最新刊期
卷 33 ， 期 2 ， 2012
- 摘要：Based on the reasonably simplified physical model, a dynamic model for surface heat-exchanger is developed by using the state-space method. The dynamic relationship between the outlet and the inlet parameters of heat-exchanger is deduced during the model development. The coefficients of heat and mass transfer in the model are adjusted as well by using the experimental data. The dynamic model is validated by experiments, which manifests that the state-space model established in this paper works well in the dynamic simulation of surface heat-exchanger.关键词：engineering thermophysics;Surface heat exchanger;State-space model;air-conditioning;dynamic simulation1907|1980|0发布时间：2024-07-18
- 摘要：In CCHP system, The waste heat quantity emitted from lithium bromide absorption refrigeration is large and low grade, so it is difficult to use directly. This paper proposes a hybrid two-stage and double-effect Lithium Bromide refrigeration - heat pump compound cycle. In this cycle, the condenser could emit higher temperature heat, which could increase the utilization rate of emitted waste heat. The cycle’s heat source is the back pressure steam, and it can take advantage of the low-grade thermal energy emitted from the refrigeration process to heat up the boiler make-up water. This paper takes existing double-effect lithium bromide absorption refrigeration and the single effect lithium bromide heat pump as contrast, the refrigeration - heat pump compound cycle system omits an evaporator and a condenser, which could decrease the temperature difference in heat exchange. And the energy analysis and the exergy analysis show that the compound cycle can improve exergy efficiency and energy utilization efficiency.关键词：pyrology;Refrigeration-heat pump compound cycle;Two-stage and double-effect;lithium bromide1996|2120|0发布时间：2024-07-18
- 摘要：The effects of fin type of outdoor coil in an air-source heat pump unit on the dynamic frosting characteristics were experimentally investigated. The fins include the flat, wavy and wavy/slit type. The decreasing orders of both the average and maximum values of the heating capacity, COP and input power are flat, wavy and wavy/slit fins under the frosting condition. The average values of heating capacity, COP and input power for the wavy/slit fin are decreased by 14.57%, 8.26% and 7.11% respectively than those for the flat fin. The performance parameters for the wavy/slit fin decrease earliest and most greatly, then for the wavy fin, and finally for the flat fin. The frost has the advantage of enhancing the air-side heat transfer coefficient due to the phase change from vapor to frost. Meanwhile, it has the disadvantage of decreasing the fan airflow rate across the outdoor coil because the frost decreases the fin spacing and increases the air pressure drop. The curves of the performance parameters have the ascending and descending segments during the frosting period, which accords with the microcosmic growth characteristics of the frost. In the early stage of frosting cycle, the frost crystal grows from the grain shape to the column one which does not decrease the fin spacing remarkably, so the advantage of the frosting is greater than its disadvantage, which results in the ascending segment of performance. In the middle and final stages, the frost crystal grows along the radius direction, then stacks up between the frost columns, so the fin spacing is decreased remarkably and the disadvantage of the frosting is greater than its advantage.关键词：pyrology;fin type;Heat pump;COP;frosting1968|2272|0发布时间：2024-07-18
- 摘要：The performance of quaternionic refrigerant mixtures, R345fa/R600a/R508b/R14, in Linde-Hampson refrigeration cycle was experimentally investigated. To get the lowest operation temperature, the components of refrigerant mixtures were optimized. The influence of ambient temperature on system operational performance was analyzed. It is shown that the lowest system operation temperature could reach from -45℃ to -85℃ when mixing the four refrigerant components at different species ratio,. If the proportion of the refrigerant mixtures charged is R245fa:R600a:R508b:R14=0.45:0.3:0.18:0.07, the operating temperature of the system can reach -85℃ when the ambient temperature is 35℃. With the same refrigerant mixtures, the system temperature can reach -89.3℃ if the ambient temperature decreases from 35℃ to 5℃.关键词：engineering thermophysics;Linde-Hampson refrigeration cycle;Refrigerant mixtures;Optimization ratio;R245fa / R600a / R508b / R142050|2451|0发布时间：2024-07-18
- 摘要：In order to meet the requirement of simulating different types of heat exchangers which are widely used in refrigerating system by a simulation tool, a general 3D distributed-parameter numerical design tool, HXSIM, is introduced. A general simulation framework was adopted to establish a general purpose solver. With the help of control volume method, all types of heat exchangers can be divided into four types, which are fin-tube control volume, microchannel-fin control volume, wire-tube control volume and plate-tube control volume. There exists three objects in each control volume, which are refrigerant, air and tube fin (tube wire or tube plate), and the governing equations for each object are established according to its heat transfer and pressure drop characteristic. OpenGL was applied in building an interactive graphic user-friendly interface, and in developing HXSIM to facilitate a modular, highly flexible and customized simulation tool. The model prediction with HXSIM were verified against experimental data, which shows the maximum deviation for heat exchange capacity is within 10% and the maximum deviation for air side pressure drop is within 1.16 Pa.关键词：pyrology;heat exchanger;Numerical design;model2073|2055|0发布时间：2024-07-18
