最新刊期
卷 42 ， 期 5 ， 2021
- 摘要：The recovery and reclamation of refrigerants is a recommended method of reducing refrigerant emissions, which requires technical support and policies to stimulate the activity. In this study, the policies for supporting refrigerant recovery as well as the quantity of recovered refrigerants reported in Japan, EU, USA, and China are summarized and compared, and the working principles, advantages, disadvantages, and recommended application conditions of five representative recovery methods are described in detail. For the reclamation of refrigerants, the procedures and application conditions of two reclamation methods, that is, simple distillation and distillation refinement, are explained, and seven destruction methods for non-reclaimable refrigerants that need to be destroyed are described. At the end of this paper, the main problems regarding refrigerant recovery and reclamation in China are presented.关键词：refrigerant;recovery;reclaimation;technique;policy1693|1759|3发布时间：2024-07-18
- 摘要：The mal-defrosting phenomenon occurs frequently when the air source heat pump (ASHP) is defrosting, which causes a decline in the heating capacity, performance, and heating loss. Therefore, it is crucial to determine the most appropriate start and end times. To control the start and end time of defrosting properly, the ASHP has a state of stable performance and energy saving and can ensure thermal comfort in the room during defrosting. In this study, the research on defrosting control methods at home and abroad are summarized, and the limitations of defrosting control methods are analyzed, including measuring the frost thickness directly, monitoring the frost degree indirectly, and determining the start and end times using an intelligent algorithm. The idea of a combination of frost suppression technology and a defrosting control method, the relationship between the type of equipment and defrosting control method, as well as an evaluation system for defrosting control methods were put forward as the future research direction in this paper.关键词：air source heat pump;frost suppression technology;defrosting control;evaluation system1543|1989|3发布时间：2024-07-18
- 摘要：In recent years, cell therapy technology for type 1 diabetes has advanced rapidly, but the lack of donor pancreatic islets and the time and space mismatch between donor and recipient limits its clinical application. Cryopreservation technology provides a way to solve this problem. However, the survival rate and functionality of pancreatic islets that are preserved by traditional cryopreservation methods are poor, and it is difficult to achieve the required standard of clinical application. This study classifies and summarizes the principles of islet cryopreservation and the factors that cause islet damage during cryopreservation. It summarizes the development of pancreatic islet cryopreservation technology in recent years in terms of the inhibition of ice crystal damage, protective agents, and hypoxia injury. Due to the development of interdisciplinary research in materials science, molecular biology, and cryobiology, many new materials and methods have been developed in the field of islet preservation, which has further improved the quality of pancreatic islets after cryopreservation. However, there are few high-throughput vitrification methods developed for islet preservation. In addition, more research is needed on the potential adverse effects and protective mechanisms of new technology and materials for islet cryopreservation. In follow-up research, the development of new materials and technologies, especially high-throughput preservation technology, and the mechanism of low-temperature damage in the field of pancreatic islet cryopreservation will be investigated.关键词：cryopreservation;type 1 diabetes;microencapsulated islets;intracellular delivery;cryogenic damage inhibition1307|1201|2发布时间：2024-07-18
- 摘要：The principle of snowmaking is simple, however the process is complex and highly dependent on environmental conditions. In recent years, to achieve the goal of "300 million people on ice and snow" and to host the "2022 Beijing Winter Olympic Games" China has attached great importance to the innovation of snowmaking technology. In this study the working principle, evaluation index, influencing factors, and technology development process of artificial snowmaking are analyzed based on the mechanism of snow formation. The formation of crystal nuclei is the key to the formation of snow, and the growth characteristics of snowflakes are related to the ambient temperature and water vapor supersaturation. The core of artificial snowmaking technology is the creation