最新刊期
卷 44 ， 期 3 ， 2023
- 摘要：Implementing active vapor-liquid adjustment during phase change processes can enhance the heat transfer coefficient (h) and decrease the pressure drop (Δp) simultaneously. In this study, the current status of vapor-liquid adjustment principles, vapor-liquid adjustment units, and heat exchangers are comprehensively reviewed. The objective of active vapor-liquid adjustment is to adjust the vapor quality to extend the highly efficient heat transfer region during condensation (liquid-separation condensation) and evaporation (liquid adjustment evaporation) processes; however, the targeted vapor qualities are different. The vapor-liquid adjustment units, namely, the orifice-baffle header, T-junction header, and header with mesh-pore structure, are considered. It was observed that the liquid drainage ratio (FL) of the orifice-baffle and T-junction headers can be up to 100% at a low inlet mass flow rate, but only 30% in headers with mesh-pore structures. The HTC of liquid-separation condensers can be increased by up to 112% compared to conventional condensers. However, the application of vapor- liquid adjustment during evaporation is limited, and its mechanisms require further investigation. The performance of vapor-liquid adjusting heat exchangers is highly correlated to the vapor-liquid separation efficiency (η) and distributions of the vapor quality and mass flow rate in the branches. Based on the co-simulation method that adds the flow pattern factors in the header (bubble, liquid film, and droplet), the mass transfer between the vapor and liquid interface and branch pressure drop improves the model accuracy of the vapor-liquid adjusting heat exchanger.1038|1159|0发布时间：2024-07-18
- 摘要：The increase in the use of residential air conditioners in Chinese households has resulted in a rapid increase in energy consumption. The rapid development of artificial intelligence technology provides a powerful tool for advancement in this field. However, there are various potential energy conservation and emission reduction paths for residential air conditioners, in addition to a wide variety of artificial intelligence technologies, which have not yet been systematically defined by the industry in combination with these two aspects. This paper summarizes and classifies various available artificial intelligence technologies with respect to achieving energy conservation and emission reduction for residential air conditioners and provides brief descriptions of these technologies. Because most artificial intelligence technologies are inseparable from data support, this study also introduces a method of efficiently obtaining training data through joint simulation.关键词：household air conditioner;energy conservation and emission reduction;artificial intelligence;data1071|1424|0发布时间：2024-07-18
- 摘要：There is significant emphasis on the destruction of HFC refrigerants in China, culminating in an urgent need to explore efficient and mild HFC refrigerant degradation methods. In this study, a typical HFC refrigerant, HFC-134a, was chosen as the object of combined experimental studies and quantum chemical calculations, and the degradation rate was considered the main criterion for exploring the high-level pathway of refrigerant degradation. In terms of quantum chemistry, the reaction paths of HFC-134a under pyrolysis and oxidative decomposition conditions were explored. Under both paths, detectable stable products such as CHF=CF2 and HF were easily produced. During pyrolysis, the first step in the chemical bond cleavage is the rate-determining step. Compared to the pyrolysis path, the oxidative decomposition path has a lower reaction energy barrier, which is conducive to the rapid occurrence of the reaction. Experimental results showed that the degradation rate of HFC-134a increased from 11% to 66% with the increase in temperature in the range of 240–360 ℃. By fitting the kinetic constant of the reaction, the pre-exponential factor (A) of HFC-134a was determined as 7471.04 s-1, and the activation energy (Ea) was 54.16 kJ/mol, which were consistent with the simulated chemical reaction energy barrier.关键词：chemical reaction energy barrier;activation energy(s);oxidative decomposition;density functional theory (DFT);HFC-134a816|997|1发布时间：2024-07-18
- 摘要：HFO-1243zf (R1243zf) is a refrigerant with a low global warming effect and high development potential. The safety classification of R1243zf is A2; therefore, its flammability cannot be ignored. The critical flammability limits of R1243zf/R134a/R227ea, R1243zf/R125/R227ea, and R1243zf/R125/R134a were 10.82%–11.12%, 10.49%–10.80%, and 10.89%–11.11% (by volume percentage), respectively, which were determined using a 12 L glass flask reaction vessel, according to an experimental method described in ASHRAE 34-2019. Furthermore, both the critical suppression concentrations and critical flammability limits were calculated using a related estimation method for flammable refrigerant blends. Compared with the test results, the relative mean deviations were 3.45% and 1.68%, respectively. Finally, reasons for deviations in the retardant effect were analyzed based on the chemical inhibition mechanism.关键词：refrigerant;hydrofluoroolefin;flammability;flammability limits;3,3,3-trifluoropropylene792|954|0发布时间：2024-07-18
