最新刊期
卷 38 ， 期 5 ， 2017
- 摘要：This paper presents a data-mining-based method with a decision tree algorithm to diagnose accumulator opposite-insertion faults for a variable refrigerant flow (VRF) system. First, the VRF experimental platform was established for data collection. Then, expert knowledge and verification methods for the data variation model were used to select appropriate model variables. The C5.0 decision tree algorithm was employed to develop a fault diagnosis model. Finally, the effect of the electronic expansion valve (EEV) of the subcooler was analyzed and validated; this effect was selected as the best variable on the basis of classification rules generated by the model. The results show that the fault diagnosis method based on the decision tree exhibits desirable effectiveness for diagnosing accumulator opposite-insertion faults, with which the fault diagnosis accuracy is up to 96%. Moreover, the proposed technique can meet the requirements for online application of fault diagnosis for VRF systems. This method incorporating a decision tree algorithm to diagnose accumulator opposite-insertion faults for a VRF system exhibits very high accuracy and reliability; therefore, the method can meet the actual demands of fault diagnosis for VRF systems. Because the occurrence of accumulator opposite-insertion faults corresponds to a reduction in the degree of superheating, increasing the opening of subcooler EXV can ensure the cooling effect and a good energy efficiency ratio.关键词：decision tree algorithm;fault diagnosis;accumulator opposite insertion;subcooler EXV;variable refrigerant flow system2247|2428|0发布时间：2024-07-18
- 摘要：A solar-powered ejector refrigeration system with double-partitioned water storage tanks was proposed and analyzed. The stratified water tank had higher energy storage capacity and better thermal stratification than the conventional design. The advantages of a partitioned water storage tank and large and small water tanks were fully utilized in the novel system to compensate for the disadvantages of low solar energy utilization and low solar-powered ejector refrigeration efficiency, which resulted from the solar energy instability. In this study, the performance of the novel system was analyzed using an hourly cooling load analysis method. The high-grade energy consumption of the novel system is approximately 1/5 that of the conventional mechanical compression refrigeration cycle. The whole-day working time increases by 4 hours and the cooling capacity increases by 36.8% compared with the solar-powered ejector refrigeration cycle for the conventional water tank. In addition, the hourly cooling capacity of the novel system and the hourly cooling load of the office are more consistent than those of the conventional system.关键词：solar energy ejector refrigeration;partitioned water tank;hourly cooling load2660|3965|1发布时间：2024-07-18
- 摘要：The installation conditions of two outdoor units were examined experimentally in an enthalpy-potential laboratory platform in this study. The influence of three installation conditions of outdoor unit on the surrounding thermal environment, air conditioner EER and groove area was studied. Three kinds of the outdoor unit installation conditions of groove were vertical installation of the same plane (two outdoor units at the same height, the length extension line of the outdoor unit perpendicular to each other and intersect), horizontal installation of the same plane (two outdoor units at the same height, the length extension line of the outdoor unit is collinear) and parallel installation in height direction along the wall (two outdoor units at different heights, the height extension line of the outdoor unit is collinear), respectively. For vertical installation in the same plane, the results suggest that horizontal distance (parallel to the exterior wall) d1 should not be less than 650 mm. Otherwise, a less favorable ambient environment will be obtained for the outdoor unit, and the return air temperature will be higher than normal, at 45 ℃. Further, the vertical distance (perpendicular to the exterior wall) d2 is recommended as 300 mm because bigger distance would cause the return air temperature to rise. If the slots do not match the installation conditions, but meet the horizontal and vertical spacing requirements (greater than 650 mm × 300 mm), the perpendicular installation method to yield vertical installation in the same plane is recommended. The return air effect is good when plane installation is employed, and the considered grooves occupy a large area. Further, neither the return air temperature nor energy efficiency ratio (EER) increase obviously when d1 is more than 70 mm; thus, the optimal distance is 70 mm. When vertical installation perpendicular to the plane is employed, the groove area is less than those for horizontal installation and vertical installation in the same plane, and the return air effect is considerably better than that for vertical installation in the same plane. In addition, the lowest return air temperature is lower than that for plane installation; thus, the optimal distance is 150 mm.关键词：outdoor unit;installation position;energy efficiency ratio;return air temperature;thermal environment2136|3772|0发布时间：2024-07-18
