最新刊期
卷 37 ， 期 4 ， 2016
- 摘要：The ejector is key to the performance of the transcritical CO2 ejector refrigeration system. Considering the complex processes, such as metastable phase change, supersonic flow, and choking phenomena et al., in the CO2 two-phase ejector, a 1D distributed model was built in this paper and the delayed equilibrium theory was employed to analyze metastable phenomena in the motive nozzle. After the comparison with the relevant experiments data, the model was validated to be reliable to predict ejector performance. Compared with the homogeneous equilibrium model (HEM), the proposed model presented a 12.39%~25.30% lower critical mass flow rate. Meanwhile, the comparison results showed that the metastable phenomena would slow down the expansion process causing higher nozzle outlet pressure than that of the HEM simulation results. Moreover, the model is used to study the effect of the dimensions on the ejector performance and the results revealed that under a certain operating condition, an optimal mixing section diameter existed for both high entrainment ratio and pressure lift. Besides, a longer mixing section with a fixed mixing section diameter would increase the pressure lift ratio.关键词：two-phase ejector;delayed equilibrium model;metastable phase change;CO22895|3585|4发布时间：2024-07-18
- 摘要：Since the operation efficiency of HVAC system is low and the operation performance of subsystems are commonly affected by each other, a multi-objective optimization method to improve the operation performance of entire HVAC system is proposed based on exergy analysis. The HVAC system of an airport terminal is chosen as the study object. Exergy analysis is applied to set up the productive structure of the HVAC system. According to the productive structure of the HVAC system, the HVAC system can be divided into three subsystems: cooling tower subsystem, chiller subsystem, and AHU subsystem. Based on the exergy models of three subsystems, MOPSO method is employed to search for the lowest exergy losses of three subsystems by optimizing the control sets of the HVAC system. A typical day test results show that the optimization method can obviously reduce the exergy losses of all three subsystems and the entire system compared with the original control. So the operation efficiency of the HVAC system can be improved by the multi-objective optimization method.关键词：HVAC system;optimal control;multi-objective optimization method;exergy analysis2347|2404|5发布时间：2024-07-18
- 摘要：The treated sewage heat pump system reuses the wasted heat in the city sewage to cool and/or heat the buildings. Biofouling, as the key problem in treated sewage heat pump systems, decreases the system efficiency and security. In this study, rotary coupon experiments were conducted, and Benzalkonium chloride, a broad-spectrum and efficient bactericide, of various concentrations was used to immerse the biofouling 10 min per day. Vital dye was used to stain the biofouling and confocal laser scanning microscope (CLSM) was used to take microphotographs of the biofouling to show the viability distribution of the bacteria cells in the biofouling. Imaris was used to calculate the biovolume of live/dead cells. The results show that benzalkonium chloride inhibits the biofouling significantly by killing most of the bacteria cells, and the inhibition effect is enhanced as the concentration increases. This research obtains insight into the biofouling inhibiting techniques and promotes the practical application of the treated sewage heat pump system by increasing the system efficiency and security.关键词：treated sewage heat pump system;biofouling;benzalkonium chloride;confocal laser scanning microscope1967|2253|0发布时间：2024-07-18
- 摘要：In order to improve the heat transfer and fluid flow performance of external gas-liquid two phase flow of plate in the evaporative condenser, the new surfaces of plate are comparatively analyzed. The effect of the different kinds of surface structure，spray density of water and air inlet velocity on the characteristics of gas-liquid two-phase flow and the performance of heat transfer are investigated. The results show that: the semicircle wavy plate has longer time of water film forming and larger heat transfer area and better performance of heat transfer; different plate structures of the evaporative condenser have different optimal spray density of spray water, and the optimal spray density are from 0.48 kg/m?s to 0.93 kg/(m?s); when the air inlet velocity is constant, the wall temperature of semi-circle wavy plate is increased and the temperature of gas-liquid interface is decreased with the increasing of spray density; when the air inlet velocity is less than 2.5 m/s, the increasing air inlet velocity can effectively reduce thickness of water film of external semicircle wavy plate and enhances heat transfer.关键词：evaporative condenser;semicircle wavy plate;spray density;enhanced heat transfer2344|2214|1发布时间：2024-07-18
- 摘要：The experiment of quick freezer’s refrigeration system is carried out to study it’s cooling curve and refrigeration performance. The experimental results show that: when the refrigeration system of the quick freezer begins to cool down, the evaporation temperature is dropped immediately to be close to the lowest evaporation temperature and the evaporator’s inlet temperature has a difference with water’s temperature about 25 ℃; the lower evaporating temperature leads to the smaller mass flow rate of refrigerant entering the compressor, and compressor’s power accounts for only about 60% of the rated power; the exergy loss is about 41% in the evaporator, thus to make the evaporation temperature match with the indoor temperature of quick freezer is an important means to increase the freezer’s cooling speed sharply.关键词：quick freezer;refrigeration performance;evaporating temperature;experimental research2087|2039|0发布时间：2024-07-18
