最新刊期
卷 34 ， 期 2 ， 2013
- 摘要：Two-phase thermosyphon heat exchangers are widely used in different industry fields. The fluid flow characteristic is very important for the design of thermosyphon. However, the existing two-phase models are not accurate enough for the simulation of two-phase thermosyphon loop .Therefore it is important to make an assessment of existing two-phase momentum models corresponding to thermosyphon loop features. The mathematical model of two-phase thermosyphon loop, which include 4 homogenous pressure drop models, 24 separated-phase momentum combination models (4 separated-phase frictional pressure drop models multiply 6 representative void fraction correlations), has been developed in the paper. The predicted results from different models are compared with the experimental results of two-phase thermosyphon with refrigerants H2O, R113 and R600a. The comparison results show that the combination of Lorkhart-Martinelli frictional pressure drop model and Tom void fraction model is better than other models. Finally, the flow features of two-phase thermosyphon loop have been simulated. It is shown that for a specific loop, the mass flux increases and then decreases slowly with the increase of heat flux. A reasonable explanation is given to the phenomenon.关键词：thermosyphon loop;two-phase flow;simulation;assessment;flow features1847|2070|0发布时间：2024-07-18
- 摘要：It is urgent to seek more suitable refrigerants as the traditional R22 used widely in air conditioners nowadays is under phase out for its environmental problems and hydrofluorocarbons (HFCs) would aggravate global warming effects, while hydrocarbons (HCs) have drawn public attention. In this paper, R290 and R1270 were adopted as refrigerants in a R22 original split room air conditioner to carry out performance experiments using air-enthalpy test method. The results indicate that under normal condition, adopting R290 as a drop-in substitute to R22 would offer 5.0% lower cooling capacity and 10.3% higher energy efficiency ratio (EER), and the use of the 20% larger displacement compressor could help increase cooling capacity by 8.9%, but reduce EER by 8.3%, however, the performance is better than that of the original R22 system. And the performance of the R1270 system is better than that of the R290 system under normal condition. The results also show that, with respect to the original R22 system, HC systems have higher increase rate and greater increment in both cooling capacity and EER with the decrease of outdoor temperature and they have better performance when outdoor temperature is relatively low. The results demonstrate that HCs are promising substitutes to R22 and deserve wide application prospects in air conditioners.关键词：room air conditioner;air-enthalpy test method;hydrocarbon;performance;R290;R12701729|1972|0发布时间：2024-07-18
- 摘要：Flow boiling phenomena of fluidic mixtures in channels exist widely in industry and is an important heat transfer method. This paper presents a state-of-the-art review on the theory development and achievements about flow boiling of mixtures in channels. And some correlations for prediction of the heat transfer coefficient in flow boiling of pure fluid or mixtures are introduced. The deficiencies on the present studies about flow boiling of mixtures are discussed, for example most of the correlations are not applicable for cryogenic fluids, the prediction precision and applicability of them are not satisfactory yet. Further study of heat transfer correlations on flow boiling is also discussed.关键词：flow boiling;mixtures;heat transfer;review1734|2050|0发布时间：2024-07-18
- 摘要：The resistance and heat transfer characteristics of a plate evaporative air cooler are investigated experimentally through varying the flow rate of air, hot water and humidification water. Correlations for the air side and hot water side pressure drop and convection heat transfer coefficient are obtained. The results of experiment show that the pressure drop of air side is not affected by humidification water. The heat transfer coefficient increases with the increase of humidification water flow rate and it is about 5 times larger than the one under dry condition.关键词：spray humidification;air cooler;pressure drop;heat transfer coefficient1761|1816|0发布时间：2024-07-18
- 摘要：Simple and effective calculation models to determine thermodynamic properties of refrigerant are very necessary for simulation of refrigeration system. Correlations of saturated vapor pressure and liquid density for HFC-32 refrigerant were presented. On basis of GMA state equation of liquid for HFC-32, Helmholtz bias function and Maxwell relationship of the thermal physical parameters, the calculation models of enthalpy, entropy and specific heat capacity were deduced. The calculation models mentioned above with no iteration can achieve high precision and stability. Comparisons between calculation models and REFPROP7 , covering saturation liquid line（275~335 ，0.862~4.095 ）, have been made. The results show that, the average relative error and maximum relative error for all calculation models are less than 0.776% and 4.464%, respectively.关键词：HFC-32 Refrigerant;calculation model;GMA state equation;thermodynamic properties1807|1876|0发布时间：2024-07-18
