最新刊期
卷 41 ， 期 1 ， 2020
- 摘要：Benefit from the progress of manufacturing technology and the improvement of heat and mass transfer theory, refrigeration systems have been developing towards miniaturization and portability. This paper introduces three kinds of main refrigeration systems: vapor compression refrigeration, semiconductor refrigeration and absorption refrigeration system. Combined with recent literatures at home and abroad, this paper demonstrates the latest developments in miniaturization of systems and core components and then, compares their advantages and disadvantages to suit different occasions. Finally, the paper discusses the bottleneck restricting the miniaturization of refrigeration system, and puts forward the prospect for the future of the miniature refrigeration system.关键词：miniature refrigeration system;vapor compression refrigeration;semiconductor refrigeration;absorption refrigeration3257|2798|2发布时间：2024-07-18
- 摘要：Electric vehicles do not have sufficient engine waste heat to meet heating demands in winter. As such, heat pump technology has become a research hotspot to achieve a higher efficiency than electric resistance heat. To meet the gradual and stringent environmental regulations, there have been many studies on the replacement of vehicle heat pump system refrigerants. This paper reviews the research on R1234yf heat pump technology in recent years. As one of the popular alternative refrigerants for R134a, R1234yf has a global warming potential (GWP) of less than 1 and physical properties very similar to R134a.The properties of R1234yf are in line with the work requirements of vehicle heat pump systems. The system operation characteristics and performance are also very similar to R134a. In terms of heat transfer, the boiling heat transfer performance of R1234yf is slightly better than that of R134a. The condensation heat transfer coefficient is different in the research conclusions of various scholars, but the pressure drop in the condensation process of R1234yf is 5%–10% lower than that of R134a, which benefits the performance improvement. In the simulation and experimental research of many R1234yf and R134a systems, the performance of R1234yf heat pump is similar to R134a, but it can surpass R134a by optimizing components, economized vapor injection (EVI), and improving working conditions. R1234yf’s saturation pressure at a low saturation temperature is approximately15% higher than R134a and can adapt to higher compressor speeds. Therefore, it has a better heating performance at low temperatures than R134a;its lower compressor discharge temperature makes the system work more stable. The relative improvement using EVI is also better for R1234yf than for R134a.Therefore, R1234yf has a better working performance and prospects for vehicle heat pumps and can, therefore, be used as an alternative refrigerant for R134a.关键词：electric vehicle;heat pump;R1234yf;heat transfer coefficient;system performance2620|2318|7发布时间：2024-07-18
- 摘要：Vapor compression air source heat pump (VCASHP) systems have been widely applied due to their simple structure and low initial cost. However, there are a series of problems when a VCASHP system is operated for space or water heating in cold regions. For example, with a decline of ambient temperature, the decreased heating capacity of the VCASHP system may be insufficient with respect to the consumer's requirement. Furthermore, its rising compression ratio may lead to an extremely high discharge temperature, resulting in shutting down. Therefore, a great deal of previous research into VCASHP systems has been carried out to address such problems. Nevertheless, the articles concentrated on VCASHP units with direct current (DC) speed regulation are scarce. In the present work, an air source heat pump water heater (5 HP) integrating flash-injection cooling, two-stage throttling, and DC speed regulation (DCAHP) that can be applied to cold and/or severely cold regions over wide-range temperature conditions, is proposed and studied experimentally. The results indicate that the proposed DCAHP performs well over a wide range of temperature conditions and reaches the heating capacity of 16548 W and 11278 W when the ambient dry bulb temperature is 7.0 and -20.0 oC, respectively. Furthermore, the heating energy efficiency ratio (EER) of the proposed DCAHP reached 3.0 and 1.6 individually. Specifically, the compressor input power tends to be reduced by 19% if the dimensionless distance between the thermometer of the expansion valve and the inlet of compressor is greater than 7/200 m/m; however, the valve capacity decline will be inevitable. While the area of evaporator was doubled, the heating capacity of the DCAHP rose by 18% at low ambient temperatures. In addition, the energy efficiency ratio of the DCAHP can be maximally enhanced by 50% with a subtle regulation of refrigeration oil volume of 3/20 kg/kg.关键词：compressor;air-sourced heat pump;heating performance;DC speed regulation2735|2209|3发布时间：2024-07-18
