最新刊期
卷 41 ， 期 3 ， 2020
- 摘要：Technologies for hydrogen liquefaction have been developing rapidly due to the increasing demand for hydrogen energy. However, hydrogen liquefaction is an industrially complicated process with highenergy consumption and relatively low efficiency. Therefore, many researchers have focused on reducing the energy consumption and efficiency of hydrogen liquefaction. In this paper, recent research and developments in the design and optimization of hydrogen liquefaction are summarized,and the basic and improved hydrogen liquefaction cycles are introduced and compared.The current hydrogen liquefaction process can be divided into two parts: the pre-cooled hydrogen liquefaction process and the cascade hydrogen liquefaction process. The specific energy consumption, exergy efficiencies, and coefficients of performance of these processes are discussed, and the main devices utilized are briefly introduced. Finally, the latest technologies for hydrogen liquefaction and future directions of development are introduced.关键词：liquefied hydrogen gas;specific energy consumption;exergy efficiency;coefficient of performance;optimization2196|2571|5发布时间：2024-07-18
- 摘要：The air-side heat transfer and friction characteristics of two fin-and-tube heat exchangers having different types of waffle configuration was experimentally explored. The Colburn (j factor) and Fanning friction factors (f) were applied to describe airside heat transfer and friction characteristics. The effects of fin type on the air-side performance of smooth wave fin-and-tube heat exchangers were analyzed. When the Reynolds number exceeded 5500, the j factor of the two heat exchangers differed by more than 6.4%, and the f factor differed by 7.8%. The predictions of 34 existing experimental correlations were verified and the results demonstrated that they exhibited a large deviation. A multiple linear regression technique was used to develop new heat transfer and resistance correlations. The mean deviations of the new correlations were 1.59% and 6.75% respectively. The distribution of deviation was uniform, and prediction accuracy was significantly higher than that of the existing correlations.关键词：air-side performance;smooth wave fin;Reynolds number;experimental correlations2069|2370|6发布时间：2024-07-18
- 摘要：The finite element simulation method was used to obtain the distribution of contact stress between the fin and the base pipe. It is proposed that the overall contact stress is not just the average value of the node contact stress, and a more reasonable method of calculation method is proposed. A heat transfer performance test of a sleeve-type heat exchanger was undertaken to determine the contact thermal resistance between the fin and the base pipe. The correlation between the overall contact stress and the contact thermal resistance was established. The finite element simulation method was used to determine the overall contact stress under various expansion factors, and to determine the optimal process dimension. Finally, the contact stress value calculated by the elastoplastic theory was used for internal verification. The relative deviation between the contact stress calculated using elastoplastic theory and the simulated value was small (7.3%).关键词：mechanical expansion;numerical simulation;contact thermal resistance;thermoelectric analogy;optimal design1940|2250|1发布时间：2024-07-18
- 摘要：Two categories of correction method for two-phase flow condensation heat transfer and pressure drop were compared for a distributed parameter model of a microchannel condenser with R134a as the refrigerant. The Cross-repeated-testing nonlinear correction method was demonstrated to be better than the conventional simple polynomial fitting correction. Using the former correction, the error of the estimation of heat transfer can be reduced by 64.5% and the mean square error was less than 3%. Similarly, the error of refrigerant side pressure drop decreased by 82.05% and the mean square error was controlled within 10%. Furthermore, this method not only proved the correctness and validity of the simulation model of a microchannel parallel-flow condenser, but also identified a way to accurate prediction of key parameters during heat transfer, including heat flux and pressure drop.关键词：micro channel parallel flow condenser;two-phase flow;heat transfer correlation;correction2034|2371|0发布时间：2024-07-18
