最新刊期
卷 39 ， 期 6 ， 2018
- 摘要：Currently, given the rapid development in food industries, food quick-freezing provides high food quality and receives extensive attention. In the review, the principle of food freezing was introduced, and food quality differences between the quick-freezing process and slow-freezing process were compared. Additionally, traditional and new methods of food quick-freezing including pressure assisted freezing, electric assisted freezing, and magnetic assisted freezing were classified to examine the status and development tendency. Furthermore, the emerging methods exhibit immense application prospects from the food quality and energy consumption perspectives. The simplified methods were summarized in the simulation process to optimize the freezing process and guide experimental studies.关键词：quick-freezing;food quality;quick-freezing method;simulation2293|2460|9发布时间：2024-07-18
- 摘要：Fin-and-tube heat exchangers are widely used in indoor units of air conditioners. When the indoor unit heat exchanger is served as evaporator, dehumidification may occur on the fin surface and dust particles easily adhere to the wet fin surface, leading to an increase of air flow resistance. In this paper, the particle deposition characteristics on fin-and-tube heat exchangers under dehumidifying conditions and the influence of deposited wet particles on the air-side pressure drop are experimentally studied. The fin types of test samples cover plate fin, wavy fin and louver fin. The range of fin pitch is 1.5-2.2 mm. The results show that the particle deposition amount is determined by the degree of dehumidification, and the particle deposition amount on windward side of fins as well as the air-side pressure drop increase as the amount of condensate droplets and liquid bridges. Louver fin or small fin pitch is more inclined to wet particle deposition as well as the increase of pressure drop and simplifying fin structure or increasing fin pitch is beneficial to wet particle prevention. The air-side pressure drop firstly increased then tended to be stable with the increase of wet particle deposition amount.关键词：fin-and-tube heat exchanger;dehumidifying condition;particle deposition;pressure drop1987|2174|3发布时间：2024-07-18
- 摘要：In the study, we focused on the vapor-liquid equilibrium property of the ternary system of R32+R161+R1234yf. The vapor–liquid equilibrium data was measured via a liquid-circulation apparatus at temperatures from 283.15 K to 323.15 K. The standard uncertainties of temperature, pressure, and mole fractions were 10 mK, 0.5 kPa, and 0.005, respectively. The Peng–Robinson–Stryjek–Vera (PRSV) equation of state (EOS) combined with the Wong–Sandler (WS) mixing rule and non-random two-liquid (NRTL) activity coefficient model were employed to predict the ternary vapor–liquid equilibrium properties by using the parameters of the binary mixture (i.e., R32+R161, R32+R1234yf, and R161+R1234yf). The average absolute deviation of pressure AADp (average absolute deviation) is 0.34%. Additionally, the average absolute deviation of vapor phase mole fractions for R32 (AADy1) and R161 (AADy2) are 0.002 and 0.001, respectively, and thus the predicted values for the ternary system exhibit good agreement with the experimental results.关键词：mixed refrigerants;thermophysical properties;vapor-liquid equilibrium;experimental measurement1943|2263|2发布时间：2024-07-18
- 摘要：In the study, the operation performance of air source heat pump water heater and heat transfer performance of spiral casing condenser were examined by using R417A as a refrigerant. The experimental conditions are as follows: inlet water temperature of the condenser is 20–55 ℃, influent flow rate of the condenser is 0.6–1.0 m3/h, and environmental temperatures are 15 ℃ and 29 ℃. The experimental results indicate that when the water flow is constant, increases in the entrance temperature result in the decrease in the total heat transfer rate and total heat transfer coefficient of performance (COP), the increase in the discharge pressure and input power of the compressor, and the decrease in the heating capacity and heating coefficient of the heat pump water heater. When the condenser entrance water temperature is constant, with increases in the water flow, the total heat transfer rate and the total heat transfer coefficient are increased, discharge pressure and the input power of the compressor are reduced, and heating capacity and heating COP of the heat pump water heater are increased. When the ambient temperature is 29 ℃, total heat transfer, total heat transfer coefficient, exhaust pressure, suction pressure, input power, heating capacity, and heating COP of the condenser exceed those when the ambient temperature is 15 ℃.关键词：heat pump water heater;spiral tube condenser;heat transfer performance1991|2025|0发布时间：2024-07-18
