最新刊期
卷 39 ， 期 4 ， 2018
- 摘要：The values of excitation shear stress for frosting cream from ultrasonic high-frequency vibration were calculated using the finite element software COMSOL, and compared with the maximum adhesion stress obtained theoretically to demonstrate the feasibility of ultrasonic high-frequency vibration defrosting technology. Meanwhile, the defrosting effects of three kinds of the vibration structure, i.e., monoblock type, T-shaped and L-shaped, of a quick-freezing cooling fan were experimentally compared and analyzed under the conditions that cold storage temperature was 20 ℃, humidity was 95%, the ultrasonic frequency was 38.76 kHz, and the loading mechanism was vibrating 10 s for every 50 s. The results show that the ultrasonic has a significant inhibitory effect on the frost on the fin surface under the working condition of high humidity and low temperature, so that the quick-freezing cooling fan can operate for a long time continuously and its efficiency is significantly improved. In addition, the vibration with the structure of the monoblock type has better defrosting effect than that with T- and L-shaped.关键词：ultrasonic;defrost;quick-freezing cooling fan2058|2412|1发布时间：2024-07-18
- 摘要：Ammonia has drawbacks associated with combustibility and toxicity, and therefore, reducing the charge in ammonia refrigeration systems is of great importance. The application of small diameter tubes offer a higher surface coefficient of heat transfer, which has the potential to improve the compactness of the heat exchanger and reduce refrigerant charge. This study conducted experiments to investigate the characteristics of heat transfer and pressure drop for ammonia flow boiling in a horizontal plain tube with an inner diameter of 4 mm. The dependencies of the heat transfer and frictional pressure drop on vapor quality, mass flux, and heat flux are analyzed in detail. The experimental results show that the surface coefficient of heat transfer increases with vapor quality. In addition, an increase in the mass flux and heat flux can lead to a higher surface coefficient of heat transfer. In addition, the two-phase frictional pressure gradient also increases with increasing vapor quality. Further, at a certain vapor quality, the two-phase frictional pressure gradient increases with an increase in mass flux.关键词：ammonia;small diameter tube;flow boiling heat transfer;pressure drop2107|2164|1发布时间：2024-07-18
- 摘要：In recent years, China’s cold chain logistics has developed rapidly. To meet the trend of energy saving and emission reduction, and quantify the influence of cold chain on the environment, a life cycle assessment method is used to analyze the carbon footprint of precooling, storage, transportation, sales, and consumption in the cold chain life cycle of fruits and vegetables, and the carbon emission factor for each link is calculated in the paper. A typical vegetable cold chain is taken as an example to quantify the carbon footprint of the entire life cycle. The results show that the cold chain carbon footprint of a vegetable is 0.0413 kg per kilogram of carbon dioxide equivalents. The refrigerated transport stage contributes the most (69%), and it is followed by the precooling stage (21%).关键词：fruit and vegetable cold chain;greenhouse gases;carbon footprint1927|2544|5发布时间：2024-07-18
- 摘要：In order to measure the carbon emissions of cold-chain logistics systems, a systematic method for calculating the carbon footprint of cold-chain logistics was proposed and a carbon footprint model for cold chain logistics system was constructed in this study. An empirical analysis of the carbon footprint of cold chain logistics was carried out throughout the course of bananas. The life-cycle assessment, input-output, and carbon emission coefficient methods were used to define the scope of the carbon footprint accounting for different circulation links of cold chain logistics, and the produce and harvest processing were measured. Carbon emissions from various links such as precooling and refrigerated transportation, storage, distribution operations, and terminal sales are calculated. Under the condition of setting parameters, the total system cost is 3.5474 million yuan, and the total amount of carbon emissions is 148.62 tons; when the total cost of the system is 3.6921 million yuan, the corresponding total system carbon emissions are 145.21 tons. After a sensitivity analysis of the carbon footprint of the cold chain logistics, the increase in the carbon tax can increase the total cost of the system by a maximum of 0.8%, while an increase in the corruption rate can increase the total system cost and carbon footprint by nearly 35% in the same trend. The research shows that this model can effectively measure the carbon footprint in cold chain logistics activities.关键词：cold chain;carbon emissions;carbon footprint model2076|2314|4发布时间：2024-07-18