- 摘要：R513A is a new environmental-friendly refrigerant blended with R134a and R1234yf, featuring a GWP100 of 574, which is significantly lower than that of R407C. To verify the applicability of replacing R407C with R513A in locomotive air-conditioning systems, theoretical calculations and experimental comparisons were performed for the two refrigerants. The results show that when the refrigeration system is not modified, the pressure ratios of the R513A and R407C systems are similar; the cooling capacity is reduced by 28.1%; the COP is increased by 25.6%, and the discharge temperature is reduced by 18.24 ℃ under nominal working conditions. Under the same conditions, the cooling capacity decreased, although the COP of the R513A system significantly increased; therefore, the drop-in replacement cannot meet the cabin heat load requirements of the vehicle driver. The cooling capacity of the system can be increased by switching to a compressor with a larger displacement and changing the R513A refrigerant charge to satisfy the cooling demand of the vehicle.关键词：locomotive air conditioning system;refrigerant;uncertainty;R513A;R407C875|1028|0发布时间：2024-07-18
- 摘要：To determine the influence of refrigerant phase change on the temperature control performance of a power battery cooling system, an electric-thermal coupling analysis method was proposed by combining a battery equivalent circuit model and a thermal resistance network model. Subsequently, a discrete system model was built based on AMESim. Numerical research on the temperature performance of the power battery was conducted, and the results were verified using experimental data. Subsequently, parametric studies were conducted to obtain the temperature control performance of the power battery cooling system, including the temperature control performance under 2 C high-rate charging and cyclic charging-discharging conditions. The results show that the liquid-vapor heat transfer and overheated heat transfer regions of the refrigerant in the cooling plate have a significant impact on the temperature control performance. Compared with the traditional liquid cooling system, the liquid-vapor region of the direct cooling system reduces the maximum temperature of the battery by 28.3%, whereas the overheated region leads to significant heat transfer deterioration and increases the maximum temperature and temperature difference. When the refrigerant changes from liquid-vapor heat transfer to overheated vapor heat transfer at the 2 C condition, the surface coefficient of heat transfer is reduced by 73.6%, which increases the temperature of the battery units by 12–14 ℃. In addition, a sufficiently low refrigerant temperature increases the maximum temperature difference, which restricts the practical application of the direct cooling system. Increasing the evaporating pressure and configuring the plates on both sides can decrease the temperature difference in the vertical direction. However, these two methods cannot eliminate overheating, and thus it is necessary to design a new system to solve the problem of heat deterioration caused by refrigerant overheating.关键词：battery thermal management;direct cooling system;electrothermal coupling analysis;phase change;overheating820|1020|0发布时间：2024-07-18
- 摘要：Heat pump heating can solve the environmental pollution problems caused by coal heating. This study used an air source heat pump system applied in Hotan area as the research object and tested the in-situ performance of the air source heat pump heating system with the radiant floor within 24 h on a typical day (the ambient temperature was -4.7–9.6 ℃ while the RH was 26%–61%). The results show that the highest COP of the heat pump heating system is 2.64 at around 16:00, and the lowest value is 1.98 at around 08:00. Owing to the relatively good insulation performance of the building, when the outdoor temperature changes, the room temperature fluctuates slightly; the room temperature can be stable between 23–24 °C all day, and the room temperature can be above 20 ℃ even for northern rooms. The air source heat pump heating system using radiant floor heating can satisfy the heating demand of the Hotan area. The system has high efficiency and broad application potential.关键词：air-source heat pump;radiant floor heating;clean heating;system performance701|882|0发布时间：2024-07-18
- 摘要：In terms of the performance characteristics of a centrifugal chiller, a performance simulation algorithm was proposed using the iterative calculation of compressor power and condenser heat transfer in the range between the maximum capacity based on the maximum current and the minimum capacity with respect to surge. Thus, a performance simulation software for the centrifugal chiller integrating the heat transfer calculation of the shell and tube heat exchanger, performance calculation of the centrifugal compressor, and surge prediction was developed. The accuracy of the simulation model was verified using the prototype test results. The results indicate that within the entire load range, the maximum error of the COP is 6.43%; the maximum error of the chilled water pressure drop is 7.28%; the maximum error of the cooling water pressure drop is 4.45%; the maximum error of the power input is 6.87%; the maximum error of the evaporator saturation temperature is 3.83%, and the maximum error of the condenser saturation temperature is 1.24%. The simulation software successfully predicts various parameters, such as chilled water temperatures, cooling water temperatures, and flow rates of the centrifugal chiller under different loads.关键词：centrifugal chiller;software development;simulation;COP780|1046|0发布时间：2024-07-18
