最新刊期
卷 40 ， 期 1 ， 2019
- 摘要：Free cooling is widely applied in data centers as a promising technology for energy conservation. A loop cooling unit driven by a miniature rotary booster for free cooling was developed for a small data center. In this study, compared with air conditioners and pump-driven loop heat-pipe units, the booster-driven loop cooling unit consumed lower power and had a higher energy efficiency ratio (EER). An improved rotary booster with a small pressure ratio was adopted in the rotary booster-driven loop cooling unit. The results indicate that with the increase in the indoor and outdoor temperature difference (ΔT), the unit cooling capacity and EER first increased and then decreased. When ΔT was 25 ?C, the cooling capacity reached 17.7 kW, and the EER was 15.2. With the increase in ΔT, the power of the unit exhibited a downward trend all the time. When ΔT was 25 ?C, the power of the unit reached 1.16 kW. The thermal performance was compared with that of the pump-driven loop heat-pipe unit. When ΔT was 25 and 10 ?C, the EER values of the rotary booster-driven loop cooling unit were 25.5% and 104.7% higher than those of the pump-driven loop heat-pipe unit, respectively.关键词：heat pipe;cooling capacity;rotary booster;data center2394|2321|2发布时间：2024-07-18
- 摘要：The air-side pressure drop of micro-channel heat exchanger (MHE) is increased and the heat exchange performance is attenuated when the MHE is covered with dust particles. In this study, a visual experimental rig was set up to investigate the effect of air velocity, type of dust, relative humidity and whether the MHE is charged or not on dust accumulation. The experimental results indicate that dust particles were mostly deposited on the windward side of the slit fins and at the front part of the tubes at an air velocity of 1 m/s. The dust extended to the trailing edge of the fin at higher wind speed. When only particle dust was present, dust could hardly accumulate. However, as the fiber content increased, the particle-deposition process accelerated. Under the conditions of 100% Particle, 95% Particle + 5% fiber, and 92% Particle + 5% fiber + 3% long fiber, the air-side pressure drop were increased by 8.8%, 451.4%, and 524.9%, respectively. Under the conditions of 95% Particle + 5% fiber and 92% Particle + 5% fiber + 3% long fiber, the air volume were decreased by 31.6% and 48.7%. When the air relative humility was 45% and 65%, the air-side pressure drop were increased by 451.4% and 385.6%, and the the air volume were decreased by 31.7% and 26.4%. When the MHE was not charged or was charged by an alternating current at 3 V, the air-side pressure drop were increased by 385.6% and 278.3%, and the air volume were decreased by 26.4% and 18.4%, respectively.关键词：micro-channel heat exchanger (MHE);particle deposition;air velocity;type of dust;relative humility;charged condition2226|2494|0发布时间：2024-07-18
- 摘要：China’s inverter air conditioner efficiency standard (GB21455—2013) adopts a single set of annual performance factor (APF) values to evaluate inverter heat-pump air conditioner charged with different types of refrigerants. Obviously, neglecting the refrigerant classification is a flaw in the standard. Thus, we obtained two types of running-time curves from meteorological statistics and standard data. Furthermore, on the basis of these curves, the APF of several inverter air conditioner with different refrigerants were analyzed in terms of the same environmental impact (the total equivalent warming impact (TEWI) was chosen). The results show that the APF values of the R290 equipment were relatively lower than those of R22 and R410A under the same environmental impact. According to the standard data results (air conditioner with 2 HP cooling-capacity), the APF differences between these refrigerants were up to 0.57 and 0.59, respectively. Finally, a refrigerant-classification evaluation in terms of the energy efficiency standards was performed. In addition to the indirect environmental influence on the equipment energy efficiency, the direct effect of refrigerants should also be considered.关键词：inverter air conditioner;APF;environmental impact;energy efficiency standard;refrigerant2265|2303|0发布时间：2024-07-18
- 摘要：The performance of compressors is an important key in air-source heat pumps under different climatic conditions. The development of compressors is reviewed in this study. Previously, the compressor used in a room air conditioner was a piston compressor. With the emergence of rotary and scroll compressors, the efficiency of compressors has increased. Both rotary and scroll compressors have been developed to adapt to low ambient temperature. Simultaneously, the key technologies that affect the development of compressors are introduced. The compressor efficiency is improved by the improvement in the motor and compressor structures. The coefficient of performance (COP) and integrated part load value (IPLV(H)) have been improved using the techniques of variable compression ratio, enhanced vapor injection, and integrated-part load adjustment. The use of DC motors instead of AC motors can increase the motor efficiency and range of frequency adjustment of both compressors. By designing the scroll compressor using asymmetric swirl disks, noise and leakage can be reduced. The symmetrical arrangement of dual rotors can enhance the compressor capacity. Scroll compressors with exhaust valves can achieve variable compression ratios to a certain extent. Rotor compressors contain exhaust valves, which offer significant advantages in varying operating conditions. Both types of compressors can use the gas injection technology to achieve a high compression ratio of the heat pump at a low ambient temperature.关键词：air-source heat pump;compressor;coefficient of performance;ambient temperature2776|3150|2发布时间：2024-07-18
