最新刊期
卷 40 ， 期 6 ， 2019
- 摘要：Thermoelectric cooling is a type of solid-state, environmentally friendly cooling technology based on thermoelectric phenomenon. The thermoelectric cooling system has advantages over other refrigeration methods including small volume, simple structure, high reliability, rapid cooling, and simple operation. This study reviewed recent advances in thermoelectric cooling from two main aspects: thermoelectric cooling applications and performance optimization. In this study, developmental history, principle, characteristics, and research direction of thermoelectric cooling were briefly introduced. Next, thermoelectric cooling applications were summarized, including the application of thermoelectric refrigerators, thermoelectric air conditioning, heat dissipation of electronic devices, and a composite system,particularly for thermoelectric cooling using solar energy and other cooling systems in the composite system. Finally, to improve a thermoelectric cooling system’s performance, many optimization methods have been described, including the structure of a thermoelectric cooler, working parameters, and hot end heat exchangers. In addition, the research progress of pulse currents has been added to working parameters. It is expected that this study will be beneficial to thermoelectric cooling system application and optimization.关键词：thermoelectric cooling;performance optimization;composite system;heat dissipation;pulse current1908|2849|12发布时间：2024-07-18
- 摘要：The performance of a counter-flow corrugated plate dewpoint evaporative coolerwas simulated by a numerical model which was verified by experimental results.The influence of the secondary-to-primary air ratio, intake air velocity, circulating water flow rate, intake air parameters, and geometrical parameters on the performance of a dewpoint evaporative cooler was investigated by the model. The results show that the cooling efficiency and coefficient of performance (COP) of the cooler are both high when the working-to-intake air ratio is 0.3–0.4, the intake air velocity is 2–2.7 m/s, the channel gap is 4.3 mm, and the channel length is 1 m. The cooling efficiency and COP are decreasedwhen the supply air temperature and the flow rate of the circulating water are increased. Therefore, the cooling performance of the cooler is improved as the flow rate of the circulating water is lower when the wet surface is totally wetted. The influence of the inlet air temperature and humidity on the cooler showsthat the wet-bulb efficiency of the studied cooler is between 110% and 115%.关键词：numerical simulation;dew-point evaporative cooler;counter flow;corrugated plate1541|1706|2发布时间：2024-07-18
- 摘要：The influence of working fluids on the performance of a cooling system is crucial and the properties of working fluids depend on the contribution sum of the different groups. Therefore, it is essential to analyze the group contribution of working fluids on system performance, which is an important guide for a suitable working fluid match. In this study, the group contribution method was used in the actual cycle of a liquid pump-driven free cooling loop according to the arrangement and combination of the molecular groups of 15 working fluids. The physical properties of the working fluids were investigated using REFPROP when the evaporation temperature was 25 ℃, the condensation temperature was 15 ℃, and the mass flow rate was 2 700 m3/h. The actual cycle of the liquid pump-driven free cooling loop is used to calculate the refrigeration capacity and energy efficiency ratio. The results show that when the working fluid is separated by a monoatomic group, the larger the number of C and H atoms, the greater the cooling capacity. When the working medium is separated by a polyatomic group, the greater the number of H atoms in the polyatomic group composed of the two atoms of C and H, the greater the amount of cooling.1368|1595|0发布时间：2024-07-18
- 摘要：A two-phase computational fluid dynamics (CFD) simulation of seven parallel evaporating branches in a separate heat pipe with two different heat loads was conducted and the flow distribution characteristics was assessed in the study. In the CFD calculation, the evaporation source term is added to the continuity equation while the surface tension source term is added to the momentum equation. The simulation results show that (1) at a lower heat load with a pool temperature of 60 ℃, the mass flow rate is higher in the branches of the two sides and smaller in the middle, and branch 1 has the highest mass flow rate of 0.025 kg/s while branch 4 has the lowest mass flow rateof 0.016 kg/s; (2) at a higher heat load with the pool temperature at 80 ℃, the mass flow rate of each branch is gradually reduced along the flow direction, where branch 1 has the highest mass flow rateof 0.025 kg/s while branch 7 has the lowest mass flow rateof 0.017 kg/s. The simulation results are compared to the experimental results regarding parallel branches of separation heat pipes, and the comparison shows that the effect of the heat load on the flow distributionin the simulation results is consistent with theexperimental ones.关键词：distribution characteristics;heat load;numerical simulation;VOF;separated heat pipes1550|1688|0发布时间：2024-07-18
