最新刊期
卷 35 ， 期 2 ， 2014
- 摘要：In this paper, heat and mass transfer during the process of ammonia vapor absorbed into the surface of stagnant ammonia-water solution under the condition of large pressure difference was studied. Physical and mathematical models of the absorption process with coupled heat and mass transfer were established. The temperature field, concentration field and the dimensionless number which represents the mass transfer at the interface were developed with constant ammonia vapor pressure. The results indicate that the concentration and temperature at the interface are fixed values which only depend on the initial conditions. By introducing the ammonia-water gas-liquid phase equilibrium equation, the semi-empirical correlation containing criterion number, initial pressure differential and initial parameters of ammonia-water solution was developed. The variation curve between time-averaged mass transfer and the absorption time was obtained. The curve shows that the time-averaged mass transfer is the largest at the beginning of the absorption and drops rapidly as the absorption time increasing.关键词：ammonia-water absorption;heat and mass transfer;mathematical model;mass transfer correlation1851|1904|0发布时间：2024-09-19
- 摘要：Based on the measured data in the cooling season, this research analyzes the impact of the operation strategy of HGSHP (Hybrid Ground Source Heat Pump) system on the performance of heat pump unit and ground heat exchanger. The objective building is a large railway station in East China. And some possible ways of operation strategy to optimize the performance is proposed, then heat transfer characteristics of ground heat exchanger in 10 years under three operation strategies is compared through a system simulation on TRNSYS. It’s concluded that the operation strategy that GSHP is at high priority with nocturnal intermittent for cooling is beneficial to a stable operation of HGSHP system.关键词：hybrid ground source heat pump system;operation strategy;heat transfer characteristics of ground heat exchanger;measured data;system simulation1706|1958|0发布时间：2024-09-19
- 摘要：Auto-cascade refrigeration system is widely used to obtain low temperature environment between -40 ℃ ~ -150 ℃. Double-pipe condenser is commonly regarded for condensing equipment in auto-cascade refrigeration system, its characteristics and structure affects refrigeration equipment system deeply. An auto-cascade refrigeration system with double-pipe condenser as the research object, the condensing process characteristics and structure dimension were studied. At the condensing pressure of 2.0 MPa, the condensing load was 1610W when the mass fraction ratio of R600a and R23 was 7:3. The structure size of double-pipe condenser was 4.842m based on the heat transfer coefficient of mixed refrigerant and cooling water. At the end of the paper the suction temperature, exhaust temperature, evaporation temperature in different condensing water flow, and inlet and outlet temperature of cooling water were analyzed.关键词：auto-cascade refrigeration;mixed refrigerant;condenser design;double-pipe condenser1810|2079|0发布时间：2024-09-19
- 摘要：The widely applications have been achieved for falling film evaporators in the fields of pharmaceutical, chemical, ocean desalinization industries. However, the employment in the refrigeration and air condition was just after 1990. As so far, the researches for falling film evaporator were mainly focused on figuring out the influence of the parameters, as well as the coupling among them. Nevertheless, due to the special configuration and complexity of heat and mass transfer in the falling film evaporator, the researches were still on the preliminary level. On the basis of the illustration of the operation mechanism, this paper discussed about the influence of configuration and height of the liquid feeder, evaporation tube (including radius, the bundles, enhanced surface), working fluid (flow pattern, flow rate) on the performance of the horizontal falling film evaporator. Consideration the great advantages of the empirical correlation in the practices, the heat transfer correlations and applied ranges were also presented. This paper can be a reference of future researches.关键词：falling film evaporator;horizontal tube;review;heat transfer1749|364|0发布时间：2024-09-19
- 摘要：The advantage of water distributed on every tube structure is that water can be distributed on every tube respectively. The influences of the spray water flow rate and the air velocity on the air flow resistance of evaporative condenser with water distributed among the whole tube bundle structure were investigated, and conventional spraying water structure was also adopted to be compared. The experiment was carried out on the condition that the water flow rate was 0.5~1.2 m3/h and the air velocity was 0.5~4.0 m/s. The results show that the air flow resistance of this new structure decreases 11.5% at parallel-flow mode and 49.7% at counter-flow mode respectively. In addition, at counter-flow mode, the air flow resistance increases suddenly when the air velocity is 3.5m/s, which is higher than that of traditional evaporative condenser. Energy-save is about 2%, comparing with the conventional spray water structure when used in refrigeration system.关键词：evaporative condenser;water distributed type;flow resistance;experimental investigation1755|2041|0发布时间：2024-09-19