- 摘要：In order to reduce the energy consumption and cost of refrigerated transportation, phase change cold storage technology is applied to refrigerated transportation equipment. Based on the principle of reducing the freezing point, organic materials (glycerol) and inorganic materials (sodium chloride) are used as raw materials to develop a low-temperature phase change nontoxic coolant. DSC (differential scanning calorimeter) is used to verify whether the phase transition temperature is ﹣31.5 ℃ and the latent heat of phase change is 175.3 J/g. The results of the performance tests show that the density of PCM is 1.15 g/mL, the thermal conductivity is 0.3682 W/(m?K), and the chemical stability maintains after multiple phase transitions, which indicates that the PCM belongs to the basic non-corrosive, and can be used as a coolant for long-term use. According to these results, the proposed coolant can be used in cold storage cars with stable operation. The economic comparison with the mechanical refrigerated car shows that, although the initial investment of the cold storage refrigerated truck is higher, the refrigeration cost is far lower than the mechanical refrigerator car. Its static payback period is 0.57 years, and it has obvious advantages in exhaust emission, environmental protection, energy saving, and stability.关键词：refrigerated transport;phase change cold-storage material;DSC;benefit analysis1987|2392|11发布时间：2024-07-18
- 摘要：In order to study the changes of life characteristics of garlic sprouts under different precooling processes, this paper adopts pressure difference precooling, taking Zhong Mou hybrid moss as the experimental material. The precooling wind speeds were set as 1.0, 1.5, and 2.0 m/s, and a case without-precooling treatment was set for comparison. The variation of hardness, weight loss rate, respiration intensity, and soluble solid content of the four groups of Garlic Sprouts during storage were studied to provide reference for the selection of the appropriate precooling wind speed for garlic sprouts. The analysis of the experimental results shows that the storage effect is much better when the precooling air velocity is 1.5 m/s, for which the hardness of garlic sprouts decreases slowly, and the hardness is about 15% higher than that of the other three groups in mid-storage. In addition, the soluble solid is decomposed slowly, which effectively reduces nutrient loss and inhibits aging.关键词：garlic sprouts;pressure difference precooling;precooling air velocity;storage;physiological indexes1752|2116|2发布时间：2024-07-18
- 摘要：The effect of different wind temperatures (50, 55, 60 ℃), wind speeds (3, 4, 5 m/s), loading capacities (1000, 1500, 2000 g) and placement methods (gill-up placed and gill-down placed) on the drying quality of mushrooms were discussed, and the curves of dry characteristic were obtained in this study. Using SPSS software, experimental data were fitted and the heat pump drying kinetics model of a mushroom was also established. The results indicate that the drying time of mushrooms indeed shortened with an increase in drying wind temperature and wind speed, and with a decrease in loading capacity. Besides, it was more conducive to the evaporation of water when the gill-up were placed at the earlier and mid-term drying stage. The heat pump drying process of mushrooms is mainly divided into acceleration and deceleration drying stages, and there was no obvious constant speed drying stage. Compared with hot-air drying, the mushrooms dried with the heat-pump drying method are superior in rehydration and color. After regression fitting, the heat pump drying kinetics model of mushroom conforms to the Page equation, which can be used to describe the mushroom heat pump process.关键词：heat pump drying;mushroom;drying properties;dynamics model1917|2223|8发布时间：2024-07-18
- 摘要：To study the effect of different factors on the differential pressure pre-cooling of white radish, we use the Pearson correlation coefficient and the orthogonal experimental method. The absolute value of the Pearson correlation coefficient between temperature and uniformity in differential pressure pre-cooling of white radish was 0.875, and the two were strongly correlated. Based on the orthogonal experimental method, taking cooling rate and cooling uniformity as evaluation indexes, the degree of influence on the cooling rate in decreasing order is porosity, air supply temperature, opening rate, and wind speed; the degree of influence on cooling uniformity in decreasing order is air supply temperature, porosity, wind speed, and opening rate. The orthogonal test results show that the smaller the air supply temperature, the greater the wind speed, opening rate, and porosity, and the greater is the cooling rate；the greater the supply air temperature and porosity, the smaller the wind speed and opening rate, and the smaller is the uniformity. The optimized experimental precooling conditions are as follows: the air supply temperature is 3 ℃, the wind speed is 0.32 m/s, the packing box opening rate is 0.08, and the porosity is 0.48. The application of the orthogonal test method and the reference of Pearson correlation coefficient improve the efficiency of the experiment and the accuracy of variable analysis.关键词：differential pressure pre-cooling;temperature uniformity;cooling rate;orthogonal experimental method;white radish2012|2245|2发布时间：2024-07-18
