最新刊期
卷 43 ， 期 2 ， 2022
- 摘要：In this study, the amount and grade of cold energy in liquefied natural gas (LNG) were analyzed. According to the principles of "high-grade-demand with high-grade-energy, low-grade-demand with low-grade-energy, temperature matching, and cascade utilization," LNG cold energy can be used in power generation, air separation, seawater desalination, CO2 capture, and low-temperature cold storage, and the process methods, temperature range of utilization, working fluid properties, and advantages and disadvantages of LNG cold energy were discussed. The temperature ranges of existing LNG cold energy cascade utilization processes were compared to achieve more suitable temperature level matching. Specific schemes for cascade utilization of LNG cold energy were provided for large LNG gasification stations, small LNG gasification stations, and large ocean-going LNG ships.关键词：liquefied natural gas;cold energy;cascade utilization;temperature range of utilization1525|1786|0发布时间：2024-07-18
- 摘要：Cryopreservation technology has enabled biomedical applications such as cell-based therapies and assisted reproductive technology. Intracellular and extracellular ice formation and growth can lead to freezing injuries. The warming and cooling rates are closely related to the formation and growth of ice. This review first introduces two typical cryopreservation methods, namely slow programmable freezing and vitrification, and the two-factor damage mechanism. Three factors influencing cell cryopreservation are discussed. Accordingly, advances in optimization strategies and devices are classified into three categories. In detail, advances in warming and cooling strategies and related devices have been discussed. Finally, the challenges and perspectives are examined.关键词：cryopreservation;freezing injury;vitrification;ice crystal;microfluid1078|1103|2发布时间：2024-07-18
- 摘要：The surface of an outdoor evaporator can easily frost when an air-source heat pump is used for heating during winter. The most common defrosting method, reverse cycle defrosting, has safety risk and long defrosting period. To improve the performance of an air-source heat pump system with reverse-cycle defrosting, a defrosting system consisting of an air-source heat pump coupled with a liquid storage gas-liquid separator is proposed in this paper. Compared with traditional air-source heat pump systems, this system can effectively delay frosting and shorten defrosting period. In this study, the thermodynamic performances of an air-source heat pump system and a traditional air-source heat pump system under six working conditions were studied experimentally. The experimental results show that the system can effectively delay frosting and shorten the defrosting period in a heating-defrosting-recovery cycle; the maximum defrosting time can be delayed by 53 min, and the maximum defrosting period can be shortened by 75 s.关键词：air-source heat pump;reverse-cycle defrosting;system performance;liquid storage gas-liquid separator1316|1098|0发布时间：2024-07-18
- 摘要：The start-stop process of units integrated with air-source heat pumps (ASHPs) and freezer affects the heating performance of the heat pump system and the performance of the freezer. In this study, the performance of the integrated unit under separate operation and combined operation conditions was studied experimentally considering the start-stop process of the ASHP system. The effect of the start-stop times of the ASHP on the performance of the heat pump system and freezer system was analyzed. The experimental results indicated that compared with the different operating conditions of the heat pump, the attenuation start time of the heat pump heating capacity in the integrated unit was delayed by approximately 10 min, and the heating capacity and COP under the combined operation condition were both higher than those in the different operating condition. Under the combined operation condition, the average heating capacity and average COP of the ASHP under the three time start-stop condition were reduced by 18.2% and 27.3%, respectively. The average power consumption was increased by 16.3% compared with that under the one time start-stop condition. Correspondingly, under the three time start-stop condition of the heat pump, the average refrigeration capacity and average COP of the freezer system were reduced by 11.6% and 11.1% respectively compared with the one start-stop condition of the heat pump.关键词：air-source heat pump;freezer;integrated unit;start-stop;combined operation1092|1121|0发布时间：2024-07-18