- 摘要：It is difficult for single refrigerant used in heat pump systems to achieve optimum results. However, according to the principle of complementary advantages, new refrigerant blends may perform much better than single refrigerant. Based on this idea, a thermodynamic model of a heat pump system was established under the nominal working conditions of heat pump water heater, and a comparative analysis was made between the refrigerant blends R1234ze/HCs and the corresponding pure refrigerant through the EES program. The results show that the R1234ze/R600 blend has the best ratio in a mass fraction of (20/80) and R1234ze/R600a in mass fraction of (40/60). The corresponding maximum heating coefficient of performance (COP) are 3.414 and 3.321, respectively. The COP of R1234ze/R290 blend, however, exhibits monotonicity with the change of mass fraction. The heating COP of the R1234ze/R600 (20/80) system is 2.7%, 17%, 0.09%, 16.3%, and 17.8% higher than that of the R1234ze/R600a (40/60), R1234ze, R290, R600, and R600a systems, respectively. The discharge temperature, condensing pressure and compression ratio of the R1234ze/R600 (20/80) system are 76.9 oC, 0.711 MPa and 6.32, respectively. The results are promising for the development of a prospective alternative working fluid.关键词：R1234ze/HCs;refrigerant blends;optimal ratio;heat pump;cycle performance2828|1934|0发布时间：2024-07-18
- 摘要：It is difficult for a conventional heat pump to achieve a 65-100 ℃ heat supply in fields of material drying, printing, textile dyeing, electroplating, etc. In this study, a novel high-temperature heat pump based on a subcritical zeotropic mixture recuperative cycle was proposed for a hot water supply with a large temperature span. The zeotropic mixture feature of a large temperature glide at the isobaric process in the subcritical region and the recuperative concept were utilized to achieve a good thermal match between the working fluid and water sides with a large water temperature span. The influences of the key parameters such as the operating pressures, mixture composition, ambient temperature, and water temperature on system performance were analyzed. Based on a genetic algorithm, the discharge and suction pressures and mixture compositions of the system were optimized. The results indicated that the mixture recuperative heat pump exhibited an excellent performance under conventional operation conditions in traditional refrigeration and heat pump fields. When the ambient temperature was 25 ℃, the inlet water temperature was 15 ℃ and the outlet water temperature is 90 ℃. The coefficient of performance (COP) of the system reached 5.5, which is comparable to the performance of a CO2transcritical heat pump under the same working conditions.关键词：heat pump;mixture;recuperative cycle;high temperature span;genetic algorithm2644|1713|1发布时间：2024-07-18
- 摘要：This paper presents a fault diagnosis model based on a convolution neural network. The kernel size and number of neurons of a3-layerconvolutionnetwork were optimized by an orthogonal experiment method. The performance of the refrigerant charge fault diagnosis model of variable refrigerant flow (VRF) system was evaluated with graphed experimental data. The results show that the model established by the "data graphing & multi-layer convolutional network" method can be effectively used for the refrigerant charge fault diagnosis of the VRF system. With 20 chosen input features, the accuracy of the 9 level refrigerant charge fault diagnosis reached 91%,surpassing the performance of traditional back propagation neural networks(BPNN).This is the first time to achieve VRF system refrigerant charge fault diagnosis by using a convolutional network, laying a foundation for the expansion of related research.关键词：VRF system;fault diagnosis;convolutional neural network;refrigerant charge fault;orthogonal experiment2816|2108|2发布时间：2024-07-18
- 摘要：After traditional thermal defrosting, a great number of water droplets still retain on the surface, which can become the base of secondary frosting and accelerate secondary frosting. Therefore, duly removing retained droplets after defrosting is of great importance. In this paper, the frost melting evolution on a superhydrophobic surface was visually observed and the effects of the surface inclination angle on defrosting droplet drainage from a bare surface and superhydrophobic surface (with a static contact angle of 88.0°and 151.1°respectively) were comparatively analyzed. The experimental results showed that the defrosting droplets, as an ice-water mixture, suspended on asuperhydrophobic surface with a Cassie state during the defrosting process on a horizontal superhydrophobic surface. Two kinds