最新刊期
卷 39 ， 期 2 ， 2018
- 摘要：R290 has been considered for use in air-conditioning systems as a low global warming potential (GWP) refrigerant. This paper describes the tribological characteristic of the vane-piston tribopair in a R290 rotary compressor. For the purpose of simulating the tribopair working conditions, the vanes and rolling pistons of a compressor were directly adopted as test specimens. All of the tribological tests were performed under sealed high-pressure conditions, with test conditions such as the relative sliding speed, loads, and temperatures set based on actual operating conditions of a compressor, and the friction coefficients, scuffing resistances, and wear depths were measured. Furthermore, the morphological changes were investigated using a scanning electron microscope after the tests. As a comparison benchmark, tests were also conducted using R410A/polyolester oil. From these tests, it was evident that the friction coefficients and scuffing load of the vane-piston interface in the presence of R290/mineral oil were respectively 0.05–0.1 and 300 N higher than those of R410A/polyolester. On the other hand, the wear resistance ability with R290/mineral oil was better than that with R410A/polyolester.关键词：friction coefficient;compressor;lubricant oil;R2902505|2591|2发布时间：2024-07-18
- 摘要：Alternative refrigerants such as R290 and R32 are gradually being applied to room air conditioners (RACs). This study tested the performances of R290, R22, R410A, and R32 in the same system. The capacity and efficiency reduction values at high ambient temperatures for R290, R32, R410A, and R22 were measured. The ambient temperatures were 35, 46, 52, and 55 ℃, respectively. The experimental results showed that R22 had the best performance under the high ambient temperature condition, while R32 had the worst. R290 was very similar to R22. The capacity decrease between R22 and R32 was 3.01%, and the decrease in the energy efficient ratio was 6.03%. Moreover, R32 had the highest discharge temperature and system pressure and was not suitable for an RAC in a high ambient temperature area.关键词：room air conditioner;high ambient temperature performance;alternative refrigerants;decrement2454|2491|0发布时间：2024-07-18
- 摘要：Automotive heat pump systems with the R134a refrigerant cannot provide sufficient heating capacity and even stop working in a low ambient temperature. Developing a transcritical CO2 automotive heat pump system would be an effective method to solve this problem. This study theoretically analyzed the impacts of key factors on the performance of a CO2 heat pump system, and experimentally investigated the developed heat pump in a ﹣20 ℃ environment. Experimental results showed that the developed heat pump system ran stably at low temperatures and had a good heating performance. Under the same compressor speed, the indoor environment temperature had a greater impact on the heating coefficient of performance (COPh)), while the outdoor environment temperature had a greater impact on the heating capacity. Under a cold condition at ﹣20 ℃, the COP reached 3.15 and the heating capacity reached 3.6 kW. When the indoor inlet and outlet air temperatures are 20 ℃ and 40 ℃, respectively, the COPh was at least 1.72. Therefore, compared to R134a, the CO2 heat pump system has a great heating performance in a low temperature environment, and thus has good application potential for electric vehicles.关键词：heating performance experiment;automotive heat pump;CO2 refrigerant;transcritical cycle;electric vehicle2333|2830|4发布时间：2024-07-18
- 摘要：Based on a theoretical analysis of an air-source transcritical CO2 heat pump system, a mathematical model for the compressor was developed using an efficiency analysis in this study. In addition, a mathematical model for the expansion valve was built using a structural analysis; and mathematical models for the gas-cooler, evaporator, and regenerator were developed using the distributed parameter method. Moreover, a mathematical model for the entire system was built by combining these models. The accuracy of the system model was verified by an experimental test, which showed that the deviation in the unit’s input power between the calculated value and measured value was less than 4.4%, the mean deviation in the heating capacity was 5.76%, and the deviation in the optimal discharge pressure was less than 0.1 MPa. Thus, it was possible to calculate the system performance by employing the mathematical simulation method.关键词：CO2 heat pump system;steady state mathematical model;optimal discharge pressure;uncertainty;coefficient of performance2123|2146|2发布时间：2024-07-18