- 摘要：This study proposes an optimization guideline for a two-phase ejector's nozzle exit position (NXP) based on the turbulent jet mixing mechanism. Under a given suction mass flow rate, the optimal NXP is the distance that the jet travels when the external boundary of the jet increases to the mixer radius. The performances of two-phase CO2 ejectors with NXP values of 3, 5, 7.5, 10, and 15 mm were studied by numerical simulations. The results show that when the NXP is 5 mm, the jet mixing pattern can exactly satisfy the above guidelines. In this case, the ejector has a maximum pressure-lift of 0.69 MPa, 46.8% higher than that of the 15 mm case. By analyzing the jet velocity profiles on different cross-sections in the suction chamber, we show that if the NXP is greater than the optimum value, the external jet boundary will exceed the mixer radius, preventing part of the jet flow from entering the mixer. In addition, a vortex region appears near the suction chamber wall, resulting in jet energy dissipation and thus degrades pressure recovery. When the NXP is less than the optimal value, the entrainment process is completed in the mixer, and the effective length is reduced, causing a 1.5% decrease in pressure recovery. This study is enlightened by the jet velocity characteristic and proposes a correlation for the initial guess of the optimal NXP, which shows a 4.2% deviation from the CFD result.关键词：ejector;nozzle exit position;optimization;jet1135|1141|0发布时间：2024-07-18
- 摘要：An integrated thermal management system for an electric vehicle requires a scroll compressor with a large displacement that runs under multiple working conditions and high loads. A design method for the scroll profile to enlarge compressor displacement was proposed. The geometric and thermodynamic characteristics of the novel scroll compressor were studied using a simulation model validated experimentally. The results show that the trapezoidal section scroll compressor can increase the displacement by 19.5% by reducing the average wall thickness by 29.9%, on the premise of ensuring the strength reliability of the root of the scroll wrap. Based on the influence of the profile parameters on the leakage characteristics, it was found that the difference of internal leakage rate between a trapezoidal cross-sectional scroll compressor and a constant-wall thickness scroll compressor is less than 2% , showing huge potential for application of trapezoidal cross-sectional scroll compressor.关键词：scroll compressor;profile;displacement;leakage1045|1004|0发布时间：2024-07-18
- 摘要：Replacing conventional boilers with an efficient heat pump system is an effective solution to achieving “carbon peaking and carbon neutrality”. In this study, a CO2 heat pump system adopting an ejector to realize dual-temperature evaporation is proposed for cascade utilization of waste heat and high-efficiency heating. Thermodynamic models of the baseline CO2 system (Base), conventional CO2 ejector system (Ej-Evap1), and CO2 ejector system with dual-temperature evaporation (Ej-Evap2) are developed based on the pinch method. The maximum coefficient of performance (COP) is achieved at the optimum discharge pressure for the dual-temperature evaporation system. Under the optimum working conditions, the results show that the maximum COP of the Ej-Evap2 system under nominal conditions is 4.84, which is 9.88% higher than that of the base. Double-temperature evaporation can significantly reduce the heat transfer irreversibility loss in the heat absorption process. The irreversible performance index of Ej-Evap2 during the evaporator process is 1.51, which is 24.50% lower than that of the base and Ej-Evap1 systems.关键词：heat pump system;CO2;ejector;temperature matching;dual-temperature evaporation;irreversibility loss1613|1240|2发布时间：2024-07-18
- 摘要：The thermodynamic performance of R600a/squalane and DME/squalane working pairs in single-effect and compression-assisted absorption refrigeration systems was analyzed in this study. The vapor-liquid equilibrium data were correlated using the NRTL model. The effects of the generation temperature, evaporation temperature, and compressor pressure ratio on the COP, exergy efficiency, and circulation ratio were analyzed. The results show that the R600a/squalane working pair performed better. The performance of the compression-assisted cycle was significantly better than that of the single-effect cycle. At an evaporation temperature of 278.15 K, peaks occur in the COP and exergy efficiency curves for single-effect and compression-assisted cycles with the increase in evaporation temperature. At a generation temperature of 363.15 K, the COP of the two working pairs increases monotonously with the increase in evaporation temperature, and the exergy efficiency curves exhibit peaks. With increasing generation and evaporation temperatures, the maximum COP and exergy efficiency values for the R600a and DME working pairs in the two cycles were 0.675 and 0.655, respectively. The performance of the DME working pair increased with an increase in the compression ratio, whereas that of the R600a working pair peaked at a ratio of 1.5. The circulation ratio decreased as the generation temperature, evaporation temperature, and pressure ratio increased.