最新刊期
卷 44 ， 期 6 ， 2023
- 摘要：Currently, China's energy consumption is heavily reliant on coal, which is difficult to replace. The development of non-fossil fuels faces multiple constraints, and the industry is adversely affected by the issues of high energy consumption, high emissions, and low energy efficiency. Therefore, innovative low-carbon technologies urgently require further development. Heating accounts for half of all energy consumption; therefore, low-carbon heating is important for achieving carbon neutrality. To meet the capacity and temperature requirements of industrial heating, high-temperature water/steam heat pumps must be developed. This paper presents an analysis of the current status of industrial heat pump technology, including system cycles, refrigerant compression technology, and steam compression technology. Based on the development status of fourth-generation low-global warming potential refrigerants, the corresponding heat pump technologies should be well developed. Furthermore, industrial heat pump development prospects are discussed based on the development status and applications. Finally, application scenarios are predicted based on the market capacity and carbon reduction potentials.关键词：industrial heat pump;high temperature heat pump;steam heat pump;low GWP refrigerant901|2027|1发布时间：2024-07-18
- 摘要：Energy saving and renewable energy utilization in buildings are key to achieving carbon neutrality in China. Radiative sky cooling, as a passive cooling technology that requires no external energy input nor refrigerants, has a significant impact on increasing energy efficiency and reducing carbon emissions in buildings. To this end, in this study, the carbon emission reduction that can be achieved if passive radiative cooling technology is applied to existing buildings in China, especially in the operational phase, was explored. The current total building area and the stock area by building type in different provinces were obtained from the Statistical Yearbook. Nine building types were modeled according to energy efficiency standards, and weather data from typical meteorological years were selected for each province. With these inputs, the baseline carbon emissions during the operational phase of each building type in each province, as well as the amount and rate of carbon emission reduction after the large-scale application of radiative sky cooling, were obtained via simulations using the building energy consumption software EnergyPlus. Regarding the building type, residential and industrial buildings were found to have higher carbon reduction rates. The spatial distribution of the carbon reduction rate in China was also analyzed. The average carbon emission reduction rate in severely cold regions was 4.92%, whereas the rates were 8.11%, 10.71%, 10.92%, and 16.77% in cold regions, hot summer cold winter regions, hot summer warm winter regions, and mild regions, respectively. The total annual carbon reduction was calculated to be 230 million tons of CO2, accounting for 10.90% of the building operation carbon emissions and 2.39% of the total energy carbon emissions. Thus, radiative sky cooling can be a significant contributor to achieving “carbon peaking” and “carbon neutrality” goals in China.关键词：prospective carbon reduction;radiative sky cooling;building energy saving;building carbon neutrality724|692|0发布时间：2024-07-18
- 摘要：As a safe, efficient, and environmentally friendly natural working fluid, CO2 is the primary choice for future automotive air conditioners. To consider the comfort and safety problem of an excessive CO2 volumetric concentration in the passenger cabin caused by refrigerant leakage, the 3D simulation software STAR-CCM+ was used to build a CO2 refrigerant leakage model in the passenger compartment. Simulations and analyses of the dynamic changes in CO2 volumetric fraction in the passenger compartment facial measurement points for two different leakage rates and leakage orifice diameters were performed. At a high CO2 leakage rate of 50 g/s, the CO2 volumetric fraction on the face can reach more than 9% when the leakage is completed. The air supply mode must be switched to provide fresh air and reduce the CO2 volumetric fraction in the passenger cabin. At a low CO2 leakage rate of 0.1 g/s, the facial CO2 volumetric fraction does not exceed 3%, which is safe for breathing, when the leakage is completed.关键词：CO2;heat-pump air conditioner;leakage characteristics;refrigerant484|682|0发布时间：2024-07-18
