最新刊期
卷 36 ， 期 3 ， 2015
- 摘要：Microfin tubes widely used in the refrigeration and air conditioning play an important role in enhancing the condensation and evaporation heat transfer. Experimental research and empirical correlations of flow boiling heat transfer in microfin tubes was reviewed based on the published papers. Effects of mass flow rate, heat flux, vapor quality, tube construction and lubricants on heat transfer coefficients and pressure drops were showed through analyzing the experimental results in previous studies. The applicability and accuracy of boiling heat transfer correlations in microfin tubes are discussed in the paper. Moreover, further research work for boiling heat transfer is proposed.14158|13831|0发布时间：2024-07-18
- 摘要：Over the past few years, more attention have been paid to the new low GWP refrigerant R1234ze(E), as a kind of ideal alternative of R134a. But, thermodynamic property and transfer characteristic are not good enough. To achieve better thermodynamic performance, mixtures of R1234ze(E)/R32 was carried out. The recent development on thermodynamic, transfer characteristic and drop-in experiments of R1234ze(E) and R1234ze(E)/R32 mixtures are introduced and compared with some common used refrigerants in the present paper. It is shown that R1234ze(E) and R32 mixtures is expected to be the new low GWP value refrigerants in the future.关键词：R1234ze(E);mixed refrigerants;thermo-physical property;heat transfer;refrigerants alternative3900|2879|10发布时间：2024-07-18
- 摘要：The long-term performance of heat exchangers in air conditioners degrades gradually as the increase of operation duration, which leads to the decline of cooling and heating capacity of air conditioner system. This paper is devoted to present the research status on long-term performance of heat exchangers in air conditioners, and focuses on factors such as dust deposition, corrosion, intermittent operation condition and bio-fouling. Research problems and direction of long-term performance of heat exchangers in air conditioners are pointed out.关键词：heat exchanger;long-term performance;dust;corrosion;intermittent operation condition;bio-fouling2835|2530|10发布时间：2024-07-18
- 摘要：In order to improve the superheat control precision of the variable capacity refrigeration system, and establish the simple superheat control method, an intelligent superheat control strategy based on the traditional PID control strategy was proposed, with various influencing factors considered. The actual superheat control effect of the intelligent control strategy was checked in a cold store with constant temperature and humidity, and was compared with the control effect of thermostatic expansion valve. The experimental results show that: the intelligent control strategy gives a better performance such as faster dynamic response, lower overshoot, and shorter oscillation time compared with traditional PID control strategy. It is advantageous to superheat stability, if the compressor frequency changes as the interference factors are inputted in advance. The intelligent control strategy is better than the thermal expansion valve on the superheat control effect, and the cold store cooling time is shortened by 37.14%.关键词：variable refrigerant flow rate;intelligent superheat control strategy;PID control;cold store2637|2383|4发布时间：2024-07-18
- 摘要：Cutting down the energy consumption of air conditioners in data centers is an urgent need for realizing emission control targets. Thermosyphon (heat pipe) free cooling is one of the effective methods. To solve the need of mechanical refrigeration in hot seasons and improve the energy-saving rate of thermosyphon free cooling, a new type integrated system of mechanical refrigeration and thermosyphon is proposed. A three-fluid heat exchanger is used to connect the mechanical refrigeration loop and thermosyphon loop, achieving the simultaneous work of refrigeration and thermosyphon and avoiding the risk brought by solenoid valve. The performance of the system is tested in an enthalpy difference lab. The results show that the best filling ratio is 100%. The three working modes all have sufficient cooling capacity. The EER of thermosyphon mode reaches 20.8 when the indoor and outdoor temperature difference is 20 ℃. The simulation results of a data center in Jinan show that the new system saves 40% energy of a year compared to traditional ones and have great application potential.关键词：computer room;air conditioner;thermosyphon;mechanical refrigeration;integrated system3271|2871|13发布时间：2024-07-18
