最新刊期
卷 44 ， 期 5 ， 2023
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Design Measurement and Analysis of Vapor Compression Heat Pump with Large Temperature Difference优秀论文
摘要：This paper proposes a ''zero-carbon heating'' model that uses the technology of an electric-driven vapor compression heat pump unit with a large temperature difference that can be used for long-distance delivery of heating. The model adapts to the operational characteristics of the power grid and the heating network, which facilitates 'power supply using 'green electricity'' and heat supply mainly with zero-carbon industrial waste heat. Hence, it is the key equipment that features the synergy of heat and power. The studied system was equally cost-effective to the conventional cogeneration system since it can significantly reduce the backwater temperature of the long-distance transmission network and increase the transmission capacity of the heat network; the return water temperature can be very low. The model has a compact structure; therefore, it can adapt to complex working conditions and land requirements. To verify the feasibility of this technical approach, the operating performance of 0.5 MW units used in Yuncheng in two heating seasons from 2020–2022 was measured and analyzed. The test results showed that the unit can operate stably and efficiently within a range of 0–100% operating load. When only the performance of the electric-driven vapor compression heat pump was calculated, the minimum and maximum heating COP were 6.5 and 13.1, respectively, while the annual average heating COP was 8.3. The minimum return water temperature of the primary network can be 33 K lower than that of the secondary network, reaching 15 ℃. When compared with gas-boilers as the baseline, the payback period was four years.关键词：zero-carbon heating;synergy of heat and power;electric-driven vapor compression heat pump;long-distance heating with large temperature difference;COP705|1068|0发布时间：2024-07-18 - 摘要：The end-face pressure distribution of screw machinery is the premise of calculating the leakage and dynamic characteristics of shaft seals. Unlike other types of machinery, the pressure distribution on the suction end face of screw machinery is related to the operating parameters and the rotor design parameters. To study the leakage characteristics of the screw mechanical shaft seal, a nonuniform pressure distribution model of the end face and a shaft-seal leakage model were established. The accuracy of the model was verified through comparison with existing experimental data. The pressure distribution on the end face, leakage of the shaft seal under different working pressures, built-in volume ratios, and shaft-seal outlet pressures were studied. The results showed that the pressure on the screw-expander end face was nonuniformly distributed, and the average pressure was far less than the working pressure. The average pressure at the end face and the leakage increased approximately linearly to the working pressure. The average pressure of the end face and leakage decreased with an increase in the built-in volume ratio. When the working pressure was increased from 500 kPa to 800 kPa, the average pressure of the end face increased by 12%, and the leakage increased to 3.8 times that of the original value. When the built-in volume ratio increased from 3 to 5, the average pressure on the end face and the leakage decreased by 7.4% and 50%, respectively. The leakage decreased with increasing labyrinth-seal outlet pressure and reduced more distinctly at higher pressures. When the outlet pressure increased from 100 kPa to 300 kPa, the leakage decreased by 37%.关键词：twin-screw expander;end-face pressure;leakage;shaft seal576|872|0发布时间：2024-07-18
- 摘要：As the core component of a valved linear compressor for a Joule-Thompson throttling refrigerator, the displacement characteristics of the suction valve directly affect the compressor's performance. A valve-displacement model was established to determine the displacement characteristics of the suction valve. The effects of the valve thickness, lift, and operating frequency on the displacement change of the valve were analyzed theoretically. A visualization experimental bench was constructed to measure and study the displacement changes in the valve and compressor efficiencies in different working conditions. The results showed that the valved linear compressor demonstrated the best performance when the thickness of the suction valve plate was 0.2 mm and that of the lift was 0.38 mm. Reasonable design of the valve-lift limiter height can improve the performance of the compressor, with less stress on the valve deformation and impact. At lower operating frequencies, the valve developed flutter, increasing the pressure loss. The research results can provide a reference for the optimization and reliable design of reed valve manifolds.关键词：valved linear compressor;suction valve;visualization;displacement characteristics;compressor efficiency591|894|0发布时间：2024-07-18