关键词：refrigerant;lubricant oil;absorption refrigeration;thermodynamic performance1065|1145|1发布时间：2024-07-18
- 摘要：This paper presents an experimental study on the oil retention and pressure drop characteristics of an R32/PVE VG68 mixture in compressor suction lines. The test samples were two smooth copper pipes with horizontal and vertical flow orientations of 10.7 mm in inner diameter. The tested conditions are saturation temperature and superheating degree (7.5/12 ℃, 7.5/6 ℃, and 10/12 °C). The refrigerant mass flux and nominal oil mass fraction (OMFno) are varied in the ranges of 90-230 kg/(m2?s) and 0-5%, respectively. The results showed that the oil retention increased with the actual oil mass fraction and mixture kinematic viscosity ratio and decreased with the refrigerant mass flux. Two consolidated databases for oil retention and pressure drop of suction lines, which involved R410A and R134a, were collected from five existing studies for comparison. Finally, based on the analysis of the oil transport mechanism, a new dimensionless parameter called the oil retention impact factor was proposed to characterize the difficulty of oil transport, which integrates the influences of geometric dimensions, working pairs, and operation parameters. It showed a relatively good relationship with the oil retention data from the amassed database and the present study.关键词：suction line;lubricant oil;oil retention;pressure drop;R321090|1058|0发布时间：2024-07-18
- 摘要：To study the heat and mass transfer characteristics of an R134a-DMF (Dimethylformamide) bubble absorption process in a vertical tube, an experimental device for bubble absorption in a vertical tube was fabricated, and a mathematical model of heat and mass transfer in the bubbling absorption process of R134a by an R134a-DMF solution was established. The characteristics of flow patterns of churn flow, slug flow, bubble flow, and single-phase flow were simulated and analyzed at an absorption pressure of 0.35 MPa, a vapor inlet temperature of 5 °C, and a weak solution inlet mass flow rate of 12.0 kg/h, by which the variation in absorption height with inlet parameters was obtained. The proportion of slug flow to the absorption height was the largest in the absorption process. As the absorption process continued, the rate of absorption increased. The variation in the vapor temperature was the largest, followed by the variations in phase interface temperature and solution temperature, and the variation in the cooling water temperature was the smallest. Furthermore, the variations at different temperatures were the largest in the churn flow state and the smallest in the bubble flow state. At the weak solution inlet mass fraction of 0.4 and the weak solution inlet temperature of 45 °C, the absorption height increased from 0.44 m to 1.88 m when the vapor inlet mass flow rate varied from 1.0 kg/h up to 2.5 kg/h.关键词：absorption refrigeration;refrigerant;bubble;coefficient of heat transfer977|1026|1发布时间：2024-07-18
- 摘要：This study uses experimental and computational fluid dynamics (CFD) methods to investigate convective heat transfer, heat convection caused by airflow, and heat conduction caused by temperature differences in large-space buildings with floor-level side wall air-supply systems. Three thermal environment experiments with different roof exhaust ratios were conducted in a reduced-scale laboratory to investigate the indoor thermal environment and load characteristics. The CFD simulation results were verified based on the experimentally obtained vertical temperature distribution of the central line and air-conditioning cooling load. Based on similarity theory, reduced-scale numerical models are extended to full-scale configurations. The results show that the heat conduction due to the temperature difference dominates the inter-zonal heat transfer in the floor-level side wall air-supply system. By dividing the entire indoor space into two zones in the vertical direction, the values of inter-zonal heat transfer coefficient Cb for the prototype building are 7.92, 6.14, and 3.81 W/(m2?°C) at 0, 10%, and 20% roof exhaust air ratios respectively. Cb is mainly influenced by the airflow characteristics, zonal division, and airflow pattern, whereas it is less affected by the roof exhaust method.关键词：large space buildings;stratified air-conditioning;floor-level side wall air-supply system;similarity theory;inter-zonal heat transfer coefficient956|1023|0发布时间：2024-07-18