- 摘要：When the central temperature of the plasma bag reaches ?30 ℃ the freezing process is finished. The cooling rate and the temperature uniformity of the plasma bag during freezing are two key factors for determining the freezing quality of plasma. In this study, the thermophysical parameters of plasma were measured experimentally. The effects of different freezing temperatures on the cooling rate and temperature uniformity of the plasma bag were investigated through numerical simulation. The results show that a lower freezing temperature can shorten the time to reach ?30 ℃, but the temperature uniformity of the plasma bag becomes worse. At different freezing temperatures, the maximum temperature of plasma is at the place where there is a gap between the plasma bag and the freezing plate, due to the relatively poor heat transfer capability of air. In summary, increasing the contact area between the inner wall of the freezer and plasma bag or increasing the air flow velocity and turbulence intensity can significantly increase the cooling rate and temperature uniformity of the plasma.关键词：plasma freezing;cooling rate;temperature uniformity;numerical simulation1838|2129|0发布时间：2024-07-18
- 摘要：Vitrification is an effective method in the field of cryopreservation since it can prevent the formation of ice crystals. Vitrification requires ultra-fast cooling rates and high concentrations of cryoprotective agents. However, osmotic injury and toxic damage can be caused by high concentration of cryoprotective agents. The minimum volume methods can significantly increase the cooling rate and reduce the concentration of cryoprotective agents in vitrification. In this paper, the latest research progresses in vitrification by minimum volume methods are reviewed. The minimum volume methods include carrier-based droplet vitrification, spray droplet vitrification, bio-printing droplet vitrification, and microfluidic encapsulation droplet vitrification. Among these, spray droplet vitrification, bio-printing droplet vitrification, and microfluidic encapsulation droplet vitrification are the combination of emerging droplet generation technology and vitrification technology. Because of the rapid generation of uniform droplets and high throughput, they have great potential in the field of cryopreservation.关键词：minimum volume methods;vitrification;spray droplet;bio-printing;microfluidic encapsulation1875|2254|3发布时间：2024-07-18
- 摘要：The Hot Disk thermal constant analyzer based on transient plane source technology is used to study the variation in ice thermal conductivity during the formation and melting. According to the system state, the ice formation and melting process can be divided into five stages, that is, the non-freezing process (pure water), freezing process (ice-water mixture), pure ice process, ice melting process (ice-water mixture), and ice completely melted (pure water). On the basis of the experimental scheme, the temperature was first reduced from 10.3 ℃ to ?11.0 ℃ and then increased to 10.3 ℃. The measured thermal conductivities at these five stages were 0.592?0.669 W/(m?K), 0.603?2.284 W/(m?K), 2.019?3.106 W/(m?K), 0.611?1.945 W/(m?K), and 0.596?0.598 W/(m?K). The results show that the system thermal conductivity varies dynamically during the process of water-ice phase change and the measured thermal conductivity may not be that of pure ice or ice-water mixture. During the ice formation process or ice melting process, the system thermal conductivity will suddenly vary, since the structure of water or ice may be changed when the temperature is near the freezing point. Due to the different densities of ice and water, the thermal conductivity of the system may be affected by the weak natural convection occurring in the local ice-water two-phase microenvironment. In the actual production activities, the formation and melting of ice generally occur successively, so the influence of the thermal imbalance on the biological environment or structural performance of the ice-related structures can be avoided if the dynamic change in thermal conductivity is taken into consideration.关键词：ice;phase change;thermal conductivity;measurement;dynamic characteristics1805|1980|2发布时间：2024-07-18
