最新刊期
卷 39 ， 期 3 ， 2018
- 摘要：This paper proposes an energy consumption diagnosis method and establishes an evaluation model based on data mining technology for evaluating the energy utilization of HVAC systems used in subway stations. First, through a correlation analysis, the key variables that influence the energy consumption of the subway’s HVAC system are determined, namely, the outdoor temperature and passenger flows. Then, according to the selected key variables, different energy utilization modes are generated using a decision tree, after which an energy benchmark is established on the basis of the energy consumption models. Finally, an energy consumption diagnosis method based on the energy benchmark of different energy utilization modes is applied to actual data of an HVAC system. The results of energy consumption diagnosis show that the energy levels can be influenced by the changes in the environment and passenger flow, but still conform to the energy benchmark. This energy consumption diagnosis method can diagnose the conditions of energy utilization and recognize modes of abnormal or low energy consumption, which can optimize energy utilization and provide a theoretical basis and practical reference for energy savings at a single subway station.关键词：data mining;HVAC system in subway stations;energy consumption diagnosis;energy rating;optimization and energy saving2309|2616|0发布时间：2024-07-18
- 摘要：With respect to solar energy utilization of buildings, a solution chemical energy storage mode is proposed based on membrane distillation technology focusing on the low density of solar radiation distribution and the imbalance between energy supply and demand, the purpose of which is to convert solar energy into solution chemical energy. A hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane with operational characteristics of a normal temperature region and low temperature difference is adopted as the membrane material, and the PVDF membrane material has a highly specific surface area microscopically and a huge contact area per unit volume; as a result, a lithium bromide solution can be concentrated and stored using the vacuum membrane distillation mode, and the concentrated solution can be used as the working medium of the absorption thermal system. Therefore, experimental tests of the vacuum membrane distillation of a lithium bromide solution were carried out under different operating temperatures, solution flow rates, and vacuum degrees. According to the experimental results, a solar-driven solution energy storage system based on membrane distillation is described. The results show that the energy storage intensity can reach 245 kJ/kg, and the hollow fiber module can produce 0.27-0.40 kW of energy storage per square meter. Thus, membrane distillation solution storage provides a new approach to absorption thermodynamic systems and storage technology.关键词：membrane distillation;hollow fiber membrane;solution energy storage;solar energy2026|2473|0发布时间：2024-07-18
- 摘要：The huge amount of energy consumed in data centers has prompted researchers to continue studying how to improve their energy efficiency, and according to a US Environmental Protection Agency report, the energy consumption in data centers is doubling every five years; in contrast, the energy consumption in data centers in China have a growth rate significantly higher than the average level globally. Improving the efficiency of the refrigeration system and optimizing the data center airflow pattern will minimize the energy consumption. This paper is the second part of an investigation aiming to find a more satisfying airflow pattern in a data center and to help provide servers with a safer and more reliable operating environment. Based on the simulation described in Part I, the optimal model, including six groups of duct structures, is verified. The odd-numbered sub-modules of the data center were taken as the measured objects, changing the perforation rate of the floor, and the angle of the baffle, to obtain the six groups of reasonable airflow patterns. A comparison of the two key parameters of the front door air supply, namely, the speed and temperature, proves the reliability of the simulated airflow. The maximum relative deviation between the measured and simulated velocity is 17%, and the maximum relative deviation of temperature is 5%, which shows that the simulated temperature and velocity fields are in agreement with the measurement. Concerning the data center heat flux density and energy consumption, the air supply conditions of the cooling system are changed to achieve a comparative analysis of the temperature field under various working conditions. The return air temperature index (RTI) is employed as an evaluation indicator to find that the recommended air supply temperature range, which is 16–19 ℃. The results of this investigation can provide reference for the design of a data center using an under-floor air distribution.关键词：data center;air duct layout;experimental verification;air-supply temperature;return temperature index(RTI)2105|2615|0发布时间：2024-07-18