- 摘要：In this study, the thermoacoustics theory is used to study the output characteristic of a Vuilleumier (VM)-type thermal compressor from the perspective of impedance matching, showing the trend of the output pressure ratio, acoustic power, and efficiency of the thermal compressor on load impedance. The matching relationship between the thermal compressor and load is also analyzed. The program Sage is used to calculate the output characteristics of thermal compressors with two different diameter regenerators. The impedance amplitude for the thermal compressor varies from 4×10-8 to 4×10-9 (Pa?s)/m3 and the phase angle changes between ﹣60° and 60°. The calculation results show that the output pressure ratio, acoustic power, and efficiency for the thermal compressor significantly change with the change in impedance amplitude and phase angle: the impedance amplitude has a significant influence on the output acoustic power when the impedance is capacitive and the influence of the impedance amplitude on the output pressure ratio for the thermal compressor is obvious. Both the impedance amplitude and angle have significant influences on the efficiency. However, the acoustic power, pressure ratio, and efficiency of the thermal compressor cannot simultaneously reach the optimal value at the same impedance. Therefore, it is necessary to comprehensively estimate the acoustic power, pressure ratio, and efficiency of the thermal compressor when matching the design of the low-temperature stage load. From the perspective of the output pressure ratio and acoustic power, the performance of the thermal compressor regenerator with diameter 30 mmis better than that with diameter 40 mm.关键词：output characteristic;numerical simulation;thermal compressor;load impedance1425|1591|0发布时间：2024-07-18
- 摘要：In this study a combined organic Rankine cycle system is proposed to utilize the waste heat of gas turbine exhaust. The thermodynamic properties of the system are analyzed in detail. Taking an engine-driven gas compressor station as an example, 13 working fluids were compared and the parameters were determined to maximize the net output work using MATLAB and REFPROP 9.0. The results show that when toluene, R141b, and acetone are selected as the working fluids of the three subsystems, the system can achieve a maximum net output power of 1 587 kW, thermal efficiency of 20.26%, and exergy efficiency of 42.68%. The maximum net output work is 23.33% higher than that of a single-stage cycle. The exergy loss of components is analyzed and it is concentrated in the evaporator, based on which an improvement scheme is proposed.关键词：utilization of waste heat of flue gas;organic Rankine cycle;working fluid;exergy1452|1617|3发布时间：2024-07-18
- 摘要：Global warming has become a problem facing human society.To mitigate the greenhouse effect, searching for new refrigerants with low carbon and environmental protection has become a hot topic in the refrigeration industry. HFO-1336mzz(Z) is an environmentally friendly refrigerant that accords with the development trend of alternative refrigerants and has a good application prospect. To systematically and comprehensively show the research progress of HFO-1336mzz(Z), the preparation, basic properties, and application of HFO-1336mzz(Z) were summarized including safety, environmental properties, chemical and physical stability, and thermodynamic properties in a refrigeration system. In addition, a review of HFO1336mzz(Z) in applications such as medium- and high-temperature heat pumps and organic Rankine cycles is presented, providing direction and reference for the next state of HFO-1336mzz(Z).关键词：high temperature refrigerant;HFO-1336mzz(Z);review;environmentally-friendly refrigerant1624|2057|4发布时间：2024-07-18