- 摘要：To improve the existing ejector heat pump air conditioning (EHPAC) system for electric vehicles, indoor and outdoor heat exchangers were designed to be separated from the front and rear rows, and ejectors were added to achieve cascade evaporation and recover the expansion work. The performance of the system was thus improved. The influences of the indoor and outdoor temperatures of the vehicle on the cooling and heating performances of the EHPAC system under summer and winter conditions were experimentally studied. The verification results show that the use of ejectors can significantly improve the heating performance of heat pump systems in vehicles. Compared with the traditional heat pump air conditioning (THPAC) system for electric vehicles, the cooling and heating performances of the EHPAC system are better at different vehicle indoor and outdoor temperature conditions. The cooling capacity increases by approximately 21.5%–35.7%. The cooling coefficient of performance (COP) increases by approximately 13.1%–21.7%. The heating capacity increases by approximately 4.4%–14.5%, and the heating COP increases by approximately 11.3%–18.3%. This also indicates that the performance of the EHPAC system is more sensitive to the indoor temperature of the vehicle than the outdoor temperature.关键词：electric vehicle;heat-pump air conditioning system;ejector;variable operating characteristics446|621|0发布时间：2024-07-18
- 摘要：Reasonable optimization of the operation strategy is essential for saving energy in the long-term operation of heat pump systems. However, the strategy optimization process is susceptible to load uncertainty, which causes the optimized strategy to save less energy than expected. To address this issue, a method of operation strategy optimization using stochastic load prediction was developed in this study. The method adopts multiple stochastic process samplings to simulate the uncertainty of the load prediction, thereby improving the robustness and energy savings of the operation strategy. The energy-saving properties of the optimization method were verified and analyzed using an air-source heat pump hot-water system. The results show that the novel optimization strategy can reduce the chance of using peak electricity and increase the utilization of off-peak electricity. In the long-term operation simulation, the novel optimization strategy was found to save 6.4% of energy costs compared with the traditional optimization method.关键词：air-source heat pump;operation strategy;stochastic process;optimization346|668|0发布时间：2024-07-18
- 摘要：A novel self-driven radiator was developed to serve as the indoor terminal of an air-source heat pump system to improve the indoor comfort level and energy efficiency for space heating. By analyzing the operating characteristics of the most important system components, a thermodynamic gray-box model was established for the system, and its reliability was verified. On this basis, the coupling characteristics of the self-driven radiator and air-source heat pump were studied. Furthermore, the hourly operation and annual performance of the system in a typical building were analyzed using EES and TRNSYS. It was found that the system performance was affected by several factors and was more sensitive to changes in the compressor operating frequency. The system had a fast thermal response, which facilitated a stable indoor temperature environment. Under the typical meteorological conditions of Taiyuan, the annual coefficient of performance of the system was 2.67. The coefficient of performance under typical conditions was found to be 50.28% higher than that of the conventional radiator system, demonstrating evident energy-saving benefits.关键词：air-source heat pump;radiator;gray box;simulation;energy efficiency406|584|0发布时间：2024-07-18
- 摘要：Capillaries are important throttling elements widely used in small cooling and heating devices. R32 is an environmentally friendly refrigerant and is extensively employed in household air conditioning. In this study, a mathematical model of adiabatic capillary tubes was first developed on the basis of homogeneous flow, energy conservation, momentum conservation, and mass conservation equations. The model affords a formula for calculating the capillary lengths in the subcooling and two-phase regions. The concept of choked flow was introduced into the model, and the critical flow was used to assess whether choked flow occurred. The incorporation of the choked flow concept improved the accuracy and stability of the model. Next, a capillary tube test platform using R32 was built to verify the accuracy of the simulation model. The mass flow rates of two capillary tubes with an inner diameter of 1 mm and lengths of 0.5 and 1 m under a condensing pressure of 2.4–3.2 MPa and a subcooling degree of 5–20 °C were obtained. Finally, a nomogram of the R32 capillary was drawn using extensive data points obtained from the simulation model.关键词：R32;capillary tube;flow characteristic;nomogram422|763|0发布时间：2024-07-18