- 摘要：The influences of the geometric parameters of a thermoelectric cooler on its cooling capacity and COP have been previously investigated under assumptions of a constant input current and fixed temperatures of hot/cold ends. However, in this paper, constant external heat exchanging conditions, instead of constant temperatures of hot/cold ends, were assumed, and the influence of each geometric parameter (number of thermo-couples and the ratio of the length of a thermo-element to its cross-sectional area) on the cooling capacity, COP, and cold end temperature were analyzed. The physical implications of each effect are given in detail, revealing the coupling between these parameters. Based on the analyses, in addition to the constraints of the cooling capacity, the COP, and cold end temperature on the selection of the geometry parameters considered, a novel design diagram was developed for choosing the best geometric structure of thermoelectric coolers with a multi-objective constraint. This diagram can obtain the optimal geometry parameters under different requirements both quickly and clearly. For example, under the boundary conditions set in this paper, when the cold end temperature is 280 K and the cooling capacity is 15 W, there is an optimal solution to the geometric parameters. However, when the cold end temperature is 240 K and the cooling capacity is 100 W, there are no geometrical parameters that can satisfy both the cold end temperature and the cooling requirements.关键词：thermoelectric cooling;multi-objective optimization;cold end temperature;geometric parameters2176|3739|2发布时间：2024-07-18
- 摘要：As a natural refrigerant, CO2 has received increasing attention from the international community, particularly in the European market, and domestic demand is also increasing. This study analyzes the key factors influencing the cooling capacity of a CO2 micro-channel evaporator, where a CO2 micro-channel evaporator test bench was built and a superheat adjustment was realized using the CO2 electronic expansion valve. The results show that the CO2 superheat has a greater effect on the cooling capacity of the evaporator than other refrigerants, and the evaporator capacity is considerably improved with a decrease in superheat, the rate of increase can be categorized into three obvious periods with different characteristics. The increase in evaporator capacity described in this study can reach up to 57.9%. In addition, thermocouples and infrared thermal imaging were used to obtain the distribution of outlet air temperatures, where the outlet air temperatures achieve better uniformity with a decrease in superheat.关键词：micro-channel evaporator;superheat;natural refrigerant;CO22281|2767|1发布时间：2024-07-18
- 摘要：A variable diameter capillary tube consisting of two serially connected capillary tubes with different diameters was invented to replace a conventional expansion device. The mass flow rates of refrigerant R410A in variable diameter capillary tubes with various sizes were tested. A model of the variable diameter capillary tube is proposed, and a numerical algorithm for the tube length and mass flow rate is developed. The experimental results show that, in a performance comparison between a variable diameter capillary tube system and a capillary tube assembly system, the cooling capacity of the former is reduced by 0.3%, their energy efficiency ratio (EER) is equal, the heating capacity is increased by 0.3%, and the coefficient of performance (COP) is decreased by 0.3%. That is, the performance index of the two kinds of throttle mechanism is almost identical. This indicates that the variable diameter capillary tube can completely replace the capillary tube assembly in an R410A heat pump type air conditioner. The model is validated using experimental data, and the results show that the model can be used for sizing and rating a variable diameter capillary tube.关键词：variable diameter;capillary tube;air conditioner;flow characteristic;R410A2196|2566|1发布时间：2024-07-18
- 摘要：Experiments were carried out to investigate the saturated flow boiling heat transfer and visualize the two-phase flow patterns for deionized water in a micro-pin-fin heat sink with cylindrical fins with a height of 500 μm and diameter of 500 μm. The test parameters were as follows: a mass flow rate G = 341–598.3 kg/(m2?s), heat flux q = 20–160 W/cm2, and steam dryness X = 0–0.2. The results show that the local boiling surface heat transfer coefficient decreases monotonously with an increase in heat flux. The heat transfer coefficient of the local boiling surface increases with the increase in the mass flow rate, and decreases with an increase in steam dryness within a low dryness region. With the influence of sub-cooled boiling bubbles, the lower the working fluid inlet temperature, the greater the local boiling surface heat transfer coefficient. The flow pattern of bubbling in the micro-channels shows a bubbly flow and an annular flow with an increase in the heat flux density. The local boiling surface heat transfer coefficient of a bubbly flow is significantly higher than that of an annular flow.关键词：micro-pin fins;saturate flow boiling;two-phase flow;visualization;boiling surface heat transfer coefficient1906|2171|9发布时间：2024-07-18
- 摘要：The effect of the temperature of the calibration tank, face velocity, and circulation rate on the performance of a CO2 air-cooler are analyzed using theoretical calculation and experimental study. The theoretical calculation is carried out by establishing a mathematical model, the results of which show that when the temperature of the calibration tank increases from ?30℃ to ?10℃, the coefficient of the heat transfer increases by 5.8%, and the corresponding refrigerating capacity increases by 5.9%. Under the calculation conditions, the best face velocity (3.2 m/s) occurs, providing the best air-cooler performance; in addition, the coefficient of heat transfer of the air-cooler increases rapidly with an increase in the circulation rate, and the growth tends to be smooth, with the best circulation rate at about three. Comparing the experimental value with the theoretical calculation of the CO2 air-cooler, the results show that the theoretical calculation is higher, the error of which is between 14.8% and 25%; however, the trends between the theoretical calculation and the experimental value are basically the same, verifying the rationality of the mathematical model.关键词：CO2 air-cooler;refrigeration capacity;coefficient of heat transfer;circulation rate2149|2641|1发布时间：2024-07-18
