最新刊期
卷 40 ， 期 3 ， 2019
- 摘要：In an effort to mitigate the difficulty of acquisition and transfer of liquid propellant in space systems, existing in-space gas-liquid separation techniques for cryogenic propellants are evaluated. In particular, the theoretical knowledge and experimental results of screen channel liquid acquisition devices (LADs) are investigated from the vantage point of three aspects—bubble point, pressure drop, and performance optimization. The following conclusions can be drawn: 1) The bubble point is generally higher for finer screens; however, as the density of the mesh increases, the bubble point of the 510 × 3600 Dutch Twill (DT) screen becomes lower than that of the DT-450 × 2750 screen; 2) Compared to ground conditions, the pressure drop of the screen channel LAD is much lower and mainly governed by the flow-through-screen pressure drop under microgravity, which corresponds to a higher critical mass flow rate and could meet the requirement of higher delivery mass flow rate; 3) Reducing the fluid temperature and using a non-condensable gas (such as helium) to pressurize the tank could enhance the screen bubble point and improve the separation performance of screen channel LAD; 4) The DT-450×2750 screen might be a preferential weave for future liquid hydrogen fuel depots, because it could simultaneously meet the requirement of high bubble point and high critical mass flux.关键词：gas-liquid separation technology;metallic screen;bubble point pressure;surface tension;pressure drop2077|2283|5发布时间：2024-07-18
- 摘要：The recent development of micro-sized Joule–Thomson (J-T) effect throttle cryocoolers is reviewed in this paper. The existing technology and research results are summarized from the theoretical research and structural evolution of the cryocooler. Based on the analysis of relevant studies, the development direction of the micro-sized J-T effect throttle cryocooler is further prospected. With the expansion of application fields and advances in processing technology, the structure of cryocoolers is becoming increasingly compact and diversified. Multi-stage, multi-layer, multi-channel, micro-sized J-T effect throttle cryocoolers fabricated by micro-etching technology have much room for development. In terms of theoretical research, the current theoretical models are mostly based on different assumptions and simplification because of the complicated operation mechanism of the micro-sized J-T throttle cryocooler. Therefore, for future theoretical research of J-T effect throttle cryocoolers, it is necessary to establish and solve more practical theoretical models, and basic research results need to be considered and applied in a timely manner.关键词：Joule-Thomson effect;micro cryocooler;structure;theoretical model2050|2801|1发布时间：2024-07-18
- 摘要：To reduce the energy consumption in data centers, a pump-driven two-phase loop system was proposed for free-cooling in data centers. Based on the exergy balance equation of a steady-flow system, the system was analyzed and optimized in this study, and exergy balance models of components for the system were established. The variation and distribution of exergy loss for both the system and every single component were compared theoretically and experimentally under three different working conditions. The results showed that the largest exergy loss was from the evaporator at over 40%. The next largest loss was that of the condenser and pump at approximately 25% each. The evaporator, condenser, and pump should be considered in sequence for system improvement. Improving the heat transfer coefficient, increasing the heat transfer area appropriately, and setting a reasonable indoor temperature could be performed for optimization of the evaporator and condenser. To optimize the pump, the pump compression should be as close as possible to isentropic compression.关键词：data centers;free-cooling;exergy analysis2012|2320|3发布时间：2024-07-18
- 摘要：A stable liquid column-air plug system forms when liquid working fluid flows in a capillary tube that meets specific requirements for the inner diameter. In this paper, a novel two-phase heat transfer system with a pulsating heat pipe is proposed for the scenario in which a liquid-vapor two-phase working fluid in the capillary tube is driven by a peristaltic pump and one-way flow forms. The heat transfer characteristics of the system with different liquid filling ratios are investigated experimentally by a self-designed experimental setup with deionized water as the working fluid under 60 W, 80 W, and 100 W conditions. The inner diameter of the capillary tube is 3 mm, and the working fluid flows in a capillary tube with a constant flow rate of 7 m/min. The experimental results show that the optimum liquid filling ratio of the heat transfer system is 20%. When the heating power is 60 W, 80 W, and 100 W, the thermal resistance of the system with the optimum liquid filling ratio is 0.52 °C/W，0.38 °C/W, and 0.30 °C/W, respectively, which is reduced by 32.5%, 45.7%, and 50%, respectively, compared with that of the traditional water-cooled heat transfer system.关键词：two-phase heat transfer system;peristaltic pump;heat transfer characteristic;liquid filling ratio;capillary tube1737|2118|1发布时间：2024-07-18