- 摘要：To enhance the steam absorption rate and refrigeration efficiency of a absorption chiller, the active carbon/LiBr suspension was made up of a little active carbon particles and LiBr aqueous solution based on higher absorption performance of active carbon. The heat/mass transfer property of active carbon/LiBr suspension was studied through the experiments, and the feasibility analysis of substituting LiBr aqueous solution with active carbon/LiBr suspension in an absorption chiller was made in this paper. It is found that when the concentration of active carbon is in the range of 0~300ng/L or the adsorption equilibrium parameter is in the range of 0~1.5, there are linear increasing of absorption ration of steam and output of chiller with increment of the concentration of active carbon or adsorption equilibrium parameter, and the viscosity of active carbon/LiBr suspension linearly increase with concentration of active carbon and linearly decrease with the increase of temperature.关键词：engineering thermophysics;Absorbption chiller;Steam absorption rate;Refrigeration efficiency;Active carbon/LiBr suspension;Absorption ration of steam;Output of chiller1739|2117|0发布时间：2024-07-18
- 摘要：Flow characteristics of CO2 fin-tube gas cooler have been investigated employing steady-state distribution parameter model. And the model was verified by comparing experimental data and numerical results. The influence of the inlet parameters of the CO2 side on the coefficient of heat transfer of refrigerant, the capacity of gas cooler and the pressure drop were studied. And optimization calculation was carried out. The effect of the configuration parameters and the branch number on the performance of the gas cooler was discussed. The result shows that the inlet pressure and the mass flow rate have large influence on the coefficient of heat transfer while the inlet temperature has small effect. There is an optimal inlet pressure for the capacity of gas cooler to achieve its maximum value, and the optimal inlet pressure increases with the increase of the mass flow rate. The pressure drop and the capacity of gas cooler both increase linearly with the increase of the inlet temperature. Moreover, the performance of the CO2 gas cooler can be enhanced by increasing the branch number and employing tubes of small diameter appropriately.关键词：pyrology;CO2;Fin-tube;gas cooler;simulation;Optimization calculation1918|2124|0发布时间：2024-07-18
- 摘要：The two fluids Eulerian model based on the kinetic theory of granular flow has been applied to predict the ice slurry flow in a vertical pipe without considering ice melting process. It can be seen that the ice particle velocity profile is symmetrical along the central axis in the vertical pipe. When ice slurry moves at low speed, the velocity gradient becomes small, and the concentration profile approaches even in the pipe cross section. When the moving speed increases, the ice particle velocity and concentration stratify. The ice particle concentration is relatively small near the pipe wall, but larger close to the central axis with a concentration peak nearby. The flow direction imposes minimal effects to velocity profiles but makes a great impact on particle concentration distribution. In addition, there are meaningful differences in pressure drop when flowing with different directions.关键词：engineering thermophysics;ice slurry;flow characteristic;numerical simulation;Vertical pipe;Two fluids model1966|2227|0发布时间：2024-07-18
- 摘要：The defrosting time, discharge pressure, indoor temperature fluctuations and other defrosting characteristics of air source heat pump were experimentally investigated at three defrosting modes, i.e., reverse cycle defrosting, hot gas bypass defrosting and phase change material defrosting. The results showed that the performance of phase change material defrosting system is better than the others. The phase change material has increased the discharge temperature and the condensing temperature, which benefits to the decrease of defrost time and energy consumption, and the indoor temperature is relatively stable.关键词：pyrology;Defrosting performance;Comparison;Reverse cycle defrosting;Hot-gas bypass defrosting;Phase change material defrosting;air source heat pump1820|2438|0发布时间：2024-07-18
- 摘要：The noise and the vibration in a twin-screw refrigeration compressor unit are tested experimentally in order to improve the operation environment and the performance. By spectrum analysis, it was found that the higher noise and the larger vibration occurred when the unit was running at integer multiple of compressor baseband frequency, which indicated that the compressor was the main source of vibration and noise of the unit. Some noise and vibration reduction methods were also presented. The results of experimental comparison of the screw compressor unit before and after improvement indicate that improving the rotor profile design, adjusting the meshing clearance of female rotor and male rotor, and enhancing the rotor machining precision are significantly effective for noise and vibration reduction.关键词：pyrology;Mechanical dynamics and vibration;twin-screw refrigeration compressor;noise;vibration;Spectral analysis1785|2592|0发布时间：2024-07-18