- 摘要：The mathematic models of two-dimensional heat and mass transfer for lithium bromide （LiBr）aqueous solution added nano-particles are developed and validated by experimental data. The research results show that: the nano-particles can significantly improve the water vapor absorbing rate of the nano-fluid and the water vapor absorbing rate is increased with the amount of added nano-particles;with the same amount of nano-particles, the water vapor absorbing rate is increased with the flow rates of the nano-fluid and the water vapor absorbing rate as a function of flow rates shows logarithmic curve pattern; the mass transfer enhancement factor is increased with the increasing amount of nano-particles; the mass transfer coefficient of absorber is increased with the amount of added nano-particles;with the flow rate (1.2 L/min) of nano-fluid the mass transfer coefficient increased 1.32 and 1.41 times for adding 0.05% and 0.1% nano-particles respectively, but the amplification is reduced with the increasing of nano’svolume.关键词：nano-particle;mass transfer;LiBr-aqueous solution;falling film absorption2452|2141|2发布时间：2024-07-18
- 摘要：The condensation process of non-azeotropic mixed refrigerant is a isobaric process. Meanwhile, the concentrations of vapor and liquid continuously change. When the outlet temperature of condenser is 300 K, the mass fraction of R600a/R23/R14 in liquid phase mixture is 78.04/12.62/9.34, respectively. The R600a is the dominant component in the liquid mixtures. However, it also contained considerable amounts of middle and low boiling refrigerants. When the condensing temperature is reduced to 280 K, the mass fraction of R600a in vapor is 9.8%. Even if the condensing temperature is decreased to 249.49 K (the bubble point temperature of 35%R600a/35%R23/30%R14), the mass fraction of R600a in vapor phase still reaches 2.67%. The vapor-liquid equilibrium gravity separation method couldn’t separate mixed refrigerants completely. The separation ratio of R23 by phase separator I and phase separator II are 12.62% and 30.27%, respectively. The rest of the R23 goes into the evaporator. Phase separator I could separate 78.04% of the refrigerant R600a with high boiling point temperature. There are 9.34% R14 (low boiling refrigerant) in liquid phase. The mass fraction of R600a in evaporator still reaches 6.31%, the low boiling refrigerant R14 accounts for 45.64%.关键词：auto-cascade refrigeration system;R600a/R23/R14;composition change characteristics;non-azeotropic mixtures2460|2203|2发布时间：2024-07-18
- 摘要：The increasing energy consumption of data centers attracts more and more attention, much of which is consumed by the cooling system. Utilizing efficient cooling methods is the urgent need for realizing emission control targets, and the free cooling is one of these methods. The free cooling technology has three categories: airside free cooling, waterside free cooling and heat pipe free cooling. Airside free cooling is easily utilized and has good energy-saving effect, while it may affect the indoor air quality and humidity. Waterside free cooling can be modified from traditional air conditioner however its energy-saving effect is limited for additional heat transfer process. Heat pipe free cooling has no disturbance on the indoor environment and its energy-saving effect is good for utilizing phase change heat transfer. The latest advances in free cooling technology is summed up, which has the referential value for research in this field.关键词：refrigeration;air conditioning;data center;free cooling;advances2194|2244|15发布时间：2024-07-18
- 摘要：Centrifugal chiller market is developing rapidly, and its negative impacts on the environment in the life cycle are also increasingly concerned. In order to identify the main stages and the key influence factors of the environment impact of the whole life cycle of the centrifugal chiller, and provide the basis for the optimization design of the product, this study contributed a life cycle assessment (LCA) model and analyzed life cycle environmental assessment by life cycle impact analysis model of CML 2002, which included the environmental impacts of full life cycle, raw material acquisition phase, manufacture phase, use phase, transportation phase, recycling and reused phase. The sensitivity analysis was also provided. The results indicate that life-cycle environmental impacts are mainly in the climate change and the acidification, while exerting little change on the impacts of stratospheric ozone depletion, eutrophication and depletion of abiotic resources etc. Based on the sensitivity analysis, the refrigerant type, energy efficiency and using-time of water chiller are identified as the key driving forces for environment impacts of centrifugal chiller.关键词：centrifugal chiller;environment impact;life cycle assessment;GWP;energy consumption2198|2100|0发布时间：2024-07-18