of behaviors, namely, single-film curling and multi-droplets coalescence, can be seen during the defrosting processes, due to a large static contact angle and tiny contact angle hysteresis. Most of defrosting droplets on an inclined superhydrophobic surface can be self-drained accompanied with ice-water mixture rolling and stripping, which differ from the bare surface. When the inclination angle is greater than 30°, the drainage ratio of the superhydrophobic surface can reach more than 90%, while that of the bare surface can only reach 70%. Furthermore, mechanical analysis of droplets on an inclined surface was applied. The critical droplet-slipping radius was deduced according to the surface wetting characteristics and surface inclination angle, which were consistent with the experiment results.关键词：superhydrophobic surface;defrosting characteristics;drainage ratio;surface inclination angle2723|2073|1发布时间：2024-07-18
- 摘要：In this paper, the motive nozzles of a CO2 ejector with a diverging angle ranging from small to large (0.076°, 0.306°, and 0.612°) were investigated. Coupled models for the homogeneous equilibrium (HEM), delayed equilibrium (DEM), and wall friction model were presented and compared with the experimental data from related literature to analyze the dominant effects of the two flow mechanisms, non-equilibrium phase change, and wall friction on the delayed expansion process in the nozzle at corresponding angles. The results showed that within the ranges of this study, wall friction was the dominant mechanism of the delayed expansion process in the nozzle with a small diverging angle at the θ1 of 0.076°. Furthermore, the non-equilibrium phase change was the dominant mechanism in the nozzle with a middle diverging angle at the θ2 of 0.306°. In addition, the expansion process of the two-phase flow in the nozzle is close to the isentropic process for the large diverging angle at the θ1 of 0.612°. It is necessary for the design and optimization of the nozzle to choose a reliable model considering the dominant mechanism. When the diverging angle is small, the simulation results of the DEM coupled with a friction model indicated that the flow could choke the downstream of the minimum-area throat; this is verified by our experimental results. In addition, the critical mass flow rate predicted by the above model was lower than those of the HEM and DEM. The critical mass flow rates predicted by the three models indicated a barely noticeable difference for the larger diverging angle关键词：two-phase nozzle;non-equilibrium phase change;friction;CO22610|2108|0发布时间：2024-07-18
- 摘要：A hot water tank test bench with phase change material (PCM) of sodium acetate trihydrate was built. The thermodynamic characteristics of the water tank were tested under the conditions of an initial water temperature of 80 °C and an inlet water temperature of 5 °C. The analytical method and the enthalpy efficiency analysis method were used to analyze the thermal stratification characteristics of the hot water storage tank with PCM when the influent flow rates were 1 L/min, 3 L/min, 5 L/min, 7 L/min, and 9 L/min, respectively. The experimental results show that when the water tank temperature was 80 ° C, the energy of the ordinary water tanks, PCM48 and PCM58, were 18.81 MJ, 19.34 MJ, and 19.07 MJ, respectively. When the inlet flow rate was the same, the closer the heat storage ball with PCM is to the water tank inlet, the better the heat stratification effect of the water tank. As the influent flow rate increased, the stratification effect decreased. The number of Ri in different water tanks reached a maximum at t*=0.5; the number of Ri decreased with the lower position of the heat storage ball with PCM. The Ri number of the PCM48 and PCM58 in the fourth layer were 7.569 and 7.78, respectively. The Ri numbers at the layer were reduced to 7.03 and 7.145, respectively, indicating that the degree of thermal stratification of the tank decreased with the higher position of the heat storage ball with PCM.关键词：temperature stratification;phase change;hot water storage tank;filling efficiency2753|2243|1发布时间：2024-07-18
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Analysis on the Temperature Stabilities for Chilled Water Flow Passing a Submerged and Heated Sphere