- 摘要：Energy consumption prediction analysis has important significance in energy management, operation strategy optimization, control optimization, etc. For variable refrigerant flow (VRF) systems, the pure support vector regression (SVR) prediction model has insufficient stability and prediction accuracy. By introducing the particle swarm optimization (PSO) algorithm, this study optimizes the selection of punish and nuclear parameters for a pure SVR prediction model and then compares the prediction results of the PSO-SVR model, pure SVR model, and theoretical formula. The results show that the overall prediction errors for SVR, PSO-SVR and theoretical formula are 1.43%, 1.08% and 1.57%, and the root mean square error are 105.36 W, 88.79 W and 91.37 W respectively. By solving for the best C and γ equal to 10,000 and 4.275, the PSO can significantly improve the performance and stability of the pure SVR prediction model. In addition, it demonstrated better results than those of the formula calculation method with less variables to be measured. It is reasonable to state that the PSO-SVR model is a convenient and economic means to solve such problems.关键词：variable refrigerant flow rate system;prediction model;operating power;particle swarm optimization;support vector regression algorithm1655|1598|4发布时间：2024-07-18
- 摘要：To improve the control precision of a control system under large and frequent perturbations, the model-based predictive control (MPC) has been developed for industrial heating, ventilation, and air conditioning (HVAC) systems. Because the thermal dynamic characteristics of HVAC systems are time-variant, nonlinear, and contain uncertainties during the control process, conventional controller methods face several challenges. In this study, a nonlinear MPC for variable air volume (VAV) systems is developed and investigated. A nonlinear autoregressive network with exogenous inputs (NARX) and particle swarm optimization (PSO) are employed for the nonlinear MPC. The NARX aims to predict the controlled parameter (room temperature) of the VAV system and the PSO serves as an optimizer to obtain the optimal control variables of the VAV system. By assigning different weight values to the objectives of the cost function, the proposed nonlinear MPC can generate different control solutions considering both the control precision and energy saving of a VAV system. Two scenarios of NARX-based MPC were investigated in an experimental VAV system. Scenario 1 only considers the control accuracy while scenario 2 considers both energy saving and control precision. The experimental results show that the NARX-based MPC under scenario 1 can achieve much higher control precision (±0.5 ℃) at room temperature than that of the constant static pressure (CSP) method with a PI controller. The NARX-based MPC under scenario 2 shows a better energy-saving characteristic, saving 23.7% of energy consumption, as compared to that of the CSP method with a PI controller. This work will contribute to the development of nonlinear MPC and its applications in HVAC systems.关键词：model-based predictive control (MPC);variable-air-volume (VAV) system;nonlinear autoregressive network with exogenous inputs (NARX);particle swarm optimization (PSO)1546|1671|3发布时间：2024-07-18
- 摘要：Because of the requirement of annual operation, an air source heat pump water heater has complex and variable working conditions. Therefore, there are higher requirements for air source heat pump water heater system control. Based on the flexible adjustment characteristics of the electronic expansion valve, this study proposes a simple control method of the fixed discharge superheated temperature. Meanwhile, the control methods of a fixed valve opening and fixed superheated temperature were used to conduct experimental research and analyze their internal process. When the ambient temperature is 22 ℃，the experimental results show that the discharge temperature dramatically decreased under the control methods of a fixed valve opening; however, its coefficient of performance (COP) is the lowest and its compression risk with liquid is high. Although the COP is the highest under the control method of a fixed superheated temperature, the discharge temperature is also the highest. Under the control method of a fixed discharge superheated temperature, its COP is slightly lower than that of the fixed superheated temperature control method. However, the discharge temperature is effectively reduced by nearly 7 K on average. Meanwhile, compared to the fixed valve opening, its average COP increased 4.9% and the risk of compressor suction with a large amount of liquid refrigerant can be avoided. Therefore, this method effectively combines the advantage of the other two methods.关键词：air-source heat pump;electronic expansion valve;fixed discharge superheated temperature control;COP1487|1740|3发布时间：2024-07-18