- 摘要：Heat exchanger tubes used in large refrigeration systems are generally enhanced, both inside and outside. Because it is difficult to attach temperature sensors for wall temperature measurements, specific test methods are required for the performance evaluation of such double-sided enhanced tubes. These include the Wilson plot method (WPM), modified Gnielinski formula (MGF), and Wilson–Gnielinski formula (W-GF), which have their own applications and limitations. In this study, a new and user-friendly test method––the undetermined exponent method (UEM)––was developed for double-sided enhanced tubes. The internal and external heat transfer coefficients can be separated effectively and efficiently by obtaining the undetermined parameters in the correlation through linear fitting and optimization. Experiments under two different conditions on a double-sided enhanced tube with R134a evaporating outside and water flowing inside were conducted, and a comparative study of the WPM, MGF, W-GF, and UEM test methods was performed. The internal and external enhanced factors obtained by the four methods were 2.88–3.23 and 3.15–3.54, respectively, and the difference in the internal and external heat transfer coefficients was within 15% and 11%, respectively. These four methods can be applied under different conditions, yet the proposed UEM is a more efficient and accurate test method with fewer restrictions and more convenience.关键词：coefficient of heat transfer;experimental methods;refrigeration heat exchanger;double-side enhanced tube379|631|0发布时间：2024-07-18
- 摘要：A transcritical CO2 system combined with an ejector and dedicated mechanical subcooling (EJ-DMS) was developed to improve the performance of the CO2 system in the space heating and cooling of buildings throughout the year. A thermodynamic model of the system was devised. Then, the discharge pressure and subcooling degree were optimized using a genetic algorithm by considering the coefficient of performance (COP) as the objective function. Using five typical cities as application scenarios, the energy consumption and annual performance factor (COPann) of the system were analyzed. The results show that, compared with a conventional mechanical subcooling system and the conventional ejector system, the heating COP of EJ-DMS is enhanced by 10.90% and 5.58%, respectively, and the cooling COP is increased by 8.99% and 18.12%, respectively. The COPann values are improved by 7.95% and 5.98%, respectively. Compared with the conventional ejector system, the discharge pressure of EJ-DMS is reduced by 0.47 MPa and 0.77 MPa in the heating and cooling modes, respectively. In addition, the COPann improvement ratio of the EJ-DMS system is the highest when operating in Guangzhou and Harbin, indicating that the EJ-DMS system is more suitable for regions with relatively high or low ambient temperatures, such as hot summer and warm winter or severely cold regions. This study provides a theoretical reference for the development and optimization of a combined cooling and heating CO2 system.关键词：natural working fluid CO2;combined cooling and heating;ejector;mechanical subcooling;COP392|620|0发布时间：2024-07-18
- 摘要：With the recent increase in power density and miniaturization of various equipment, the requirements for compactness and efficiency of heat exchangers become increasingly stringent. Micro-structured surfaces have a significant impact on flow patterns and heat transfer mechanisms during flow boiling. To examine the effect of heterogeneous wetting surfaces on the flow boiling process, an experiment on subcooled vertical flow boiling on heterogeneous wetting surfaces in a narrow rectangular microchannel was conducted using a high-speed camera. Deionized water was used as the working fluid, and the cross-section of the channel was 0.5 mm × 5 mm. The mass fluxes of the subcooled flow boiling were 300 kg/(m2?s) and 400 kg/(m2?s). The heat flux was within 30–300 kW/m2. The experiment was conducted under atmospheric pressure, and the subcooling degree was 10 K. Hydrophobic patterns perpendicular (HC) and parallel (HP) to the flow direction were compared. The subcooled boiling curves, heat transfer coefficient, and pressure drop were investigated with respect to the variations in heat flux and mass flux, and their trends were analyzed along with the flow patterns. The heat transfer coefficient of flow boiling on heterogeneous wetting surface HC was enhanced by as much as 39.55% compared with a silicon surface with less pressure drop. During the boiling process, the dominant heat transfer mechanism was nucleate boiling, with numerous nucleation sites between the hydrophilic/hydrophobic stripes.关键词：flow boiling;microchannel;heterogeneous wetting surface;flow pattern340|516|0发布时间：2024-07-18