- 摘要：Because of restrictions on the size of the overall framework, heat exchangers with limited structure are called limited heat exchangers. Based on the limited model in air-handling unit, a lumped parameter model was established to study different performance of fin-tube heat exchangers. The dichotomy iteration was employed to solve the model. The results show that the model will not only design and calculate the number of tube rows along the airflow direction, but also analyze and predict the performance of fin-tube heat exchangers with variable condition and structure. The calculated results of the model were verified by the experimental data: the mean relative deviations are lower than 2% and the maximal relative deviations are lower than 8%. Experiments of enthalpy difference were conducted to analyze the heat transfer and friction characteristics of fin-tube heat exchangers with variable parameters, which optimize the design of the heat exchanger and provide the basis for the selection of heat exchanger operation method.关键词：limited space;fin-tube heat exchangers;design model;performance analysis1824|2189|0发布时间：2024-09-19
- 摘要：Based on nano-fluid made of lithium bromide(LiBr) aqueous solution, nano-particles and its relevant dispersants, the stability and thermal-physics properties of the nano-fluid were researched through a contrastive experimental method that surface tension and boiling temperature of nano-fluid and pure LiBr aqueous solution were tested respectively. It was discovered experimentally that the surface tension of solution added nano-particles reduces significantly and granularity of the nano-fluid decreases obviously through temperature processing. The nano-particles almost completely dissolves into LiBr aqueous solution, simultaneity the solution shows better stability and both its surface tension and boiling temperature both have a decrease compared with pure LiBr aqueous solution. The study shows that best composition nano-fluids is related to the types and contents of nano-particles and relevant dispersants.Through strict temperature processing, the nano-fluid has a better engineering application than the pure LiBr solution as its good stability and better thermal-physics properties.关键词：nano-LiBr aqueous solution;comparative analysis approach;stability;boiling temperature1721|2088|0发布时间：2024-09-19
- 摘要：Influence of suction refrigerant state on system performance and discharge temperature was carried out through a variable speed rolling piston compressor test stand. Results show that under the most air-conditioning conditions and the most operating frequencies, when suction vapor quality is about 0.95~0.98, system capacity and COP will reach peak value, and discharge temperature will be effectively decreased to the corresponding theoretical discharge temperature of isentropic compression process. Considering running safety, the appropriate suction vapor quality should be among 0.95~0.98.关键词：discharge temperature;suction vapor quality;rolling piston compressor;experimental study1928|2676|0发布时间：2024-09-19
- 摘要：In order to solve the problem of heating by electric vehicle air conditioning system in winter, and adapt to the compressor operating characteristics of single stage pressure ratio increasing in winter air condition, therefore, the coefficient of heating performance was decided to be the thermodynamic optimization objective function of scroll compressor. It was determined to the optimal middle pressure of compensation refrigerant in the scroll compressor orifice accordingly. The geometric position and shape of compensation refrigerant orifice have been built, in which has a quasi two-stage compression function. Based on the method of air enthalpy difference, the heat pump type scroll compressor was installed on the electric vehicle air conditioning system, the heating and refrigerating performance experiments had been finished in refrigeration laboratory. By optimized the structure of static scroll plate, the experimental results show that the capability of heating and cooling for the heat pump type electric scroll compressor could be met the comfort requirements of 5 seat electric vehicle drivers and passengers in summer and winter. Furthermore, the performance coefficients of heating and cooling have been improved accordingly. The purpose of energy conservation has been achieved to enhance the automobile air-conditioning system thermal economy of heat pump and refrigeration cycle.关键词：electric automobile air-conditioning;scroll compressor;heat pump;optimization;performance experiment2058|3320|0发布时间：2024-09-19