- 摘要：The experimental results of a refrigerator system with linear compressor showed that there was a period of piston stroke fluctuation as the supply power remained unchanged after an initial start-up adjustment. The maximum fluctuation rate of the piston stroke was 3.8% and that of the input power was 21.3%. The period of fluctuation was approximately 220 s. In this paper, the mechanism of this fluctuation is analyzed based on a simulation model set up for linear compressor. The fluctuation of the suction pressure is the dominant cause of stroke fluctuation. The fluctuation of the discharge pressure has little influence on the stroke fluctuation, while the stroke fluctuation has a significant effect on the discharge pressure. The fluctuation of the discharge pressure caused by the adjustment of the stroke control transfers to the suction part and causes the unstable fluctuation.关键词：linear compressor;refrigerator;operating conditions1903|2193|0发布时间：2024-07-18
- 摘要：A series of visible frosting experiments on vertical superhydrophobic surfaces (153.2°) that were prepared by chemical etching and bare copper surfaces were conducted under natural convection conditions. The effect of hydrophobicity on the frosting process was investigated and compared under liquid nuclei and no-nuclei frost deposition mode. Furthermore, the effect of hydrophobicity on frost deposition was studied for cold surface temperatures (?50 to ?30 °C) and different air relative humidities (30%–70%). The experimental results showed that there was no liquid nucleation at the beginning of the experiment when the cold surface temperature was lower than ?30 °C at an ambient air temperature of 16 °C and a relative humidity between 30% and 70%. It was found that the frost crystals on the superhydrophobic surface were much denser compared than those on a copper surface under the no-nuclei frost deposition mode. This result was completely different from that of the liquid-nuclei frost deposition mode in which the frost formation on the superhydrophobic surface was suppressed significantly during the initial period of frost deposition. The frost crystal coverage of the cold surface was defined to characterize the density of the frost crystal distribution. It was revealed that as the relative humidity increased and the cold surface temperature decreased, the effects of hydrophobicity on frost deposition was mitigated, the frost crystal coverage difference between the superhydrophobic and plain copper surfaces was reduced, and the time during which the frost coverage difference lasted was shortened. The maximum frost coverage difference between the superhydrophobic and plain copper surfaces was greater than 15% and lasted for approximately 35 min in the case of cold surface temperatures ?30 °C, with the ambient air temperature at 16 °C and the relative humidity at 30%. The hydrophobicity had little effect on the frost deposition once the cold surface temperature was reduced to a sufficiently low temperature. The phenomena observed were also analyzed according to the theory of cloud physics and nucleation. It was found that the concave pits and the CuO crystal particles on the superhydrophobic surface provided advantageous sites for desublimation nucleation.关键词：hydrophobicitiy;cold surface temperature;frost deposition;experiment1885|2256|4发布时间：2024-07-18
- 摘要：In this paper, the variation in the indoor temperature and humidity when FP85 series fan-coil units are used to treat indoor return air to its equilibrium point is analyzed based on the experimental comparison between an air conditioning system with a moderate water temperature and a conventional air conditioning system. Then, the influence of a chilled water supply temperature and tube numbers on the heat transfer performance of a fan-coil unit is simulated and analyzed by a coil simulation method. The experimental results show that when the temperature of the chilled water supply increased from 7 °C to 9 °C, the latent heat capacity of the 3-row FP85 fan-coil unit was reduced. As a result, the indoor humidity cannot be guaranteed in the comfortable range. As the chilled water supply was increased by 1 °C, the relative humidity of the indoor equilibrium point increased by 11.03%–12.05% accordingly. For the 6-row FP85 fan-coil unit, the temperature and humidity of the indoor equilibrium state can meet the design requirements of comfortable air conditioning,system with a chilled water supply temperature in the range of 9–12 ℃. Moreover, the simulation results state that the 4-row, 5-row, and 6-row FP85 fan-coil units can ensure an equilibrium indoor temperature and humidity in the comfortable range for an indoor return air with dry bulb temperature 27.01 °C and wet bulb temperature 19.51 °C, respectively. The heat exchange and dehumidification coefficients of the 4-row fan-coil unit decreased by 6.13% and 0.045, respectively, when the supply chilled water temperature increased by 1 °C. The heat transfer coefficient and dehumidification ability of the 4-row fan-coil unit are superior to that of the 5-row and 6-row fan-coil units. Therefore, the 4-row FP85 fan-coil unit is more appropriate for an air conditioning system with moderate water temperature. This study indicates that the air conditioning system with moderate water temperature has great application potential, and provides a theoretical basis for the design of air conditioning system with moderate water temperature.关键词：air conditioning system with moderate water temperature;coil simulation;heat transfer performance;dehumidification ability1956|2407|0发布时间：2024-07-18