摘要：In this paper, the design of the chilled water system that is used to neutralize heat was investigated. First, the stability of the water temperature was defined as: 1) The steady-state temperature; and 2) the time to reach steady-state temperature distribution in the pool. Then,a formula was deduced, by considering the heat transfer between the chilled water and heat sources, to represent the average temperature of the water in the pool over time. The main influencing factors of the theoretical minimum flow for cooling, steady-state temperature, required time, (e.g., initial water temperature in the pool) mass flow rate, and temperature of the chilled water, were also analyzed. Finally, by determining key parameters, such as the mass flow rate and temperature of the chilled water in accordance to theneed in a real project, the temperature distribution of the pool water was examined using both computational fluid dynamics (CFD) simulation and theoretical calculation. The results showed that when the temperature of the chilled water was 17 ℃ the theoretical minimum flow was calculated as 83.67 t/h. After 6–7 months, the average temperature of the water in the pool could reach the steady-state temperature of 22.44 ℃.关键词：temperature stability;lumped parameter method;CFD simulation;heated sphere;parameters of chilled water2825|1801|1发布时间：2024-07-18 - 摘要：The present study measured the effects of the ambient temperature and substrate surface on the freezing process of a water droplet. We built the experimental setup for the measurement of the droplet freezing process in a low-temperature test chamber. An air pressure controller was used to control the pressure inside the droplet generator to produce water droplets. Then, a camera recorded the details of the droplet freezing process. The results showed that the heat conductivity coefficient of the substrate surface had a significant influence on the freezing time. When the ambient temperature was -22.0 ℃, the freezing time of the droplets on red copper was 3.8 s and the freezing time of droplets on stainless steel was 5.0 s, both of which were less than the 15.2 s measured for the glass surface. In addition, despite the appearance of protrusions during the water droplet freezing process in all the cases, the collapsing bulge phenomenon happened only in the glass surface case.关键词：ice shell;freezing process;cold surface;low ambient temperature2715|1873|1发布时间：2024-07-18
- 摘要：The applicability of popular air-side heat transfer models of a flat fin-tube heat exchanger with high prediction accuracy are summarized in this paper. Their performance in a low ambient pressure (40–100 kPa) is analyzed under typical air conditioning conditions (air dry bulb temperature 27 oC, wet bulb temperature 19.5 oC, approach velocity 1?–4 m/s, inlet cooling water temperature 7–13 oC, and water flow rate 1.8 m/s). To check the applicability of these models, three heat exchangers with different tube rows (2/3/4) were tested. Experimental results showed that the data with large deviation appeared in the cases with a low ambient air pressure and the deviation could be +127.4%-–-36.6%. The predictions with models under atmospheric pressure were generally greater than the test results as the influence of atmospheric pressure on the Re number of the air side heat transfer was not considered. The effect of the number of tubes under a low-pressure environment on the heat transfer remains there and is more apparent. A correction term of ambient pressure was proposed based on the experimental data in this study. There was a substantial improvement of these three models’ prediction accuracy after this correction as follows: under the experimental conditions, the maximum deviation dropped to 32.63%, 24.91%, and 21.74% respectively; the average deviation was 1.79%, -2.90%, and -8.59% respectively; and the error range of ±20% covered 90.97%, 93.75%, and 88.96% respectively of the experimental values. Furthermore, pressure correction makes the models applicable to a more extensive range of ambient pressures.关键词：heat transfer factor;ambient pressure correction;airside heat transfer;fin-tube heat exchanger2679|1971|2发布时间：2024-07-18
- 摘要：A prediction method based on simulation is proposed to reduce the difficulty and the large error in measuring the power of variable-speed compressor. The threshold and weight of a back propagation (BP) neural network were initialized by particle swarm optimization to measure the power of the variable-speed compressor. In this study, a total of three kinds of simulation models were established for comparison, i.e., a BP neural network model, a genetic algorithm (GA)-BP neural network model, and a particle swarm optimization (PSO)-BP neural network model. Then, the power of variable-speed compressor was predicted through the interpolation of three models, as well as the extrapolation of evaporation temperature and condensation temperature. The predicted results and the average relative fitting degree error were compared and analyzed. The results showed that the BP neural network model based on the particle swarm algorithm optimization was superior to the other two models. For the extrapolation tests of condensation temperature , in particular, the relative error of BP neural network model was reduced by 1.11% and 2.64%, respectively, compared with the other two neural networks. For the three methods, the average relative error was within 1% and the fitting degree was above 0.9, indicating that the BP neural network model based on the particle swarm algorithm optimization can adequately obtain the power of variable-speed compressor and has a strong generalization ability.关键词：variable-speed compressor;measurement of compressor power;particle swarm optimization;BP neural network2557|1917|4发布时间：2024-07-18