- 摘要：Rotarymagnetocaloric cooling system is the mainstream technical solution of magnetocaloric cooling technology. However, there are multiple key issues constraining their performance. To address these key challenges, this paper discussesand reviews the latest progress in research and proposes future research directions for the following four aspects: highly efficient heat transfer of active magnetocaloric regenerators; flow control among multiple regenerators; multi-layered regenerators; and magnetic assembly and system integrations.This paper also addresses multiple approaches and thoroughly investigates theirpotential for intrinsically improving the cooling performance and scope of application via a combination of magnetocaloric and other cooling technologies.Discussion of the key challengessummarizedin this paper will also help to clarify the future research directions of magnetocaloric cooling, and provide ideas for the development of highly efficient magnetocaloric cooling systems.关键词：magnetocaloric cooling;heat transfer enhancement;coupled cooling2191|2575|5发布时间：2024-07-18
- 摘要：The condenser is one of the important components in an automotive air conditioning system. A traditional condenser is designed on the premise that the inlet air volume is evenly distributed. However, in reality, condenser inlet air is not uniform due to the presence of the anti-collision beam, which makes the thermal performance rapidly decline. In this paper, a new design of condenser layout was studied. The middle region is the superheating area, the upper and middle lower parts are the two-phase area, and the lower part is the super cooling area, which expresses the maximum heat dissipation potential of the condenser. Experimental analyses demonstrated that the heat exchange capacity, COP, system flowrate, and other comprehensive performance indices of the condenser with new process layout were 10%–15% higher than a traditional condenser. Furthermore, this enhancement in performance was greater in the presence of a car anti-collision beam. The cooling effect of the condenser was 4 °C higher than that of the original construction, which greatly reduced the influence of the uneven distribution of air velocity caused by the car’s anti-collision beam on system performance.关键词：condenser;anti-collision beam;non-uniform air velocity;process layout design;heat exchange capacity2015|2168|0发布时间：2024-07-18
- 摘要：Exterior heat exchangers of heat pumps in electric vehicles are prone to frost when operated in winter. This project experimentally investigated this phenomenon. A relationship between frost growth and reductions in the surface temperature of the external heat exchanger was demonstrated. Furthermore, the distribution of frost on each flow channel was uneven, reflecting the different refrigerant densities of gaseous and liquid phases within the channel and the influence of gravity, which leads to a separation and uneven distribution of the two-phase refrigerant in the flow channel. In addition, the increase of frost on the exterior heat exchanger will result in decreased refrigerant temperature within the exterior heat exchanger, and decreased suction and discharge pressures of the compressor and heating capacity, while causing an increased unit power consumption of the compressor. With an ambient temperature of 0 °C, when the rate of frost coverage reaches 77.4%, the reduction of suction pressure, discharge pressure, and heating capacity were 33.4%, 12.1%, and 25.8%, respectively. Further, the increase of unit power consumption was 32.0%, which reduced the stability of operation and led to an unacceptable level of heating.关键词：automotive air-conditioning;heat pump;frosting characteristics;microchannel heat exchanger1884|2777|5发布时间：2024-07-18
- 摘要：To save experimental resources and shorten the experimental cycle, a three-dimensional distributed parameter model was used to study the heat transfer performance of air-cooled condensers. Four kinds of circuit arrangements and five groups under different refrigerant flow conditions were compared, and the reliability of the model was experimentally verified. The relative error of the simulation model for predicting the heat transfer of refrigerants was less than ±10%, compared with the experimental values under the same working conditions, and the relative error of the predicted value of refrigerant pressure drop was less than ±15%. Simulations demonstrated that the optimal mass flowrate ranges corresponding to the confluences number of the circuit arrangements of 0, 2, and 3 were 511~540kg/h, 472~511kg/h, and 432~472kg/h, respectively, reflecting ahigh heat transfer and low entropy production. The pipeline with confluence exhibited more advantages in the low mass flowrate area, while the non-confluence pipeline exhibited better heat transfer characteristics in the high mass flowrate area.关键词：air-cooled condenser;circuit arrangement;flow and heat transfer;numerical study2150|2115|1发布时间：2024-07-18