- 摘要：The use of -80 ℃ low-temperature cold storage is increasing in blood stations, hospitals, and medical research institutions. Low-temperature cold storage primarily uses traditional cascade refrigeration systems. In this paper, Stirling refrigeration is used to cool a -80 ℃ low-temperature cold storage. The Stirling refrigerator provides high-efficiency performance at low temperatures; low-temperature cold storage with a volume of 1500 L at -80 ℃ was designed. The structural characteristics of the low-temperature cold storage were analyzed, and the composite insulation layer with a vacuum insulation panel (VIP) and polyurethane was studied. Calculation methods for the heat load of low-temperature cold storage were presented. Based on the experimental performance of the Stirling refrigerator, the feasibility of the design scheme was verified. A single Stirling refrigerator can reach a cooling temperature of -80 ℃ in less than 10 min under no-load conditions with 200 W of input power; the minimum cooling temperature was stable at approximately -160 ℃ after 50 min, with a cooling capacity of 180 W with 500 W of input power, corresponding to a COP of 0.36. This research provides theoretical guidance for future ultra-low temperature cold storage with Stirling refrigerators.关键词：cold storage;heat load;cryogenic refrigerating machine;Stirling cycle563|791|0发布时间：2024-07-18
- 摘要：Severe energy and environmental crises hinder sustainable development and realization of carbon peaking and carbon neutrality; therefore, more energy-efficient cooling systems must be developed for data centers. In this study, an indirect–direct evaporative cooling chiller coupled with a heat-pipe backplane air-conditioning system was designed, with four operating modes throughout the year. In Nanjing, the water supply and return temperatures of the chiller were designed to be 10 °C and 16 ℃, respectively. A mathematical model of each component was established; it was found that free cooling was used 59.9% of the year, and completely free cooling was used 42.6% of the year. When the supply and return temperatures increased, the free-cooling time increased. In addition, we explored the factors influencing heat-pipe backplane performance. The temperatures of the supply and return water had a great impact – the cooling capacity decreased as the temperature increased. The height difference between the CDU and the backplane had little effect once the power requirements of the refrigerant cycle were met. The diameter of the copper tube in the heat exchanger was reduced from 7 mm to 5 mm, and the cooling capacity and air-supply volume were improved.关键词：evaporative cooling;heat-pipe backplane;data center;full operating conditions;refrigeration performance603|948|0发布时间：2024-07-18
- 摘要：Rotary desiccant wheels have gradually become mainstream in the field of air dehumidification owing to their compact structure, high efficiency, and continuous dehumidification and regeneration processes. To effectively reduce the energy consumption of traditional rotary desiccant wheels, we constructed a numerical model of a desiccant wheel and verified it through experiments. A weight factor was introduced to combine the energy consumption and dehumidification performance of the system as the optimization objective. An energy-saving optimization control model of the desiccant wheel system was proposed with an improved PSO as the solution algorithm. The energy-saving optimization effects with different weight factors, ambient humidity ratios, and ambient temperatures were analyzed using the optimization control model. The results showed that when the weight factor λ=0.3, the humidity ratio requirements at the outlet were met and the energy savings were maximized. When the ambient humidity ratio was in the range of 16–22 g/kg dry air, the average and maximum energy savings were 76.4% and 95.6%, respectively. In the ambient temperature range of 24–30 ℃, the average energy saving was 40.2% and the maximum energy-saving rate was 42.1%.关键词：desiccant wheel;numerical modeling;optimal control;PSO;energy savings510|917|0发布时间：2024-07-18