- 摘要：In the study, thermal performances of direct contact condensation refrigeration cycle with R290 were analyzed and compared with conventional one stage compression refrigeration cycle with R290. The following conclusions are obtained. The maximum coefficient of performance and minimum condenser heat load of direct contact condensation refrigeration cycle with R290 are obtained at the optimum condensation temperatures of the main cycle. With the increases in the supercooling degree of the supercooled liquid in the main cycle, the optimum condensation temperature of main cycle is increased，the maximum coefficient of performance is reduced, the minimum condenser heat load is increased, and the refrigerant mass flow rate of evaporator is decreased. When compared with conventional one stage compression refrigeration cycle with R290 in the range of evaporating temperature from ﹣15 ℃ to﹣6 ℃, the coefficient of performance of direct contact condensation refrigeration cycle with R290 is increased by 7.5%–14.9%, refrigerant mass flow rate of evaporator in cold room cooling equipment is reduced by 26.5%–36.7%，and condenser heat load is reduced by 1.5%–3.7%. The results indicate that the direct contact condensation refrigeration cycle with R290 is promising.关键词：R290;direct contact condensation;refrigeration cycle;performance1780|2396|2发布时间：2024-07-18
- 摘要：In the study, the flow condensation heat transfer characteristics of R410A inside a horizontal internal ribbed tube was experimentally investigated, and the influence of hydraulic conditions and structural parameters of a test tube on the refrigerant surface coefficient of heat transfer and pressure drop inside the tube was analyzed. The experimental results indicate that the surface coefficient of heat transfer and pressure drop increase with the increase in the mass velocity and the decrease in the condensation temperature. However, the surface coefficient of heat transfer decreases with the increase in Re of the water flow, and the pressure drop is slightly affected by the Re of the water flow. The surface coefficient of heat transfer under a unit pressure drop was used to evaluate the comprehensive performance of the heat exchanger. The results reveal that it decreases with the increase in the mass velocity, and increases with the increase in the condensation temperature. The experimental data was also compared with the prediction of some classical correlations. For the smooth tube, the correlations obtained by Shah and Thome et al. overestimate the experimental data, and the Thome et al. correlation exhibits the highest prediction accuracy although the correlation obtained by Akers et al. underestimates the experimental data. With respect to the internal ribbed tube, the Cavallini et al. correlation exhibits the highest prediction accuracy, and correlations obtained by Koyama et al. and Miyara et al. underestimate the experimental data.关键词：flow condensation heat transfer;surface coefficient of heat transfer;pressure drop;horizontal internally ribbed tube1902|2299|3发布时间：2024-07-18
- 摘要：A novel transcritical CO2 refrigeration cycle by utilizing zeotropic mixture as working fluid for the mechanical subcooling (MS) cycle is proposed in this study, which can be utilized to subcool the CO2 fluid flowing from the gas cooler. A maximum overall COP is achieved at the optimum discharge pressure and optimum subcooling degree. The results indicate that the maximum overall COP, optimum subcooling degree, and discharge pressure are closely related to the temperature glide. Additionally, the energy efficiency of CO2 refrigeration cycle is improved efficiently and the high pressure is reduced significantly when mixtures with proper temperature glide are used as the refrigerant of MS cycle. When compared with the base CO2 refrigeration cycle, the overall COP is enhanced by 46.53%, and discharge pressure is reduced by 2.758 MPa at an evaporation temperature of ﹣40 ℃ and ambient temperature of 35 ℃ when R32/R152a (40/60) is employed. The overall COP enhancement is significantly linked to the temperature glide. Furthermore, the thermal performance of the overall cycle is more significantly enhanced for hot or warm climate regions or relatively low evaporation temperature applications such as freezing and cold storage.关键词：CO2;zeotrope working fluid;mechanical subcooling;refrigeration cycle;temperature glide1810|2183|2发布时间：2024-07-18
- 摘要：Thermoelectric cooler（TEC）chips do not work in an ideal condition with uniform temperature in engineering applications due to various reasons, which leads to local high-temperature region. A non-uniform temperature distribution was applied to simulate the working condition while a 3D finite element method was used in the numerical analysis of TEC chips in the study. The influences of variations in the working temperature of the hot end（th：20~40 ℃）, maximum temperature difference （θm：5~30 ℃）, and area ratio of hot space （ω：7/16~12/16） on the performance of TEC chips were considered. The results indicate that the relative refrigerating capacity deviation reaches to -8.788%, the relative power deviation reaches to 2.608%, and the relative coefficient of performance (COP) reaches to -10.9%.关键词：thermoelectric refrigerator chip;refrigerating capacity;COP;non-uniform heat dissipation;finite element analysis2036|2175|2发布时间：2024-07-18