- 摘要：The flow path numbers of an outdoor heat exchangerare always constant from the inlet to the outlet and cannot vary with the different refrigerant properties between the inlet and the outlet, which results in bad heat transfer. This study proposes a distributed flow path for an outdoor heat exchanger to improve the annual performance factor (APF) of air conditioners. The distributed flow path, with an increased path number from the low-quality zone to the high-quality zone, is configured according to the refrigerant property of the entire outdoor unit. Both the heat transfer and the pressure drop of the outdoor heat exchanger with the distributed flow path were analyzed by heat exchanger simulation software. Finally, the advantages of the distributed flow path on the heat transfer capacity were experimentally validated. The results showed that, compared with air-conditioning outdoor heat exchangers with fixed flow paths, the APF of the air conditioner systems with distributed flow paths increased by 1.8% to 5.8%;the rated heating capacity, low-temperature heating capacity, and ultra-low-temperature heating capacity of outdoor heat exchangers also increased by approximately 4.3%, 7.5%, and 5.9%, respectively.关键词：air conditioner;outdoor heat exchanger;annual performance;distributed flow path2822|1921|7发布时间：2024-07-18
- 摘要：The flow boiling heat transfer of R404A in a 5 mm micro-fin tube was studied. A number of flow boiling heat transfer models were selected by comparing the deviation between experimental results and theoretical calculations through a large amount of data to demonstrate the applicability of the models. The experimental conditions were as follows: The heat flux was 5–25 kW/m2, saturation temperature 0 oC, mass flow rate 200–500 kg/(m2?s), and vapor quality 0.1–0.9. The results show that the Zhang Xiaoyan et al.’s model overestimates part of the data because of the great difference of thermophysical properties. Furthermore, the Liu Zhongliang et al.’s model underestimates the influence of the heat flux and underestimates most of the experimental data. The model proposed by S. M. Kim et al cannot reflect the decrease of the heat transfer coefficient in high vapor quality areas and its prediction accuracy is low. K. E. Gungor et al.’s model well explains the process of heat transfer inside a tube with a 27.46% mean absolute deviation; 98.18% of the predicted points is within a ±30% range and the mean absolute deviation is 8.95%after multiplied by a modified ratio1.372.关键词：heat transfer correlations;two-phase flow;boiling;small diameter;R404A2653|1783|0发布时间：2024-07-18
- 摘要：Given the high-energy consumption of a display cabinet and the serious decrease of refrigeration capacity in cases of high ambient temperature, a refrigeration display cabinet with microchannel condenser was developed. The performance of the developed display cabinet was tested and compared with the one with traditional wire-tube condenser. It shows that display cabinet with microchannel condenser solves the problems resulting from the poor refrigeration effect of display cabinets under high-temperature conditions and the shutdown of the compressor because of the high heat transfer coefficient as the condenser. Furthermore, it significantly reduces the energy consumption of display cabinet. At ambient temperatures of 16 ℃, 25 ℃, and 32 ℃, the energy can be saved by 11.67%, 24.85%, and 45.64% respectively. Moreover, the on/off ratio is decreased by 7.20%, 14.90%, and 31.70%, respectively.关键词：micro channel heat exchanger;display cabinet;condenser;energy conservation2754|1802|0发布时间：2024-07-18
- 摘要：A new-type of loop heat pipe (LHP), which is enhanced by the pressure head due to evaporation, was proposed and studied. Its wick was separated from the heating surface and a steam chamber was formed in which the phase change of the working fluid occurs and the pressure head due to evaporation can be effectively used. In the experiment, different charging ratios were considered to explore the operation characteristic. Results showed that the temperature oscillation occurred when the charging ratio was high (60%). Furthermore, higher charging ratios resulted in higher operating temperatures; namely, 101.9 ℃, 102.4 ℃, and 107.9 ℃ corresponding to 55%, 60%, and 70% of charging ratio, respectively. In addition, the specific operating model, a dropping-evaporation process, was found through the visual observation of the evaporator when the charging ratio was 55%. The vapor-liquid interface moved downward on the surface of the wick and finally, the liquid dropped on the heating surface, illustrating the specific operation process for this kind of LHP. If the period is defined as the time needed to complete the dropping and evaporation cycle for the working fluid, the cycle time was 120 s when the head load was 55 W.关键词：loop heat pipe;phase change;visual observation of the evaporator;operating temperature;dropping-evaporation process2616|1763|0发布时间：2024-07-18