- 摘要：Variable refrigerant flow (VRF) systems are widely used in buildings. Soft faults are common and difficult to identify during VRF operation, making the system less efficient. In this study, a soft-fault level identification model for VRF was proposed based on a classifier chain using one-dimensional convolutional neural networks as the base classifiers. The structure and parameters of the base classifiers were set according to a fault diagnosis model using the experimental data of fouling faults in the outdoor unit; two new methods for encoding data labels were proposed. After establishing the initial soft-fault level identification model, the number of convolution kernels in the base classifiers was further adjusted and a magnification factor was proposed to improve the label encoding. The results showed that the improved classifier chain model can diagnose fouling faults in the outdoor unit with an accuracy greater than 96%, corresponding to an increase of 2%–3% from the baseline. The encoding methods proposed in this study did not diagnose faulty conditions as normal and are suitable for use in the classifier chain model.关键词：variable refrigerant flow;fault detection and diagnosis;fault level identification;classifier chain;convolutional neural network477|751|0发布时间：2024-07-18
- 摘要：Based on a three-dimensional distributed parameter model, a simulation model of a small-diameter heat exchanger in the indoor unit of a split-household air-conditioner was established, and the performance metrics were computed, including the total heat load, sensible heat load, latent heat load, refrigerant-side pressure drop, and air-side pressure drop. The effects of the tube length, refrigerant mass flow rate, air volumetric flow rate, air inlet temperature, and air inlet relative humidity on the heat exchanger performance metrics were determined under different working conditions. For the 5 mm diameter heat exchanger considered in this study, the corresponding tube length range was 0.6~0.7 m, achieving good heat transfer with a small pressure drop. Owing to the comprehensive influence of the heat transfer coefficient and the effective mass transfer time, when the volumetric flow of air was in the range of 600–700 m3/h, the latent heat load reached a maximum of 426 W. With an increase in the air inlet temperature, the sensible heat load first increased and then decreased.关键词：small-diameter heat exchangers;distributed parameter model;heat load;pressure drop566|1018|0发布时间：2024-07-18
- 摘要：R32 is widely used in room air-conditioners, with heat-transfer characteristics affected by the intermiscibility of the oil. Therefore, it is necessary to determine the optimal intermiscibility of the oil to improve heat transfer characteristics. This study investigated the influence of stratification, caused by the intermiscibility of the R32-oil mixture, on the heat transfer characteristics. The flow boiling heat transfer coefficient and pressure drop of a completely miscible R32-oil mixture, a partially miscible R32-oil mixture, and a completely immiscible R32-oil mixture were tested experimentally. To cover the working conditions of air conditioners and reflect the different intermiscibilities of the R32-oil mixtures, the test conditions included evaporating temperatures from -5 ℃ to 15 ℃, vapor quality from 0.2 to 0.7, and averaged oil concentrations of 1% and 5%. The results showed that partially miscible oil had the highest heat transfer coefficient and the lowest pressure drop; at an evaporating temperature of 5 ℃, vapor quality of 0.7, and averaged oil concentration of 5%, the advantage of a partially miscible R32-oil mixture over that of the completely miscible and completely immiscible mixtures increased. The maximum increases in heat transfer coefficient were 36.8% and 357.8%, and the maximum decreases in pressure drop were 9.0% and 58.2%, respectively. Among the three types of oils, the partially miscible oil exhibited the best heat transfer and pressure drop characteristics and thus has the best application prospects.关键词：R32;lubricating oil;intermiscibility;flow boiling;heat transfer coefficient605|738|0发布时间：2024-07-18
- 摘要：To solve the problem of high temperatures during the operation of power batteries, a double-layer liquid-cooling plate heat-dissipation system with an I-shaped flow channel is proposed based on structural theory. The heat production model of the battery was established through charging/discharging experiments, and the computational fluid dynamics model of the liquid-cooling plate was established using FLUENT software. The effects of three structural parameters (length ratio, width ratio, and channel thickness) on the temperature and pressure drops were investigated using the orthogonal experimental design. The optimal combination of a length ratio of 0.70, width ratio of 0.85, and channel thickness of 2.5 mm was determined. In addition, the effects of different inlet velocities on the performance of liquid-cooling plates were considered. The comprehensive performances of I-shaped and serpentine channels were compared at the constraint of constant heat transfer area and inlet velocity. The results showed that with an increase in the flow rate, the maximum temperature of the liquid-cooling plate decreased 17.493 2 K, the standard deviation of the surface temperature decreased by 63.4%, and the maximum pressure increased by 726.789 Pa. The maximum temperature of the I-shaped flow channel liquid-cooling plate was 1.3330 K lower than that of the serpentine flow channel; the standard deviation of the surface temperature was 1.3865 K smaller, and the pressure drop was 24.38% lower than that of the serpentine channel.关键词：battery cooling;plate heat exchanger;I-shaped flow channel;heat transfer coefficient587|931|0发布时间：2024-07-18