- 摘要：A leakage monitoring method in a refrigeration system based on a theoretical model of refrigerant charge is proposed. In this method, a theoretical model based on a temperature signal is developed, and the refrigerant mass in each component of the refrigeration system can be calculated and the leakage in the refrigeration system can be monitored. For the theoretical model of refrigerant charge, a division criterion of control volumes and governing equation of the phase zone are established using the multi-zone method for the heat exchanger. A temperature-based calculation model of refrigerant mass in the heat exchanger is developed; the refrigerant mass models for the compressor and the connecting pipe are developed by establishing theory-based explicit equations. The validation results show that the maximum deviation is 3.18%.关键词：refrigerant system;leakage monitoring;refrigerant mass1356|1630|0发布时间：2024-07-18
- 摘要：In this study, a building in Shanghai is taken as the study object and the existing floor radiant cooling system of the building is simulated using Trnsys. Then, according to the actual condition of the building, a roof radiant cooling system is designed for the building which is compared to the floor radiant cooling system. The results show that the roof radiant cooling system can more rapidly adjust the indoor environment and has a smaller thermal inertia than that of the floor radiant cooling system. During the entire cooling season, the energy consumption of the floor radiant cooling system is 35 826.2 kW?h and that of the roof radiant cooling system is 34 181.9 kW?h, which is 4.59% lower. Given the continuous operation of the air-conditioning system in the building, a running schedule for the roof radiant cooling system is designed that can reduce the energy consumption of the system on the premise of meeting the indoor thermal environment standard. On this basis, given the long-term constant operating conditions of the air-conditioning system in the building, a variable water flow rate control system and variable water temperature control system are designed, respectively, and the actual operation effects of the two control systems are compared. The results show that the variable water temperature system more quickly responds to the changes in indoor thermal environment and consumes less energy. After improving the system running schedule and adopting variable water temperature control, the total energy consumption of the roof radiant cooling system during the cooling season was 14 665.3 kW?h, much lower than the energy consumption of the original system.关键词：air-water air-conditioning system;variable water flow rate system;variable water temperature system;system energy consumption1457|1859|2发布时间：2024-07-18
- 摘要：In this study, the effects of three types of V-shaped slit nozzles of different structures on the heat transfer of impingement quick-freezing equipment under 170-Pa and 190-Pa pressure conditions are compared by both numerical simulation and experiment. The outlet wind velocity, cross flow wind velocity and Nussel number (Nu) are investigated under different conditions. The results show that the nozzle outlet with a longerK, nozzle extension length, has a higher wind speed and more uniform flow field. However, the longer K will weaken the convective heat transfer intensity. The nozzle with a smaller angle α between the nozzle shrinking and extension sections has a lower wind speed and higher uniformity in the transverse flow direction and is less affected by the transverse flow; however, it has no obvious effect on improving the convective heat transfer intensity. When the length of the K of the V-shaped slit nozzle is 10 mm and the angle α between the nozzle contraction and extension sections is 165°, the average Nussel number and the convective heat transfer intensity are at a maximum.关键词：frozen food;impingement quick-freezing technology;computational fluid dynamics;nozzle structure1525|1675|3发布时间：2024-07-18
- 摘要：Pool boiling heat transfer characteristics of a refrigerant on heating surfaces of metal foams of different structures were experimentally studied. The test samples were copper foams of different pore densities (5–40 PPI), porosities (0.90 and0.95), and thicknesses (4–8 mm). The experimental results show that the maximum surface heat transfer coefficient of the metal foam increases by 26.4% as pore density increases from 5 to 40 PPI. The foam metal pool boiling heat transfer first increases and then decrease with an increase in thickness and the maximum surface heat transfer coefficient of the metal foam with a porosity of 0.90 is 13.2% larger than that with a porosity of 0.95. According to the experimental results, the boiling heat transfer correlation of the refrigerant on the surface with different structured metal foam is developed. The deviation between the prediction value of the correlation and 95% of the experimental data is within ±30% and the average deviation is 12.2%.关键词：metal foam;structure;pool boiling;heat transfer1517|1674|3发布时间：2024-07-18