- 摘要：This paper proposes an energy-saving system which is used to test the reliability of reciprocating refrigeration compressor. This system is established based on the principle of condensing of the partial refrigerant with high temperature and high pressure. The condensed refrigerant and the uncondensed refrigerant are mixed into a saturated vapor entering the suction of the compressor. The refrigerant mass flow of the condensed and the uncondensed are calculated. The result indicates that only a small fraction of refrigerant is needed to be condensed and the selection of a condenser with small power can satisfy the experiment requirements. The proposed system is built and its availability is testified by carrying out the durability test of a reciprocating compressor, which shows this test system is featured with simple, energy-saving and low cost.关键词：refrigeration compressor;durability test;reciprocating refrigeration compressor;reliability1710|1856|0发布时间：2024-07-18
- 摘要：To meet the requirements on computation speed, accuracy, application range for modelling non-adiabatic capillary tube for refrigeration system simulation, a fast calculation method for a non-adiabatic capillary tube is proposed. The approximation correlations for thermodynamic properties of refrigerant are proposed for subcooled zone, two-phase zone and superheated zone, respectively, and then the explicit approximate analytic solutions for the three zones are obtained using integral method. In the solution for two-phase zone, approximation correlation for thermodynamic properties is obtained by curve-fitting method, and the length is obtained using Green’s theorem. Case studies on R134a, R600a, R12, R410A and R407C show that the deviation between the predicted results of the proposed method and those of the existing distributed parameter model is less than 2% while the computation speed of the proposed method is 1000 times faster. The proposed method can meet the requirements for refrigeration system simulation.关键词：capillary tube;non-adiabatic;calculation;refrigerant1995|2387|0发布时间：2024-07-18
- 摘要：Electrical heating is mainly used as heat source in experimental research on bubble pump. Operational term is long, operation is complicated, deviation is distinct and accurate experimental data is not obtained. In view of the above question, In order to grasp the bubble pump performance more accurately, this system the bubbles’ movements with a device injecting air is simulated to realize the bubble pump’s normal operation under a cold condition and is used to study bubble pump’s performance. According to the experiment results, the bubble pump’s performance influencing factor is analyzed.And that is found that keeping other influencing factors constant, the gas input and immersion ratio and heating power is proportional to the amount of liquid lifted. And it is demonstrated that the hot experiment and cold experimental results are consistent. The bubble pump system’s performance parameters with actor analysis method is analyzed and is the relevant function equation between the heating power and the amount of liquid lifted attained. The function equation indicates that with a fixed immersion ratio the amount of liquid lifted is proportional to heating power.关键词：bubble pump;experiment under the cold state;heating power;actor analysis method1841|1980|0发布时间：2024-07-18
- 摘要：A kind of automatic defrosting control technology, named time-temperature difference method, was developed, which can indirectly identify the change of refrigerating capacity of refrigerator. Based on the compressor running time, degree of attenuation of the refrigerating capacity was estimated according to the change of the difference between the evaporation temperature and freezer temperature, while unsteady-state disturbances were removed. Experiments of typical ambient temperature and heat and moisture load were carried out, internal temperatures were measured when electric air door and box door was opening or closing. Then the automatic defrosting control rule was established under above results. The application of this new kind of defrosting control technology in the BCD-350W shows that the refrigerator can work properly in wide range of ambient temperature and different heat and moisture loads, the anti-interference ability and adaption ability to environment is strong, the percentage of defrosting energy consumption in total energy consumption is decreased by about 40% and energy saving effect is obvious.关键词：pyrology;defrosting control;air cooled refrigerator;evaporation temperature;temperature difference1819|2322|0发布时间：2024-07-18