- 摘要：In order to research the effect of the gravity on the critical heat flux of flow boiling, a two-phase boiling heat transfer test system was established. Using distilled water as the working fluid medium, the characteristics of fluid critical heat flux and flow resistance in narrow channel under different heating orientations were investigated through changing mass velocity, inlet subcooling and heating orientation. Their effects on the critical heat flux of flow boiling were analyzed. The results show that the maximum critical heat flux appears at the orientation angel of 0° and the minimum at 180°. The increases of mass velocity and inlet subcooling will increase the critical heat flux. The experimental data were compared with the calculated values based on the correlations of Ivey-Morris, Sudo and Wojtan, respectively, which shows that Sudo correlation was not suitable to the present experiment conditions. The predicting values with Ivey-Morris correlation and Wojtan correlation agree well with the experimental data as the orientation angel is at 0°, and the relative deviation is within 30%. However the predicting values are greater than the experimental data under other orientations.关键词：flow boiling;critical heat flux;heating orientation;narrow channel;empiric correlation13750|14778|2发布时间：2024-07-18
- 摘要：Compared with the conventional adsorption refrigeration cycle, resorption refrigeration cycle as a new cooling method has simpler structure and higher COP under the same operation condition. Therefore it has a good prospect. However, performance of the system is still greatly influenced by different adsorbents, temperature and pressure for adsorption. In this research, adsorbent with the matrix of expanded natural graphite treated with sulfuric acid is developed to study its thermal conductivity and permeability as well as select the superior one. Based on the basic physical properties of the adsorbent and refrigerant, simulation of whole resorption refrigeration process is set up to obtain the performance parameters under different conditions. According to the simulation results, the highest COP is more than 0.3 while the best SCP is 161 W/kg.关键词：adsorption refrigeration cycle;expanded natural graphite treated with sulfuric acid;coefficient of performance;simulation3052|2617|2发布时间：2024-07-18
- 摘要：The energy consumption pattern and operation strategy of a combined cooling, heating and power generation (CCHP) system at a thermal power plant in Shanghai was introduced and the heat-to-electric ratio in all seasons were analyzed. The operation of the plant was optimized by evaluating the environmental and economic benefits by comparing CCHP to the system that separates cooling, heating and power generation. The results shown that, to generate the same amount of steam, the coal consumption could be reduced by 3.94 % by using the CCHP system compared to the independent system. The NOx and SO2 emissions could also be reduced by 0.1 t and 7.1 t, respectively. Furthermore, theoretically speaking, the coal consumption could be reduced by 23% and 11% in summer and transition season, respectively, after optimizing the operation of the plant.关键词：CCHP;energy consumption;operational data;operation strategies and optimization2608|2387|1发布时间：2024-07-18
- 摘要：New HFO refrigerants, R32 and their mixtures have been developed and interested by air conditioner industries for their low GWP. In this paper, R410A was chosen to compare the performance with its potential replacements R32 and R447A. The RAC capacity, energy efficiency and discharge temperature were tested while changing the compressor speed, outdoor temperature. It was found that both R32 and R447A had better efficiency than R410A. Moreover, R32 has largest cooling capacity and also highest discharge temperature, and R447A had potential advantages for high ambient temperatures and high compressor speed conditions.关键词：refrigerant;room air conditioner;refrigeration performance test;replacement2900|2822|1发布时间：2024-07-18
- 摘要：A modular computation method for predicting the flow distribution characteristics in duct system of indirect cooling refrigerator was presented. Firstly, the air duct is divided into several modules according to the position; secondly, the characteristics of air duct resistance and flow rate for each module is obtained; thirdly, the modules are connected into a network according to the actual series or parallel connections of air duct; finally, the flow distribution characteristics is obtained by solving the air duct resistance and flow rate equations. The model was experimentally verified, and the result shows that the deviation of the air flow rate between modular computation method and experiment is within 5%. The modular computation method has the advantages of high accuracy, convenience for modeling and solving, generalization. It is capable to be applied in indirect cooling refrigerator design.关键词：indirect cooling refrigerator;air duct;flow distribution characteristics;modular3162|2803|2发布时间：2024-07-18
- 摘要：In order to test the heat transfer performance of horizontal doubly-enhanced tubes, a new method called water-ring method was put forward. The basic process was that the annulus side correlation of the smooth heat transfer tube wrapping copper wire spirally was firstly obtained by a series of experiments in the self-designed annular tubes test bench. Then the convective heat transfer resistance of the doubly-enhanced tube with the same form of copper wire could be separated from the total thermal resistance to fit out the heat transfer correlations of the inside tube. The condensation surface heat transfer coefficients of refrigerant R123 and the convection surface heat transfer coefficients of water were measured by using the correlations. The experimental study and theoretical analysis shows that the result using water-ring method is more accurate than the normal thermal resistance separation method.关键词：doubly-enhanced tubes;heat transfer coefficients;R123;experimental investigation2518|2400|0发布时间：2024-07-18