- 摘要：The temperature field of indoor space is non-uniform, and the temperature measurements at different locations are usually different. The thermostat is usually installed on the wall near the door in air-conditioned room, and the measured temperature does not always represent the temperature of the working area. Moreover, the requirement in working area cannot be met under the room temperature is controlled with this measured value as feedback. In this paper, the effective draft temperatures of all the measuring points was obtained by setting multiple temperature and wind speed measuring points in the horizontal plane at different vertical heights in the air conditioned room. Then, the weighted fusion algorithm based on modified error learning was used to fuse and analyze the sampled data, and the indoor fusion effective draft temperature was obtained. The influence of the variation in air volume on the indoor effective draft temperature, indoor thermal comfort, and energy consumption of the air-conditioning system under the control of fusion effective draft temperature were studied. The experimental results show that at the height of 1.5 m, the effective draft temperature and air diffusion performance index of the measuring point was ?1.7 to 1.1 and 100%, respectively, when the design air supply volume was 70%, which could be the optimal sensor installation position.关键词：variable air volume air conditioning;effective draft temperature;data fusion;comfort1783|2410|0发布时间：2024-07-18
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Effect of Water Supply Temperature on the Performance of Low Temperature Air Source Heat Pump System
摘要：In this paper, the effect of the water supply temperature on the thermal performance of a heat pump is analyzed. The influence of the water supply temperature on the performance of a heat pump system is investigated for an ambient temperature ?12 °C and ?6 °C and an initial water supply temperature of 20 ℃. The experimental results indicate that, under the same initial temperature, the heating capacity of the compressor system first increased and then decreased, with a maximum heating capacity reached for a water supply temperature of 40 ℃. When the ambient temperature was at ?12 ℃, the water was heated by the heat pump from 25 ℃ to 55 ℃. The power consumption of the system increased from 11,905 W to 24,417 W, an increase of 105%, and the system energy efficiency decreased from 4.03 to 2.11, a decrease of 47.6%.关键词：low temperature air source heat pump;water supply temperature;heating capacity;COP1722|2018|5发布时间：2024-07-18 - 摘要：This study addresses the experimental performance of the alternative refrigerant R290 in the R22 low-temperature heat pump system. Results show that when R22 was directly replaced by R290 in the original system, both the heat exchange and coefficient of performance (COP) of the system decreased, and the exhaust temperature and pressure of the R290 system were higher than those of the original R22 system at low temperatures. Through the analysis of the system components, reducing the displacement of the compressor of the R290 heat pump system can effectively improve overall performance and reduce the discharge temperature and pressure. After the optimization of the compressor, the R290 system achieved a 6.5% higher COP compared to the original R22 system, and the exhaust temperature was decreased to 80 °C, which is 36% lower than the R22 system.关键词：heat pump;compressor;refrigerant replacement;R2901886|2476|3发布时间：2024-07-18
- 摘要：To recover waste heat from household bath wastewater and improve energy efficiency, a heat pump water heater with waste heat recovery was designed. Experimental benches were set up for experimental studies. The experiment was carried out with an inlet water temperature of 16 °C and an outlet water temperature of 36–46 °C to study the effects of changing parameters, such as the refrigerant charge amount, water output, heating capacity, and heating coefficient of performance (COP). The experimental results show that increasing the refrigerant charge benefits the heating and heating COP stability. However, the maximum heating capacity is 7.9 kW, and the heating COP is 7.7 at the minimum refrigerant charge. For the outlet water temperature of 36–46 °C, the device can effectively recover the heat in the waste water, the heating output is stable at approximately 7.5 kW, and the heating COP is above 6.0.关键词：refrigeration and cryogenic engineering;waste heat recovery;heat pump water heaters;refrigerant charge1941|2129|1发布时间：2024-07-18