- 摘要：A serious problem confronting theoperation of air source heat pumps is the degradation in performance caused by frosting ofoutdoor units. In practical applications, the probability of frosting in local climatic conditions determines the applicability of most defrosting technologies. The degree of frosting of air source heat pumps is not only affected by climate, but also affected by system performance and even the user's usage habits. Consequently, it has been difficult to make a quantitative judgment of how to overcome these problems. Therefore, the concept of freezing degree hours is proposed to characterize the effects of climatic conditions on frost formation. In order to make the calculation of freezing degree hours closer to reality, this study collected operational data of air source heat pumps in many cities. The characteristic temperature difference between evaporation temperature and outdoor dry bulb temperature, with different power types, was obtained by fitting the operational data. The characteristic temperature difference can be used to correct the specific fixed value that is assumed in traditional designs. Finally, according to the analysis of freezing degree hours under different characteristic temperature differences, combined with the frost characteristics of different power types in 275 cities, the frost climate zones of these cities were classified, thereby providing a reference for the design of air source heat pump systems across different frost climate zones and the development of control strategies.关键词：air source heat pump;freezing degree hour;fitting analysis;climate partition1865|2397|0发布时间：2024-07-18
- 摘要：In this study the boiling heat transfer characteristics of R290 in a 1, 2, and 4 mm horizontal micro-tube were investigated experimentally. The effects of mass flow rate [50-600 kg/(m2?s)], quality (0-1), and heat flux (5-20 kW/m2) on the boiling heat transfer coefficient at a saturation temperature of 15 °C were analyzed. The results showed that increased mass flow velocity can enhance the heat transfer coefficient and the influence of mass flow rate on the heat transfer coefficient with low quality is smaller than that with high quality. The heat transfer coefficient increased with the increased heat flux, and the effect of critical quality on the heat transfer coefficient was apparent in 2 and 1 mm tubes. The heat transfer coefficient tended to decrease precipitously for 2 and 1 mm tubes. The transverse heat transfer coefficient increased with the decreasing pipe diameter under some conditions. In addition, this study also verified the adaptability of some existing correlations of R290.关键词：R290;Micro-tube;boiling heat transfer1859|2086|2发布时间：2024-07-18
- 摘要：To study the effect of a variable rotation speed compressor on the performance of a cascade heat pump, an experimental platform was constructed. The changes of discharge temperature, intermediate temperature, heating capacity, power consumption, and Coefficient of Performance (COP) with different rotation speeds of a high-temperature compressor were studied experimentally. Experimental results demonstrated that the system operated safely and reliably under the condition of a condensing temperature of 46 °C and an evaporating temperature between -35 and -10 °C. As the high-temperature compressor speed varied from 1200 to 6000 r/min and the condensing temperature was 46 °C and the evaporating temperature -25 °C, the heating capacity increased by 129.7%, and the low-temperature compressor power decreased by 43.4%. In addition, the COP initially increased and then decreased with the increase of high-temperature compressor speed; there was a maximum COP and corresponding optimal high-temperature compressor speed.关键词：ascade heat pump;cycle performance;variable rotation speed;COP;heating capacity1818|2105|1发布时间：2024-07-18
- 摘要：Sweet corn (Zeamays) was precooled by slurry ice and then stored at 0 °C to determine the effect of slurry ice on the subsequent quality of the corn. Changes of sensory index, total soluble solids (TSS), soluble protein content, soluble starch content, soluble total sugar content, and vitamin C (Vc) content were determined. Compared with the conventional 0 °C treatment, slurry ice maintained the sensory quality of sweet corn to 28 d, inhibited the decomposition and decline of TSS, soluble protein, soluble starch, soluble sugar and Vc contents, maintained the nutritional quality of sweet corn, and retained the smell and taste of sweet corn. Thus, slurry ice precooling can reduce stress-induced damage, while maintaining the storage quality and prolonging the shelf life of sweet corn.1751|2040|3发布时间：2024-07-18