- 摘要：To solve the problem of droplet entrainment at the outlet of a falling film evaporator and the liquid carryover of a compressor, the spatial distribution of droplet entrainment and the fluid hydrodynamic parameters of the evaporator were investigated in this study by utilizing computational fluid dynamics (CFD) during the phase change process. The accuracy of the numerical method was verified by the test results of prototypes K1 and K2, and the objective control parameters, including the amounts of droplet entrainment (φ≤0.37%), average velocity of horizontal flow (vH≤0.24 m/s), and average flow velocity at the outlet of baffle (vB ≤2.18 m/s) were established to evaluate the risk of the droplets entrainment at the evaporator outlet. Based on the established objective control parameters, the risk assessment of the falling film evaporator models (K3~K6) was carried out. The results showed that K3 and K4 met the requirements of the control parameters and had a lower risk of carrying liquid. In comparison, K5 and K6 had a higher risk of carrying liquid. Based on the predicted high-risk model with droplet entrainment, control parameter groups, such as reducing the outlet velocity of the distributor, increasing the diameter of the cylinder, and adjusting the gaps between the tube bundles, were adopted in the optimization design, and the distribution of the flow pattern outside the heat exchange tube was analyzed. The results indicated that the entrainment rate of droplets with the optimized evaporator is reduced by more than 75% compared to that before optimization, the state of the outside tube mainly exists in the form of droplet flow, and the distribution of the liquid phase outside the tube is relatively uniform. It was found that there is no liquid at the outlet of the falling-film evaporator through an optimized test (K5, K6), which is expected to provide a fundamental basis for the optimization design of the subsequent falling-film evaporator.关键词：falling film evaporator;numerical simulation;gas-liquid two phase flow;droplets entrainment;optimization design994|1049|0发布时间：2024-07-18
- 摘要：The coupled system of evaporative cooling and solid desiccant dehumidification is feasible to solve the problems of energy consumption and air quality of data centers compared with the traditional cooling method. It is also one of the primary means of expanding the application scope and period of evaporative cooling technology in the southern humid and hot regions. A single-and double-stage solid desiccant dehumidification device filled with silica gel particles was designed and built in this study. Experiments were conducted during the transitional season in Guangzhou, a typical city in southern China’s humid and hot regions. Theoretical calculation models were also established. The results show that: better dehumidification performance can be achieved under 25.2 °C and RH 56.4%~74.9%; the maximum dehumidification efficiency and average dehumidification efficiency of the double-stage solid desiccant dehumidification system are 2 times and 2.9 times of the single-stage solid desiccant dehumidification system, respectively; and the time constants of moisture absorption rate β of the single-stage and double-stage solid desiccant dehumidification systems are between 0.35~1.00 and 0.33~1.18, respectively; the time constants of moisture ratio α are between 0.37~1.10 and 0.41~1.30; and the theoretical calculation model can fit the actual change curve well, with an average relative error below 10%.关键词：solid desiccant dehumidification;dehumidification performance;hot and humid region;data centers971|1057|0发布时间：2024-07-18