- 摘要：To model the electrical efficiency of a compressor that can apply a suction refrigerant state under both superheated and two-phase conditions, the performance of an R32 variable frequency rotary compressor, which varies with the compressor frequency, pressure ratio, and evaporating temperature, is analyzed in this paper. The results show that when the system is at a fixed pressure ratio and evaporating temperature, the electrical efficiency linearly decreases with the declining superheated temperature and an increase in suction vapor quality. Moreover, the slope under two-phase suction is above that under superheated suction. In addition, the electrical efficiency of the system at a fixed pressure ratio is inversely proportional to the evaporating temperature, and that of the system at a fixed evaporating temperature is also inversely proportional to the pressure ratio. The more the pressure ratio varies, the smaller the influence of the evaporating temperature. To demonstrate the precision of the model, the theoretical value is compared with the experiment results in this paper. The maximum of relative error is 1.83%, and the minimum is 0.03%. The performance of a compressor at low frequency will deteriorate, which leads to the inaccuracy of the model, and therefore the model is suitable for operating conditions with a frequency higher than the rated frequency and a suction vapor quality higher than 0.88.关键词：variable frequency compressor;electrical efficiency;modeling;two phase2053|2457|2发布时间：2024-07-18
- 摘要：This paper summarizes the energy efficiency standards of air conditioning and heat pumps in China. The relationships between seasonal energy efficiency ratio (SEER), integrated part load value (IPLV), and annual performance factor (APF) are expounded. The development process of energy efficiency (grade) standards is analyzed. The air-cooled air-conditioning and heat pump change from single operating conditions using the energy efficiency ratio (EER) or coefficient of performance (COP), to a SEER and heating season performance factor (HSPF), whereas the water-cooled air-conditioning and heat pump change from single operating conditions using COP to an integrated part load value. This paper puts forward the three-stage IPLV(H) recommended value of a low ambient temperature air-source heat pump. The current situation and problems in the energy efficiency standards are pointed out. For example, theoretical knowledge needs be strengthened, the evaluation indicators are not unified, some of the energy efficiency standards are deficient, and other energy efficiency standards do not correspond to the product standards. A direction for the energy efficiency standards is also suggested.关键词：air conditioning and heat pump;energy efficiency standards;energy efficiency standards grade;performance index;existing problems2671|4935|3发布时间：2024-07-18
- 摘要：In this paper, the effects of a refrigerant charge on the system performance of a heat pump water heater and the regulating characteristics of the electronic expansion valve were studied experimentally. The system performance under different regulation modes of electronic expansion valve was also quantitatively analyzed. The experimental results show that 1.1 kg is the best refrigerant charge when the valve opening is 16% and the superheat temperature is 10 ℃. The corresponding maximum coefficient of performance (COPa) was 3.05 and 3.68, respectively. Excessive refrigerant charge reduces the system performance and the adjustment range of electronic expansion valve. To avoid the liquid suction of compressor, the adjustment of superheated temperature is better than that of valve opening. The system performances of the two regulating modes are compared under the optimum refrigerant charge, and the results show that the superheat regulation method is the best.关键词：air-source heat pump;variable refrigerant mass flow rate;coefficient of performance;electronic expansion valve;degree of superheat2204|2509|3发布时间：2024-07-18
- 摘要：To solve the problem of low energy efficiency and driving mileage reduction when pure electrical vehicles are heated using electric heating, two kinds of heat-pump air-conditioning system, i.e., with four-way valve and four magnetic valves, were designed, and performance and reliability were investigated experimentally. The charge amount of refrigerant in the two systems was scientifically determined based on the subcooled temperature and refrigerating capacity, and was 500 g and 700 g, respectively. The results show that the refrigerating capacity and heating capacity under normal conditions can reach 2 kW in both heat-pump air-conditioning systems. In addition, the heating capacity under low-temperature conditions drops to 800 W in both heat-pump air-conditioning systems, and the four-way valve causes a phenomenon called “gas bypass” under a vibration condition of 3 g @ 33 Hz, which easily leads to instability of the system, even damage to the compressor; however, the heat-pump air-conditioning system using four magnetic valves works steadily under the same vibration conditions.关键词：electrical vehicle;heat pump system;refrigerating capacity;heating capacity;experimental study2081|2865|5发布时间：2024-07-18