- 摘要：The heating, ventilation, and air conditioning (HVAC) system accounts for a large portion of the total energy consumption of a building. When aiming to achieve energy efficiency, the vital factor is optimal operation of the chiller plants, which constitute a large percentage of the system energy consumption. In fact, chiller plants are often configured with multiple chillers, in order to meet the requirements for energy efficient operation of the HVAC systems of public buildings under partial loads. The chiller sequence control plays a significant role in satisfying the indoor load demand and facilitating energy-saving operation. In this paper, to improve the energy efficiency of the air-source heat pumps, an optimal sequencing control strategy is presented, taking an office building as an example. To develop this strategy, a variable-speed heat-pump model and the objective function for optimization of the heat-pump sequence control were first established, so as to determine the optimal solutions under partial building loads. Here, the variation of the actual capacity under different operation conditions was taken into consideration. In addition, the annual cooling and heating loads of the selected office building were analyzed using eQUEST software. It was found that loads greater than 70% of the peak loads occupy only 24% of the cooling time and 8% of the heating time. Finally, the optimal sequencing control strategy was contrasted with the traditional strategy based on the typical daily loads in the summer, winter, and transition seasons; the results indicate that the heat-pump energy consumptions are reduced by 14.5%, 12.3%, and 3.3%, respectively. In addition, the energy consumption for the entire year was analyzed. The results show that the energy consumed by the heat pump is reduced by 14.1% during the cooling season and 9.0% during the heating season following adoption of the optimal sequencing control strategy. Thus, the optimal sequencing control strategy for the heat pump has a remarkable energy saving effect.关键词：air source heat pump;frequency conversion;part load;optimal sequencing control;energy efficiency2235|2575|2发布时间：2024-07-18
- 摘要：Based on the Peng Robinson (PR) equation of state combined with the Wong-Sandler (WS) mixing rule, and combined with the UNIFAC group contribution method used in the Predictive Soave Redlich Kwong (PSRK) equation, a gas-liquid equilibrium prediction model of the mixture (PRWS-UNIFAC-PSRK) was constructed. The results indicate that for the R32/R1234yf binary mixture, the deviations between the experimental and calculated data for the pressure and vapor phase mass fraction are within ±2.5% and 0.02, respectively. For R134a/R1234yf/R600a ternary mixture, the relative deviation between the measured pressures and calculated results are within ±3% and the absolute deviation of vapor phase mass fraction is within ±0.04. In ternary phase equilibria diagram of R1234yf/R290/R134a, the mass fraction of R1234yf/R290/R134a at around 0.25/0.7/0.05 has an azeotropic point. The VLE (vapor liquid equilibria) prediction model can be further improved by using the multi-parameter equation of states, improving the activity coefficient models and obtaining more accurate binary interaction coefficient.关键词：vapor liquid equilibria;R1234yf;computer simulation;azeotropic point2110|2976|0发布时间：2024-07-18
- 摘要：To increase the thermal conductivity of organic fatty phase change material (PCM), different mass fractions of nanoparticles with high thermal conductivity, including 10?30-nm copper powder, alumina, and iron oxide, were individually added to composite PCMs of capric/caprylic acid (with a 30:70 mass ratio). The experimental results show that the composite PCMs exhibit good thermal stability and zero precipitation after the addition of nanoparticles at a mass fraction of 0.1?0.4%. Compared with the original material, the thermal conductivity is greatly improved by 5.1%-6.5%, 4.0%-12.4%, 6.7%-17.5%, for the copper powder, alumina, and iron oxide, respectively. The fluctuation range of the phase change temperature is small (±0.39℃). The phase change latent heat varies little and the increase range is 2.2%-5.5%. Therefore, the selection of appropriate amounts of nanomaterials can improve the thermal properties of the original PCMs, which may have wide potential application.关键词：composite phase change materials;thermal properties;nanomaterials2057|2291|5发布时间：2024-07-18