- 摘要：A flexible design scheme for a direct expansion solar-assisted heat pump system is presented. Based on the flexible theory for the virtual operating point of the basis design, which was stored in the flexible space, all of the operating points within the flexible space could achieve almost the same heat transfer effect. The weights of the environmental factors for the system’s coefficient of performance (COP) were obtained in a simulation and verified in an experiment, including the irradiation intensity (52.2%), temperature (34.7%), and wind speed (13.1%). A total of 25 sets of systems were simulated under typical weather conditions. The purpose was to verify the operating points that fell in the flexible space based on the weights for the optimal combination of virtual operating points obtained. The values of the irradiation intensity (It), ambient temperature (T0), and wind velocity (uw) were 559.97 W/m2, 21.6 ℃, and 2.89 m/s respectively. The simulation results showed that the variance in the system’s COP was 0.156，which was superior to the traditional static design result.关键词：solar assisted heat pump water heater (DX-SAHPWH);direct expansion;mathematical model;flexible design;COP2154|2233|0发布时间：2024-07-18
- 摘要：Recently, the Paris Agreement which many nations agreed to limit greenhouse gas emissions, has come into effect. According to the agreement, many of the compounds currently used in the refrigeration sector are scheduled for phase out due to ozone depletion concerns and/or contributions to global warming. There is current interest in developing working fluids with low global warming potential (GWP). One such fluid is 2,3,3,3-tetrafluoroprop-1-ene (R1234yf). Although the thermophysical properties are critical for the selection of the potential refrigerant, only a few studies have been conducted on the thermophysical properties of refrigerant mixtures containing R1234yf. In this work, we focused on the viscosity of R32 and the binary mixture of R32 + R1234yf. The liquid viscosity of R32 and binary mixture of R32 + R1234yf were presented over the temperature ranges of (263 to 350) K and (263 to 360) K at pressures up to 30 MPa using the vibrating wire viscometer. The measurements of mixtures containing the mole fraction (0.2448, 0.4108, 0.6086 and 0.8356) of R32 were carried out. The overall uncertainties of these results were ±2.0 %. The experimental results of the pure R32 and the mixture were correlated with hard-sphere scheme. The average absolute deviations between the experimental results and the correlations were 0.28 % for R32 and 0.69 % for R32 + R1234yf, and the maximum absolute deviations were 0.92 % and 2.09 %, respectively. Comparisons between measurements of this work and literatures were also presented.关键词：mixed refrigerants;thermophysical properties;viscosity;R32/R1234yf2361|2340|2发布时间：2024-07-18
- 摘要：The excess Gibbs free energy-equation of state "(" "G" ^"E" "-EoS) " is a new method for predicting the vapor liquid equilibrium (VLE) with respect to the equation of state (EoS) and activity coefficient method. In this study, the Peng Robinson (PR) equation of state was employed in combination with the Wong-Sandler (WS) mixing rule to predict binary and ternary systems coupled with the activity coefficient model: the modified universal quasichemical functional group activity coefficient (UNIFAC) used in the predictive Soave-Redlich-Kwong (PSRK). So a gas-liquid equilibrium prediction model of the mixture (PRWS-UNIFAC-PSRK) was constructed EoS (PRWS-UNIFAC-PSRK model). The to calculated VLE data of R161/R1234yf, R32/R125/R134a, and the strong zeotropic ternary system of R1234yf/R170/R14 were calculated. The results indicated that for R161/R1234yf, the relative deviation of the pressures and the absolute deviation of the vapor phase mass fraction between the experimental and calculated data were within ±1.5% and ±0.02, respectively, which were better than those found using the REFPROP9.0 software, while the deviations for R32/R125/R134a were within ±4% and ±0.02, respectively. The calculated VLE data and three-dimensional phase equilibrium diagrams showed that the temperature glide phenomenon of R1234yf/R170/R14 was the most obvious at the mass fraction ratio of 0.4/0.2/0.4, and the maximum sliding temperature reached 72.5 K. The dew-point and bubble-point temperatures increased with the increase in the mass fraction of R1234yf.关键词：vapor liquid equilibria;G^EEoS model;mixed refrigerants;temperature glide;R1234yf2147|2222|1发布时间：2024-07-18
- 摘要：Based on particle phase dynamics, the Euler-Euler model in FLUENT was selected to numerically simulate the ice slurry flowing in a piping system such as a straight pipe, 90° elbow pipe, and T type pipe without considering the ice melting process. The simulation results revealed that the pressure drops in these three pipe types at the entrance were obvious. In the 90° elbow pipe, the inside pressure was less than the outside pressure after the bend, and the highest and lowest pressures appeared in the shunt of the T type pipe. The ice slurry flow experiment results showed that the specific pressure drop increased with the velocity and ice particle fraction. Among the three pipe types, the pressure drop of the straight pipe was the smallest, and that in the T type pipe was the largest. A comparison of the numerical simulation and experimental results showed that the pressure drop was consistent with the flow velocity within an error range of 20%, but the simulated value was larger than the experimental value at high flow rates. Determining the flow characteristics of an ice slurry will play an important role in the popularization of ice slurry engineering applications.关键词：ice slurry;numerical simulation;flow characteristic;specific pressure drop;pressure lose coefficients2175|2185|5发布时间：2024-07-18