- 摘要：In order to apply the user defined compressor model to the air-conditioner system simulation software and to protect the product data, a product-data interactive theoretical model of variable-speed compressor is developed. The model transforms the compressor theoretical model to the form that can be fitted directly by the product data. The linear mass flow rate equation is derived by linearizing the frequency item in the theoretical model using interpolation method, and the non-linear power equation is solved by least error method. For security concerns, the product data is defined as private functions with corresponding interface functions, and then packaged by the dynamic link library. The results show that the developed model is capable of predicting compressor performance, and the maximum error is less than ±5%. The developed compressor model can be applied to system simulation and the product data is well protected.关键词：variable-speed compressor;linearization;model;system simulation;product data2501|2387|1发布时间：2024-07-18
- 摘要：Based on the climate characteristics of the Yangtze River in China and the disadvantages of radiation air conditioning, an energy-saving and temperature-controlled fresh air dehumidifier of radiation air conditioning was designed to remove fresh air load and latent heat load, which would enhance the indoor thermal comfort and energy efficiency combined with radiation air conditioning system. To meet the dehumidification and temperature control demand of fresh air in different seasons，three operating control modes were presented. The running performance and dehumidification performance in summer and transition seasons of the design dehumidifier was tested in standard enthalpy difference laboratory. With the change of outdoor dry bulb temperature ,the suction and exhaust pressure and temperature of compressor, the dry-bulb temperature and wet-bulb temperature in indoor side, the moisture content in indoor and outdoor side, the unit’s dehumidification capacity were tested. Results showed that in summer the dehumidification capacity ranged from 1.34 kg/h to 2.23 kg/h while in transition season, under the dehumidifying it was 2.19 kg/h to 10.2 kg/h for model A, and 0.37 kg/h to 0.9 kg/h for model B，which meet the dehumidification requirements of general residential building with radiation air conditioning.关键词：HV∾radiation air-conditioning;dehumidifier;performance experiment;dehumidification and temperature control2697|2808|4发布时间：2024-07-18
- 摘要：A new type of double-flow accumulator was developed, which can automatically adjust the amount of circulating refrigerant on the system of multi-functional air-conditioning/hot-water heater so that the system was more stable and efficient under multi-working modes. Based on the principle of maximum COP , the optimal refrigerant charge of the variable refrigerant flow rate system was determined by experiment for the modes of refrigeration only and both refrigeration and hot water in the summer. The tested results showed the optimal amounts of charge for the two modes were 6.5 kg and 7.5 kg respectively, and its maximum COP were 3.80 and 5.88 respectively when the outdoor temperature was 32 ± 1℃. When the refrigerant charge changes, by controlling the throttle valve, the COP could be close to the case with the optimal refrigerant charge. Moreover, a series of performance parameters, such as COP, the refrigerating capacity, the degree of subcooling and superheat at optimal refrigerant charge, were investigated with the opening degree of the throttle valve. The results show that when refrigerant charge is the same, the COP and the refrigerating capacity of both refrigeration and hot water mode is bigger compared with refrigeration only mode. Experimental results also show that the double throttling accumulator plays an important role in regulating the refrigerant cycle and saving energy.关键词：variable refrigerant flow rate;throttle valve;energy efficiency ratio;double-flow accumulator;heat pump water heater2918|2817|4发布时间：2024-07-18