- 摘要：To meet the cooling system requirements of intermittent high-power electronic equipment, we investigated a cascade cooling system with a phase-change energy storage that is based on a traditional R134a vapor-compression cycle cascaded with a mechanicalpump cycle. The operating principle and refrigerant features were theoretically analyzed and the operating characteristics of an energy storage device were reviewed in this research. The cooling capacity and operating performance of the system were experimentally measured during its start-up and stable operation. The main conclusions drawn from this study were that at the startup stage of the mechanical pump, the system pressure first decreased and then increased by an amplitude of 30 kPa. When the heat source started up, the system pressure first increased then decreased and remained stable. It was determined that the accumulator can effectively store the excess working medium of the system and indirectly control the phase change temperature and pressure in the heat sink. Furthermore, the energy storage device can maintain a mechanical pump inlet super cooling degree of 5 ℃ in the system operation process. The energy storage device can also meet the demand of the heat load and maintain 5 ℃ of super cooling before the working fluid is interred in the mechanical pump, indicating that this device was reasonably designed and its operation stable. Although the cooling capacity of the refrigeration system reduced gradually with the running time, it was able to run for 5 minutes with a heat load of more than 10kW, thus meeting the design requirements of the subject.关键词：refrigeration system;phase-change;energy storage;heat load2672|1994|0发布时间：2024-07-18
- 摘要：Despite its small volume and quick refrigeration, semiconductor refrigeration plates have good application potential in refrigerated transportation. To examine the cooling capacity of the storage box with a semiconductor, an experimental bench was established to investigate the working performance of a storage box with two semiconductors types, namely, TEC1-12706 and TEC1-12712. The twice experiments started with 2 000 mL ice cubes and the combination with 1 500 mL ice cubes, 3 kg foodstuffs , and 3 bottles of mineral water with a volume of 500 mL respectively in the storage box. Meanwhile, different heat dissipation method of the hot side and fan arrangement of the cold side were both considered during the test. The results show that the TEC1-12712 with water-cooling has a larger cooling capacity than the TEC1-12706 with air-cooling. Comparing the performance of same type of refrigeration chip using water and air-cooling, it was inferred that the water-cooling has a better cooling effect and a shorter resistance time. Moreover, a better airflow distribution appears when the fan is arranged below the cold side of the refrigeration chip rather than beside it. With the cold storage demand for a volume of 0.1 m3, two chips of the TEC1-12706 type with air-cooling on the hot side are preferred. Over 10 hours, the center temperature of the box was maintained at 6 ℃ and the minimum value in the box was approximately 0 ℃. With the freezing demand, two chips of type TEC1-12712 with water-cooling on the hot side and the fan below the cold side are preferred. With this application method, the center temperature is controlled below 0 ℃ within 3 hours.关键词：cold chain;semiconductor refrigeration;refrigeration performance test;temperature field;operating conditions2749|1823|2发布时间：2024-07-18
- 摘要：A test rig for condensation heat transfer was developed and the cooling heat transfer characteristics of R22 and R410Ain small-diameter tubes were compared. The test conditions were as follows: the mass flow rate 200–800 kg/(m2?s), saturation temperature 40 ℃, the range of quality 0–1, and the outer diameter of the horizontal smooth copper tube5 mm. The effects of the mass flow rate and quality on condensation heat transfer were analyzed and the correlation formula applied to the traditional pipeline was compared with experimental data. The analysis results showed that the condensation surface heat transfer coefficient was positively correlated with the mass flow rate and quality; in addition, the condensation surface heat transfer coefficient increased significantly in the high quality area. The