- 摘要：The velocity field in the area of heat and mass transfer in a drying chamber of heat pump was investigated experimentally and an optimal configuration was determined. Four kinds of inlet velocity (1.50, 2.00, 2.50, and 3.00 m/s) were used and five kinds of chamber structures, i.e., no static pressure layer and no variable cross section, with a static pressure layer but no variable cross section, with both static pressure layer and variable cross section whose angles were arctan (3/40), arctan (1/10), and arctan (1/8) respectively, were compared. Furthermore, the suitable inlet temperature range for the optimized structure was investigated by changing the inlet temperature (40, 50, and 60 ?C). The results show that the structure with both static pressure layer and variable cross section whose angle was arctan (1/10) was the optimal and the inlet velocity was recommended as 2.50 m/s. The inlet temperature can be determined using the dried materials because the suitable inlet temperature range is large.关键词：drying chamber for heat pump;experimental analysis;velocity field;temperature field2036|2065|0发布时间：2024-07-18
- 摘要：A serrated leading-edge blade for a multi-blade fan of an air conditioner is designed. The main objective is to reduce the vortex near the blade, thus reducing the flow loss and aerodynamic noise of the flow field of the multi-blade fan. Whereas it is different from the common reformed blade, no improvement in the width of the whole blade but a front disk along the leading edge by one-third of the impeller width was made. The various serrated structures were simulated based on the geometric-similarity principle using the FLUENT software. The simulated results show that the serrated structures destroyed the accumulated vortex close to the front disk. In contrast to the prototype blade, all vortices in the volute tongue, trailing edge, and internal leaves were obviously decreased with the use of the serrated blade. Meanwhile, the fundamental frequency noise was decreased. The experimental data indicated that the air volume of the leading-edge serrated blade of the centrifugal fan varied a little under different speeds. The noise and input power were decreased by 0.9–1.2 dB (A) and 2.75–3.55 W, respectively. Thus, the serrated leading-edge blade can not only benefit the air-duct performance but also play a role in energy savings and noise reduction.关键词：serrated blade;numerical analysis;multi-blade centrifugal fan;energy saving;noise reduction2058|2795|2发布时间：2024-07-18
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Study on Condensation Heat Transfer Performance of Natural Convection outside a Drop Tube Containing
摘要：Based on the double-film and boundary-layer theories, a mathematical model of the gas- and liquid-film thicknesses and the heat transfer coefficient of a drop tube were established, which considers the vapor-liquid interfacial thermal resistance. The distributions of the gas- and liquid-film thicknesses and heat transfer coefficient along the tube wall under different initial parameters and curvatures were obtained by simulation. The results indicate that the heat transfer coefficient is decreased (by approximately 30%) and the liquid-film thickness is increased (by approximately 7%) with the increase in the mixing gas pressure (when the pressure is from 81 325 to 121 325 Pa). With the increase in the non-condensable gas mass content (when the non-condensable gas-mass content is from 0.1% to 10%), the film thickness is decreased (by approximately 52%), the mass content of the non-condensable gas in the gas film is increased (by approximately 58%), and the heat transfer resistance of the gas film is increased (by approximately 61%). For an equivalent drop-tube diameter with the other conditions remaining unchanged, the larger the curvature is, the easier the separation of the liquid film is, and the larger the heat transfer coefficient is.关键词：drop tube;non condensable gas;condensation;heat transfer characteristics1881|2318|0发布时间：2024-07-18 - 摘要：The performance of a bubble pump directly influences the performance of a single-pressure absorption refrigeration cycle. On the basis of a guided bubble pump with a current equalizer and multiple tubes, this research was focused on analyzing the influence of different immersion ratios on the bubble pump performance under different heating power, which used water as a working fluid. According to the experimental results, when the bubble pump operated for a short time from starting, the total lifting capacity decreased with the increase in the immersion ratio. For example, when the heating power and immersion ratio were 1 250 W and 0.5, respectively, the total lifting capacity was 3.04 kg heavier than that under the heating power and immersion ratio of 1 450 W and 0.5, respectively. However, the bubble pump performance under a long term working condition can be significantly improved by increasing the immersion ratio. In addition, the performance of the guided bubble pump can be effectively optimized by adding a current equalizer. The total lifting capacity and efficiency of the bubble pump can also be increased.关键词：refrigeration technology;single-pressure absorption refrigeration;bubble pump;immersion ratio;two-phase flow1803|1897|1发布时间：2024-07-18