- 摘要：Based on the incomplete superheating cycle of a refrigeration system (from suction superheat of the compressor to two-phase compression), the characteristics of the change in the performance of a refrigeration system, such as the coefficient of performance (COP), refrigeration capacity, pressure ratio, compressor power consumption, electric efficiency, and exhaust temperature, are investigated by running the rolling rotor compressor in different low-frequency conditions. An optimal control strategy is then put forward. The results show that if the compressor operating frequency is properly reduced and the quality of refrigerant is controlled at 0.98 ≤ x < 1 for a short time, the cooling capacity would be increased by 8.3% to 16.6% compared to the conventional superheat control conditions (5–10 K), and the COP would increase by 12.5%–15%. In addition, the electrical efficiency of the compressor was only 0.3%–0.7% lower than that of the conventional superheat control condition, and the electrical efficiency at the lowest frequency (25 Hz) in the experiment was the largest. At the lowest frequency in the experiment, the energy-saving effect was significant, and the pressure ratio was further reduced. The temperature of the exhaust gas was greatly reduced by 40.3% when x<0.90.关键词：superheat;dryness;frequency;coefficient of performance (COP)1858|2191|4发布时间：2024-07-18
- 摘要：Truck logistics (LTL) receives much attention in cold-chain transportation logistics. To improve the economy of logistics and ensure the quality of the refrigerated transport of fruits and vegetables, two types of multi-temperature-zoned refrigerated incubators were designed. 87% C8H16O2 (n-octanoic acid) + 13% C14H28O2 (myristic acid) and H2O + 0.03 g/ml C6H7KO2 (potassium sorbate) were selected as cold storage and heat preservation materials. The experimental results show that the phase transition temperatures, latent heat and thermal conductivity of the two phase-change materials were 7.1 °C and 2.5 °C, 146.1 J/g and 256.2 J/g, 0.2832 W/(m?K) and 0.9427 W/(m?K), respectively. Additionally, the two phase-change materials showed excellent stability from the point of view of thermophysical properties under 100 freezing/melting cycles. Combined with vacuum insulation technology, the temperature test system of the heat preservation box in the multiple temperature zones was established by using the verification equipment of the product supply specification (good supply practice, GSP). The test results show that the large multi-temperature-zoned refrigerated incubator can maintain the temperature at 7–9 °C for approximately 13 h in Zone 2, and at ?2 to 0 °C for approximately 14 h in Zone 3. The small multi-temperature-zoned cold storage box can maintain the temperature at 7–8 °C for approximately 19 h in Zone 1, and at 0 °C for approximately 16 h in Zone 2.关键词：cold chain logistics;multi-temperature zone;insulation box;phase change material1948|2165|6发布时间：2024-07-18
- 摘要：In this paper, theoretical analysis and visual experimental research are reported on the flow-state characteristics during the heat transfer of CO2 flow boiling in a horizontal tubule. A CO2 theoretical flow-state prediction model under low evaporation temperature is updated based on visual experimental results. Experimental conditions are as follows: heat flux (7.5–30 kW/m2), mass flow rate (50–600 kg/(m2?s)), saturation temperature (?40 to 0 °C), vapor quality (0–1), and inner diameter (1.5 mm). Theoretical analysis indicates that the mass flow rate determines the flow pattern experienced during the boiling process. The form of annular-dryout and the dryout-mist flow areas in the theoretical flow pattern diagram mainly depends on the heat flux of boiling, while the flow-state transition depends on the saturated temperature. Visual research shows that the flow pattern prediction of CO2 during boiling in the horizontal tubule was satisfactory based on the theoretical flow pattern chart, as well as the trend under different conditions. However, there was a large deviation between the dry region and the mist flow region under experiment conditions. Thus, an updated critical heat flux prediction model was proposed based on experimental data by adding dimensionless factors of the liquid-gas viscosity ratio. Based on the updated model and experimental data, the transition curves of the annular flow-dry region, dry region-mist flow, and intermittent flow/slug flow-annular flow in the primary theoretical flow pattern chart were updated by introducing the boiling number Bo, considering the effect of mass flow rate and heat flux. ,89.4% of the flow pattern data obtained from the visualization study is consistent with the updated model.关键词：CO2;tubule;flow boiling;flow pattern diagram1997|2669|3发布时间：2024-07-18