- 摘要：The physical model of a CO2 micro-channel air cooled tube and micro-channel flat tube was established and the grid was divided. The effects of mass flow distribution were simulated when the depth f was 4, 5, and 6 mm and the inlet tube was at 1/6 and 1/2 of the length of collector tube. The predicted wall temperature distribution was verified by the experimental results of CO2 micro-channel gas cooler with flat tube. The predicted results show that when f is 4 mm and the inlet pipe is at 1/6 location of the collector tube, mass flow distribution is the best with an unevenness of 0.4×10-3. The predicted heat transfer of CO2 in the flat tube shows that with the increase in mass flow of CO2, the heat exchange in the flat tube increases. When the mass flow rate is increased from 2.3 kg/h to 2.5 kg/h, the heat exchange rate is increased by 21.4%. When the mass flow is kept constant, the outlet temperature of CO2 increases with the increase in CO2 inlet temperature. Besides, under the condition of different CO2 inlet temperatures, the error range of the micro-channel flat wall surface temperature between experimental and simulation values is within 10%, which verifies the accuracy of this simulation. Therefore, the results can guide the engineering design of micro-channel cooling unit.关键词：CO2 micro-channel gas cooler;flow distribution;heat transfer characteristic;numerical simulation2004|2214|0发布时间：2024-07-18
- 摘要：To investigate the influences of volume flow rate, groove depth, and groove width on the performance of the spray cooling system, an opened spray cooling system with distilled water was established. The experimental results indicate that if the groove depth is 0.8 mm, the surface coefficient of heat transfer increases by 41% and 8.5% at the volume flow rate of 0.45 L/min and 1.25 L/min respectively as the groove width reduces from 4 mm to 1 mm. If the groove width is 2 mm, the surface with a groove depth of 0.8 mm has the largest heat flux enhancement at the volume flow rate of 0.45 L/min, and the heat flux and surface coefficient of heat transfer are 198.5 W/cm2 and 2.75 W/(cm2?K) respectively, which are enhanced by 21.25% and 30.95% relative to the flat surface at the volume flow rate of 0.45 L/min. When the volume flow rate is 1.25 L/min, heat transfer is enhanced with the increase in groove depth. On the above basis, non-dimensional criterion equations about micro-grooves surface were derived, in which the structure parameters of micro-grooves surface on heat transfer were considered.关键词：spray cooling;surface coefficient of heat transfer;surface temperature;micro-grooves surfaces;mass flow rate1904|2130|0发布时间：2024-07-18
- 摘要：A pump-driven two-phase cooling system was proposed for cooling and energy conservation at data centers. An experimental unit was built to study the effects of influencing factors like internal resistance of heat exchangers, face velocity of heat exchangers, mass flow rate, and type of refrigerant etc. on the performance of the unit. The results show that the decrease in internal resistance benefits the decrease in unit power and promotion of EER (energy efficiency ratio). Both too high and too low face velocity of heat exchangers is disadvantageous to the performance of the system. The performance of R32 is better than that of R22 under the working conditions of pump-driven two-phase cooling systems, but its feed liquid is insufficient under low frequencies of the pump when the outdoor temperature is high.关键词：integrated refrigeration;pump-driven;data center;natural cooling;environment friendly refrigerant2018|2206|7发布时间：2024-07-18
- 摘要：In this article, a model used to predict the R290 refrigerant charge in a high-powered commercial water chiller was developed, and the error is within 3%. Meanwhile, the influences of the ambient temperature and outlet water temperature on a commercial high-powered water chiller system have been studied by applying R290 and R22. The results suggest that when the system is in operation, the major refrigerant is stored in a condenser and liquid pipes, with 56.95% and 7.37% of the total refrigerant charge, respectively. Based on the experimental results, it is easy to conclude that under high ambient temperature, R290 has a huge advantage compared to R22. At the same water outlet temperature, the R290 system COP is improved by 13.9% compared to R22 at an ambient temperature of 50 ℃, whereas the R22 and R290 systems have the same tendency with an increase in water outlet temperature.关键词：R290;refrigerant charge model;commercial water chiller;extreme high temperature1968|2423|0发布时间：2024-07-18
- 摘要：A 2-kW small-scale organic Rankine cycle power plant system targeted for medium-low temperature heat sources was established in this study. The experimental research was aimed at investigating how expansion parameters affect the system performance. The performance indicators include isentropic efficiency, filling factor, cycle thermal efficiency, and output electricity. The results indicate that the expander pressure ratio is an important parameter that influences the cycle performance. The output electricity increases with the increase of pressure ratio, while there exists an optimum point for both isentropic efficiency and cycle thermal efficiency. Considering the effect of internal leakage and mechanical friction loss, the optimum operating pressure ratio should be slightly higher than the built-in volume ratio of the expander. It turns out that increasing the expander rotational speed can effectively decrease the internal leakage.关键词：organic Rankine cycle;pressure ratio;filling factor;isentropic efficiency;cycle thermal efficiency1976|2032|2发布时间：2024-07-18