- 摘要：The temperature and humidity control processes in a variable-speed direct-expansion air-conditioning (DX A/C) system are significantly coupled, which makes it difficult to realize the precise control of indoor air temperature and humidity simultaneously when traditional methods are used. Based on a fuzzy proportional-derivative (PD) control logic and steady-state artificial neural network (ANN) model, a novel temperature and humidity simultaneous control strategy was developed in this study. This control strategy uses the updating temperature and humidity errors to calculate the actually required control signals, the compressor, and the fan speeds to achieve simultaneous control of the temperature and humidity. Controllability tests were carried out to examine the performances of the novel controller including command following tests and disturbance rejection tests. The command following test results showed that the air dry-bulb and wet-bulb temperatures can be controlled to their new set points within 720 s with an oscillation of no more than ± 0.2 ℃ after the set points are changed. The disturbance rejection test results showed that, when a disturbance is introduced into the cooling load, the controller can respond immediately if the temperature differences between the set points and the present values reach 0.5 ℃ and maintain the dry-bulb and wet-bulb temperatures at their set points within 600 s, with a moderate oscillation of ± 0.2 ℃. Thus, the experimental results suggest that the novel control strategy established in this study can realize the simultaneous control of the indoor air temperature and humidity using a variable-speed DX A/C system.关键词：air conditioning system;artificial neural network(ANN);fuzzy PD;simultaneous control of temperature and humidity1988|2779|0发布时间：2024-07-18
- 摘要：A regenerator has a significant influence on the energy efficiency of a liquid desiccant system. A conventional packed regenerator has a low specific surface area, which leads to the huge size of the equipment. An ultrasonic atomization method can greatly increase the specific surface area of a regenerator through atomizing the liquid desiccant into micron droplets, which will certainly reduce the equipment size. For the sake of development of ultrasonic atomization regeneration technology, this paper describes a theoretical study conducted on an ultrasound-atomizing regenerator. A model for the ultrasound-atomizing regenerator was established based on some necessary assumptions, and the model was validated experimentally. An index of specific energy consumption (SEC) is also suggested, and the model is used to investigate the energy consumption characteristics of an ultrasound-atomizing regenerator under different regeneration conditions, including the inlet solution temperature and concentration, as well as the inlet regeneration air temperature and humidity. The following conclusions can be drawn from this study: 1) A lower solution temperature is beneficial to improving the efficiency of an ultrasound-atomizing regenerator, but it should satisfy the practical application requirements of liquid desiccant after the regeneration. 2) The SEC of the regeneration of the liquid desiccant shows a clear increase with an increase in the inlet solution concentration. The SEC increases by nearly 40% as the solution concentration increases from 0.28 to 0.33. 3) A higher regeneration air temperature will lead to lower energy efficiency. The SEC of the solution regeneration increases from 3.263 to 4.629 kJ/g as the regeneration air temperature increases from 30 to 41 ℃ under the conditions applied in this study. 4) The higher regeneration air humidity will lead to higher energy consumption. Under the simulation conditions described herein, the SEC of the solution regeneration increases from 3.23 to 10.56 kJ/g as the regeneration air humidity increases from 10 to 28 g/kg (dry air).关键词：liquid desiccant;regenerator;ultrasonic atomization;specific energy consumption (SEC)2082|2440|0发布时间：2024-07-18
- 摘要：An artificial environment laboratory provides test conditions specified in the national standards for air conditioning and refrigeration equipment; the more uniform and stable the flow field are and the smaller the change in gradient around the test sample under the working conditions is, the lower the uncertainty in the performance test results is. Specifically, the internal flow field achieved in a laboratory is closely related to the air outlet of the pipelines used in the lab. In this paper, the outlet speeds of a square duct (control group), and air supply ducts with 30?, 45?, and 60? slopes, are analyzed and compared with an air supply duct with a continuous slope at a constant height and an air supply duct with a continuous slope under a constant air volume. Further, the calculated results are verified experimentally, and the maximum relative error of the measured and calculated results is 16.35%. The results show that the approximate calculation method has a noticeable value when designing an artificial environment laboratory, and the air velocity in the supply air duct is recommended to be within 2–6 m/s. Finally, a comprehensive index, i.e., the uniformity index/ventilation efficiency (drop) index, is put forward to evaluate the performance of supply air duct in this investigation. It is shown that an air supply duct with a 60? slope works best based on the comprehensive evaluation index.关键词：artificial environment laboratory;airflow configuration;approximate calculation;experimental verification;evaluation index2234|2456|0发布时间：2024-07-18