of a low-temperature environment by throttling refrigeration to catalyze the formation of crystal nuclei. The snow crystals are seeded with the crystal nuclei, and the crushed fog droplets are then adsorbed to form snowflakes. The wet-bulb temperature is the trigger for artificial snowmaking activity. The latent heat of the phase change and convective heat transfer of droplets are different at different wet-bulb temperatures, and -2 ℃ is generally considered as the snowmaking activity threshold. The optimization direction of artificial snowmaking technology is the structural optimization of snow core making nozzlesand spray nozzles, the addition of water source active agents, external precooling nucleation, and intelligent control. Development of Chinese artificial snowmaking technology started late, and it needs to be improved in the directions such as snowmaking mechanisms, technologies, components, machines, and systems in the future.关键词：artificial snowmaking;snowmaker;spray nozzle;Winter Olympics1987|1567|6发布时间：2024-07-18
- 摘要：The application of environmentally friendly refrigerants to air-conditioning systems is receiving considerable research attention; however, the flammability of the refrigerants cannot be ignored. Leaks represent a significant potential safety hazard. In this study fault tree analysis is used to establish a split air-conditioning system leakage model using statistical data from an air-conditioning manufacturer with a high market share. A qualitative and quantitative analysis of the causes of leakage and the components involved, is conducted. The results show that the probability of leakage on the outdoor side of the split air-conditioning system is approximately 2.72×10-3, which is higher than the probability of 2.74×10-4 on the indoor side. The most likely components to become a source of leakage by descending probability on the outdoor side are the outdoor pipe connection bell mouth, condenser, four-way valve, and two-way valve. In contrast, on the indoor side the most likely components to become a source of leakage by descending probability are the evaporator piping, evaporator elbow, evaporator inlet, and outlet connecting pipe. The causes of system leakage by descending probability are process defects, improper brazing, improper operation, and fatigue cracks. This study provides data support for the in-depth study of the selection of leak-prone points for split air-conditioning systems and provides comprehensive guidance for leakage prevention.关键词：air-conditioning system;refrigerant;leakage;fault tree analysis1271|1270|0发布时间：2024-07-18
- 摘要：China has entered the end of the hydrochlorofluorocarbon (HCFCs) refrigerant phase out, and will soon start to reduce its production and consumption of HFCs simultaneously in 2024. In this study the process of refrigerant recovery and regeneration is investigated. The carbon emission evaluation model for the process of refrigerant recovery and regeneration is constructed based on the life cycle climate performance model LCCP. The economy of the regeneration of refrigerant is analyzed, and the carbon emission and regeneration economy of the automobile air-conditioning refrigerant R134a is calculated using the evaluation model. The results show that the equivalent CO2 emissions can be reduced by approximately 42% by recycling the R134a refrigerant. The economic performance of refrigerant recycling is mainly dependent on the unit price of the refrigerant after regeneration and the wage cost of workers. When the monthly minimum wage standard is used, the price of the refrigerant after purification is more than 11 Yuan/kg (50% of the price of new refrigerant), and the process is profitable within two years.关键词：global warming potential;refrigerant recovery;greenhouse effect;refrigerant;R134a1507|1373|0发布时间：2024-07-18
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Study on Energy-saving Optimization Strategy and Simulation of Central Air-conditioning Water System
摘要：The energy consumption of central air-conditioning water systems in public buildings accounts for a high proportion of their total energy consumption. The optimal start and stop strategy for each device and the settings of the control parameters play a key role in the system energy saving. In this study, a start-stop optimization strategy for the chiller and water pump and the global optimization method for the control parameters is proposed while aiming to satisfy the terminal cooling load and to minimize the total energy consumption of the system. The chilled water supply temperature and cooling water flow were considered as independent control parameters, and an energy consumption model of the central air-conditioning water system was established. The change in cooling load in one example building was simulated using DeST software, and the proposed optimization method was verified. The results indicate that the average coefficient of performance of the chiller was improved by 10.9%, the average energy consumption was reduced by 8.9%, and the average energy consumption of the water pump was reduced by 18.6% within the load rate range of 5% to 100%. On typical summer days, the central air-conditioning water system saves energy consumption by 20.4% on average.