- 摘要：Regeneration is among the key processes in a liquid desiccant and its efficiency directly affects the entire performance. A device is proposed in the studyin which low-temperature waste heat (40–80 ℃) from power plant is transferred through a heat pipefor solution regeneration. The regeneration experiment is conductedwith a 30–45% calcium chloride solution and water separation rateis taken as the indicator of the solution regeneration performance. The results show that low temperature heat source of 40–80 ℃ with heat pipe heat transfer can realize high-efficiency regeneration of calcium chloride solution in a vacuum environment. The equilibrium pressure in the vacuum regenerator is mainly limited by the cooling water temperature when the regeneration solution has a low flow rate. The pressure decreases with a decrease in temperature and the separation rate increases with an increase in the heat source temperature. Particularly when the heat source temperature increases from 60 to 70 ℃, the water separation sharply increases. As the concentration increases, the primary separation rate of the water decreases; the water separation rate can be significantly improved by controlling the falling flow rate because the calcium chloride solution has a special molecular structure of water absorption.关键词：low temperature heat;solution regeneration;vacuum;water separation rate1397|1639|1发布时间：2024-07-18
- 摘要：The suction state of a compressor is among the most important indicators of its safety and efficiency, but the suction state cannot be measured accurately, particularly for a system with a large refrigerating capacity and high refrigerant flow rate. Based on a certain number of measured parameters, such as temperature, pressure, and other parameters, asuctionstate prediction model is established to determine whether the suction state is in the superheated or two-phase region and calculate the superheating degree and vapor quality of suction, respectively. The results show that the compressor exhaust, condensation, and evaporation temperatures have a linear effect on the vapor quality of suction. The model works in a wide range, with the evaporation temperature﹣35–12 ℃, the condensation temperature 35–68 ℃, and the minimum vapor quality 0.76.关键词：compressor;wet compression;vapor quality;superheating degree1521|1626|0发布时间：2024-07-18
- 摘要：The efficiency of an electric vehicle heat pump system has a great influence on the vehicle mileage. In this work, two evaporators/condensers of different configurations were designed forelectric vehicle heat pump system. The effects of experimental conditions and the position of refrigerant inlet and outlet were experimentally investigated. The heating performances of the heat pump air conditioner system under different conditions were explored as well. The experimental results show that there was little discrepancy in the condenser performance between those of a horizontal structure andvertical structure, but when the evaporator/condenser was under an evaporator mode, the performance of the horizontal structure wasimproved by 20% compared to that of the vertical structure. Moreover, the evaporator performance was improved when the inlet of the refrigerant was placed close tothe flat tube at the bottom. During a frosting experiment, there was no obvious attenuation of the heating performance of the two heat exchangers of different structures under the conditions of -7/-8 ℃ and 7/6 ℃. In addition, the evaporator/condenser with a horizontal structure had an obvious advantage during frosting and defrosting under a condition of 2/1 ℃.关键词：electric vehicle;heat pump air conditioner;evaporator-condenser;frosting;heating performance1661|2218|2发布时间：2024-07-18
- 摘要：A heat and moisture transfer model of an experimental room under the combined cooling mode of radiant panel cooling and a fan coil unit was established in this study. It was proposed to consider the radiant panel as a special “cooler”. The radiant panel was divided into a dry condition and wet working condition when processing indoor air. Under the dry condition, the radiant panel treated the air in a constant vapor content. Under the wet condition, the radiant panel treated the air withan enthalpy reduction and a dehumidification. During the summer, experimental measurements were taken on parameters such as the temperature and humidity of the radiant cooling system and state points were expressed on apsychrometric chart. The load of the fan coil unit and the radiant panel were calculated. The results show that when the water temperature of the radiant panel is 20 ℃, the radiant panel only bears the sensible heat load at a size of 0.85 kW; when the radiant panel water temperature is 10 ℃, the radiant panel operates under wet conditions and the latent heat load is 0.10 kW. Critical state conditions are obtained for controlling the radiant panel without condensation based on the psychrometric chart, i.e., the state of the convective air from the radiant panel has equal enthalpy of the indoor air state.关键词：air conditioning;heat-moisture treatment;psychrometric chart;radiant terminal;latent heat load1625|1801|0发布时间：2024-07-18