- 摘要：In this study, the effects of quick-freezing through sprayingof liquid nitrogen (-40, -60, -80, and -100 °C) and slow- freezing (-18 °C) on microorganism biochemical activity and fruit quality were studied with pitaya (Stenocereusgriseus L) blocks as raw materials. The rate of freezing of the sample accelerated with decreasing freezing temperature, and the freezing time was reduced from 1.25 to 0.367 min as freezing temperature declined. However, the sample exhibited low temperature fracturing after quick-freezing at -100°C. The liquid nitrogen quick-freezing treatment inhibited the activity of polyphenol oxidase, and the residual activity of polyphenol oxidase decreased to 47.27%after -80°C freezing, while it increased to 301.09% after the slow-freezing treatment. The texture of the sample after liquid nitrogen quick-freezing was better than that of the slow-freezing treatment and the rate of juice loss was between 8.88% and 10.50%. In contrast, the rate of juice loss was as high as 38.29% after the slow-freezing treatment. The content of titratable acid, soluble solids, total phenol, anthocyanin, and ascorbic acid increased with the decreased freezing temperature of liquid nitrogen. The -80°C liquid nitrogen quick-freezing treatment maintained the best quality of the sample.关键词：liquid nitrogen quick-freezing;pitaya blocks;quality1786|1953|5发布时间：2024-07-18
- 摘要：In traditional capillary radiation air conditioning systems, water is used as the coolantinthe terminalsof the capillary. However, the secondary heat transfer reduces the energy efficiency and freezing of pipes in winter is a potential danger. In this study, a multi-connected dry capillary radiation heat pump (MDCHP) with refrigerant as the cooling medium has been proposed. Thermal tests of the unit were undertaken in winter at the experimental platform of the Ningbo Institute of Engineering. Indoor dry and wet bulb temperature, and air velocity in heating mode were tested for ducted air conditioning unit and MDCHP respectively when the target condensation temperature was set to 48 ℃.The thermal comfort of the two heating terminals were compared and analyzed with the thermal comfort evaluation index of PMV-PDD. During an 8 h running period of the MDCHP, the indoor temperature field distribution was uniform, the maximum horizontal temperature difference at 1.5m was0.56 °C, and the maximum vertical temperature difference was0.37 °C. During the process of oil return, the temperature drop was less than 1 °C, the relative humidity was maintained at 60%–65%, and the thermal comfort index of PMV and PDD were maintained at-0.5–0.0 and0%–10%, respectively. These results demonstrated that the MDCHP can achieve a First Class standard of thermal comfort and every comfort index was superior to that of ducted air conditioning unit.关键词：multi-connected dry capillary radiation heat pump;ducted air conditioning unit;indoor thermal environment;predicted mean vote (PMV);predicted percentage of dissatisfaction (PPD)1854|1879|0发布时间：2024-07-18
- 摘要：The correct outlet blade angle can maximize the capacity of an air-conditioning system and effectively improve the flow field and temperature distribution in the car, thereby greatly improving the thermal comfort of passengers. In the current study, a class A vehicle model with a scale ratio of 1:1 was simplified and the range of outlet blade angle was equally divided. Simulations and experiments were carried out in conjunction with assessment of a thermal comfort evaluation index to evaluate the flow field and temperature distribution. The results showed that the optimal air outlet blade angle was 50°, i.e., the air was blown to the upper side of the front passenger's shoulder and the outside of the passenger’s cheek.关键词：air outlet;temperature field;air speed distribution;vehicle thermal comfort1805|2006|0发布时间：2024-07-18