- 摘要：Because two-stage compression technology is rarely used in small-scale and medium-scale chillers, a two-stage compression water-cooled screw chiller with a nominal cooling capacity of 615.48 kW was designed in this study. A two-stage variable-frequency screw refrigeration compressor was developed by adopting a new rotor profile and structural design. An experimental test was also conducted on the developed screw compressor and chiller according to national standards. The results show that the volumetric efficiency of the two-stage variable-frequency twin-screw refrigeration compressor developed in this study is generally higher than 96% and the maximum isentropic efficiency reaches 84.4%. The coefficient of performance (COP) of the chiller reaches 7.01 under the nominal operating condition in which the outlet temperature of chilled water is 7 ℃. This value is16.83% higher than the first-degree energy efficiency specified in GB 19577—2015 standard. The integrated part-load value is 10.45, which is 39.33% higher than the first-degree energy efficiency specified in GB 19577—2015 standard. Furthermore, the two-stage compression technology effectively improved the performance of the water-cooled screw chiller. Compared with those of the case without intermediate cooling, the cooling capacity and COP of the chiller with intermediate cooling increased by more than 11% and 8%, respectively.关键词：water chiller unit;screw compressor;two-stage compression;intermediate cooling783|1120|0发布时间：2024-07-18
- 摘要：Vertical-fin microchannel heat exchangers (VMHXs) have efficient thermal-hydraulic performance and favorable drainage performance, such that they are capable of being utilized in air source heat pumps under wide operating conditions. In this study, a CFD (computational fluid dynamics) model was used to analyze the air-side thermal-hydraulic performance of VMHXs under dry conditions. The model was verified using experimental results with an error of less than 20%. Subsequently, the sequence and connection of waves and louvers on composite fins were compared, and the effects of fin pitch, fin length, tube pitch, and fin thickness were investigated. Finally, parametric optimization was conducted using the Taguchi method. The results show that under constant pumping power, the heat transfer enhancement of the composite fin with the front louver fin and the reversely connected rear wavy fin is the best. When the comprehensive index performance evaluation criterion (Pec) was used to evaluate the performance of the VMHXs, the tube pitch and fin length were determined as the main influencing factors. Within the range of parameters practically available, the best performance is obtained by a combination of 1.8 mm fin pitch, 25.6 mm fin length, 12.0 mm flat tube pitch, and 0.12 mm fin thickness.关键词：air-source heat pump;condenser;microchannel heat exchanger;heat transfer coefficient760|976|0发布时间：2024-07-18
- 摘要：The evaporation heat transfer characteristics of R32 in an annular area outside a stainless steel sandblasted tube, dimple tube, dimple/sandblasted tube, and smooth tube with an outer diameter of 19.05 mm were investigated, and the effects of the mass flux [50–140 kg/(m2?s)], vapor quality (0.2–0.8), and saturation temperature (279–288 K) on the heat transfer coefficient were analyzed. The results show that the surface heat transfer coefficient is highest for the dimple/sandblasted tube, followed by the dimple tube, and lowest for the smooth tube. The surface heat transfer coefficient and frictional pressure drop are positively correlated with the mass flux and negatively correlated with the saturation temperature. The average vapor quality at high mass flux has a significant effect on the surface heat transfer coefficient. The enhanced heat transfer effect was quantified by introducing the enhancement factor ηEF and the performance evaluation factor ηPEF. The dimple/sandblasted tube combined the advantages of sandblasted and dimple surfaces, thus exhibiting the best evaporation heat transfer performance with the highest ηEF and ηPEF values of 2.84 and 2.31, respectively. The composite treatment of sandblasted and dimple heat transfer tube surfaces increases the heat transfer area and the number of vaporization cores, improving the turbulence intensity, such that the liquid film is stretched and thinned to promote evaporation outside the tube.关键词：evaporation heat transfer;composite micro-nano heat transfer tube;surface heat transfer coefficient;frictional pressure drop;annular area663|783|0发布时间：2024-07-18