- 摘要：A balance between condensing and boiling heat exchange is an important prerequisite for the efficient and stable operation of two-phase immersion liquid cooling systems. In this study, the effects of the condensate tube type and cooling water parameters on the balance of the condensing and boiling heat transfer of the system were studied experimentally. The results show that the system achieved heat balance when the heat exchange rate of the condensate tube was not lower than the pool boiling heat transfer rate of the dielectric liquid, and the required flow rate of the cooling water was minimized when the heat exchange in the system was exactly balanced. The performance of the 3D-enhanced tube was better than that of the smooth tube, and a lower cooling water flow rate was required for the system to achieve the same cooling water inlet temperature. The highest coefficient of performance (COP) of the system was obtained when the heat exchange in the system was perfectly balanced. At a heat load of 210 kW/m2, the highest COPs of the system obtained using the smooth tube, outer enhanced tube, and double-sided enhanced tube were 4.5, 6.9, and 7.6, respectively. However, the COP decreased as the flow rate of the cooling water increased after the heat exchange balance in the system was achieved. When the flow rate of the cooling water increased to 1.5, 2.7, and 3.8 times the flow rate that achieves heat exchange balance, the COP of systems with the smooth tube, outer enhanced tube, and double-sided enhanced tube decreased by 39.0%, 60.1%, and 69.2%, respectively.关键词：condensate tube types;cooling water parameters;heat balance;efficiency analysis461|563|0发布时间：2024-07-18
- 摘要：The properties of new serrated fins were numerically investigated to improve the heat transfer properties of a serrated fin radiator while controlling the increase in pressure drop loss. The effects of different fin surfaces, windward surface structures, and dimensional parameters on the heat transfer Nusselt number Nu, pressure loss Δp, and overall performance η were analyzed. The results indicate that the heat transfer performance has a trivial dependence on the shape of the grooves or bumps on the fin surface; however, the circular shape has the least increase in pressure loss and the best overall performance. Owing to the circular grooves and bumps on the fin surface, the windward surfaces of the fin are changed to circular; this can improve heat transfer, reduce pressure loss, and improve overall performance by as much as 12.2%. The balance between heat transfer and pressure loss is optimal for the circular grooves and a bumps size R = 0.15 mm, and the average pressure loss remains the same as that of the conventional serrated fin, with an average improvement of 8.7% in both heat transfer and overall performance.关键词：serrated fins;surface coefficient of heat transfer;enhanced heat transfer;structural parameters338|589|0发布时间：2024-07-18
- 摘要：As a new functional thermal fluid, microencapsulated phase change material slurry (MEPCMS) has development potential in thermal management and other fields. In this study, the discrete phase model (DPM) was used to investigate the heat transfer characteristics of MEPCMS in a horizontal rectangular minichannel under nonuniform heat flux conditions. The results show that the heat transfer can be enhanced by the phase change of particles in the slurry, and the slurry can reduce the wall temperature rise by 8.79% and the fluid temperature rise by 15.14% at a heat flux distribution of 9–5–5 W/cm2, inlet velocity of 0.40 m/s, and mass fraction of 10%. Thermophoretic force causes the particles to migrate to the low-temperature region during the flow. Compared with the uniform heat flux condition, the region and magnitude of the local heat flux affect the heat transfer characteristics in this and later regions. As the inlet velocity and particle mass fraction increase, the cooling effect of the fluid on the wall improves. However, the pressure drop also increases owing to the influence of the streamwise resistance and two-phase interaction.关键词：microencapsulated phase change material slurry;discrete phase model;non-uniform heat flux;heat transfer enhance406|525|0发布时间：2024-07-18