- 摘要：In this paper, a refrigerant heat sink for the electronic control system of an inverter air conditioner is designed according to the characteristics of an inverter heat pump unit and the principle of refrigeration cycle. The contact arc between the U-shaped heat dissipation device and the refrigerant piping was a 3/4 arc structure, and the contact point was tangent at a 45° bevel. The temperature of the refrigerant passing through the heat dissipation device was in the optimal temperature range of 40 to 50 °C. The performance of the heat dissipation device was comparedexperimentallywith natural cooling under the standard working conditions (ambient temperature of 43 °C and outlet water temperature of 15 °C).The heat generated by the inverter's power device can be removed by the refrigerant heat sink, and the cooling effect was apparent. The temperature difference between the control component of the inverter and the refrigerant inlet temperature was both calculated and tested, and the effect of installing a refrigerant heat sink was verified.关键词：inverter air conditioner;refrigerant cooling device;power module cooling1700|1915|0发布时间：2024-07-18
- 摘要：The performance of a variable refrigerant flow type of rotor water source heat pump was experimentally investigated at different compressor frequencies (from 40 to 60 Hz) andopenings of the electronic expansion valve (from 6% to 60%). As the suction of the compressor changed from an overheated state to a gas-liquid state, the adjustment range of the opening of the electronic expansion valve decreased first and then increased. As the opening of the expansion valve increased, the compressionratio of the system continuously decreased.Furthermore, when the suctiongas contained a small amount of liquid (0.98关键词：water source heat pump;rotor compressor;electronic expansion valve;system performance1787|2163|0发布时间：2024-07-18
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Influence of Ambient Temperature on the Snow Removal Performance of Self-heating Photovoltaic Panels
摘要：The removal of snow on photovoltaic (PV) panels has become an important issue in current research on PV panels. In this study, the influence of ambient temperature on the snow removal effect ofself-heating PV panels was studied using the basic principles of PV cells, heat transfer and mechanics. When the snow thickness was 6 cm, heating power was 230 W/m2, snow density was 420 kg/m3, and the inclination angle was 18°, the pre-melting time was shortened by approximately 6 min, the melting time was reduced by approximately 11 min, the total snow removal time was shortened by approximately 17 min, and the power consumption of snow removal was reduced by approximately 380.9 kJ for every 1 °C increase in ambient temperature. Thus, the total snow removal time was greatly affected by ambient air temperature.关键词：photovoltaic panel;snow removal;self-heating;ambientair temperature1683|2293|0发布时间：2024-07-18 - 摘要：Spiral wound heat exchangers are often used for LNG（liquefied naturalgas）vaporization on ships because of the advantages of their high efficiency, compactness, and high mechanical strength. The structure of heat exchangers should be designed properly to prevent the problem of freezing blockage. This paper proposes a design to prevent the freezing blockage when meeting the process requirements. Firstly, the basic idea of designing an anti-freeze heat exchanger is to figure out the key parameters of heat exchangers under the condition that the temperature of water in the tubes is higher than freezing point and the outlet temperature on the tube side is evenly distributed. A 3D-distributed-parameter model is adopted to verify the heat transfer, pressure drop, and anti-freeze performance of the heat exchanger. Finally, the structure readjustment is developed. The proposed design method is used on a practical LNG spiral wound heat exchanger. The designed heat exchanger meets the requirements for preventing freezing blockage, and satisfies the requirements of heat transfer and pressure drop. The design results show that the minimum wall temperature on tube side is 7.32℃,whereas the even outlet temperature on the tube sideis 31.42℃, which achieves the purpose of preventing freezing blockage.关键词：vaporizer;design;freezing blockage prevention;spiral wound heat exchanger;liquefied natural gas1740|2202|1发布时间：2024-07-18