- 摘要：A novel multiple micro-jet impinging cylindrical fin heat sink was constructed. The heat sink was designed as a sandwich structure with a compact structure, where the upper part was an air chamber and the middle part was a jet orifice plate. In addition, a return channel was arranged on the jet orifice plate, which reduced the influence of the transverse flow on the jet impingement heat transfer. At the bottom was a gas chamber, which was equipped with a cylindrical fin plate. Cylindrical fins can increase the heat transfer area and enhance the fluid disturbance to enforce heat transfer. The effects of Reynolds number, heat flux, and height-diameter ratio on the heat transfer characteristics of the heat sink were studied using experimental and numerical methods. The results show that a cooled surface with a cylindrical fin has a lower temperature, and the average convective heat transfer coefficient of the cooled surface increases by 1%–3% compared with that of a surface without a fin at jet Re of 1596–2 874; the jet impact heights H were 4 mm, 6 mm, and 8 mm. As the Re increases, the heat transfer performance gradually improves. When the Re of the jet was 2 874, the maximum average convective heat transfer coefficient of the cooled surface of the cylindrical fin plate reached 1 360 W/(m2?K).关键词：enhanced heat transfer;jet impingement array;return structure;heat sink with cylindrical fin;numerical simulation627|838|0发布时间：2024-07-18
- 摘要：In response to the power increase in electronic devices with high heat flux density, new efficient cooling technologies should be developed to ensure the safe operation of these electronic devices. The application of micro-pin-fin structures under high-degree subcooled boiling is a promising way of enhancing the cooling capacity. In this study, subcooled boiling on a micro pin-fin surface was observed, and the effects of the subcooled temperature on the heat transfer coefficient and critical heat flux were measured. Moreover, the heat transfer coefficients of the micro-pin-fin structure were compared with those of a smooth surface, and the heat transfer enhancement mechanism of the micro-pin-fin structure was investigated. The results show that the heat transfer coefficient of the micro-pin-fin surface increases with an increase in the subcooled degree when the heat flux is greater than 200 W/cm2.The critical heat flux increases from 228 W/cm2 to more than 400 W/cm2 when the subcooled degree increases from 50 ℃ to 95 ℃. The heat transfer coefficient of the micro-pin-fin surface is always larger than that of the smooth surface under the same working conditions, and the effect of the micro-pin-fin surface is more obvious under high degrees of subcooling and high heat flux. The enhancement factor is 1.28 when the heat flux is 250 W/cm2 and the degree of subcooling is 95 ℃.关键词：enhanced heat transfer;micro-pin-fins structure;degrees of subcooling;subcooled boiling706|921|1发布时间：2024-07-18
- 摘要：A leakage of oil lubricants affects the heat transfer and flow of refrigerants in vapor compression refrigeration (VCR) systems. In this study, a numerical model of a VCR system using a linear compressor and R1234yf as the refrigerant was developed. The proposed model was validated in terms of pressure drop and cooling capacity through experimental tests under oil-free conditions using a VCR system with an oil-free linear compressor. The mean absolute percentage error of the cooling capacity and pressure drop were 3.9% and 8.2%, respectively. The results showed that the discharge temperature was inversely proportional to the evaporating temperature and the oil circulation ratio (OCR). The cooling capacities under oil-free conditions were 4% and 22% higher than those at 2% and 6% oil circulation ratio, respectively, at a condensing temperature of 50 ℃ and evaporating temperature of 2 ℃in the VCR system. The pressure drop under oil-free and 4% OCR conditions were 61 kPa and 99 kPa, respectively, at a condensing temperature of 50 ℃ and an evaporating temperature of -11 ℃. The pressure drop of the oil-containing system was 5%–82% higher than that of the oil-free system, and the pressure drop in the heat exchanger increased with an increase in the oil circulation ratio.关键词：vapor compression refrigeration system;heat transfer coefficient;evaporator;oil circulation ratio745|955|0发布时间：2024-07-18
- 摘要：This study proposed a multi-tube (polyvinyl chloride, PVC) array thermal energy storage structure based on butyl stearate phase change material, aiming to develop a simple and low-cost thermal energy storage device for solar greenhouses. The thermal environment of a greenhouse with a multi-tube array thermal energy storage device was studied through a series of experiments. The results indicated that the heat storage capacity of the device with a black surface was 66.7% higher than that with a white surface under similar irradiation conditions. Compared to devices with diameters of 50 mm and 110 mm, the discharging performance was the best when using a 75 mm PVC pipe containing butyl stearate. Moreover, in contrast to traditional solar greenhouses, the nighttime average temperature of the solar greenhouse with the multi-tube array thermal energy storage device was higher by more than 1.2 ℃, and the in-situ thermal energy storage capacity of the unit with butyl stearate reached 163 kJ/kg (including sensible heat). Therefore, multi-tube array thermal energy storage devices, which are economical, safe, and simple, can be widely applied in solar greenhouses.关键词：solar greenhouse;phase-change thermal energy storage;multi-tube array;butyl stearate;application771|920|1发布时间：2024-07-18