- 摘要：Motor cooling is key to the reliable operation of centrifugal refrigeration compressors with gas bearings. A mathematical model of a centrifugal refrigeration compressor with gas bearings was devised, and the influences of different refrigerants on the motor cooling process and refrigeration system performance were analyzed. The results show that the internal temperature of the motor reaches the highest when R1234ze (E) is used, and the maximum temperature of the permanent magnet of the motor is 60–90 °C higher than that with R134a and R1234yf. When using the three refrigerants, the average winding temperature of the motor decreases with an increase in the cooling inlet temperature. When R134a and R1234yf are used, the maximum temperature of the permanent magnet decreases with an increase in the cooling inlet temperature. When R1234ze (E) is used, the maximum temperature of the permanent magnet first increases and then decreases with the increase in cooling inlet temperature. The maximum temperature is reached when the cooling inlet temperature is approximately 25 ℃. The outlet vapor quality of the motor cooling circuit decreases by approximately 3%–5% when the cooling inlet temperature increases by 4.5 °C. Compared with traditional systems, systems with motor cooling branches can control the motor temperature within a safer operating range. However, systems using R134a, R1234yf, and R1234ze (E) have COPs reduced by 1.23%–1.82%, 1.23%–1.65%, and 1.14%–1.17%, respectively.关键词：compressor;gas bearing;refrigerant;COP462|620|0发布时间：2024-07-18
- 摘要：A closed-loop integrated microfluidic cooling system was designed to mitigate the heat dissipation problem in a high-power bare chip. The heat dissipation capabilities of a microchannel manufactured in the cavity and an unmanufactured cavity were compared. Moreover, the heat dissipation capabilities of a straight microchannel cavity and a cross-linked microchannel cavity were compared. The results show that the heat dissipation capability of the bare chip with a microchannel cavity was better than that of the unmanufactured one, and the heat dissipation capability of the bare chip with a cross-linked microchannel cavity was better than that of a straight microchannel one. The bare chip was welded to the diamond heat sink by eutectic soldering, and the diamond heat sink was welded to the power module cavity by eutectic soldering, which reduced the thermal resistance between the power module cavity and the bare chip by a factor of 280–360 from traditional methods. Experiments and simulation calculations of the heat dissipation ability of the microfluidic cooling system were performed. The experimental and simulation results are in notable agreement, and the maximum deviation was only 7.16%. The results show that the microfluidic cooling system has a strong heat dissipation ability that can handle a 320 W/cm2 heat flux on the bare chip at 70 °C ambient temperature.关键词：heat dissipation;micro-channel;eutectic soldering;diamond453|565|0发布时间：2024-07-18
- 摘要：The grain size of artificial snow in a simulated indoor environment was measured using a laser particle size analyzer to examine the growth law of snow crystals. The change in snow grain size with different heights of snow falling region, air-to-water pressure ratios, and ambient temperatures was analyzed. The experimental results show that the snow grain size increases with an increase in snow falling height, and the growth rate of the particle size gradually decreases. At a height of 80 cm, the crystal nucleus grows to a mature snow crystal, whose Sauter mean diameter is 57–73 μm. At this height, the snow grain size roughly follows a normal distribution, and the air-to-water pressure ratio and ambient temperature have a significant impact. When the air-to-water pressure ratio is 0.5 to 0.4, the snow-forming effect is good, manifested by a larger snow grain size and a more uniform distribution. Low-temperature environments can accelerate snow crystal growth. With a decrease in ambient temperature, the proportion of small snow crystals decreases, and the proportion of large snow crystals increases.关键词：artificial snow;refrigerating system;particle size measurement;operating conditions374|557|0发布时间：2024-07-18
- 摘要：When a dual-loop coupled refrigerator operates in a coupled state, the condensation pressure of the freezing loop decreases, such that the refrigerant outlet of the condenser is not completely condensed. Hence, the cooling capacity provided by the freezing loop is used to treat the refrigerant that is not completely condensed. It is therefore difficult for the system to take full advantage of the energy-saving ability of the design. To solve this problem, we propose a dual-loop coupled system with two-stage throttling. By adding a throttling expansion device between the freezing condenser and coupled subcooler, the system can operate stably. In this study, the refrigerant is R600a. Under the conditions of ambient temperature of 25 °C and freezer temperature of ?18 °C, we simulated the operating state of the system using Matlab, which was validated by an experimental device. The research results show that the system can maintain stability in both independent and coupled operations when the system works under the design conditions, and the coefficient of performance (COP) of the coupled operation is approximately 9% higher than that of the independent operation.关键词：compression refrigeration cycle;dual-loop coupled;two-stage throttling;refrigerator374|551|0发布时间：2024-07-18