Shah correlation was not ideal in predicting the test data and the maximum deviation from the actual values reached 60%. However, the Shah correlation was ideal for predicting data in a low mass flow rate and low quality area; when the mass flow rate (G=200 kg/(m2?s)) was small, the condensation surface heat transfer coefficient of R410A was lower than that of R22. Furthermore, with the increases in the mass flow rate (G=400 kg/(m2?s)), the disparity between the two condensation surface heat transfer coefficients decreased. The condensation surface heat transfer coefficient of R410A was similar to that of R22 when a medium to high mass flow rate (G=600 kg/(m2?s)) was reached. When the mass flow rate (G=800 kg/(m2?s)) continued to increase, the condensation surface heat transfer coefficient of R410A rose higher than that of R22 as the quality increased.关键词：surface heat transfer coefficient;cooling heat transfer characteristics;mass flow rate;correlations2766|1980|0发布时间：2024-07-18
- 摘要：Sensors mainly play monitoring and controlling roles in air-conditioning systems and affect their normal operation, thereby causing adverse effects such as increased energy consumption if there are faults in sensors. In this study, an improved principal component analysis method combining wavelet transform data optimization and neural network-based fault diagnosis optimization is proposed for the sensor fault detection and diagnosis in an air-conditioning system. By comparing the results of principal component analysis before the data optimization and the results of the principal component analysis after the data optimization, it was found that in the principle of the same 0.8500 cumulative contribution rate after the wavelet transform used to remove noise, the number of principal components was reduced by two; the detection effect was improved by 0.0207, 0.0208, and 00415respectively; and the effect of the airflow sensor fixed deviation failure detection was improved by 0.1606. To find the source of the fault, the principal component analysis was used as the input of the neural network to test five sensor fixed deviation faultsbased on the wavelet transform and principal component analysis. The fault diagnosis results were 0.7667, 0.8667, 0.9000, 1.0000, and 1.0000, respectively.关键词：fault detection and diagnosis;principal component analysis;neural network;wavelet denoising;air-conditioning system2566|1888|0发布时间：2024-07-18
- 摘要：An improved loop heat pipe (LHP) with high performance was developed in this paper. It has temperature controlling and heat-dissipating characteristics for multi-distributed heat sources by detaching the driving and dissipating power. To investigate the precise temperature controlling performance, the improved LHP was tested for the thermal control of four charge-coupled device (CCD) components on a camera in a vacuum chamber; stable operating tests, heat compensation power tests, and different powers on the evaporator tests were carried out. Test results showed that the improved LHP can control the temperature of the CCD in the range of ±0.5 oC by controlling the accumulator temperature. Three methods to maintain the CCD temperature stability were introduced for the temperature fluctuations caused by device switches and their feasibilities were verified through experimental and theoretical analysis.关键词：loop heat pipe;temperature control;CCD;thermal vacuum environment2184|1739|0发布时间：2024-07-18
- 摘要：Current research on the properties of skin is far from perfect. This poses certain difficulties for hyperthermia and related clinical research. Rats were used as experimental subjects to study the changes of thermophysical properties and mechanical parameters during heating and the influence of temperature and moisture was discussed. The results suggested that the stress and strain curves of the skin tissue were approximately linear during heating (37–47 ℃). The elastic modulus was related to the temperature and decreased gradually when the temperature increased. As the temperature increased, Poisson's ratio for the tissue changed similarly. In addition, during the initial stage of heating (37-45 ℃), the water content of the tissue was not significantly reduced. The thermal conductivity increased very slowly with the increasing temperature and remained almost unchanged. However, as the temperature and time increased, the tissue began to lose water. The effect of the water content on the thermal conductivity was higher than the effect of the temperature. When the temperature reached 45 ℃, the thermal conductivity began to drop sharply;from 45 ℃ to 47 ℃, the thermal conductivity value decreased by 5.4% and the specific heat capacity changed similarly.关键词：skin tissue;thermophysical property;biomechanics;moisture content2125|1743|2发布时间：2024-07-18
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