关键词：central air-conditioning system;water system;energy-saving;optimization1395|1282|2发布时间：2024-07-18 - 摘要：Chilled water systems with large temperature differences are important for the design of energy-saving heating, ventilation, and air-conditioning systems, as they can reduce the energy consumption of chilled water pumps. However, the water-side heat transfer coefficient of the evaporator gradually decreases as the design temperature difference increases, and the chilled water flow rate decreases. This has become the main factor limiting the energy efficiency of chillers. In this study, the effect of the large temperature difference on the heat transfer performance of the evaporator is analyzed theoretically according to the heat transfer mechanism of the evaporator. The influence of different water circuit passes on the performance of centrifugal chillers designed with large temperature differences was compared experimentally in which the chillers were run in series. The results showed that, under the design conditions of a 10 ℃ temperature difference, the efficiency of the chillers in series can achieve a 6% improvement when the evaporators use dual passes rather than a single pass. The efficiency of the whole unit is optimized when the load proportion of the upstream and downstream units is approximately 55%:45%, owing to the intermediate temperature of the series scheme.关键词：centrifugal chiller;chilled water system;large temperature difference;in series;efficiency1472|1133|0发布时间：2024-07-18
- 摘要：The air leakage rate, thermal comfort index, and temperature homogeneity indicators are used to evaluate the criteria of the key design parameters and the matching of the design and ambient parameters of the air curtain for the hot-air curtain used in winter. The evaluation uses a railway depot in northwestern China as an example. When the air supply velocity increases from 5.4 m/s to 9.3 m/s, the air leakage rate increases by 71.8%. A discharging angle of 10°–20° helps in reducing the leakage rate by 24.9% compared to the 0° discharge angle. While the temperature of the air supply does not affect the air leakage rate, it has a significant impact on the thermal comfort inside the plant. Furthermore, the ambient air direction and temperature have a trivial contribution to thermal comfort and the air leakage rate. Most importantly, the air leakage rate increases by 40% when the ambient velocity is > 2.6 m/s; therefore, measures other than the air curtain should be deployed to reduce air leakage in these regions.关键词：railway transport;high and large depot plants;energy saving;air curtain;air tightness1399|1175|0发布时间：2024-07-18
- 摘要：Considering the shortcomings of temperature and humidity-independent control in small and medium-scale residential and office buildings, a novel water chiller/heater based on dual evaporation temperatures was developed. The operating conditions of the unit were investigated through experiments in which the compressor speed and valve opening were varied. The compressor speed was varied from 30–80 Hz and the high and low-temperature sides of the electronic expansion valves (EEV1 and EEV2) were opened from 80%–100% and from 10%–50%, respectively. The experimental results were analyzed to reveal the operational and regulatory characteristics of the unit. The results showed that the cooling and heating capacities of the unit were proportional to the compressor speed in the cooling and heating modes. In the cooling mode, when the EEV2 opening was < 30%, the cooling capacity at the high and low temperature sides and the total cooling capacity of the unit decreased as EEV1 opening increased. When the EEV1 opening was fixed and the EEV2 opening increased, the cooling capacity on the high-temperature side was largely constant. The cooling capacity on the low-temperature side and the total cooling capacity first increased and then decreased, reaching a maximum with EEV2 opening at 30%. The highest low-temperature cooling capacity suggests a better dehumidification capacity.关键词：temperature and humidity independent control;water chiller/heater;dual evaporation temperatures;operation and regulation characteristics1354|1151|0发布时间：2024-07-18
