss, total color difference, and system-specific energy consumption could be reduced by 85%, 77%, and 47%, respectively. Moreover, excellent texture parameters could be maintained.关键词：vacuum sublimation-rehydration thawing;rehydration water volume;thawing efficiency;thawing effect (quality);specific energy consumption32|40|0发布时间：2024-09-02
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