- 摘要：A new kind of emulsion was prepared as a cold storage material for ice slurry using high-speed stirring and an ultra-sonication bath. Liquid paraffin and a compound of sodium oleate and cetyl trimethyl ammonium bromide (CTAB) were chosen as the oil phase and emulsifier, respectively. The experimental results for the electrical conductivity indicate that the emulsion is oil/wate (O/W) type. The D50 diameter of the emulsion is approximately 1.56 μm and its maximum diameter is 4.47 μm. Further, the use of ethyl alcohol and butyl alcohol is effective for preventing ice adhesion to the breaker wall with polymethylpentene (PMP), glass, and stainless steel. Early after supercooling dissolution, the highest and lowest ice formation rates occur in the stainless steel breaker and the PMP breaker, respectively. At the same time point after supercooling dissolution, the ice packing factor (IPF) of the system with added ethyl alcohol is higher than that having added butyl alcohol. The difference between the IPFs obtained by adding ethyl alcohol and butyl alcohol is reduced with increased ice formation time. The ice has a granular morphology and disperses well. The IPF is in the 55%-65% range at 3 hours after supercooling dissolution.关键词：ice slurry;secondary refrigerant;degree of subcooling;freezing point;emulsion2101|2395|0发布时间：2024-07-18
- 摘要：In this study a cooling-fan simulation model was established using the steady-state distributed parameter method, and the performance of a cooling-fan prototype was tested in an air-blower performance test rig. Further, a cooler heat transfer performance analysis was conducted based on the experimental data and numerical simulation. For a temperature calibration of ?25-0 ℃ and a circulation rate varying in the range of 2-5, it was found that the total heat transfer coefficient increases with increasing calibration-box temperature. When the refrigerant is CO2, the cooling capacity of the cooling fan is obviously higher than that for an NH3 refrigerant. Further, the cooling capacity is 42% higher when the temperature in the tank is 0 ℃ and 26% higher for a tank temperature of ?20 ℃. The pressure drop of inner side of the tube increases with increases in the circulation rate. Further, the heat transfer coefficient first increases and then decreases with increases in the circulation rate. The circulation ratio is approximately 3, corresponding to the maximum change in the thermal coefficient. The simulation results exhibit the same trend as the test results, but some errors exist. The error of heat transfer coefficient between the numerical and test results is approximately 16% for the NH3 system, and approximately 8% for the CO2 system.关键词：heat transfer coefficient;calibration temperatures;pressure drop inside the tube;circulation rate2020|2620|2发布时间：2024-07-18
- 摘要：CO2 heat pump thermal battery system consists of a water-source transcritical carbon dioxide heat pump coupled with hot and cold thermal storage, and its performance gradually decreases during the process of thermal energy storage. This paper presents experimental studies of a CO2 heat pump thermal battery system. The performance of this system was tested under a variable water-circulation flow rate for the hot/cold tank, a variable compressor frequency, and electronic expansion valve (EEV) opening. The results show that adoption of a lower water-circulation flow rate allows the tank to obtain good thermal stratification and a larger capacity. Further, a high compressor frequency benefits the system performance. The EEV opening also influences the system performance. The overall coefficient of performance (COP) reaches a maximum of 5.49 when the compressor frequency is 50 Hz, the EEV opening is 330 pulse, and the hot and cold water flow rates are 0.1 and 0.2 m3/h, respectively. Moreover, through mathematical fitting, a correlation was established between the COP, the outlet temperatures of the hot and cold tanks, and the control parameter. Overall, the total COP is 6.29 when the optimal control strategy based on the genetic algorithm is applied.关键词：CO2;heat pump;thermal storage;performance test;genetic algorithm2095|2466|0发布时间：2024-07-18
- 摘要：Control of the electronic expansion valve in an air-source heat-pump water heater has considerable influence on the system performance and should be the focus of investigation. In this study, the effect of the opening of the electronic expansion valve on the performance of an air-source heat-pump water heater was analyzed. The results show that, when the system operates with the same valve opening, the heating capacity and coefficient of performance (COP) exhibit a declining trend after an initial ascent. For different valve openings, the system COP is in direct proportion to the opening when the average cistern temperature is 20-30 ℃, whereas it is in inverse proportion to the opening for an average cistern temperature of 45-55 ℃. The system COP trend lines for each valve opening indicate a cross each other. As compressor suction with little liquid refrigerant can improve the system performance, the intersection occurs close to the point at which the superheated temperature reaches 0 K, but does not coincide with it. Although the maximum optimization ratio on system COP for the method of controlling the electronic expansion valve via the average cistern temperature (optimization #1) can reach 24.8%, its feasibility is poor. The maximum optimization ratio on system COP for the method of controlling the electronic expansion valve via the superheated temperature in the compressor suction (optimization #2) is lower than that for optimization #1, at 4.2%. However, the results of the confirmatory experiment verify the feasibility of optimization #2.关键词：air-source;heat pump;electronic expansion valve;control2130|2664|5发布时间：2024-07-18