- 摘要：Gas hydrate is a novel cool-storage medium. However, its engineering application is impeded by its long induction time for crystallization, large super-cooling requirement, and poor growth rate. A homogeneous nucleation method was used to investigate the effect of promoters on the growth rate during the growth period. Samples prepared using 0.1% (w/v) sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), perfluoroalkyl ether alcohol ammonium anion Intechem-01 (FC-01), tetrabutylammonium bromide (TBAB), and tetrahydrofuran (THF) and a blank sample were kept in water bath at 3 ?C to observe the HCFC-141b hydrate growth rate. The experimental results show that thermodynamic promoters TBAB and THF displayed little influence on the growth rate of the hydrate, but the kinetic promoters—surfactants SDS, SDBS, and FC-01—exhibited considerable promotion of the hydrate growth rate, and FC-01 played the best role. By analyzing the droplet size using Malvrern Zetasizer, the results show that the dispersion and stability of the FC-01 sample was the best at an average droplet size of approximately 350 nm, which provided further proof that a kinetic promoter with outstanding dispersion and stability can exponentially enhance the growth rate of hydrates.关键词：cool storage;phase change;clathrate hydrate;promoter;surfactants;size distribution1899|2176|3发布时间：2024-07-18
- 摘要：According to the theory of flash evaporation, an experimental apparatus was designed for a water-dynamic vacuum flash under the influence of ethanol and ultrasound. The effects of the different rates of ultrasonic power, flow rate, and ethanol concentration were investigated. The experimental results show that compared with the flash evaporation without ultrasound, ultrasound exhibited an obvious effect on the flash enhancement. Furthermore, the depressurization and cooling-down rates were increased with the enhancement of the ultrasound, and a higher ultrasonic power rate was conducive to the dynamic flash and improving the ice-making efficiency. Further, the final stable pressure was increased with the increase in the flow rate under the same ultrasonic power. A large flow rate was not conducive to the continuous process of flash vaporization. Ethanol additives could make the solution temperature be decreased below 0 ?C, and the higher the concentration was, the lower the temperature was. Adding 5% ethanol was more favorable for ice crystal production关键词：vacuum;ice slurry;ethanol solution;ultrasound;flow rate;supercooling degree2053|2085|2发布时间：2024-07-18
- 摘要：Pulse-tube refrigerators are widely used in our society today, but research on the microscopic mechanism of the dynamic process of gas flow inside the pulse tube is lacking. In this study, the molecular dynamic simulation method was used to establish a channel model, and the channel was inflated and deflated to simulate the compression and expansion of a pulse tube. Subsequently, with variations in time, the axial pressure, density, velocity, and temperature of the pulse tube were studied. The results show that the pressure and density gradient in the axial direction of the gas gradually decreased until a balance was reached when the process continued, but a slight reversed gradient occurred. Expansion and compression processes occurred at 64 ps, and the maximum velocities near the channel exit were 775 and 864 m/s, respectively. As the reaction progressed, the maximum velocity gradually moved toward lower pressure. The phases of the pressure and velocity waves in the channel varied with the position. In the compression process, the high temperature of the channel near the closed end reached up to 500 K. Simultaneously, the temperature away from the closed end could be reduced to 223 K, and the expansion process was opposite that in the previous condition. The average time integral at the hot end was 375 K at the time of one temperature cycle superposition, and the average time integral at the cold end was 244 K. Thus, cooling of the environment at the hot and cold ends of refrigeration was facilitated.关键词：molecular dynamics simulation;pulse tube cryogenic cryocooler;thermodynamic properties;phase1983|2088|1发布时间：2024-07-18