- 摘要：Carbon peaking and carbon neutrality goals have been set, and the Kigali Amendment to the Montreal Protocol has officially come into force. The vigorous development of hydrogen fuel cell vehicles has become an important means of energy conservation and emission reduction in the transportation sector. Nevertheless, current fuel cell vehicles have problems including a narrow operating temperature range, the greenhouse effect produced by the thermal management working fluid, and low efficiency owing to the independent thermal management system. Thus, based on a transcritical CO2 heat pump, a novel thermal management scheme was proposed that uses multiple control algorithms and combines the thermal management systems of vehicle cabins and proton exchange membrane fuel cells (PEMFC). AMESim was used to simulate this system. After a comprehensive analysis, the results showed that the integrated thermal management system can ensure that the cabin and battery quickly reach and maintain their respective ideal temperature. Compared with a traditional independent thermal management system, the new system has better energy utilization efficiency over the entire operating range, with greater overall efficiency and energy savings.关键词：hydrogen fuel cell vehicle;thermal management;CO2 heat pump;AMESim718|1013|0发布时间：2024-07-18
- 摘要：To investigate the mechanism of vehicle cabin temperature on driver cognitive ability, a vehicle simulation driving platform was built. The driver's physiological parameters, psychological feelings, and cognitive ability were investigated at different cabin temperatures (20 ℃, 23 ℃, 26 ℃, and 30 ℃). The results showed that the cognitive ability of the driver decreased with an increase in cabin temperature. Heart rate increased significantly, and the thermal sensation, thermal comfort, and brain load scores increased; the environmental acceptability, job satisfaction, and job willingness scores decreased. At 20 ℃, the completion time of the cognitive ability test was the shortest, the number of errors was the smallest, and drivers maintained high cognitive ability. At 23 ℃, the driver’s subjective thermal comfort was the best. When the vehicle cabin temperature exceeded 26 ℃, drivers began sweating on their palms, forehead, and back. Therefore, for better cognitive performance and thermal comfort, the vehicle cabin temperature should be maintained at 20–23 ℃. These research results can provide a reference for temperature standards in vehicle cabin design for safe driving.关键词：vehicle cabin;thermal environment;cognitive ability;thermal comfort;physiological reaction520|743|0发布时间：2024-07-18
- 摘要：On the front-end cooling module of electric vehicles (EVs), geometric models of the low-temperature radiator (LTR) with inclination angles of 0°, 15°, 30°, 45°, and 60° were established and numerically simulated. At the same flow rate, the larger the inclination angle, the better the heat transfer of the LTR, the higher the resistance, and the lower the comprehensive performance, as verified by the test results. By fixing the position of the air-inlet grille, geometric models of the LTR with a shroud at different inclination angles were established for simulation. With an increase in the inclination angle, the shroud resistance decreased; the airflow distribution uniformity and heat transfer performance of the LTR were improved; the resistance increased, and the comprehensive performance decreased. By optimizing the shroud structure, the flow distribution was improved; the flow resistances of the shroud and LTR were reduced, which led to improved heat exchange. It was concluded that the larger the inclination angle, the better the comprehensive performance of the cooling module. Comprehensively considering the arrangement of the front compartment, an inclination angle between 45° and 60° was more applicable.关键词：cooling module;shroud;inclination angle;performance;enhanced heat transfer;airflow distribution617|1035|0发布时间：2024-07-18