- 摘要：HKF-60FH, a compound refrigeration unit with heat pipe for data center and other electronic equipment has been researched and developed. It contains three work modes: vapor compressing refrigeration, compound refrigeration and refrigeration with heat pipe respectively. Two independent cooling loops are formed by four scroll compressors where two of them are parallel. In this way, this unit can regulate cooling capacity by changing volume of compressors. Heat pipe unit uses the second refrigerant, which is driven by a liquid pump. In the air-cooled side, a combined heat exchanger was used, which contains the heat exchanger of heat pipe unit, condenser of compressing refrigeration unit and fan. Vapor compressing refrigeration begins to work when the ambient temperature is high. In this work mode, the first refrigerant provides total cooling capacity for the second refrigerant by heat transfer in the evaporator-condenser. Compound refrigeration mode works in transition seasons under full load operation of the heat pipe unit and compression refrigeration unit remedies the cooling capacity. When the ambient temperature is low, heat pipe unit operates and makes full use of the natural cold source. HKF-60FH unit is applied to high performance computer system, the evaporators are established in the truss and its internal air-flow distribution uses the method of horizontal air supply and closed circulation. The recirculating air temperature of the evaporators is set to 33℃. According to the above parameters, the refrigeration capacity and COP of vapor compressing refrigeration mode can reach 61.3 kW and 3.23 W/W (the ambient temperature is 35 ℃). Furthermore, the capacity and COP of heat pipe mode achieve 59.8 kW and 11.3 W/W (the ambient temperature is 10 ℃).关键词：data center air-conditioning;compound refrigeration unit with heat pipe;research and development;application2072|2172|1发布时间：2024-07-18
- 摘要：Test rig is established to measure the stratification characteristics of a water storage tank with new stratifier. When the initial temperature of the tank is 50℃ and the inlet temperature of the water is 20 ℃, the temperature of each layer in the tank is measured when the flow rate is 1.18 L/min,3.19 L/min,5.20 L/min respectively,. The results show that, when the larger the flow rate is, the larger is the slope of the sudden change in temperature curves, the destruction of stratification is more obvious. Based on the first law of thermodynamics and the second law of thermodynamics, the methods of volume, energy and exergy are used to describe the stratification characteristics of the tank. The results show that, when the flow rate is1.18 L/min,3.19 L/min,5.20 L/min respectively, the extraction efficiency is 93.7%, 95.7%, 96.7% respectively; the discharge efficiency is 98.2%, 95.7%, 92.3% respectively, which indicate that high extraction efficiency and discharge efficiency is got in three flow rates; when the dimensionless time is 0.7, the exergy efficiency is 13.3%, 14.6%, 17.6% respectively, and the stratification is worse for high flow rate than that with low flow rate.关键词：solar energy;stratification;storage tank;stratifier;discharge efficiency;dimensionless exergy2165|2012|5发布时间：2024-07-18
- 摘要：It is interesting to improve the performance of the refrigeration system by the utilization of the high pressure refrigerant. Based on the field synergy theory, a new type of refrigeration system was provided, in which the high pressure refrigerant was injected into the evaporator coil from the hole opened on the capillary inserted in the evaporator coil. The change law of the synergy angle between the flow and heat flow along the hole diameter and the capillary diameter was analyzed theoretically. And the visual experiments were carried out. The theoretical results show that the synergy angle is reduced with the decrease of the hole diameter and the capillary diameter, but the effect of synergy angle is also reduced with the decreasing of the capillary diameter. The experimental results show that compared with the conventional refrigeration system, the refrigerant mass charge is reduced more than 70%, COP is improved about 9% and the time needed to be stable is reduced 70% in the hole opening system.关键词：capillary cube diameter;injection hole diameter;field synergy2322|2196|0发布时间：2024-07-18
- 摘要：The influences of superheat degree on R22 and R32 refrigeration system’s performances are studied experimentally with variable frequency rolling piston compressor refrigeration loop test bench. With the quantitative analysis, some change trends of R32 refrigeration system under the superheat condition are summarized, and the optimum superheat adjustment range of R32 commercial air conditioning is studied by comparing the system’s parameters of R32 with R22’s under the condition of Case 1,. The experimental results show that: the change trends of the system’s parameters for R32 are similar with that for R22, and the R32 refrigeration system has a higher refrigerating capacity; under the condition of Case 1, the refrigerating capacity and COP of R32 are improved about 42% and 6.8% respectively compared to R22; the system’s pressure ratio is increased about 7%, which indicates R32 system is more stable. At the air-conditioned state, the better energy saving effect can be reached when the superheated degree of R32 system is controlled less than 4℃.关键词：R32;R22;system’s performance;superheat degree;rolling piston compressor2303|2306|2发布时间：2024-07-18