- 摘要：The chimney effect in a super high-rise elevator shaft is significant in winter, which may cause difficulty in opening and closing the elevator doors and can produce obvious aerodynamic noise. In this study, the improvement effect of different cooling methods on the elevator shaft chimney effect is analyzed, including natural ventilation cooling with air volume of 2.12–6.68 m3/s, a radiant cooling panel with height of 10 m and temperature of 10 ℃, and a variable refrigerant volume cooling system (VRV) with cooling capacity of 20–100 kW. A super-high-rise elevator shaft thermal noise control scheme is proposed that combines natural ventilation and heat pump technology, and the feasibility of the proposed scheme is verified through on-site tests. The results show that when both natural ventilation and VRV systems are adopted, the pressure difference between the two sides of the elevator door is 49 Pa less than when only the natural ventilation system is adopted, and is 20.4 Pa less than when only the VRV system is adopted. At the same time, when both natural ventilation and the VRV system are adopted, the noise is 2.1dB less than that when only the natural ventilation scheme is adopted, and it is 1.6 dB higher than the noise when only the VRV system is adopted. Therefore, the simultaneous use of natural ventilation and VRV cooling systems can effectively reduce the chimney effect and simultaneously control the noise in the elevator shaft.关键词：heat pump;chimney effect;elevator shaft;thermal pressure;elevator thermal noise;super high-rise building1401|1121|0发布时间：2024-07-18
- 摘要：The airside mass transfer characteristics of two-plate fin-and-tube heat exchangers with different fin spacings were experimentally studied under low ambient pressure and dehumidifying conditions. The experimental conditions comprised an ambient pressure range 40–100 kPa, inlet air velocity 0.5–4 m/s, inlet air relative humidity 50%–90%, inlet air dry bulb temperature 27 ℃, and water flow velocity 1.65 m/s. The effects of ambient pressure, air velocity, fin spacing, and relative humidity of the inlet air on the airside mass transfer characteristics of the heat exchanger were investigated. The results showed that under low ambient pressure, the effects of face air velocity, fin spacing, and inlet air relative humidity on the air side mass transfer coefficient of the heat exchanger is consistent with that under normal ambient pressure. When the ambient pressure increased from 40 kPa to 100 kPa, the air-side mass transfer coefficient decreased by 18.2%–23.6%. Under low air velocity and ambient pressure, the effects of fin spacing and inlet air relative humidity on the air-side mass transfer characteristics are more significant.1370|1070|0发布时间：2024-07-18
- 摘要：Dynamic ice-making technology using supercooling water is expected to realize large-scale applications. In industry, the ultrasonic field is often used to release the supercooling state of supercooling water and generate ice slurry. In this study, the effect of different ultrasonic fields on the supercooling characteristics of crystallization, the size of the ice crystals, and the particle size distribution of ice crystals of 3% sodium chloride solution, were studied experimentally. The results showed that the introduction of an ultrasonic field of a certain power and frequency can quickly release the supercooling state. It was also found that the solution nucleation temperature was close to the ultrasonic irradiation temperature, and the ultrasonic field with high power and low frequency was more conducive to nucleation. The power, frequency and irradiation temperature were varied from 10.0 W to 40.0 W, 28 kHz to 40 kHz, and 0 ℃ to 4 ℃, respectively. The optimal ultrasonic field scheme was set as the power at 40.0 W, the frequency 28 kHz, and the irradiation temperature 2.0 ℃. An ultrasonic field can significantly reduce the crystal size. With the extension of the ultrasonic irradiation time after nucleation, the size of the ice crystals first increased and then leveled off. The changes in ultrasonic power and frequency had no obvious effect on the size of the ice crystals.关键词：degree of supercooling;particle size;ultrasonic field;ice slurry;supercooling solution1288|1104|0发布时间：2024-07-18