- 摘要：Porous substrate materials are essential for desiccant wheels that typically act as the carrier of desiccant. The study investigated the performance of three types of promising porous substrate materials including wood pulp filter paper (WPFP), ceramic fiber paper (CFP), and glass fiber paper (GFP). The elementary properties of the three types of materials were measured via a hot disk, scanning electron microscopy (SEM), mercury injection apparatus, and a micromeritics gas adsorption analyzer (ASAP2460). The materials were repeatedly immersed in JN-30 silica sol to obtain the gluing rate. The dynamic adsorption experiments were conducted at a constant temperature and humidity chamber under high temperature and high humidity conditions to evaluate the gluing adsorption ability while the desorption ability was compared via desorption experiments. The results indicate that a similar influence is induced by increasing the number of gluing times. Unnecessary over-gluing leads to a reduction in the every-time gluing rate and enhanced saturated adsorption quantity. The suggested maximum gluing times corresponds to 5. Furthermore, the hydrophilicity of WPFP leads to a stronger adsorption and desorption capacity when compared with those of CFP and GFP, and the gluing rate of the WPFP exceeds that of the other two candidates. Therefore, the hydrophilicity dominates the gluing rate as opposed to the porosity. Finally, the highest adsorption quantity per unit area and the saturation time of WPFP during the whole process are observed in the adsorption experiment, and this is in good agreement with the LDF model fitting results. Given that the results of the study verify the numerous advantages of the WPFP, it is the most suitable material that can be applied in a desiccant wheel.关键词：dehumidification;porous media;gluing rate;adsorption kinetics1919|2219|2发布时间：2024-07-18
- 摘要：The application of intelligent control technologies and internet technologies to room air conditioning systems is based on the performance monitoring of air-conditioning systems. In the study, the method of real-time monitoring of the performance of room air-conditioning system was proposed. First, temperature measuring points were arranged in the air conditioner, and the temperature and circuit data were transformed into refrigerant state parameters. Subsequently, the mass flow rate of refrigerant was calculated via a semi-empirical compressor model, and the heat exchange of the indoor unit was calculated via the enthalpy difference. Finally, the power was calculated by using circuit data. Thus, the mass flow rate, capacity, power, and energy efficiency were monitored. The test results indicate that the average deviation of the calculated performance obtained by the method in the study is less than 15%. The deviation is mainly attributed to the calculation of evaporating pressure that significantly influences the calculation of the mass flow rate.关键词：refrigerating system;performance monitoring;compression refrigeration cycle;refrigerating capacity1926|1977|0发布时间：2024-07-18
- 摘要：Currently, China’s inverter air conditioner efficiency standard (GB 21455—2013) adopts the annual performance factor (APF) to evaluate heat-pump inverter air conditioner. Specifically, APF of air conditioner is calculated by a single set of running time curves (cooling and heating) nationwide. However, China includes diverse regions and climates. Therefore, in the study, two types of running time curves covering all five architectural thermo-technical design zones were initially obtained by using meteorological statistics and investigation data, respectively. Furthermore, the APFs of nine variable speed air-conditioners were analyzed by the standard method based on running time curves. The results indicate that the regional difference of APF of the variable speed air-conditioner is significant, and the APF difference between southern China and central China ranges to 1.86 based on the investigation data. Finally, regional evaluation of energy efficiency standards was proposed and verified by an example. The results indicate that the seasonal energy efficiency ratio (SEER) and heating seasonal performance factor (HSPF) values of different regions should be considered in addition to the APF value.关键词：variable speed air-conditioner;APF;energy efficiency standards;regional difference;running time curves1812|1960|1发布时间：2024-07-18
- 摘要：In order to improve uneven distribution of the bubbles in the guided bubble pump with multiple tubes in a working process, and enhance the performance of Einstein refrigeration, the performance of an ordinary guided bubble pump with multiple tubes and guided bubble pump with multiple tubes with current equalizer is compared. The experiment is conducted at atmospheric pressure with water as the working fluid, and the number of tubes in guided bubble pump is varied. Experimental results show that in the lifting process of the bubble pump the total lifting capacity increases in amplitude for two kinds of bubble pumps, and large improvement and little improvement appear alternately under low power. However, the elapsed time for little improvement of total lifting capacity is decreased for a bubble pump under high power. When tube number is 3, the diameter is 10 mm with an immersion