- 摘要：How the performance of the heat pump dishwasher in drying process is changed under different parameters is explored in the study. An unsupervised data mining framework of “data pre-processing - association rule mining - knowledge interpretation” is established to study the energy-saving operation strategy and achieve the goal of reducing the power consumption in the drying process of the dishwasher. The Apriori algorithm is used to mine the overall set of items to obtain three key factors, namely refrigerant charge, ambient temperature, and air supply method, and the influence of these factors on the overall drying performance is further investigated. The research results show that the heat pump system provides sufficient heat to ensure the drying performance of the system, but too much heat cannot effectively improve the drying performance. The air supply method is the key factor in improving the drying performance of the dishwasher, and alternating the upper and lower air supply can achieve the best drying effect. Therefore, to meet the minimum heat requirement of dishwasher drying, the system’s energy efficiency can be improved by adjusting the air supply method and other factors to achieve energy-saving operation.关键词：heat pump drying;dishwasher;association rule;energy saving strategy994|1111|0发布时间：2024-07-18
- 摘要：Ice slurry has been widely used in air conditioners, food, and other industries owing to its good performance in flow, heat transfer and cold storage. To study the effect of solid particle size on the rheological characteristics of ice slurry, three kinds of polyethylene particles (density about 0.922 g/cm3) with average particle sizes of 0.31 mm, 0.43 mm, and 0.51 mm were selected as the solid phase in this study. The pressure drop of the mixed slurry flowing in a horizontal circular pipe was measured by changing its velocity and solid-phase content. A piecewise fitting rheological equation was determined based on the relationship between shear stress and shear rate. The effect of particle size on the rheological properties of two–phase liquid such as ice slurry was studied. The results show that the shear stress of the mixed slurry increases with increasing particle size, solid-phase content, and shear rate. The slurry behaves as a shear-thickening fluid, and its rheological index is always greater than 1. The rheological coefficient of the slurry increases with an increase in the solid-phase content under the condition of constant particle size. When the solid content is lower than 15%, the rheological coefficient increases significantly with increasing particle size.关键词：ice slurry;solid-liquid two-phase flow;particle size;rheological property;non-Newtonian fluid1029|943|0发布时间：2024-07-18
- 摘要：To optimize the uniformity of the temperature field distribution inside the core freezer and control the temperature fluctuation range, a test rig of core model and a three-dimensional RNG k-ε turbulence model were built based on the similarity principle to investigate the influence of air supply parameters (air supply temperature is from -3?2 ℃, and air supply velocity is from 3.5?4.7 m/s) on the temperature field distribution inside the freezer and provide theoretical support for the core freezer project. The results showed that under the zero-load condition of the core freezer, the simulated temperature at each monitoring point agreed well with the experimental ones, and the maximum deviation did not exceed 0.6 ℃. The model could accurately reflect the distribution law of the temperature field inside the freezer. When the freezer was fully loaded with six layers, and the air supply velocity was constant at 4.2 m/s, the temperature distribution inside the freezer was positively correlated with the air supply temperature; when the air supply temperature was 0 ℃, which was the best air supply temperature, the temperature field distribution inside the freezer was uniform and reasonable, and the cores of each layer met the storage requirements. When the freezer was fully loaded with 6 layers, and the air supply temperature was constant at 0 ℃, increasing the air supply speed could strengthen convective heat exchange and effectively solve the problem of local overheating. When the air supply speed was increased from 4.2 m/s to 4.7 m/s, the local temperature in the freezer was lower than the optimal storage temperature range of the cores, and 4.2 m/s was the optimal air supply speed considering the comprehensive energy consumption and uniformity of airflow organization.关键词：core;freezer;air supply parameters;numerical simulation;temperature field991|943|0发布时间：2024-07-18