- 摘要：The thermal conductivity of phase change materials (PCM) within latent heat storage devices is small and the rate of heat storage is low, which is problematic to the widespread utilization of latent heat storage devices. Consequently, the phase change process of a two-stage series cascade heat storage device based on composite phase change materials was numerically studied. By comparing and analyzing the results of different PCM with different thermal properties, the heat storage characteristics of the device were obtained. The results show that there is an optimal thermal diffusivity, so that the PCM with fixed melting point achieves "a uniform constant-velocity phase change". At the same time, increasing the thermal diffusivity of the PCM can effectively reduce the heating surface temperature, but the decline in heating surface temperature was minimized with a continuous increase in thermal diffusivity. By analyzing the Stefan number, the optimal parameters of the device were obtained. Finally, the correctness of the rule was verified by an experimental study when the Stefan number was 2.88.关键词：heat storage characteristics;cascade heat storage;composite phase change material;thermal diffusivity1754|2167|7发布时间：2024-07-18
- 摘要：In this paper, the frosting at a bare copper cold plate in a natural convective environment were studied. The temperature and relative humidity of the inflowing air were 25 °C and 49%, respectively, and the copper plate was maintained at -20 °C.An AC magnetic field with the strengths of 2.0×10-3, 2.5×10-3, 3.0×10-3, 3.5×10-3, 4.0×10-3, 4.5×10-3, 5.0×10-3, 5.5×10-3, and 6.0×10-3 T were applied to the frosting process. The results showed that thesupercooling degree of the crystals increased, but the driving force fornucleation decreased when magnetic field existed. Compared with the absence of a magnetic field, the droplet condensation time and the droplet size were reduced. Visualization studies demonstrated that the polar water molecules were arranged in the bottom plate in an orderly manner, the system’s entropy was reduced, and the driving force for crystallization was increaseddue to the additional magnetic field. The time to form a dense frost layer was reduced by 6%. In addition, with increased magnetic field strength, the amount of frost per unit area of the plate decreased under a weak AC magnetic field. A high correlation of the amount of frost deposited with the AC magnetic field strength was apparent and the fitted relationship was given in the paper.关键词：AC magnetic field;droplet;degree of supercooling;frosting intensity1516|1853|1发布时间：2024-07-18
- 摘要：The influence of the pressure head of evaporation on the operation of a loop heat pipe (LHP) is important to the performance of LHP. In this paper, the wick was separated from the heating surface;consequently, a steam chamber was formed. Simultaneously, the heat and mass transfer in the evaporator were separated. Consequently, the driving force (especially the pressure head of evaporation) was enhanced. Heat leakage was decreased as much as possible due to the low thermal conductivity of the wick. Experiments were conducted to investigate the effectof different partial vacuums(95.3–101.1 kPa) on the start-up performance for the new LHP. This newdesign was able to operate at different partial vacuums; the operating temperature, start-up time, and thermal resistance decreased with increasedpartial vacuum. Simultaneously, this LHP showed a lower thermal resistance (0.14oC/W) compared with that of LHP driven by capillary forces.关键词：loop heat pipe;evaporation pressure;vacuum degree;operating temperature;thermal resistance1665|1865|0发布时间：2024-07-18
- 摘要：Cryopreservation is the usual method for long-term preservation of natural and engineered tissues. However, homogeneous loading of tissues with CPAs constitutes one of the major hurdles in tissue cryopreservation. In this study, computer tomography (CT) was used as a non-invasive imaging method to determine the effective diffusion of Vs55 in tissue-engineered collagen scaffolds, and the effective diffusion constant (Deff) was calculated by the theoretic model. The kidney activation energy was calculated according to the effective diffusion constant obtained by CT. The results demonstrated that the higher the loading concentration, the faster the rate of diffusion. When Vs55 concentration was 8.4 mol/L, the diffusion rates were 1.77××10-6cm2/s at 4 °C,2.94××10-6cm2/s at 22 °C, and 3.93××10-6cm2/s at 37 °C, respectively. The model was demonstrated to predict the spatial and temporal distribution of Vs55 in the kidney. The coefficient of determination (R2) and the mean relative error (MRE) were 0.960–0.993 and 3.07%–6.74%, respectively. This observation was temperature-dependent, with slower permeation at lower temperatures. This study demonstrated the effectiveness of CT to measure Vs55 permeation into rat kidney.关键词：CT;visualization;Vs55;effective diffusion coefficient1428|1852|2发布时间：2024-07-18
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