ratio of 0.5, and a heating power of 450 W, water begins to exit from the outlet tube after 75.2 min. The lifting capacity between large and little improvement appear alternately from 75.2 min to 100.1 min. In addition, the problem of uneven distribution of the bubbles is improved by the tube number multiplication with a current equalizer, such as a diameter of 10 mm and immersion ratio of 0.4. When tube number is 1, the maximum liquid lifting capacity rate is 15.00 g/s in an ordinary guided bubble pump with multiple tubes; when the tube number is 3, maximum liquid lifting capacity rate is 26.50 g/s for the ordinary, but 36.50 g/s for that with current equalizer. Finally, mesh aperture and installation position of current equalizer are found to have a certain influence on the improvement of bubble pump performance.关键词：Einstein refrigeration;bubble pump;current equalizer;experiment research1751|2076|2发布时间：2024-07-18
- 摘要：In the study, a new novel graphene 3D printing rapid freeze forming platform was developed based on the Peltier device. It exhibits advantages including low noise, light weight, high reliability, and compact structure. Experiments were performed on a platform to determine the control strategy. The study on temperature control was conducted via the Fuzzy-PID control method．Six groups of the experimental results indicate that the quick frozen processing platform continuously adjust the temperature between 40 ℃ and 0 ℃, the overshoot volume is within 4.8%. -5, -10, -15, -20, -30, -40 ℃is 4.8%, 3.9%, 3.3%, 2.8%, 2.2% and 0, respectively, and the adjusting time corresponds to 88, 94, 106, 124, 76, and 92 s. The setting temperature near the set value is almost constant. A temperature gradient is absent on the surface of the forming platform. Graphene ink forming with high accuracy satisfies graphene 3D printing requirements.关键词：semiconductor refrigeration;prototyping platform;rapid freeze prototyping;3D printing;graphene1702|2076|0发布时间：2024-07-18
- 摘要：Heat storage technique is important to solar thermal energy utilization. Furthermore, it a key technology that uses water as a thermal storage medium. To improve the performance of water storage tank, a novel equalizer was proposed in the study. Richardson number (Ri), Mixed number (MIX), and filling efficiency (ξ) analysis method were used to analyze thermal characteristics of the novel equalizer under an initial temperature of 70 ℃, an inlet temperature of 10 ℃, and different flow rates (corresponding to 1, 2, 3, 4, 5, and 6 L/min). The performance of water storage tank with the novl equalizer was compared with the water tanks with the direct inlet structure and three-layer orifice structure. The results indicate that with increases in the inlet flow rate, the ξ of the direct inlet structure and the three-layer orifice structure water tank are reduced while the ξ of the equalizer is initially enlarged and subsequently reduced. When the flow rate is 6 L/min, the Ri for the three modes is 6, 4×104, and 4×106; the ξ corresponds to 0.534 93, 0.584 93, and 0.814 05, respectively. The results demonstrate that the proposed equalizer reduces the mixing process and improve the thermal stratification in the heat storage water tank. In addition, the stratification performance of water tank can be effectively evaluated with filling efficiency because it contains the influences of both temperature and flow rate which are the key factors for thermal stratification in a water tank. Therefore, the filling efficiency can be used to analyze the stratified characteristics of water tank quantitatively and qualitatively.关键词：equalizer;thermal stratification;thermal energy storage;fill efficiency1944|2058|1发布时间：2024-07-18
- 摘要：The characteristics of system cycle and cool storage of CO2 Hydrate with an initial charge pressure of 3.5–4.0 MPa were investigated in the direct-contact type cool storage test bench. Based on the experimental data, the p-h diagram of the cycle and cool storage rate under different initial charge pressure were drawn. The experimental results indicate that the system cycle corresponds to a sub-critical cycle when the initial charge pressure is 3.5 MPa or 3.6 MPa. Additionally, the system cycle corresponds to a trans-critical cycle when the initial charge pressures are 3.7, 3.8, 3.9, and 4.0 MPa, and the time in the trans-critical cycle corresponds to 8, 10, 9, and 8 min, respectively, while the proportion of time that the system cycles through the trans-critical region corresponds to 38%, 58%, 60%, and 73% respectively. When the initial charge pressure is increased, the cool storage time is decreased, the decrease of cool storage rate is accelerated, and the cool storage performance is improved.关键词：ice storage tank;compression refrigeration cycle;supercriticality;CO2 hydrate1802|2103|4发布时间：2024-07-18