- 摘要：For gravity feeding refrigeration system, when the hydraulic head was greater than the resistance to the evaporator, liquid refrigerant can recycle in loop formed by the evaporator and vapor-liquid separator. The strength of recycling was expressed by circulating rate, which was connected with hydraulic head and evaporation temperature. Resistance formulas to a small system were derived and a special recycling evaporator was designed. Resistance balance calculation in homogeneous flow model was completed. Then the effect of hydraulic head and evaporation temperature on the circulating rate of refrigeration system was experimentally investigated using the air-side heat balance method. The results showed the precision can be satisfied with the engineering demand. Cycling rate decreases as evaporation temperature increases, and the lower the evaporation temperature is, the smaller the change of cycling rate. Cycling rate increases as hydraulic head increases, and the augment formed by one unit hydraulic head increases with the decrease of hydraulic head. The changing rate decreases with the increase of evaporation temperature and there exists optimal cycling rate which is recommended as 4~5.关键词：pyrology;Recycling evaporator;Gravity feeding refrigeration evaporator;Homogeneous flow model;Circulating rate1961|2535|0发布时间：2024-07-18
- 摘要：Aiming at meeting the requirements of air conditioning in wide temperature range and high temperature environment, HLD-45B high temperature air-conditioner has been developed. Heat transfer area and air mass flow of condenser is 15%~20% larger than normal. Both enthalpy and wide temperature range method experiments have been done. The results show that the air-conditioner has good operating performance: 1) Temperature difference between inlet and outlet has small variation and refrigerating capacity decreases less than 15% from standard condition to 75℃ high temperature condition. The air-conditioner operates stably and reliably. 2) Under 75℃ high temperature condition, discharge pressure and temperature, both of which are in ideal safety range, are 2.84 MPa and 121℃ respectively. The use of mixture of high and intermediate temperature refrigerants can improve the performance and reliability of the high temperature air-conditioner and widen its operating temperature range.关键词：pyrology;High temperature air conditioner;R22/R142b;Research1872|2659|0发布时间：2024-07-18
- 摘要：Carrots are selected as the research subject, and the investigation of a new type of low temperature vacuum drying method in the non-frozen state of the product under drying processing is carried out through experiments. Low-temperature vacuum drying and vacuum freeze-drying and hot air drying method were compared to study the impact of low temperature vacuum drying of carrot nutrients (such as reducing sugar, Vitamin C, etc.) and rehydration characteristics. The results show that: by comparing the Vitamin C content of three kinds of drying methods, hot air drying and vacuum freeze-drying of carrots, Vitamin C loss rate is about 2.14 times and 2.47 times of low-temperature vacuum drying.关键词：Food package and preservation;food processing technology;Drying characteristics;Low temperature vacuum drying1784|2544|0发布时间：2024-07-18
- 摘要：When vacuum cooling the cooked food with soup, there was the phenomenon of soup splashing. In this paper, the tomato egg soup boiling and splashing during vacuum cooling process were studied through an observation window opened in the container. Adopting the means of controlling the filling gas valve opening and closing, and using segmented depressurization method and back pressure method can effectively prevent the occurrence of the boiling splash. The water loss rate is decreased 38%, but the relative cooling time is extended.关键词：Food package and preservation;vacuum cooling;Cooked food with soup;Splash;Prevention1863|2096|0发布时间：2024-07-18
- 摘要：Effects of four different low storage temperatures-higher refrigeration temperature(8℃),lower refrigerated temperature(4℃), hyo-on temperature(-2℃) and freezing temperature(-20℃) on the quality of orange juice were studied. Results show that: 1)In juice stored under hyo-on storage condition, changes of soluble solid content are the smallest; total number of detected volatile flavor compounds, numbers of hydrocarbon terpenes and numbers of alcohols are the largest; relative content of alcohols and esters are the highest. 2)In juice stored under freezing storage condition, vitamin C level detected in the fifth week and relative content of aldehydes in volatile flavor compounds are the highest. 3)In juice stored under refrigeration condition, variation in content of soluble solid in the one stored under higher refrigeration temperature appears to be greater ; number of detected volatile flavor compounds is the smallest; however, relative content of hydrocarbon terpenes is the highest; relative contents of myrcene, linalool and citral are the lowest. 4)Under all storage conditions, differences in changes of total acid, pH and color of the orange juice are not significant.关键词：Food package and preservation;Orange juice;quality;refrigeration storage;Hyo-on storage;Freezing storage1861|2450|0发布时间：2024-07-18
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