- 摘要：The road transport process was simulated in the vibration bench, the natural frequency of selected strawberry package was found to be 20.5 Hz by scanning frequency experiment. Fifteen same strawberry packages have been tested in the fixed frequency experiment under 17 Hz, 19 Hz, 20.51 Hz, 22 Hz and 24 Hz, respectively. After the fixed frequency experiment, strawberries in the fifteen packages were divided into three groups to be stored at 0 ℃, 5 ℃ and 10 ℃ respectively. The effects of mechanical vibration on the hardness and SSC, titratable acid, vitamin C and MDA contents of each group of strawberries have been analyzed. The results showed that the storage qualities of strawberry were determined by both mechanical vibration frequencies in the transport process and storage temperature. At the same storage temperature, the qualities of the strawberries suffered natural frequency vibration test are the worst. After 9 days of 0 ℃ storage, the strawberry’s hardness has been reduced by 15.5%, while the strawberry MDA content has been increased by 30%. 0 ℃ is the best storage temperature for strawberries suffered same frequency vibration test.关键词：road transport;vibration frequency;strawberry2092|2112|11发布时间：2024-07-18
- 摘要：Aimed at the problem of infrared exposure of the gateway resulted from the traditional dealing way of surplus heat of diesel power station in protective engineering, three application schemes of the phase-change thermal storage reservoir are put forward, which can reduce underground reservoir volume , extend the time of electricity power supply and improve energy efficiency. After building an experimental table of the latent heat storage system, the effects of the unit dimension, the flux and temperature of the fluid on the temperature distribution and the heat storage rate of thermal storage reservoir are analyzed. The results show that the rate of heat transfer is significantly improved when the unit dimension decreases or temperature difference of the heat transfer fluid increases, whereas the effect of the increasing volume of the heat transfer fluid is comparatively weak.关键词：thermal storage;phase change material;surplus heat of power station;protective engineering2267|2169|4发布时间：2024-07-18
- 摘要：Experiments are carried out separately under horizontal condensation tube arrangement and vertical condensation tube arrangement to examine energy efficiency ratio of hot-wall refrigerator. Theoretical calculations are made to analyze in-tube condensation heat transfer coefficients of horizontal and vertical tubes under the experimental conditions. The results show that: although the theoretical calculations of the in-tube condensation heat transfer coefficients of horizontal tubes are much higher than that of vertical tubes, but the experiment results indicate that there is a smaller difference on the whole heat transfer performance. Generally speaking, the energy efficiency ratio of horizontal tube arrangement is just about 2% higher, the outside air’s heat resistance plays a main role in hot-wall condenser, and the in-tube heat exchange difference caused by two tube arrangements has a small effect on the general heat transfer performance for hot-wall refrigerator.关键词：refrigerator;hot-wall condenser;tube arrangement;condensation heat transfer coefficient2233|2210|2发布时间：2024-07-18
- 摘要：In the internet era of energy, district heating and cooling system will change from a single form of energy to the various forms of energy, especially renewable energy and untapped energy. Integration of different grades of heat sources will cause system energy change. The energy bus system is a multi-source and multi-user thermal energy system that can make integration of renewable energy sources or untapped energy sources in large scale for district heating and cooling. This paper focus on analysis of exergy change in multi-source water mixing and heat recovery process of energy bus system comparing with the conventional system. The energy bus system can be modeled as integration of a series of Lorenz cycles. Through the theoretical analysis of the ideal thermodynamic model of energy bus systems and conventional distributed systems, exergy change law and its influencing factors in multi-source water mixing and heat recovery process of energy bus system are analyzed. Results show that many factors affect exergy change of multi-source system. Different design parameters can cause the energy to increase or decrease, or unchanged. In this paper, heat recovery process of energy bus system is also analyzed theoretically, and the related parameters which affect the heat change of the bus side are obtained and the heat variation law is found, also the way to get the optimum bus water temperature T_EBS1.关键词：energy bus system;energy planning;Lorenz model;heat recovery;exergy2338|2140|2发布时间：2024-07-18
- 摘要：Vacuum cooling (VC) and immersion vacuum cooling (IVC) were carried out to explore their effects on the quality of different parts of water- cooked pork. The weight loss, cooling rate and qualities (pH, color and TPA) of different parts of the meat were measured after cooling. Results showed that IVC could achieve a lower weight loss (P<0.05) compared to VC. However, a better temperature uniformity of the sample was found during VC compared to IVC. Both the brightness and redness values of the central and internal parts have not presented significant differences (P>0.05) between the samples undergone VC and IVC respectively. However, IVC can increase the lightness value of the external part significantly (P<0.05) compared to VC. Both the hardness values and chewiness values of both the central and internal parts were significantly reduced (P<0.05) after IVC, while there was no significant difference between the samples treated by VC and IVC respectively for the springiness and resilience values of all locations inside samples except external part.关键词：vacuum cooling;water- cooked pork;weight loss;qualities2330|2150|2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