- 摘要：In the study, a heat pump system with three heat exchangers was applied on an air-conditioning system of an electric vehicle, in which R134a is the refrigerant. The bench of the heat pump system was constructed, and performance were tested in five conditions with respect to cooling and heating, and the effects of compressor speed, air volume, and ambient conditions on the system performance were examined. The tested performances under various operation conditions were used to analyze the feasibility of the system for electric vehicles. The experimental results indicate that when compressor speed corresponds to 3000 r/min at ﹣20 ℃, (1) the coefficient of performance (COP) of the system is approximately 1.5; (2) with the increases in the compressor speed, the COP initially increases and subsequently decreases; (3) the COP of the system increases with increases in the amount of air of the heat exchanger. Thus, the results reveal that the heat pump system saves electricity and improves the cruising range of vehicle mileage.关键词：heat pump system;low temperature heating;refrigerant;electric vehicle2040|2472|9发布时间：2024-07-18
- 摘要：The study took banana as the research object to achieve precise thermal control of freeze-drying process and improve the quality of freeze-dried products. Specifically, the effects of pressure (10, 30, 50 Pa) and freeze-drying temperature (﹣20, ﹣30 ℃) on effective thermal conductivity in the complete banana freeze-drying process were investigated based on the model of steady state heat flux. The sublimation process inside the banana was observed and analyzed by micro-CT scanning, and the relationship between porosity and effective thermal conductivity was also discussed. The results indicate that the effective thermal conductivity increases from 0.036 W/(m?K) to 0.072 W/(m?K) with the increase in the pressure from 10 Pa to 50 Pa. Additionally, the primary drying temperature increases from ﹣30 ℃ to ﹣20 ℃, and the corresponding effective thermal conductivity decreases from 0.084 W/(m?K) to 0.058 W/(m?K). During the freeze-drying process (30 Pa, ﹣20 ℃), the sublimation interface gradually moves to the center of the banana dice, the porosity increases from 0.059 to 0.252, and the corresponding effective thermal conductivity decreases from 0.695 W/(m?K) to 0.123 W/(m?K).关键词：freeze-drying;effective thermal conductivity;vacuum;porosity1812|1956|2发布时间：2024-07-18
- 摘要：Cell cryopreservation provides high quality cells for clinical application and scientific studies. Specifically, 20% (v/v) FBS supplemented with 10% (v/v) DMSO are widely used in cryoprotectants. However, high concentrations of DMSO are cytotoxic to cells, and FBS exhibits problems related to diseases such as bovine spongiform encephalopathy and viral infections. Silk protein is a type of natural macromolecule fiber protein with good biocompatibility. The aim of the study involved testing the effectiveness of the silk protein as cryoprotectant and developing a novel FBS-free and low concentration DMSO freezing medium. Meishan pig ear fibroblast cells were cryopreserved by using a freezing medium in the presence of various mass concentrations of silk sericin and various volume fractions of silk fibroin. The preservation efficiency was evaluated by trypan blue dye exclusion test, MTT assay, and the 24 h adherent rate after thawing. The results indicate that the survival rate of cryopreserved cells does not significantly differ when the cells are cryopreserved with a freezing medium containing 1% (w/v) sericin and 20% (v/v) FBS, and this indicates that sericin can substitute for FBS in the freezing medium. A significant difference is absent between 10% (v/v) fibroin protein with 5% (v/v) DMSO and 10% (v/v) DMSO, and thus the fibroin decreases the concentration of DMSO. Finally, 5% (v/v) DMSO supplemented with 1% (w/v) sericin and 10% (v/v) fibroin exhibit similar results as a control group.关键词：cryoprotective agent;silk protein;FBS-free freezing medium;pig ear fibroblast cells2111|2271|0发布时间：2024-07-18
- 摘要：The dynamic variation characteristics of an onion epidermal cell structure under different cooling rates and the impact of intracellular ice crystal on the cell structure were investigated experimentally. The internal relations between pressure and volume were also discussed. The relationship between the supercooling degree, crystallization time, and cell deformation was analyzed. Additionally, the structural feature of the cells after rewarming was shown. The results indicate that the number of intracellular ice crystals formed is decreased and their size is increased with the decrease in the cooling rate, which result in more mechanical damage of cell. The average gray scale decreases by 27.5% from 2 ℃/min to 15 ℃/min and 37.5% from 2 ℃/min to 90 ℃/min. The volume of the cell decreases with increases in the internal pressure, and the cell collapses at a critical internal pressure. When the cooling rate is 2 ℃/min, the internal pressure is increased by 0.388×10-2 Pa and the volume is decreased by 2.264×10-13 m3 following the freezing–thawing process. The differences in the cooling rates have influence on the supercooling degree, crystallization time, and cell deformation. When the cooling rate is 90 ℃/min, relative volume change in the cell is 1.24% following the freezing–thawing process.关键词：frozen food;intracellular ice crystal;cellular pressure;supercooling degree;freezing point2130|2037|1发布时间：2024-07-18
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