- 摘要：This article described the composition and working principle of the thermodynamic venting system (TVS) for the in-orbit management of cryogenic propellants. Based on the volume of fluid (VOF) multiphase model, a user-defined function (UDF) was compiled to consider the heat and mass transfer phenomena inside the tank, and computational fluid dynamics (CFD) was applied to simulate the pressure evolution and temperature field distribution in the tank during the TVS operation. A comparison study showed that the CFD model could well simulate the characteristics of the TVS, which might verify the effectiveness of the CFD approach in analyzing TVS performance. Moreover, the variable conditions of different initial liquid filling rate, throttling ratios, and other influencing factors were simulated to reveal the working rules of the TVS. The pressure control performance of the TVS under microgravity was also calculated. The feasibility of the TVS under microgravity was verified, and its operational rules were obtained.关键词：cryogenic propellant;pressure control;CFD simulation;microgravity1675|2077|2发布时间：2024-07-18
- 摘要：In this study, a BP (back-propagation network) neural network, optimized by PSO (particle swarm optimization) was applied to the fault diagnosis of a centrifugal chiller. Seven typical faults, including four component-level and three system-level faults, were investigated. Results showed that the performance of fault diagnosis was significantly improved (for both single- and double-hidden BP layers) compared with the model without PSO. The optimization simplified the structure of the neural network from 18 neurons to 10 neurons for a single-hidden-layer network and from 25 neurons to 12 neurons for a double-hidden-layer network. This increased the correct rate of fault diagnosis from 89.42% to 95.30% and from 97.87% to 98.11% for single-hidden-layer network and double-hidden-layer network, respectively. There are also considerable savings in diagnostic time, especially for the double-hidden–layer network, to only 23% of that before optimization. The cases of "false report" and "leaked report" have been reduced, and the false alarm rate is also lower than before. Moreover, the diagnosis performance of the system-level fault, especially the RefLeak (Refrigerant Leakage), and the recognition rate of the normal condition are greatly improved. Through PSO, the BP network is able to jump out of the local minimum and greatly improve the fault diagnosis performance for the centrifugal chiller.关键词：chiller;fault diagnosis;particle swarm optimization (PSO);back-propagation (BP) network;false alarm rate1975|2124|5发布时间：2024-07-18
- 摘要：To study the optimum operating condition of industrial ice making, an experimental system of the vacuum flash of ethanol solution under adsorption was designed based on the theory of flash evaporation. Under the same initial flash pressure (100 Pa), the effects of concentration, environment temperature, and size of multi-walled carbon nanotube (MWCNT) on the flash properties were studied. The results indicated that adding ethanol could not only avoid recrystallization but also decrease the supercooling degree of water. Higher concentrations were found to be adverse to the flash process. The flash property of 5% mass concentration of ethanol was stable, and the supercooling degree of water could be decreased by as much as 60.62%. With the rise in the environment temperature, the flash rate increased as the flash percent factor increased from 25.45% to 44.04% for an increase in the environment temperature from 10 °C to 20 °C. Thus, lower environment temperatures were shown to be beneficial to the flash process. With the decrease in the practical size of MWCNT, the supercooling of the MWCNT-ethanol solution decreased. The ice packing factor (IPF) of the solution to which 5–18 nm MWCNT was added was 51.45% higher than that of the 5% mass concentration ethanol and 38.22% higher than that of water. The supercooling degree of the solution was 24.36% smaller than that of ethanol and 70.21% smaller than that of water, which shows the MWCNT-ethanol solution has a significant effect on reducing the supercooling degree of water and improving the IPF.关键词：ethanol solution;vacuum;evaporation;supercooling degree;IPF1854|2267|1发布时间：2024-07-18
- 摘要：The subsurface near the vertical borehole heat exchanger (BHE) contains different geological layers and thermal properties that are variable with depth. The stratified subsurface, variable thermal properties, and groundwater flow would make the heat transfer of BHE more complex. Thus, the traditional homogenous model inevitably leads to some problems for the design of BHE in a layered subsurface. In this study, through a borehole field test in Nanjing, a numerical model considering five strata was developed and verified. Comparing the numerical multilayered model with the traditional homogenous FLS and MFLS models shows that the outlet temperature of the numerical model is 0.5 °C lower than the FLS model after 60 d of heating and 0.3 °C higher than the MFLS model. This also indicates that the temperature response is different at different layers. Furthermore, the axial temperature profiles of different layers at different distances under different heating times are presented and explored.关键词：borehole heat exchanger (BHE);temperature response;multilayered subsurface;groundwater flow1898|2043|1发布时间：2024-07-18