- 摘要：The drying characteristics of CO2 in horizontal micro-tubes in a high qualityregion were studied under the conditions of heat flux (7.5–30 kw/m2), mass flow rate (300–600 kg/(m2?s)), saturation temperature (-40-0℃), inlet vapor quality (0–1), and inner diameter (1.5 mm). The results show that the inlet vapor quality decreases with an increase in the mass flow rate, heat flux, and saturation temperature when dryout occurs. Based on the experimental data and analysis of the dryout mechanism, a new theoretical prediction model of critical heat flux and dryness are obtained, and the validity of the new theoretical prediction model is verified. The calculation model is predicted using density theory and the validity of the new prediction model is verified. The results show that the new - model has a better prediction effect within the experimental range of this study.关键词：CO2;micro tubes;dry-out characteristics;theoretical model;coefficient of heat transfer1517|1585|2发布时间：2024-07-18
- 摘要：Gut microbiota plays an important role in the health of humans and animals. The preservation quality of the fecal samples has a direct impact on the results of study. This paper summarizes the main application of fecal bacteria preservation, introduces the mechanism of cryopreservation, and summarizes the preservation methods of fecal bacteria, including cryopreservation, freeze-drying preservation, 4℃ refrigerated storage and other non-cryogenic preservation methods. This paper shows that the samples frozen at -80 ℃ have a relatively stable DNA and microbial communities. We propose that the addition of an effective cryoprotectant can prevent the formation of ice crystals and increase the activity of fecal bacteria. This review discusses the main factors affecting the preservation of fecal bacteria (such as sample storage temperature, time, species types, homogenization, etc.), and prospects some new feasible methods.关键词：cryopreservation;fecal bacteria;gut microbes;lyophilization1542|2012|1发布时间：2024-07-18
- 摘要：Blood vessels have been studied as an important factor in normal tissue and tumors during cryosurgery. It is of great significance to study the effects of blood vessels during the freezing process. A three-dimensional heat transfer model based on a flexible cryoprobe was established to study the effects of blood vessel during cryosurgery. A tumor model with blood vessels (R= 0.7 mm) was utilized to study the effects of blood vessels at a distance of 3and 6 mm from flexible cryoprobe with different directions. The effects of blood vessels within a temperature distribution, at contours of ﹣1, ﹣8, ﹣20, and ﹣40 ℃, and the degree of tissue damage were analyzed. The results show that the greater the decrease in distance between the blood vessels and flexible probe, the greater the effects in temperature distribution. A blood vessel of X = 3 mm has the greatest impact on temperature distribution while a blood vessel of Z =﹣3 mm has the minimum impact on tissue damage. There is a great impact on temperature distribution when the blood vessels are parallel to the flexible cryoprobe and a great impact on tissue damage when the blood vessels are perpendicular to the flexible cryoprobe.关键词：cryosurgery;blood vessels;bio-heat transfer model1508|1690|1发布时间：2024-07-18
- 摘要：In the organic Rankine cycle system, the influence of different working fluids on the thermal performance of the system has always been an important direction of research. R11, R123, R245fa, R600 and R600a are used as organic Rankine cycle's working fluids in this paper, when the temperature of the low temperature waste heat source is constant, the system thermal performance was studied under the conditions of evaporation temperature of 85-145 ℃ and condensation temperature of 25-45 ℃. The comparative performance parameters include: cycle specific work, specific net work, system thermal efficiency, and system exergy loss. The working fluids were comprehensive evaluated in combination with environmental protection, thermal properties and system thermal economy of organic working fluids, the results showed that R600 had the highest efficiency and the least irreversible loss, so the refrigerant R600 is selected as the best working fluid. The optimal system performance reaches when the evaporation temperature is 110-140 ℃ and the condensation temperature is 25 ℃.关键词：organic Rankine cycle;organic working fluids;performance parameters;evaporation temperature;condensation temperature1610|1731|3发布时间：2024-07-18
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