- 摘要：There are many high-temperature heat sources in industrial buildings, and the formed thermal plume has a significant impact on air distribution. In this study, using a new energy battery material production workshop as an example, six air supply speeds and six air supply port heights were used to study the interaction of a multi-heat source heat plume and supply air jet, as well as the effect of the interaction on the thermal environment of an industrial building. The results show that the multi-heat source coupled heat plume is dominated by the high-temperature heat source, the plumes close to each other form a concentrated entrainment space, and the maximum axial velocity is approximately 0.64 m/s. Using a thermal plume to guide the upward movement of air distribution, high-temperature air can be quickly exhausted to effectively improve the thermal environment of the building work area. Reducing the air supply speed can reduce the inhibitory effect on the upstream heat plume. When the air supply speed decreases from 14.80 m/s to 2.96 m/s, the workshop working area temperature decreases from 39.2 °C to 31.6 °C. Reducing the height of the air supply outlet can increase the promotional effect on the upstream heat plume. When the height of the air supply outlet decreases from 5.0 m to 1.7 m, the temperature of the workshop working area decreases from 34.9 °C to 30.3 °C. These results can be helpful for the ventilation design of industrial buildings.关键词：industrial building;thermal plume;supply air jet;interaction;thermal environment370|660|0发布时间：2024-07-18
- 摘要：The cold thermal energy storage characteristics of CO2 hydrates were studied in different mass concentrations of SDS surfactant (0.4, 0.5, and 0.6 g/L), SDBS surfactant (0.2, 0.3, and 0.4 g/L), and compound surfactants (SDS+SDBS) using a vapor compression refrigeration system. Compared with a pure-water system, SDS, SDBS, and compound (SDS+SDBS) surfactants improve the CO2 hydrate cold thermal energy storage performance, and the best concentrations of the surfactants were 0.5 g/L, 0.3 g/L, and 0.5 g/L(SDS)+0.3 g/L(SDBS), respectively. Comparing the cold thermal energy storage performance of SDS, SDBS, and compound (SDS+SDBS) surfactants, the compound surfactant 0.5 g/L(SDS)+0.3 g/L(SDBS) had the best cold thermal energy storage performance: the precooling time (21.51 min) and cold thermal energy storage time (27.56 min) were the shortest. The latent heat storage capacity (1 308.27 kJ), total storage capacity (2 967.35 kJ), average charging rate (1.79 kW), and hydrate formation mass (2.55 kg) were the largest. The findings indicate that the compound surfactant had the most significant effect on the CO2 hydrate cold thermal energy storage characteristics of this system.关键词：vapor compression refrigeration cycle;cold thermal energy storage;CO2 hydrate;compound surfactants414|535|0发布时间：2024-07-18
- 摘要：Natural evaporation of microdroplets was studied as a new method for the addition of cryoprotectants. The effects of the initial volume and concentration on cell permeation characteristics and damage during cryoprotectant loading by natural evaporation of microdroplets were investigated systematically using image processing techniques. Combined with theoretical analysis of cell permeation and damage models, the results were compared with traditional cryoprotectant loading methods (one-step and two-step loading). The results show that, the faster the evaporation rate, the easier it was for the cryoprotectant to achieve the required concentration, which could reduce the loading time (by 4907 s for 1 μL compared with 5 μL).?As the initial concentration of the protectant decreased, the loading time increased gradually (2460 and 1346 s for 0.5 and 2.5 M, respectively); however, the cell volume change caused by extremes was significantly reduced (14% and 43% of the initial volume for 0.5 and 2.5 M, respectively), as was the cumulative toxic damage (23.05 and 47.53 for 0.5 and 2.5 M, respectively). Compared with the usual loading approach, microdroplet loading by natural evaporation considerably enhanced cell survival and proliferation (P< 0.05). Cell survival was 96.73% ± 0.54%, a 16% increase over one-step loading, and cell wall adherence was considerably better at 48 h than that with two-step loading. This innovative technique substantially reduced cell damage while simplifying the cryoprotectant loading process.关键词：cryopreservation;cryoprotectants;droplet evaporation;osmotic injury;toxic damage370|565|0发布时间：2024-07-18
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