- 摘要：To accurately forecast freeze-drying time, COMSOL software was used to simulate the sublimation drying process of pitaya slices based on the theory of heat and mass transfer in this study. The thickness of the red pitaya slices was 12 mm, and the radius was 4 cm. By simulating the water vapor flow coupled with the heat and mass transfer of the sublimation drying stage, the temperature distribution characteristics of pitaya slices, the movement of the sublimation interface, and the condition of ice sublimation, the sublimation cycle was forecast. Experiments were conducted to validate the model. The results show that the errors are low: the absolute error between the simulated and measured pitaya center temperatures is 0.9 ℃, the comparative error between the forecast and measured moisture ratios is only 1.2%, and the relative error between the simulated and measured dehydration rates is 6.63%. It can be concluded that the model can accurately simulate the dynamic changes in heat and mass transfer during the sublimation drying process. By comparing the simulated sublimation cycle of pitaya slices with different thicknesses, and considering the quality and production of freeze-drying products, it is concluded that 12 mm is the best thickness of red pitaya slices for freeze-drying.关键词：vacuum freeze-drying;heat and mass transfer;dehydration rate;pitaya965|1072|4发布时间：2024-07-18
- 摘要：Cryopreservation of testicular tissue is a potentially effective method to preserve fertility in infertile patients who cannot obtain sperm or prepubertal boys who have cancer and require radiotherapy or chemotherapy. In this study, the vitrification of massive mouse testicular tissue was studied. Massive testicular tissue was immersed in vitrification solutions with different concentrations for different immersion time. Thermal analysis was conducted using a differential scanning calorimeter, and the testicular tissue was vitrified. The results showed that ice crystals were formed in the tissue during the cooling process in the low-concentration CPA group. In contrast, vitrification was achieved during the cooling process in the high-concentration CPA group. According to the negative rate of apoptosis of spermatogenic cells, the optimal vitrification loading protocol was to incubate in 20% DMSO for 1 min, followed by incubation with spermatogonial cells 78.6%, spermatoblast cells 90%, sperm cells 70.1%, and Sertoli cells 89.1%. Compared to slow freezing with vitrification, slow freezing can maintain the morphological integrity of testicular tissue and reduce the apoptotic rate of spermatogenic cells, making it more suitable for freezing massive testicular tissue.关键词：vitrification;slow freezing;testicular tissue;thermal analysis1016|1052|0发布时间：2024-07-18
- 摘要：During the dehydration process, tissue cells in different locations undergo diffusion and evaporation of water, and other microstructural changes such as cell shrinkage, rupture, and pore formation often occur. Changes in the cell microstructure affect the moisture and temperature distributions in the material and the quality of the material. Therefore, studying the change law of the cell microstructure at different positions is vital for improving material quality. This study used microscopic observation and image processing technology to study the changes in the morphology of cells in different positions of the sample during the process of water migration, and the changes in size parameters (relative diameter, relative perimeter, relative area, and area) and shape parameters (roundness and elongation) of cells at different positions at 0 oC and 8 oC were analyzed. The results showed that during the dehydration process, the maximum value of the size parameter at different moments at 0 oC was obtained at the middle of the section center and the lower tissue edge. The maximum value at 8 oC was obtained at the center of the section. The relative cell diameter, relative perimeter, and relative area changes exhibited the same trend, but the relative area changed more. The shape parameters were distributed within a range without obvious uniformity. At 0 oC, the cell roundness was roughly distributed in the range of 0.85 to 0.95, and the cell elongation rate was concentrated in the range of 1.2 to 1.8. At 8 oC, the cell roundness was roughly distributed in the range of 0.80 to 0.90, and the cell elongation rate was concentrated between 1.2 and 1.9. At 0~30 min, the change in the dimensional parameters at each position increased with an increase in temperature. Compared to that at 0 oC, the shrinkage of the cells was significantly higher at 8 oC during the dehydration process, and the overall change trend of the cell shape was more uniform.关键词：cell deformation;water migration;microstructure;broad bean1266|1005|0发布时间：2024-07-18
- Address：10/F, Yindu Mansion, 67 Fucheng Road, Haidian Dist, Beijing, China Postal code：100142
- Tel：010-68711412 Email：editor@car.org.cn
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0