- 摘要：A reasonable heat transfer coefficient correlation for a finned-tube air cooler was established by applying the methods of dimensional analysis and function analysis. This approach focused on an air cooler design in which the refrigerant phase changes in the tube. A pump-feeding ammonia air cooler was chosen as the experimental study object. Further, a multi-factor and multi-level experimental scheme was designed for this machine type. The scheme included the structure parameters, face velocity, ambient temperature, driving temperature, and circulation ratio. The heat transfer coefficients were tested under various conditions using a calibrated-box method according to the scheme. Moreover, the heat coefficient correlation of the pump-feeding ammonia air cooler was obtained through a nonlinear fitting method based on the test results. It was found that the relative errors between the calculated correlation values and the test values range from ?10% to +10%. Furthermore, the tube side heat coefficient is larger than the outside heat coefficient, which is consistent with practical experiments. These results show that the established correlation is reasonable and sufficiently accurate for use in practice. The calculated correlation values are 1.11 to 1.30 times the experimental values at the common design points for the pump-feeding ammonia air cooler. Thus, the heat transfer surface can be reduced by 11%-30% when the correlation is applied in the design of this type of air cooler. This correlation is helpful for reduction of the machine dimensions and to enhance its economic efficiency.关键词：air cooler;finned tube;heat transfer correlation;calibrated box method2417|2851|0发布时间：2024-07-18
- 摘要：To analyze the influence of different working frequencies and room temperatures on the cooling span of a reciprocating room-temperature magnetic refrigeration system, a setup for such a system was designed with granular Gd (particle size: 0.3-0.5 mm) as the magnetic working mass. The cooling temperature of the reciprocating room-temperature magnetic refrigeration system was then analyzed, combined with the heat transfer characteristics in the active cooler during the experiment. A 1.5 T permanent magnet field strength was maintained, and the changes in the cold- and hot-end temperatures of the cold accumulator were measured at different operating frequencies (0.07, 0.12, 0.16, 0.19, 0.22 Hz) and room temperatures (14.5, 15.9, 16.7, 18.1 ℃). The results show that, when the operating frequency is 0.22 Hz, the maximum refrigeration temperature span of the system is 12.8 ℃. Further, when the Gd temperature is lower than the Curie temperature of 20 ℃, the room temperature has no effect on the cooling capacity of the magnetic refrigeration system over a finite time period.关键词：room temperature magnetic refrigeration;active magnetic regenerator;refrigeration performance test;gadolinium2163|3161|0发布时间：2024-07-18
- 摘要：In this study, a cabinet semiconductor cooling device was designed and its refrigerating capacity and cooling efficiency were tested using a test platform. The performance parameters were obtained according to test-based analyses of the refrigerating capacity, cooling efficiency, and other factors. According to the test results, for an average indoor temperature of 26 ℃ and 200-360 W input power, the cooling efficiency first increases and then decreases, reaching a maximum value of 69.5% when the input power is 232 W. Meanwhile, the average amount of refrigeration throughout the test is 455.46 kJ and the power of the semiconductor cooling device is 151.8 W, which can remove 3.04% of the energy in a 5 kW communication cabinet.关键词：communications cabinet;semiconductor refrigeration;refrigerating efficiency2025|2701|0发布时间：2024-07-18
- 摘要：A multilayer micro-channel Joule-Thomson (J-T) cryocooler was designed by combining several layers of rectangular micro-channels with a coke soup cooler. The heat recovery section was constructed using three layers of high- and low-voltage rectangular channels. Experiments were conducted using nitrogen as a refrigerant with inlet pressures ranging from 4 to 8 MPa, and the temperatures of each of the measuring points of the multi-layer microchannels in the J-T cryocooler were collected. The cooling characteristics of nitrogen in the various stages of the refrigeration system were analyzed, and the experimental results obtained when nitrogen and argon were used in the J-T cryocooler were compared. The results show that, when the inlet pressure is 4-8 MPa, a lower temperature for the nitrogen cold end with increasing pressure corresponds to a shorter time period to reach a stable cold-end temperature. When the inlet pressure is 8 MPa, the cold-end temperature reaches 1.7 ℃ at approximately 200 s. The argon cold-end temperature is lower than that of the nitrogen at the same inlet pressure; however, the time required for the nitrogen to reach the cold-end temperature is shorter than that for the argon. When the inlet pressure is 7 MPa, the temperature of the cold-end argon gas occurs approximately 450 s ahead of time. Further, the temperature drops for nitrogen at an 8-MPA inlet pressure and argon at a 4-5 MPa inlet pressure are similar. In addition, the nitrogen cooling time is shorter. Thus, the use of nitrogen instead of argon can reduce the cooling costs.关键词：Joule-Thomson effect;rectangle micro channel;velocity of temperature falling2060|2342|1发布时间：2024-07-18