- 摘要：Twin-screw refrigeration compressor has been widely applied because of its unique advantage in air-source heat pump. In this paper, the performance variation of the twin-screw refrigeration compressor during the reverse cycle defrost process has been studied by experiment. The results showed that the twin-screw refrigeration compressor would receive a marked impact because of the reverse cycle defrost behavior of the system. The discharge pressure of compressor would drop sharply to 0.65MPa and then rise gradually during the first half of reverse cycle defrost process, but the suction pressure would rise perpendicularly and then decrease rapidly, even to 0.1MPa, after that it would go up gradually in this period of time. In the second half of reverse cycle defrost process, the discharge pressure and the suction pressure would have a strong oscillation and then tend to steady. During the reverse cycle defrost process, the variation of the discharge temperature and the suction temperature would be slow and lag behind the changing of pressure. The discharge temperature would drop firstly from 90℃ to 75℃, and then up to 100℃, finally, decrease and tend to steady. However, the suction temperature would rise and keep the high temperature for some time, and drop finally. The consumption power of compressor would have the similar experience as the discharge pressure. The heat capacity of this system would decrease and offer cooling capacity to environment. At that time, the frost on the fins would be melted.关键词：reverse cycle defrost;air-source heat pump;twin-screw refrigeration compressor;experimental study1898|2033|0发布时间：2024-09-19
- 摘要：By analyzing the motion of vane compressors for car air conditioner we proposed a mathematical model for the vibration of the discharge valve and determined its natural frequencies and mode shape in combination with the calculation using UG NX Nastran software. We show that the refrigeration efficiency can be maxima when the valve sheet takes the optimized thickness of 0.305 mm based on the vibration analysis. At the same time, test results revealed that the discharge flow pulsation and system noise are effectively controlled, and the both are lower than the upper limit of the "GMW Standard" of the U.S. General Motors Corporation. The study may be significant to enhance the refrigeration efficiency of the system and reduce discharge flow pulsation and noise of vane compressors.关键词：automotive air conditioner;vane compressor;discharge valve;optimization design;modal analysis1827|2360|0发布时间：2024-09-19
- 摘要：he metal based composite adsorbent is made of composite adsorbent which is coated on the surface of the aluminum foil. Silica gel with different particle size is used as the matrix for production of samples. It is found that, in experimental conditions, large particle size contributes to the improvement of the coating amount on the surface of the aluminum foil. The silica gel of preferred particle size is adopted to make samples, and a comparison study of composite adsorbent and single silica gel samples is made. When the samples are completely dried and the environment condition is kept constant, compared with silica gel, the maximum moisture uptake of composite adsorbent is 30%-45% higher, within which the adsorption rate and maximum moisture uptake of lithium chloride composite adsorbent is higher than calcium chloride composite adsorbent. When the samples are not completely dried and the environment is periodically changes from adsorption condition to desorption condition, the cycle adsorption amount of composite adsorbent is 70%-120% higher than silica gel, and in high relative humidity conditions, calcium chloride composite adsorbent is higher than lithium chloride composite adsorbent.关键词：dehumidification materials;metal based composite adsorbent;comparison experiment;adsorption property1753|2262|0发布时间：2024-09-19
- 摘要：In order to get the thermophysical properties of mixed refrigerants R134a/R290, the author built PVTx experimental system with high accuracy. Based on the Burnett method, the author measured the PVT properties of R134a/R290 with mass fraction 50%/50%, 55%/45%, 60%/40% in the range of 252K-320K, and fitted the gas virial equation of these mixed refrigerants. The average error between experimental data and equation is about 1%.It turned out that the experimental data agreed with the equations highly.关键词：R134a/R290;PVTx;virial equation1956|2147|0发布时间：2024-09-19
- 摘要：Cryogenic siloxane removal system need a long unsteady buffering time from starting up state to stable operation state, this situation greatly reduced efficiency and stability of Cryogenic siloxane removal system. Two function was get by the two groups of contrast test; the functions are about evaporator temperature variation with time, and just can be used in unsteady buffering time . It is concluded that main reasons lead to a long unsteady buffering time were thermal inertia of precooler and evaporator and the coupling relationship of them.关键词：siloxane removal system;unsteady state;experimental research;coupling;thermal inertia1731|2363|0发布时间：2024-09-19
- 摘要：Temperature and humidity independent control systems handle sensible load and latent load separately. They are usually more efficient and consume less energy than traditional air conditioning systems. In this paper, a novel humidity control system (DESICA), and the temperature and humidity independent control system constituted of DESICA and VRV (variable refrigerant volume air conditioning system), are studied through field experiment under winter conditions. Comparisons have been made to common adopted joint heat recovery ventilator (HRV) and VRV system. The results show that DESICA&VRV system provides more indoor thermal comfort (21℃, 50%) and consumes 9% less energy than HRV&VRV system.关键词：temperature and humidity independent control;thermal comfort;energy saving;field experiment;winter conditions1818|1949|0发布时间：2024-09-19