- 摘要：With the establishment of mathematical and physical model and numerical simulation of vertical tube by FLUENT, characteristics of buried tube heat exchanger of ground source heat pump (GSHP) was analyzed. Based on this information, combined with the simulation and measurement of summer discontinuous operation results, the law of different buried tube space on the radial variation of soil temperature and coherent effects of buried tubes heat transfer were got.关键词：GSHP;buried tube space;numerical simulation;coherence effects;discontinuous operation1777|2001|0发布时间：2024-07-18
- 摘要：The natural convection outside micro-slender cylinders placed vertically with outer diameters from 39.9μm to 350.1μm with air is experimentally investigated. The Joule heat method is employed to obtain the Nusselt numbers in the experiment. The results are compared with the values of classical correlation equations. The investigations show that all values of classical correlation equations are different from each other, and the differences will decrease with decrease of the diameter of micro-slender cylinder. The deviation between experimental results and values of classical correlation equations will increase with decrease of the diameter, which can reach 50％.The heat transfer coefficient of natural convection increases with the decrease of the diameter of the micro-slender cylinder. These phenomena may be due to the enhancement of the natural heat transfer caused by the thinner boundary layer which resulted from the edge effect when the diameter of the micro-slender cylinder becomes smaller.关键词：natural convective heat transfer;micro-slender cylinder;classical correlation equations;Nusselt1793|2036|0发布时间：2024-07-18
- 摘要：In order to preserve porcine kidney at cryobiological relevant temperatures, the effects of different concentrations of glycerol on the freezing point, apparent specific heat, the latent heat of porcine kidney were investigated between -80~20℃ by using Differential Scanning Calorimeter (DSC). Thermal constant Analyzer (Hot Disk) was used to measure the thermal conductivity of porcine kidney in varying mass fraction of glycerol. Results show that as the mass fraction of glycerol increases, the thawing phase transition range of porcine kidney shift to the lower temperature range, the freezing point and the apparent latent heat both decrease. The change of apparent specific heat can be divided into three phases. Before the phase change, apparent specific heat increase with the increases of mass fraction of glycerol; in phase-change region, apparent specific heat is significantly reduced as the mass fraction of glycerol increases; and after the phase change, apparent specific heat are lower for higher glycerol mass fraction. And the thermal conductivity goes down as glycerol mass fraction increases. The thermal characteristics can provide theoretical basis for organ cryopreservation.关键词：glycerol;porcine kidney;thermal properties;DSC1986|2067|0发布时间：2024-07-18
- 摘要：The structure of automatic cascade refrigeration system is simple, and the operation is reliable. Since the non-azeotropic mixed refrigerants are used, whether the condensing separation is complete or not will directly affect the cooling efficiency. A new type of multistage condensing filtration disengaging gear is proposed in the paper. A test-bed of automatic cascade refrigeration system equipping with the device is set up for actual application research. The results show that the device can separate high and low boiling point group efficiently. Because of its simple structure and low cost, the device may have important potential of practical application.关键词：automatic cascade refrigeration system;non-azeotropic mixtures;multistage condensation filtration disengaging gear;efficient separation1584|2003|0发布时间：2024-07-18
- 摘要：Based on a practical project in shanghai, this paper will give a yearly test on single U-shaped ground heat exchanger of ground-source heat pump in central air conditioning system, and analyzes the change of surface ground temperature field, inner ground temperature field and outer ground temperature field of the pipes. The test results show that: throughout the year , temperature fluctuation is larger in the shallow soil (more than 25m depth）which is outside the tube group , and time of the highest temperature of the shallow soil appears later than that on the ground . In the inside tube group, the soil temperature will increase along with the system’s continuous and steady operation. Thus, it makes the temperature difference smaller between the surface of the ground heat exchanger and soil temperature around, which leads to the heat exchange capacity decline. Through the contrast analysis，this paper also found that ,for buildings where ground source heat pump is used and its cooling load is greater than the heating load ， the impact of the system's continuous and steady operation on the heat transfer between buried pipes and soil is significantly higher in the summer than that in the winter. At the same time, the experiment results prove that, increasing borehole spaceand intermittent operation of the ground source heat pump system are very important to enhance the heat exchange between the buried tube heat exchanger and soil.关键词：ground source heat pump;single U-shaped ground heat exchanger;heat exchange capacity;intermittent operation1871|1894|0发布时间：2024-07-18