- 摘要：As the humidity load of an air-conditioning system accounts for 40%-60% of the cooling load of the entire system, exploiting the advantages of solid desiccant can effectively reduce the energy consumption of the air-conditioning system. The major source of energy consumption for the desiccant system is the regeneration energy consumption of the solid desiccant, and the traditional regenerative mode is characterized by high energy consumption, low regenerative efficiency, etc. In this study, comparative tests were conducted on the regeneration performance of solid desiccant materials under application of the microwave and hot-air methods. Hence, a model was established, and analyses were conducted considering the regeneration effect and energy consumption. Solid desiccants in the same state were tested under hot-air regeneration modes of 50-90 ℃ (power: 857-1 204 W) and for microwave regeneration powers of 440-800 W. The test results indicate that the maximum regeneration rate for the hot-air method is 49.89%-86.23% of the microwave technique. However, the microwave energy consumption is only 25.2%-37.7% of the hot-air method. Thus, the average energy utilization of the microwave regeneration method is 2.51-3.21 times that of the hot-air technique.关键词：solid desiccant;microwave regeneration;hot air regeneration;energy utilization2056|2528|2发布时间：2024-07-18
- 摘要：Establishing a high-quality biobank is very important, but the cryoprotective agent (CPA) type and concentration have a considerable influence on the cryopreservation effect. In this paper, HBL-100 human breast cells were treated with 10% Me2SO combined with trehalose (0-0.3 mol/L) and fetal bovine serum (FBS; 20%-60%) in Dulbecco’s modified Eagle’s medium (DMEM). Through gradual reduction of the temperature, the cells were cooled in a ﹣80 ℃ freezer for 4 h and then quickly transferred into liquid nitrogen. After storing for 7 days, the cells were shaken quickly at 37 ℃. The cell survival rate was assessed using the trypan blue test, cell counting kit (CCK) assay, and the attached rations after 24 hours. The results show that, compared with the control group, the effects of the trehalose and FBS are very obvious. In particular, when the trehalose concentration is constant, a higher FBS volume fraction yields a better effect. The FBS has no significant effect without trehalose. Further, when the FBS volume fraction is constant, the optimal effect is obtained for 0.2 mol/L trehalose. A high trehalose concentration may weaken the effect of the FBS. Considering the cost and other factors, the most suitable CPAs for the cryopreservation of HBL-100 human breast cells are 10% Me2SO + 40%-60% FBS + 0.2 mol/L trehalose.关键词：cryopreservation;viability;trehalose;fetal bovine serum1968|2231|1发布时间：2024-07-18
- 摘要：The ejector is the key component in a heat-driven ejector refrigeration system, and its performance is of considerable importance to the system efficiency. The limiting operating condition is defined as the working condition when the secondary mass flow rate is equivalent to zero, and the performance under this working condition is important to the ejector working mechanism and application. In this study, experimental apparatus to study the ejector performance under the limiting operating condition was designed and constructed, using R134a as a refrigerant. The effects of the primary flow pressure and ejector back pressure on the back pressure of the converging-diverging nozzle were studied experimentally under the limiting operating condition, i.e., when the secondary mass flow rate was zero. The experimental results show that both the primary flow pressure and ejector back pressure have considerable influence on the back pressure of the nozzle under the limiting operating condition. The nozzle back pressure decreases with an increase in the primary flow pressure, but increases with an increase in the ejector back pressure. In this study, detailed values were obtained for the lowest evaporating pressure of the system. The findings indicate that the primary flow pressure is in the range of 1.5-3.2 MPa and the ejector back pressure is in the range of 0.66-0.96 MPa. These results can provide guidance for ejector refrigeration system application.关键词：refrigeration system;ejector;test condition;R134a2065|2605|3发布时间：2024-07-18
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