- 摘要：As one of the five most common fruits in China, grapes are deeply loved by the vast majority of consumers. However, the problems of decay and softening of grapes are prevalent during storage and long-haul transportation. The activities of enzymes play important roles during this process. To study the effect of storage temperature on grape pectin content and related enzyme activities, the effects of four different storage temperatures—two super freezing temperatures (?3 °C and ?2 °C), freezing temperature (?1 °C), and common freezing temperature (4 °C)—on Italy grape pectin content and the pectinase activity have been analyzed. The study found that with the increase in storage time, the pectin content of the Italy grape pulp and pericarp decreased, and the soluble pectin increased. The decrease of the pectin content in pulp and the increase of soluble pectin content in pulp were the smallest at ?3 °C and the largest at 4 °C. In addition, changes in the content of pectin esterase and polygalacturonase in pulp and pericarp under the condition of super freezing temperature at ?3 °C were also less than those of other conditions. There was a significant positive correlation between the hardness of the Italy grape and the pectin and a significant negative correlation with the soluble pectin. This indicates that the super freezing temperature at ?3 °C can inhibit the hydrolysis rate of Italy grape pectin, so that the soluble pectin content can be controlled at a relatively low level, which can prevent the grape from softening. It can also inhibit the activity of pectin esterase in grape, reduce the promoting effect of polygalacturonase on grape pectin hydrolysis, and prevent Italy grapes from deteriorating during the storage period, which will further extend their storage time.关键词：storage temperature;grape;pectin;enzymes activities2030|2038|2发布时间：2024-07-18
- 摘要：The variation in dew point temperature at the attached layer of radiant ceiling was examined when the number of indoor occupants was increased in this study. Through numerical simulation and linear regression performed by SAS software, the influence of various factors on the air dew point temperature of the attached layer was obtained. Furthermore, the dynamic relationship between the main influence factor and the dew point temperature of the attached layer was obtained, and the experimental data was used to verify the simulation and calculation results. The results show that the air dew point temperature increased by approximately 1.5 °C and 2.5 °C when adding two and four people, respectively. The distance between the personnel and the attached layer, as well as the number of personnel have a great influence on the dew point temperature of the attached layer, with the contribution rate accounting for 43% and 48%, respectively; and the contribution from the other impact factors can be ignored. The dynamic change of the air dew point temperature of the attached layer is in the form of a negative exponential function. The influence of the distance between the attached layer and the personnel on the dew point temperature of the attached layer is greater than that of the increase in personnel number.关键词：radiant ceiling;dew point temperature;regression analysis;factor contribution rate2004|1937|0发布时间：2024-07-18
- 摘要：A higher survival rate of frozen-thawed biological samples is required for clinical use and translational medicine. The cooling rate of samples is one of the most important factors affecting survival. In this study, a new sample quick freezing platform using an 80-W Stirling refrigerator as a cold source was designed. The structure of the cooling stage was determined by heat transfer simulation to obtain the fastest cooling rate using finite element simulation software (COMSOL). The results show that the distance between the sample vials has no significant effect on the cooling rate of the samples. The height of the cooling stage is the main factor that influences the cooling rate and temperature uniformity of the samples. A height of the cooling stage H = 25 mm gives the best results, which is slightly lower than the height of the samples. In addition, when the radius of the cooling stage is smaller, the cooling rate of the samples is faster, and the temperature difference of the samples is relatively larger; however, the result gap is not significant. An optimization and improvement plan has been put forward based on the simulation results. The conclusion of this study will provide a reference for the follow-up design of a cooling stage with greater power and different volume samples.关键词：cryopreservation;quick freezing device;cooling stage structure;numerical simulation;Stirling cycle1971|2178|2发布时间：2024-07-18
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