- 摘要：The liquid floodback in a compressor has an adverse impact on the variable refrigerant volume (VRF) air-conditioning system, which will cause energy loss. Nowadays, Big Data is being broadly utilized in fault detection and diagnostic (FDD). Thus, the PCA-Clustering method, which is combined with Big Data, was proposed to diagnose compressor liquid refrigerant floodback fault. First, data quality was improved by data preprocessing; secondly, the principal component analysis (PCA) method was employed to obtain the new dimensional variable data; finally, the new principal variables were clustered to get the classification label of liquid refrigerant floodback fault data. The results show that the model can preferably diagnose the liquid refrigerant floodback problem in the absence of real label data, with the diagnostic rate of the compressor liquid refrigerant floodback reaching 94.29%.关键词：VRF air conditioning system;compressor liquid refrigerant floodback;FDD;clustering analysis;PCA2065|2314|1发布时间：2024-07-18
- 摘要：Aiming at the problem of large volume and difficulty in the maintenance of compression-type air-conditioning umbrellas, an air-conditioning umbrella with semiconductor refrigeration is introduced. A test bench was built to measure the temperature and flow field in the umbrellas with different diameters ( 36 cm, 38 cm, and 40 cm). Based on the Peltier effect and the structural characteristics of the air conditioning umbrella, the lower air supply mode was applied within the air-conditioning umbrella with semiconductor refrigeration. Experimental results indicate that the air speed in the umbrella with a diameter of 38 cm is between 0.23 m/s and 0.47 m/s, and the maximum temperature difference between air-conditioned area and ambient environment is 3.04 ℃, which can thus create a comfortable local environment.关键词：air-conditioning umbrella;semiconductor refrigeration;temperature field;flow field2071|2306|0发布时间：2024-07-18
- 摘要：To improve the efficiency of a variable-frequency screw compressor with an economizer, the effect of parameters such as the discharge pressure of the compressor, motor frequency, injection pressure of the economizer, and volumetric efficiency on the efficiency of compressor were studied experiementally, and the injection pressure change rule of the economizer was obtained by changing the discharge pressure of the compressor or the motor frequency. Under the condition of a condensing temperature of 40 ℃ and evaporating temperature of 5 ℃, the economizer injection pressure rises by 88.3 kPa with the motor frequency changing from 200 Hz to 50 Hz, and only by 4.9 kPa when the discharge pressure was increased by 30%, which resulted in a 2% drop in volumetric efficiency of the compressor. The result shows that motor frequency has a greater effect on the injection pressure and volumetric efficiency compared to the discharge pressure of the compressor.关键词：motor frequency;discharge pressure;economizer;injection pressure1982|2456|0发布时间：2024-07-18
- 摘要：With the deepening of energy conservation and emission reduction, the improvement of energy efficiency, integrated system coupling refrigeration with heating is bound to be further promoted and applied. Compared with traditional refrigeration system and heating system, the integrated system can comprehensively utilize the energy of both cold and heat. Therefore, whether the calculation of the energy efficiency of individual cold and heat is still applicable to the new system. In this paper, two kinds of integrated system coupling refrigeration with heating of integrated system A with cascade unit and heat pump, and integrated system B with conventional refrigeration unit and heat pump are constructed, and three methods of energy efficiency calculation are proposed. Through specific experiments, three coefficients of performance (COP) calculation methods and results are given for discussion and analysis within the industry. Among them, the third calculation method take into account the cooling capacity of the refrigeration system and the heating of the heat pump system, and the shaft power of the whole system is regarded as the compensation energy, it is the most reasonable method.关键词：integrated system coupling refrigeration with heating;energy efficiency calculation standards;COP1845|2312|2发布时间：2024-07-18
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