- 摘要：According to the characteristics of high temperature and humidity in a basement, a variable air volume (VAV), constant temperature and humidity unit was manufactured and investigated experimentally. Two sets of experiments were carried out on a prototype, namely, a unit performance test and an operation test, to simulate the thermal environment of a basement. An intelligent load simulator was designed to generate the required sensible and latent load, and the independent handling capacity to sensible and latent load and operation characteristics of the unit were studied. The results show that the sensible heat and latent heat handling capacity of the unit can be regulated based on the variable air volume, and the heat and moisture can be processed almost independently with an error of about 5%. The unit can operate under fixed sensible heat and a change latent heat, or fixed latent heat and a change sensible heat. The room temperature and humidity can be controlled very well with a temperature fluctuation ±0.2 ℃ and a relative humidity fluctuation ±3%.关键词：constant temperature and humidity air conditioner;cascade control;VAV operation;condensation heat recovery;performance test2006|2246|0发布时间：2024-07-18
- 摘要：Two kinds of binary composite phase change materials (PCMs) were prepared using a melt blending method with myristic acid (MA) and cetyl alcohol (HD) as the raw materials. The eutectic temperature and latent heat in phase change were tested using DSC, and they are 35.5 ℃ and 218.23 kJ/kg, respectively. After 300 thermal cycles applied during the experiment, the results show that the MA-HD eutectic temperature in phase change undergoes a change of less than 0.2 ℃. This indicates that the thermal stability of the MA-HD binary composite phase change material is good. A high-low temperature box within a temperature range of 18–58 ℃ was used to simulate the outdoor temperature during the summer. The temperature response for a PCM-filled window and a hollow window was tested. The experimental results show that the temperatures of the outer and inner surface of PCM-filled window are 5.9 ℃ and 0.6 ℃ lower than those of a hollow window, respectively. The surface temperatures of the PCM-filled window remain constant for 100 min, and the effects of the temperature control are good, which shows that the PCM-filled window has a good load transfer capability.关键词：phase change materials;PCM-filled window;heat load;test conditions;heat transfer1929|2814|1发布时间：2024-07-18
- 摘要：Based on the basic rules of the flow process, a set of dimensional correction coefficients is introduced according to the design method of the liquid–liquid ejector. The optimum correction coefficient is determined using an experimental verification method, and the design method of the liquid–liquid ejector in the jet refrigeration cycle is proposed. Experiments using R22 as a refrigerant, a two-phase ejector, and a full-liquid ejector replacing the dry evaporator in a traditional compression refrigeration cycle were conducted to achieve a jet refrigeration cycle. Labview8.5 was applied as the real-time data collector. Through a data analysis, it was found that the injection coefficient of the injector is the highest when the correction value is δ = 0.95, and then drops. When the operating conditions of the injector are a working pressure of 0.95 MPa, ejecting pressure of 0.45 MPa, mixing pressure of 0.5 MPa, and correction coefficient of δ = 0.95, the working conditions of each measuring point are in accordance with the design conditions, and the error between the measured value of the injection coefficient and the empirical formula is less than 3%, proving that the design method for this dimension is feasible.关键词：ejector;experimental investigation;two-phase flow;design method2130|2983|1发布时间：2024-07-18
- 摘要：One of the important challenges in developing successful cryopreservation protocols for biological samples relies on avoiding the freezing damage imposed by the intracellular ice formation (IIF). Experimental studies have shown that the formation of a traceable quantity of IIF is lethal. This complex phenomenon is affected by various factors including the cooling rate, water transport, cell membrane integrity, extracellular ice, and cryoprotectant. The main goal of this work is to review the four classical intracellular ice formation theories that have been previously proposed: 1) external ice grows through pores in the cell membrane and catalyzes the IIF, 2) external ice causes a conformational change in the cell membrane, transforming it into an effective heterogeneous form and causing IIF, 3）the IIF is catalyzed heterogeneously through intracellular structures or homogeneously, and 4) the IIF is a result of plasma membrane damage. The latest experimental observations support the idea that the contact between the external ice and cell membrane leads directly or indirectly to the formation of intracellular ice. Aquaporins are likely a key factor affecting the IIF. The use of an aquaporin inhibitor and a gene knockout to study the IIF is also proposed in this article.关键词：cryopreservation;cryoinjury;intracellular ice;ice nucleation;aquaporin2105|2691|6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