- 摘要：A swirl nozzle is a vital component in an outdoor snow-maker, directly affecting the rate and amount of snow production. An atomization experimental facility was designed and established to test swirl nozzles in outdoor snow-makers. The influence of the water supply pressure on the atomization effect of the nozzle and the heat transfer performance between water droplets and the environment were experimentally studied. The results showed that the spray shape was a hollow spindle with poor atomization in the low-pressure section. With an increase in the inlet pressure, a dramatic increase in the spray cone angle was observed. At high pressure, the spray shape was a hollow cone with a relatively stable cone angle. When the spray had a stable shape, the mass flow rate increased, the Sauter mean diameter decreased with an increase in the inlet pressure, and the atomization cone angle stabilized at 76°. Moreover, the increased pressure improved the heat transfer efficiency of the spray, resulting in a shorter heat transfer time to the ambient. This study supports the structural design of snow-maker atomization components.关键词：outdoor snow-maker;swirl nozzle;spray;droplet diameter543|859|0发布时间：2024-07-18
- 摘要：Since the Beijing Winter Olympic Games, the domestic ice and snow industry has grown rapidly, driven particularly by artificial snow parks with higher requirements in terms of both the quantity and the quality of artificial snow. This research showed that the quality of artificial snow was closely related to the droplet size distribution in the spray field. The droplet size distribution was affected by droplet collision, polymerization, and separation, as well as the nozzle distribution of the artificial snow-making system. Therefore, PIV and particle sizing systems were used to measure the overall morphology and droplet size distribution of the spray field generated by atomization of the gas-liquid mixed artificial snow-making system to study the effects of the gas-liquid mass ratio (gglr) and nozzle spacing on the droplet size distribution of the spray field. Our results showed that with an increase in gglr, the overall morphology of the spray field exhibited an inward shrinking trend, and the minimum average droplet size occurred below the nozzles. When gglr was constant, the interference between the two nozzles increased with a decrease in nozzle spacing, and the average droplet diameter increased with an increase in the axial distance, presenting an M-shaped distribution with a change in the radial distance.关键词：artificial snow;particle-size distribution;gas-liquid mass ratio;nozzle spacing512|789|0发布时间：2024-07-18
- 摘要：Experiments were conducted with flow rates between 1.0 m/s and 2.5 m/s, ice mass fractions between 10% and 30%, and initial particle sizes between 350 μm and 550 μm to study the effects of these parameters on the evolution of ice crystal size in ice slurry isothermal flow. The results indicated that the ice particle-size distribution of the ice slurry prepared using a supercooling method presented a lognormal distribution. Under turbulent conditions, the Sauter mean diameter at the outlet was significantly smaller than that at the inlet. This indicates that the effect of breakage on the ice particle-size distribution was more significant than that of aggregation, resulting in an increase in small ice particles and a decrease in large ice particles. Large ice particles are more likely to break into smaller particles; the effect of breakage becomes more significant with an increase in the flow rate. With an ice mass fraction of 10%, the velocity increased from 1.0 m/s to 2.5 m/s, and the Sauter mean diameter difference between the inlet and outlet (Δd32) increased from 16.1 μm to 34.6 μm. These findings have significance in the safe transportation of ice slurries.关键词：ice slurry;particle-size evolution;aggregation;breakage505|864|0发布时间：2024-07-18
- 摘要：Ice slurry has good application prospects owing to its good cold thermal energy storage capacity and flow heat transfer ability. In this study, soybean oil microemulsionswere prepared using the Shah method, where soybean oil was used as the oil phase, Tween80 and AEO-3 as surfactants, and amyl alcohol as a cosurfactant. The influence of the mass ratio of the oil phase to the surfactant, HLB value of the surfactant, and mass ratio of surfactant to cosurfactant (Km value) on the water increase in the microemulsion was investigated experimentally. The optimum ratio of the microemulsion was obtained, where the mass ratio of the oil phase to surfactant, the mass ratio of Tween80 to AEO-3, and the Km valuewere 1:4, 6:4 (HLB value 11.6), and 2:1, respectively. The properties and structure of the microemulsions were analyzed in terms of particle size, electrical conductivity, and stability. Ice slurry was prepared using the microemulsion. The ice storage rate, apparent viscosity, and cycle stability of the ice slurry prepared using the microemulsion were tested and analyzed. The experimental results show that the soybean oil microemulsion with 50% water content isa W/O microemulsion with good stability. The prepared microemulsion ice slurry exhibitsa good ice storage rate and fluidity.关键词：microemulsion;ice slurry;ice storage rate;cycling stability;soybean oil471|689|0发布时间：2024-07-18