- 摘要：Based on the premise of recycling the low-temperature waste heat from a 90–150 ℃ source, a test bench was designed for an organic Rankine cycle power generation system, and experimental research was performed. The effects of the evaporating temperature on the expander performance and system performance were investigated by adjusting the inlet pressure of the turbo expander and the evaporation temperature. The experimental results showed that when the evaporation temperature increased from 76 ℃ to 84 ℃, the expander inlet temperature gradually increased. Thus, the expander speed increased by approximately 9.11%, the output power increased by 1.26 kW, and the highest isentropic efficiency was 80.6%. At the same time, the cycle net power, thermal efficiency, irreversible loss, and exergy efficiency increased with the evaporation temperature by 37.9%, 3.5%, 15.4%, and 27%, respectively.关键词：ORC;turbo expander;thermal efficiency;exergy efficiency1947|2111|1发布时间：2024-07-18
- 摘要：Alternatives to the sorbents and heat storage materials used for a heat storage sorption air intake driven by solar energy were examined in this study. These included thermal conductivity and the sorption kinetic performance of composite sorbents using expanded natural graphite treated with sulfuric acid (ENG-TSA) and activated carbon fiber (ACF) felt as porous host matrixes, and thermal conductivity and differential scanning calorimetry (DSC) test for the composite phase-change thermal energy storage materials, i.e., stearic acid (SA)/ENG-TSA. The results revealed that the best thermal conductivity of the composite sorbent ENG-TSA-LiCl was 5.67 W/(m?K), and the largest water uptake was 1.54 g/g. The sorption performance of the composite sorbent ACF-LiCl using a vacuum impregnation method was better than that when using the atmospheric impregnation method. The water uptake of the consolidated sorbent of ASLi40 was 1.59 g/g, which can be applied to mass production. ENG-TSA-SA was suitable for solar energy and other low-grade heat energy recovery applications, with a high radial thermal conductivity (22.2 W/(m?K)) and appropriate internal phase transition temperature (65.9–77.1 ℃). The addition of a heat reservoir significantly slowed down the decrease to the desorption temperature.关键词：air intake;composite sorbent;phase change material;thermal conductivity;solar energy2324|2153|1发布时间：2024-07-18
- 摘要：A sub-module (three-row cabinet as an example) of data center with the cold channel closed in an array of odd-numbered columns is taken as the subject to be investigated. A computational fluid dynamics simulation was used to visualize the compound effect of the plenum height and floor perforation rate on the airflow in the data center. The temperature fields of 25 typical models with various combinations of plenum heights and floor perforation rates were analyzed to find the best match of 600-700 mm (plenum height) and 20%–50% (perforation rate). Furthermore, eight plenum height and perforation rate models that fell within the above range were compared to find the best uniform temperature distribution inside the cabinets. Based on the results, a baffle was erected in the plenum at four angles from -15° to 45° to obtain the most satisfying cooling effect. The results showed that the optimal model for the data center sub-module had a plenum height of 600 mm, perforation rate of 20%, and 15° baffle.关键词：data center;air duct layout;temperature field;plenum height;perforation rate;baffle angle2233|2316|2发布时间：2024-07-18
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Simulation and Comparison of Cooling Performances of Refrigerated Vehicles with Different Structures
摘要：The reasonable optimization and improvement of the structure of the refrigerated compartment plays an important role in efficiently improving the cooling effect of a refrigerated truck, which ensures the quality and safety of the goods during refrigerated transport. It is also an effective way to deal with the needs of cold chain suppliers. In this study, four kinds of refrigerated trucks with the same working conditions but different structures were examined, with apples used as the test material and based on the same goods stack. Computational fluid dynamics simulations were used for the internal temperature distributions of the four compartments under specific wind speed and cooling temperature conditions. The cooling performances (temperature distribution, cooling time, cooling uniformity) of the four