- 摘要：Theoretical analysis of multistage thermoelectric cooler was done in this paper. The cooling temperatures of four different multistage thermoelectric coolers were obtained in three different conditions by ANSYS simulation software. A test bench was conducted to verify the simulation. The simulation results showed that the cooling temperature of thermoelectric cooler was influenced by the distance of the thermoelectric couple, and the distance of thermoelectric couple should be considered in designing the cooler. The test results showed that the optimal operating voltage of the thermoelectric cooler was equal to 12V. The refrigeration temperature was extremely influenced by the external environment. The insulation material had an important impact on the performance of multistage thermoelectric cooler. The test results also showed that the input current and power would decrease with the hot end temperature increasing；The largest temperature difference and cooling temperature would increase with the hot end temperature increasing.关键词：multistage thermoelectric cooler;ANSYS simulation;experimental research2144|2197|0发布时间：2024-09-19
- 摘要：Acid paper documents are selected as the research subject, and the influence of procedure parameters (heating temperature, paper document thickness, pressure in drying room) on freeze-drying time and quality were explored, and obtained the sequence of importance and dehydration rate by orthogonal method. The results indicate that the different treatment levels of procedure parameters had remarkable influence on both vacuum freeze-drying time and the quality, and the importance sequence of the three factors both as follows: paper documents thickness, heating temperature, and pressure in drying chamber. The optimal parameters were a thickness of 7mm, heating temperature of 25℃ and pressure of 10~20Pa by optimization analysis.关键词：vacuum freeze-drying;deacidification protection;paper documents;procedure parameters1884|2521|0发布时间：2024-09-19
- 摘要：During the cooling capacity measurement of small and medium size air conditioner, the indoor cooling capacity calculation formula of room-type calorimeter didn’t take the dehumidification of air handling cabinet into consideration. In order to eliminate the impact of this influence on the test results, the mass weighing method was proposed to measure the humidification water of inner and outer chamber of the calorimeter, as well as the condensate water of air conditioner under test respectively. By analyzing the two sets of test results of five test units which were tested by means of room-type calorimeter based on the mass weighing method: It turns out that, when the rated cooling capacity of the air conditioner under test is smaller than the input power of the test chamber, the test error is increased by the air handling cabinet’s dehumidification amount, and the test error arises with the decrease of cooling capacity of air conditioner. The indoor cooling capacity calculation formula is modified to improve its accuracy according to the test results.关键词：room-type calorimeter;weighing method;condensate measurement;validation2326|2500|0发布时间：2024-09-19
- 摘要：This study focused on a vertical open-type display cabinet with double air curtain, and investigated the effect of pre-cooler on supply and return air of air curtain in display cabinet. The experimental investigation was undertaken in the test room with temperature of 25℃ and relative humidity of 60% to characterize the effect of pre-cooler on supply and return air of air curtain in display cabinet. The results showed that: the temperature of the supply air was not obviously elevated, and the return air temperature was reduced by 5℃; the inner supply air and the return air relative humidity of air curtain changed little, the outer supply air relative humidity dropped from 69% to 60%; and the enthalpy of outer supply air kept a fixed value, and the enthalpy of the return air decreased by 21.4%. The decreases of return air temperature and enthalpy could lead to significant decrease in the display cabinet load.关键词：food storage technology;display cabinet;pre-cooler;air curtain12872|15611|0发布时间：2024-09-19
- 摘要：According to the heat transfer between radiant ceiling unit and surrounding environment, based on the reasonable simplification of configuration of radiant ceilings, set up theoretical calculation models of single piece of the capillary cooling radiant ceiling unit and two units in series combination to calculate their cooling capacities. Then tests their cooling capacities under the condition of 25℃ room temperature, 15~19℃ supply water temperature. The comparison between measured data and calculation results show that theoretically calculated cooling capacity of single unit and of two series-connected units approach the experimental testing data, which shows that the theoretical calculation models are reasonable and feasible and can be used to predict the cooling capacities under real conditions.关键词：radiant ceiling unit;experimental test;cooling capacity;theoretical calculation model2359|2428|0发布时间：2024-09-19
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