- 摘要：In this paper, an experimental investigation is conducted on the heat transfer performance of evaporative condenser with parallel flow and counter flow. An experimental platform which test heat transfer performance of evaporative condenser is built, which can present theoretical and experimental study on the influence of condenser’s spray density and face velocity under the condition of parallel flow and counter flow. The results showed that: the total heat transfer increases with the increase of face velocity and spray density under the condition of parallel flow and counter flow, and finally reaches a maximum value; the heat transfer performance under the condition of counter flow is better than that of parallel flow. When the face velocity and spray density are 3.28 m/s and 0.057 kg/(m?s)respectively, the maximum value of total heat transfer is 616 W/(m2?K) for parallel flow, and 628 W/(m2?K) for counter flow. At the same condition, the mass transfer coefficient and EER of counter flow is better than that of parallel flow.关键词：evaporative condensers;parallel flow;counter flow;performance9371|5138|4发布时间：2024-07-18
- 摘要：The thermal expansion caused by the growth of ice crystals is the main reason for low-temperature fracture of articular cartilage. With non-isothermal DSC method，this article investigated the thermodynamics and crystallization kinetics parameters of the pig cartilage.The results for four kinds of cryoprotectants were analyzed by the modified Avrami kinetic equations. It shows that the crystallization peak of the cartilage becomes wider with increasing cooling rate which lead to an incomplete crystallization; freezing from 0 ℃ to ﹣60 ℃，the value of Avrami is 4.156 when only 4.5 mol/L 1, 2 - propanedio is added. The crystallization would exhibit three - dimensional spherical growth on heterogeneous nuclei and contribute best protective effect compared to other cryoprotectants. While different effects of cooling rate on crystallization and thermal expansion also suggest that low temperature injury is not only determined by the growth of ice crystals，but also affected by the buffering of extracellular matrix.关键词：articular cartilage;DSC thermo analysis;cryoprotectant;crystallization kinetics2823|2628|0发布时间：2024-07-18
- 摘要：In this paper, the discharging performance of phase change thermal storage system recovering the condensation heat of heat pump air-conditioning system was experimentally investigated. Variation of outlet temperature of the hot water and paraffin in the heat storage tank were respectively tested under different inlet temperature of cold water and different water flowrate. The experiment results show that the solidification process of paraffin is less affected by the water flowrate. When the water flowrate or the temperature of cold water is increased, the time of getting hot water will be shortened to some degree, however, the energy consumption will increase. When the initial temperature of paraffin is raised, the rate of releasing sensible heat of paraffin becomes faster and the time of getting hot water will be shortened. The improvement of efficiency of the thermal storage system is significant for the recycling and utilization of the condensation heat.关键词：discharging process;phase change thermal storage;phase change material;experimental study2651|2643|4发布时间：2024-07-18
- 摘要：In order to study the heat pump low temperature drying characteristics of biological material, the tenebrio molitors, as drying materials, was dried with heat pump under the conditions of different air temperatures, air velocities and blanching time. The drying characteristics of tenebrio molitors were studied and the drying processing was correlated by typical drying model. The results show that the drying process of tenebrio molitor could be divided into three stages, i.e., acceleration drying period, constant-rate drying period and falling rate drying period. The drying time can be shortened with the increasing of air temperature, air velocity and blanching time. An optimum model was chosen based on their coefficients of determination R2，root mean square error(RMSE) and sum of squared error(SSE). It is shonw that the Midilli model was superior to others in describing the drying curves of tenebrio molitors, and the R2, RMSE and SEE value respectively were 0.99971, 0.00559 and 0.00104. The experimental data of MR was in agreement with the predicted results of Mildilli model.关键词：heat pump low temperature drying;moisture ratio;drying rate;mathematical model2812|2849|4发布时间：2024-07-18
- 摘要：In order to study the relationship between cryoprotective and its molecular structure, Pyris-diamond DSC was used in the experiment to study the physical properties of seven kinds of cryoprotective agent, including phase transition temperature, the area melting peaks phase, transition enthalpy value and hydration properties. The unfrozen water share of cryoprotectant was calculated by cooling curve of the phase transition temperature and that of the phase transition enthalpy value. We have discovered that there is a positive correlation between the protective effect of cryoprotectant and the linear arrangement of hydroxyl; the more hydroxyl in the linear arrangement, the better protective effect of cryoprotectant. As a result, the protective effect of cryoprotectant adding sorbitol solution is the highest in seven kinds of cryoprotective agent because sorbitol has five hydroxy.关键词：cryopreservation;hydration properties;polyalcohols;hydroxyl2880|2871|3发布时间：2024-07-18
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