refrigerated trucks were compared and analyzed. The results showed that the installation of both a side ventilation trough and ground rail was the best way to improve the cooling performance of refrigerated trucks. The coefficient of temperature variation was 0.0013, with 62.06% of the goods were within a temperature range of 3–4.5 ℃. However, there was no obvious improvement in the cooling performance compared with the single installation of a side ventilation trough, where the coefficient of temperature variation was 0.0015, and 59.26% of the goods were within a temperature range of 3–4.5 ℃. However, compared with the single installation of the guide rail, the single side ventilation trough could significantly reduce the cooling time and improve the cooling uniformity. Compared with a refrigerated truck with no guide rail, although there was no obvious reduction in the cooling time, the installation of the guide rail by itself could improve the uniform cooling of the cargo. The coefficient of temperature variation for the single installation of the guide rail was 0.0021, and the coefficient of temperature variation of the no guide rail was 0.0024. A comparison of the experimental and simulated values for the wind speed and temperature showed good agreement, with temperature maximum root mean square errors of 0.221 ℃ and 0.198 ℃, respectively, and maximum average relative errors of 18.35% and 16.91%, respectively. The maximum air speed deviation between the simulated and measured values was 0.3 m/s. This study provided some reference values for the optimization of different cold chain requirements to ensure the quality and safety of agricultural products during refrigerated transportation.关键词：refrigerated truck;temperature distribution;numerical simulation;cooling performance1950|2160|6发布时间：2024-07-18 - 摘要：In order to discuss the heat transfer performance of a vertical U-tube in protective engineering, the changes in the inlet and outlet water and soil temperatures were analyzed under two different conditions based on a ground source heat pump experimental platform for underground engineering. The underground temperature was measured during the test, and the thermal diffusion ability of the soil was studied. The results showed that the heat exchange gradually decreased under the condition of 24 h continuous operation. Under the condition of 12 h intermittent operation, the local heat exchange at the beginning was significantly smaller than that of the continuous operation, but the average heat transfer capacity was larger than that of the continuous operation. A continuous operation model should be used when protective engineering deals with raids, while the thermal stability time and heat exchange at that time should be recommended as indexes to evaluate the ability of a buried pipe system when dealing with raids. The time and heat exchange measured in this experiment were 14 h and 1 310.4 kJ/m. However, an intermittent operation model should be adopted when the engineering is used over a long period because it effectively slows down the heat accumulation.关键词：heat pump;U-type buried pipe;protective engineering;soil temperature;heat exchange2011|2128|0发布时间：2024-07-18
- 摘要：This paper presents the development of a hybrid model for simulating a vertical U-tube geothermal heat exchanger under actual climate. The model consists of a 3D model representing a pair of U-tubes buried in symmetric boreholes and a supplementary 2D model that can be applied to real site scenarios. The temperature series at the wall of the borehole and initial soil temperatures at different depths derived from the simulation results of the 3D model serve as the input boundary conditions of the 2D model. Hence, the hybrid model shares the respective advantages of both subordinate models and therefore provides comprehensive simulation results that span approximately 10 months at a slight cost in implementation complexity. Meanwhile, the model is limited by numerous assumptions such as the consistency between the ground surface and air temperatures and physical uniformity of the materials. Simulations were performed based on the conditions obtained at a real site in the city of Hangzhou. The simulation time range was June 12, 2015, to March 17, 2016, which covered an entire cooling, transition, and heating season. The collected data revealed that the soil within an effective radius of 2 m gained an absolute increase in internal energy of 0.292 MJ after the simulation. The relative increases in the internal energy and average temperature were 1.037 MJ and 0.28 K, respectively, compared to those affected only by climate, which indicated an unwanted accumulation of heat beneath the ground. Moreover, the temperature at a deeper soil depth showed a lag in phase behind that of a shallower depth. This lag was approximately 2 weeks between a point at the center of the entrance and exit of the U-tubes and a point 1 m below it. Moreover, the fluctuation patterns of the inlet/outlet fluid temperatures showed a significant shift from the air temperature toward the annual averages, which were -8.313 K in the cooling season and 9.077 K in the heating season. Finally, the temperature distribution among pipe-clusters at different depths showed that the heat accumulation mainly occurred at a depth greater than 7 m, and the accumulation was more severe at a shallower depth and at the corners of clusters.关键词：ground source heat pump;3 dimensional modelling;implementation complexity;underground heat transfer field2019|2141|0发布时间：2024-07-18