- 摘要：Based on the computational fluid dynamics (CFD) software, the effect of fins on the heat transfer process of a phase-change heat exchanger was considered in terms of the heat transfer area and flow field. The influences of the fin height and fin arrangement on the heat transfer performance under three types of structures (double-finned, triple-finned, and quadruple-finned) were analyzed, and the optimal structure and specification parameters were obtained. The results show that the fins with a double-finned structure substantially improve the thermal energy storage performance of the phase-change heat exchanger. The heat exchanger with a triple-finned structure can reach the expansion period of the flow field faster, and the symmetrical quadruple-finned heat exchanger has a relatively high melting rate in the vertical and horizontal directions. Under the same heat transfer area, the double-finned structure has obvious advantages. When the ratio of fin length to heat exchange tube length is 1.5, the discharge time is shortened by 80%, and the total solidification mass increases to 87%, which is 76% higher than that of the bare tube.关键词：shell-and-tube heat exchanger;heat transfer enhancement;structure optimization;phase change thermal energy storage735|1060|0发布时间：2024-07-18
- 摘要：To simultaneously deliver multi-categories of fresh products at multiple storage temperatures and to ensure the continuous operation of the cold chain for “the last kilometer”, the development of appropriate cold chain distribution equipment is crucial. Through the e-commerce market research of fresh products and the analysis of distribution demand, a cold thermal energy storage delivery box with multiple storage temperatures was developed, following the relevant standards. The details of structure design, temperature zone distribution, thermal insulation materials, and cold thermal energy storage material, were presented. The performance test of the heat transfer coefficient was also conducted. The test results show that the thermal insulation structure is stable, and the total heat transfer coefficient of the box is 0.68 W/(m2?K), which satisfies the technical requirements of ordinary temperature refrigerated transport vehicles.关键词：fresh produce e-commerce;cold thermal energy storage multi-temperature delivery box;heat transfer coefficient;thermal insulation materials825|989|0发布时间：2024-07-18
- 摘要：This study proposed a heat exchanger plate design scheme for an air handling unit used in a data center. In this study, the thin plate design idea was introduced step by step, and the flow and heat transfer performance were investigated using a numerical model. Circular estrade dimple and rod-shaped dimple arrays with different concave and convex directions were applied to the plates to enhance heat transfer. The numerical results show that the improved plates have a better heat transfer enhancement effect at larger Reynolds numbers (Re). When the Re is 15 091, compared with the baseline plate, the improved plate 3 enhances the heat transfer by 37% at the same pumping power, while the improved plate 3 enhances the heat transfer by 20% at Re of 5 000. It is found that the axial direction and the transverse directions of the rod-shaped dimple array have a significant influence on the enhancement of heat transfer. When the Re is 15091, compared with the improved plate 1, the improved plate 3 enhances the heat transfer by more than 11% at the same pumping power, by adjusting the arrangement of the rod-shaped dimple array.关键词：data center;heat transfer enhancement;dimple structure;numerical simulation922|910|0发布时间：2024-07-18
- 摘要：To explore the effects of freeze-thawing on the physicochemical properties of different muscle types during refrigeration storage, the white and red muscles of spotted silver carp were studied. The water retention (drip loss, water activity, and water distribution), color, protein thermal stability, and texture of muscle were analyzed under direct refrigeration storage (4 ℃ stored for seven days) and freeze-thaw refrigeration storage (frozen at -18 ℃ for one day, stored at 4 ℃ for six days after thawing). The results showed that the drip loss of muscle increased significantly during freeze-thaw storage. After freeze-thawing, the changes in the relaxation time, the peak area percentage of immobilized water, and free water in white muscle were more apparent than those in red muscle. Freeze-thawing significantly increased the lightness value L* of white muscle, and the yellow value b* of red muscle increased by 104%. In addition, the stability of protein structure was related to the muscle type, and freeze-thawing aggravated the decrease of myosin enthalpy. In addition, the hardness and chewiness of muscle decreased significantly during storage, and the white muscle was more prone to dry consumption after freeze-thawing. Therefore, red muscle fibers may have better freeze tolerance, and freeze-thawing may have less effect on the physicochemical properties of red muscle.关键词：spotted silver carp;refrigeration storage;freeze-thawing;white muscle;red muscle;physicochemical properties767|837|0发布时间：2024-07-18
- Address：10/F, Yindu Mansion, 67 Fucheng Road, Haidian Dist, Beijing, China Postal code：100142
- Tel：010-68711412 Email：editor@car.org.cn
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0