- 摘要：A variable air volume（VAV）system exhibits the feature of limited sensors and similar characteristics of fault conditions. A traditional passive fault detection and diagnosis（FDD）method does not diagnose all faults in VAV systems due to limited information. Thus, it is necessary to obtain more diagnostic information while not necessitating additional sensors and labor. In the study, a proactive fault detection and diagnosis method was proposed to solve the problem. The method obtains more valuable diagnosis information via the introduction of small disturbances during working time immediately when faults occur. Hence, this further aids in diagnosing suspicious faults that cannot be separated via passive methods. The passive method was also combined with proactive methods to improve the FDD efficiency. In order to verify the feasibility of the method, a VAV air conditioning system was constructed in the TRNSYS simulation platform. Additional diagnosis information was obtained by introducing faults in VAV terminals and introducing proactive action. Additionally, the simulation results indicate that the method can effectively detect and diagnose 12 common faults in VAV terminals. Furthermore, the diagnostic and detection mechanism is more advanced when compared with that of traditional passive methods.关键词：VAV system;fault detection and diagnosis;proactive;VAV terminals2061|2121|0发布时间：2024-07-18
- 摘要：This paper proposes an energy consumption-prediction method for metro heating, ventilation and air-conditioning (HVAC) systems based on an auto-regressive moving average (ARMA) model using a time-series data analysis. Firstly, stationarity analysis and white-noise analysis (also known as pure stochastic analysis) were carried out on the collected energy-consumption data from actual metro HVAC systems. Secondly, optimal model parameters were determined using the autocorrelation function (ACF), and partial autocorrelation function (PACF) and Akaike information criterion (AIC). Finally, an effective energy consumption-prediction model was established. Four different methods were employed to test the effectiveness of the established ARMA model. Meanwhile, two performance indexes, namely, mean absolute error and root mean square error, were adopted to evaluate its performance in terms of fitting the observed energy consumption data. The results demonstrate that the proposed method based on the ARMA model could extract useful information from the energy data and is thus effective for energy consumption prediction of metro HVAC systems.关键词：time series;ARMA model;metro HVAC systems;energy consumption prediction1956|2137|1发布时间：2024-07-18
- 摘要：According to the features of protective engineering, an index for energy efficiency evaluation of an air-conditioning system is proposed, which is named as operating-demand energy efficiency ratio. Its definition and calculation method are provided in this paper. The energy efficiency evaluation strategy of an air-conditioning system is established from the whole system and its components, and the limiting values of the energy efficiency are provided. By taking a small underground engineering in hot summer and cold winter zones as an example, the energy efficiency evaluation of the air-conditioning system was carried out. The evaluation result shows that the system exhibited a daily low level of energy efficiency. On the basis of the result, the original project was retrofitted, and the energy efficiency of the system was improved by 18.9%, which verifies the feasibility and rationale of the proposed evaluation method.关键词：protective engineering;operation demand energy efficiency ratio;operating conditions;air-conditioning system;heat load;dehumidification2091|2055|0发布时间：2024-07-18
- 摘要：A new type of composite polyvinyl alcohol/sodium polyacrylate (PVA-PAAS) nanofibrous membranes (NFMs) was prepared using the electrospinning method. The adsorption and desorption performance of these materials was compared with the PVA-PAAS solution-casted membranes (SCMs) experimentally. The test results show that the PVA-PAAS NFMs with 20% mass fraction of PAAS could adsorb 0.3 kg/kg of water vapor at 25 ?C and 80%RH, whose adsorption capacity is 78% larger than that of pure PVA NFMs under the same state. Approximately 90% of the adsorbed water vapor could be removed within 5 min, and adsorption equilibrium could be achieved in 15 min by the PVA-PAAS NFMs. Similarly, the PVA-PAAS NFMs exhibited a fast desorption rate and took only 15 min to reach desorption equilibrium, which is 1/200 of the required time for the PVA-PAAS SCMs to reach the same. When the regeneration air conditions were at 45 ?C, 4000 kPa and 50 ?C, 6000 kPa, both the desorption rates of water vapor in the PVA-PAAS NFMs were higher than 80%. Thus, the PVA-PAAS NFMs can be regenerated under low-temperature conditions, which make their utilization in low-grade energy possible. After 10 cycle tests, the capacity and rates of adsorption and desorption of the PVA-PAAS NFMs did not change, which indicates that this type of desiccants possesses good stability.关键词：dehumidification;adsorbent;nanofibrous membranes;low-temperature regeneration;cycle stability2218|2815|0发布时间：2024-07-18