- 摘要：An experimental system that used a constant hot-water-heating heat pipe was constructed to study the performance of a parallel-type pulsating heat pipe under normal temperature. With methanol as the medium and a heat pipe diameter of 4 mm, the effects of different cooling forms, heating and cooling temperatures, and liquid filling volumes on the starting characteristics were studied. The influence of different diameters (2 mm, 4 mm, 6 mm, and 8 mm) on the isothermal property was researched with methanol as the medium, and the heat-transfer capabilities with different heating lengths (20 cm, 25 cm, and 30 cm) under methanol and R600a as working media were investigated. The results showed that a condenser section that used water cooling was better than natural air cooling for heat pipe start-up. A higher heating temperature and lower cooling temperature were advantageous for the heat pipe start-up. The start-up time of the heat pipe increased with the filling quantity. During the running period, the heat pipe had a good isothermal property in the longitudinal and transverse directions, and the isothermal property gradually decreased with an increase in the heat pipe diameter. With an increase in the heating temperature, the changing laws for the heat-transfer capability were different when the working media are methanol and R600a. Shortening the evaporation segment length could alleviate the adverse effects of overheating on the heat pipe关键词：pulsating heat pipe;starting characteristic;temperature uniformity;heat transfer capability2075|2311|2发布时间：2024-07-18
- 摘要：Variable refrigerant flow (VRF) valve fault detection and diagnosis usually face the problems of too many features and low efficiency. Therefore, a high-efficiency hybrid model based on a genetic algorithm (GA) and back propagation neural network (BPNN) was proposed. In this hybrid model, the feature subset is extracted from the original feature set of the VRF using the GA, and then the parameter-optimized neural network is used to detect and diagnose VRF valve faults. In this study, the hybrid model was used to detect and diagnose faults with electronic expansion valve sticking, leaking, and a four-way valve. The results showed that the hybrid model proposed in this paper could effectively and reliably diagnose faults. The integrated correct rate of fault diagnosis reached a peak value of 99.27%. In particular, the correct rate of electronic expansion valve sticking fault diagnosis was improved by 8%. In addition, the hybrid model obviously improved the detection and diagnosis efficiency, decreasing the operating time by 52.17%.关键词：VRF;valve fault detection and diagnosis;feature extraction;genetic algorithm;back propagation neural network2521|2193|6发布时间：2024-07-18
- 摘要：Experimental study of R134aduring condensation heat transfer inside the micro-fin tube for the condensation temperatures of 35 ℃、40 ℃ and 45 ℃ was made. The mass flux, condensation temperature, structural parameters of micro-fin tube were chosen as influencing factors and the total heat transfer coefficient, water-testing heat transfer coefficient, refrigerant heat transfer coefficient and pressure drop were selected as evaluation indexes. Experimental results show that: the total heat transfer coefficient, refrigerant heat transfer coefficient and pressure drop increase with increasing mass flux, and decreasing condensation temperature and tube diameter, but the water-testing heat transfer coefficient slightly decreases with increasing mass flux and the condensation temperature has a small influence on it. The thermal resistance analysis shows that the water-testing thermal resistance increases and refrigerant thermal resistance decreases with increasing mass flux, and the refrigerant thermal resistance is always less than the water-testing thermal resistance. To evaluate the comprehensive performance of micro-fin tubes, the ratio of refrigerant heat transfer coefficient and pressure drop (the heat transfer coefficient of unit pressure drop) was proposed, results show the ratio decreases first and then increases with the increase of the mass flux, and increases with decreasing condensation temperature and tube diameter in the micro-fin tubes.关键词：condensation;micro-fin tubes;the thermal resistance analysis;the heat transfer coefficient of unit pressure drop2446|2359|0发布时间：2024-07-18
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