- 摘要：To develop a self-cleaning technique for fin-and-tube heat exchangers by adopting the method of dust layer freezing and expansion, the mechanism of water vapor permeability in porous dust layers on fin surfaces should be investigated. In this study, a visualization experimental rig of water vapor permeability in a porous dust layer on a cold metal fin surface was designed and developed, and the effects of the temperature of the cold plate, thickness of the dust layer, and relative humidity of the inlet moist air on the water vapor permeation mass were studied. The ranges of the experimental parameters cover the temperature of the cold plate ranging from 5 ℃to 7 ℃, the thickness of the dust layer ranged from 3 mm to 8 mm, and the relative humidity of the inlet moist air ranged from 15% to 90%. The results show that the water vapor in moist air may preferentially transfer into the inside of the dust layer along the permeability channels constituted by the dust aggregation and cause a morphological change in dust aggregation. The low temperature of the metal plate helps in increasing the water vapor permeation rate by approximately 20% as the metal plate temperature decreased from 7 ℃ to 5 ℃. The large thickness of the dust layer is beneficial to the water vapor permeation mass, and the maximum water vapor permeation mass increased by approximately 15% as the dust layer thickness increased from 3 mm to 8 mm. The high relative humidity of moist air facilitates the water vapor permeation rate, but the water vapor may not permeate into the porous dust layer if the relative humidity of moist air is lower than 30%.关键词：porous dust layer;fin;water vapor permeation;freezing expansion1271|1194|0发布时间：2024-07-18
- 摘要：In this study, a composite phase change heat storage material was prepared based on paraffin wax and foamed metal copper, and a visual heat storage experimental device was designed and developed. The enhanced heat transfer mechanism of the foamed metal copper filling rate in the paraffin heat storage process was analyzed. The experimental results showed that when the filling rate of metallic copper increased from 0 to 2.13%, the melting time of the composite phase change heat storage material was shortened from 901 s to 782 s (12.21%). When the filling rate of the foamed metal copper was 2.13%, the temperature gradient inside the paraffin wax was the lowest (22.52 K). In addition, with the increase in the foamed metal copper filling rate, the heat storage capacity of the composite phase change heat storage material was reduced from 15 932 J to 13 296 J (16.55%), and the heat storage rate first decreased and then increased (18.41 J/s, 18.33 J/s, 18.64 J/s, and 19.13 J/s). When the filling rate of foamed metal copper was 0.99%, the heat storage capacity of paraffin wax in the heat storage device was 14 539 J, and the heat storage rate was 18.52 J/s, which indicated improved heat storage performance of the composite phase change heat storage material.关键词：phase-change heat storage;metal foam;paraffin wax;heat transfer enhancement;heat storage properties1421|1214|2发布时间：2024-07-18
- 摘要：The uneven distribution of refrigerants in parallel flow microchannel heat exchangers is one of the reasons that limit their further promotion and application. When the parallel flow microchannel heat exchanger is used as an evaporator, the refrigerant at the inlet of the evaporator is in a vapor-liquid two-phase state, which causes an uneven distribution of vapor and liquid refrigerant in the evaporator. In this study, a two-phase R134a refrigerant was used as the working fluid, and a numerical simulation model which was verified by previous experimental data was proposed. Four schemes to improve the refrigerant distribution characteristics by changing the protrusion depth of different flat tubes are proposed. Numerical simulation models were used for the calculation. When the mass flow rate is 100 kg/(m2?s) and the refrigerant quality is 0.4, it is found by changing the protrusion depth of different flat tubes in the header, the liquid phase refrigerant distribution characteristics can be improved by 29.4%–52.4%.关键词：microchannel heat exchanger;numerical simulation;flat tube protrusion depth;fluid distribution;uniformity1677|1360|4发布时间：2024-07-18
- 摘要：Conventional air convective driers for drying seaweed consume large amounts of energy as it uses fossil fuels, biomass, or electricity. Enclosed systems assisted by vapor compression heat pumps are much more energy-efficient and are widely applied to many drying processes. However, the existing simple heat pump dryer is not suitable for seaweed drying because of the significant air flow rate required. In this study, a novel seaweed heat pump dryer is proposed to recover latent heat through air bypass and cooling energy using a subcooler. The system is optimally designed with the aid of a simulation and working domain evaluation. A prototype was built for the model validation and performance analysis. The results show that the proposed system can achieve a specific moisture extraction rate (SMER) of 2.61 kg/kWh under typical seaweed drying conditions (return air temperature of 46 ℃ and relative humidity of 40%). The SMER peaks at a bypass air ratio of 0.77, and subcooling of 25 ℃, and is maintained above 1.88 kg/kWh when the return air fluctuates within a certain temperature range (46±3)℃ and relative humidity range (40%±10%).关键词：drying;heat pump;energy-saving;latent heat and cooling energy;heat recovery1414|1140|0发布时间：2024-07-18