- 摘要：Water loss is inevitable during vacuum cooling because the temperature is decreased through the loss of water in vegetables. The cooling effect of leafy vegetables in vacuum cooling is evident, but that of root vegetables is not obvious because their tissue is compact. Iceberg lettuce, cabbage and carrot were studied by using three type vacuum cooling methods, i.e., direct vacuum cooling, spray water vacuum cooling and water absorbent film package vacuum cooling. The results show that vegetables packaged with water absorbent film have the fastest temperature decreasing rate, the shortest cooling time and the lowest water loss rate. When the temperature of iceberg lettuce in water absorbent film package vacuum cooling is decreased from 25℃ to 5℃, the time taken is 43% less than direct vacuum cooling, and the water loss rate reduces 76.3%. When the temperature of cabbage in water absorbent film package vacuum cooling is decreased from 27℃ to 5℃, the time taken is 48% less than direct vacuum cooling, and the water loss rate reduces 76.7%. When the temperature of carrot in water absorbent film package vacuum cooling is decreased from 24℃ to 8℃, the time taken is 37.5% less than direct vacuum cooling, and the water loss rate reduces 91%. So water absorbent film package vacuum cooling is an effective method to improve temperature decrease rate and reduce water loss.关键词：vacuum cooling;pre-treatment;water absorbent film;vegetable1754|1890|0发布时间：2024-07-18
- 摘要：The dramatic changes of interior air temperature and humidity induced by heat and mass transfer can make the quality of food no longer be assured while the door of the refrigerated truck is opened in the distribution. Comparative experiments are conducted according to the problems in the unloading process. The variations of temperature and humidity under different conditions are analyzed. The conclusion shows that the temperature difference between the inside and outside air is the main factor which impact the temperature rise of interior air, and the use of PVC curtain can effectively inhibit the elevated temperature inside the vehicle and ensure food safety to some extent.关键词：refrigerated truck;opening;PVC curtain;variations of temperature and humidity1776|2128|0发布时间：2024-07-18
- 摘要：For the purpose of increasing the glass transition temperature (Tg ') of frozen dough, the method to measure the Tg' using dynamic mechanical thermal analysis（DMA）, and experimental analysis of the impact of different additives on Tg ' of dough were studied. The dough samples padded with a tissue piece at the bottom were frozen in the DMA test furnace, and then measured using the dual cantilever. The Tg' of dough can be accurately detected from the glass transition "peak". According to the Tg' level, the Tg ' of dough added with different additives were as follows: ascorbic acid (-25.09℃), sodium stearoyl lactylate（SSL） (-26.32℃), trehalose (-27.67℃), diacetyl tartaric acid esters of mono and diglycerides（DATEM）(-27.69℃), sodium tripolyphosphate (-28.12℃), sodium dihydrogen phosphate (-28.26℃), six partial sodium (-29.35℃), Artemisia seed gum (-32.54℃), guar gum (-35.22℃), lecithin (-39.56℃ ). In the design of the frozen dough recipe, the right amount of additives can improve Tg ' of dough, thereby improving the storage stability of frozen dough.关键词：DMA;frozen dough;glass transition;ascorbic acid;SSL1822|2141|0发布时间：2024-07-18
- 摘要：The control of battery thermostatic in full electric vehicle includes two aspects. One is warming the electric vehicle battery package in the severe cold districts in the winter to reduce discharge velocity in low temperature conditions and increase the battery’s endurance. The other is cooling the battery package in the high temperature districts in the summer to slow down the aging velocity of inner units in high temperature environment and prolong the using lifetime. Targeted on the problem of energy battery in full electric vehicle, the method for controlling battery temperature using assistant thermostat is proposed?—liquid constant temperature control method. A set of devices which could modulate the battery package temperature through the air conditioning and heating system is established so that the battery package can work well in any weather conditions. The water heating method, which makes use of antifreeze solution in the water storage tank whose temperature is modulated by PTC(Positive Temperature Coefficient) thermostat, is used for heating; the refrigerating fluid –R134a is used for cooling. The thermostat’s construction and working principle are introduced. Finally, the performance and feasibility of the thermostat are analyzed through testing and simulating.关键词：electric vehicle;battery package;thermostat modulation;PTC (Positive Temperature Coefficient1855|1949|0发布时间：2024-07-18
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