- 摘要：To reveal the effect of inlet temperature on the supersonic liquefaction characteristics of natural-gas mixtures, a mathematical model for the supersonic condensation flow of two-component natural gas mixtures was established in this study. The spontaneous condensation process of methane-ethane mixed gas in a Laval nozzle at different inlet temperatures was studied. The results indicate that when the inlet pressure and gas composition of the Laval nozzle remained the same, with the decrease in the inlet temperature, the nucleation position of the mixed gas moved forward; the nucleation rate, droplet radius, droplet number, and liquid mass fraction were all increased; and the liquefaction characteristics was improved. By using the Laval nozzle structure designed in this study, inlet gas pressure of 6 MPa, inlet gas temperature of 265 K, methane content of 90% and ethane content of 10% resulted in maximum nucleation rate of 0.9822×1021 (m3?s)?1 in the Laval nozzle, maximum droplet radius of 4.7194×10?7 m, maximum droplet number of the unit mass of 5.0704×1014 kg?1, and maximum liquid mass fraction of 7.8121%. The liquefaction efficiency of the Laval nozzle sharply decreased when the inlet temperature was higher than 275 K. In an actual production, the liquefaction efficiency of the Laval nozzle can be improved by lowering the inlet temperature and reducing the heat exchange between the Laval nozzle and outside environment.关键词：natural gas;liquefaction;Laval nozzle;inlet temperature;condensation1874|2473|3发布时间：2024-07-18
- 摘要：In this work, a high thermal stability amino-functional ionic liquid 3-aminopropyl-tributylphosphonium glycine ([aP4443][Gly]) aqueous solution and CO2 were used as absorbent to form a new type of absorption working pair. The solubility of CO2 in [aP4443][Gly] under the conditions of 300–510 K and 1–10 MPa was fitted with the solubility data of CO2 in [aP4443][Gly]. The specific heat capacity of [aP4443][Gly] aqueous solution was tested under different temperatures which ranged from 285 to 365 K, and the enthalpy of the [aP4443][Gly] aqueous solution was calculated. The absorption enthalpy of CO2 in the [aP4443][Gly] aqueous solution was calculated using two methods, and the enthalpy of this system was obtained. Then the abovementioned data were used to calculate the CO2-[aP4443][Gly] absorption refrigeration cycle efficiency. The results show that the CO2-[aP4443][Gly]-H2O working fluid can work at very high temperatures. When the generator temperature was 393.15 K and evaporation temperature was 278.15 K, the refrigeration-cycle efficiency could reach 0.85. At higher generator temperatures, the refrigeration cycle efficiency could reach up to 0.91, indicating that the working fluid can possibly become a new type of absorption refrigerant.关键词：amino ionic liquid;aqueous solution;CO2;absorption refrigeration2363|2104|1发布时间：2024-07-18
- 摘要：A new countercurrent dew-point indirect evaporative cooler was developed, and its cooling performance was experimentally studied in this work. The wet-bulb efficiency, dew-point efficiency, and cooling capacity of the cooler were tested and analyzed under various working conditions simulating dry area, moderate-humidity area, and high-humidity area in an enthalpy-difference laboratory. The experimental results show that the wet-bulb efficiency reached 105.6% and the dew-point efficiency reached 76% under standard drying conditions (dry-bulb temperature 38 ℃ and wet-bulb temperature 23 ℃) and air-flow ratio of secondary air/primary air = 1.1. The cooling capacity was tested as 2.83 kW, and the dry-bulb temperature decrease of the cooler reached 15.2 ℃. By the experimental results simulating the working conditions of Urumqi and standard dry environment, the dew-point indirect evaporative cooling technology shows many advantages and broad application prospects in the hot and dry areas in northwestern China.关键词：dew point indirect evaporative cooling;test conditions;cooling efficiency;refrigerating capacity2124|2337|5发布时间：2024-07-18
- 摘要：A theoretical model for analysis of single stage LiBr-H2O absorption heat pump was established and computer simulation for its thermodynamic cycle performance was conducted. The effects of varying operation conditions (circulation ratio, inlet temperature of low temperature waste water, inlet temperature of hot water and inlet temperature of high temperature vapor) on the four performance criteria (COP, entransy efficiency, exergy efficiency and entropy generation) are investigated, and the consistency of the four criteria are examined. It is found that the performance was degraded with the increases circulation ratio, inlet temperature of hot water and inlet temperature of high temperature vapor. Only when the inlet temperature of waste water increased, the performance was improved. It is also found that the variation trends of the four criteria with the operation conditions were different, and some were even opposite. To be specific, the increase of hot water inlet temperature worsens the system performance according to COP and entransy efficiency while improves the system performance according to exergy efficiency and entropy generation. However, the results obtained by the COP agree well with those by the entransy efficiency, indicating that the entransy efficiency is feasible for the heat pump performance analysis.关键词：absorption heat pump;COP;performance analysis;entransy;exergy efficiency;entropy generation2162|2334|5发布时间：2024-07-18
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