- 摘要：Due to the large temperature difference between ambient temperature (25 ℃) and the temperature under standard atmospheric pressure and its large sensible heat storage capacity, ethanol slurry can be used as a cold thermal energy storage medium in the cold-chain transportation market. The flow characteristics (particularly the pressure drop) of the ethanol slurry are important parameters in various applications. Combined with the two-fluid model based on particle phase dynamics proposed by Gidaspow, changes in the flow rate and pressure drop of an ethanol slurry flow with solid phase fraction in a horizontal straight pipe were studied using FLUENT. When the flow rate increased from 0.51 m/s to 0.92 m/s, the pressure drop increased from 5.184 kPa/m to 63.707 kPa/m and the solid phase fraction changed from 10.4% to 30.5%. The model was consistent with the experimental observations; the average deviation between the experimental results and the numerical simulation was 12.8%.关键词：cold thermal energy storage medium;ethanol;pressure drop characteristics;solid-liquid two-phase system450|756|1发布时间：2024-07-18
- 摘要：To optimize the thermal performance of a medical refrigerator, a composite cold thermal energy storage plate was considered. A design scheme for a composite cold thermal energy storage plate in a medical refrigerator with a uniform and controllable temperature field was proposed. An experimental platform was developed. A medical refrigerator and the composite cold thermal energy storage plate were designed according to the principle of composite cold thermal energy storage. From the perspective of the equal mass scheme and the equal phase-change latent heat scheme, the inner-wall temperature change and cold thermal energy storage time of the phase-change materials (n-tetradecane, CaCl2?6H2O, and water) in the cold thermal energy storage plate were compared. It was found that an equal mass combination of 1.5 kg n-tetradecane in the inner layer and 1.5 kg CaCl2?6H2O in the outer layer of the cold thermal energy storage plate produced the best performance. Further, the cold thermal energy storage duration, average temperature, maximum inhomogeneous coefficient, and the cooling discharge rate of the cold thermal energy storage plate with the best performance at 2–8 ℃ were compared with different positions in the medical refrigerator (horizontally located on both sides, stacked on both sides, diagonally placed, and perimetrically placed). The results indicated that the composite cold thermal energy storage plate placed diagonally had the longest storage duration; the average temperature for the four placement positions was within 2–8 ℃. When the two sides were stacked, the maximum inhomogeneous coefficient was the lowest, and the cold discharge rate of the cold thermal energy storage plate was the highest. Considering temperature uniformity as the priority, the cold thermal energy storage effect of an equal-mass combination scheme stacked on both sides was preferred. The experimental results provide a reference for promoting the application of composite cold thermal energy storage plates for medical refrigerators in cold-chain transportation.关键词：medical refrigerator;phase change;composite cold thermal energy storage plate;temperature distribution;placement513|846|0发布时间：2024-07-18
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Numerical Study on Cooling and Crystallization Characteristics of Solid Surface Vitrification Method
摘要：Solid surface vitrification (SSV) has been increasingly applied in the field of cell cryopreservation. However, most studies based on empirical experimentations have not included simulation analysis and physical mechanism explanation, consequently affecting the universality of the designs and innovation efficiency in SSV-related technologies. This study focused on the non-isothermal crystallization characteristics and established a thermal diffusion model of SSV coupled with a non-isothermal crystallization source. A propylene glycol solution with the mass fraction of 35% was selected as the sample for analysis. Additionally, the effects of the pre-cooling temperature, sample volume, and sample shape on the temperature and crystallization characteristics of the SSV method were investigated. The results show that the established model can directly reveal change patterns of the temperature and the crystallinity inside the sample during the freezing process. The region most likely to undergo crystallization is located at the upper part of the sample away from the precooled surface, and the most crystallizable region is not necessarily located at the top of the droplet sample. Furthermore, vitrification of the sample is easier to achieve because of the lower precooling temperature, smaller sample volume, and flatter shape.关键词：cryopreservation;solid surface vitrification;precool;rapid cooling;non-isothermal crystallization497|887|0发布时间：2024-07-18
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