- 摘要：To study the dynamic load of assembly cold storage under actual operating conditions, this study used prefabricated cold storage in Shanghai as the research object and tested its actual load with a refrigerated area. The results showed that the relative error of the dynamic load model of the assembly cold storage was reduced from 17.8% to 5.26% after considering the factors of goods entering, which improved the calculation accuracy of the dynamic load of the cold storage and proved that the model was accurate. MATLAB was used to establish a mathematical model of factors related to cold storage load. The results show that when the pressure difference between the inside and outside of the cold storage exceeded the optimal operating range of the air curtain machine, the load of the cold storage caused by personnel entry and exit increased with the increase in internal and external environmental differential pressure, outside relative humidity, outside temperature, and frequency of personnel entry and exit. For this type of small assembly cold storage, the load of cold storage under a high utilization rate was mainly caused by the heat and mass exchange at the door. From an economic point of view, optimizing the relevant parameters of the air curtain to extend the optimum operating range of equipment could further reduce the load of cold storage and achieve energy saving.关键词：front warehouse;assembly cold storage;3R2C model;cooling load1459|1118|1发布时间：2024-07-18
- 摘要：The outbreak of COVID-19 has revealed significant challenges in the field of public health security worldwide, especially in rural regions where public infrastructure is poor and public health security is insufficient. In this study, a new type of gas conditioner that combines the functions of sterilization, insect repelling, and carbon-rich fertilization is proposed considering the characteristics of rural anti-epidemic measures. The conditioner unit is based on gas-solid adsorption and solid chlorine dioxide technology. The unit adopts the method of combining four-bed electric swing adsorption carbon capture combined with a pressure swing adsorption nitrogen generation cycle method to enrich CO2 and N2. At the same time, solid chlorine dioxide is applied to the adsorbent to achieve sterilization. Based on test data and simulation models, we analyzed the effects of the temperature difference on the adsorption and desorption temperatures in the carbon capture cycle, and the outlet flow rate. We also analyzed the effects of the adsorption pressure in the nitrogen generation cycle on the separation performance (recovery rate, purity, and productivity) and energy-efficient performance (specific energy consumption, minimum separation work, second-law efficiency) of the gas conditioner. The results show that the CO2 recovery rate, purity, and productivity all increase with temperature difference; the purity of N2 decreases with an increase in outlet flow rate, and increases with the adsorption pressure; the N2 recovery rate and productivity improve with an increase in outlet flow rate and adsorption pressure; the specific energy consumption of the system increases with the increase in the adsorption pressure, and decreases with an increase in the temperature difference and the outlet flow rate; the second law efficiency shows the opposite trend to the specific energy consumption. The simulation results show that when the temperature difference is 105 K, the outlet flow rate is 0.01 m/s, and the adsorption pressure is 1 MPa, the purity of CO2 and N2 both reach the maximum, which are 80.6% VOL and 97.05% VOL, respectively. The specific energy consumption of the system was 2.13 MJ/kg, the efficiency of the second law was 4.71%, and the energy efficiency performance was better. Even under other operating conditions, the purity of CO2 is generally better than 60% VOL, N2 is generally better than 95% VOL, and other performance parameters of the system can also reach a higher level.关键词：gas conditioner technology;CO2 capture;gaseous fertilization;green disinfection;solid chlorine dioxide1337|1079|0发布时间：2024-07-18
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