最新刊期
卷 38 ， 期 1 ， 2017
- 摘要：The long-term performance of fin-and-tube heat exchangers with different fin structures will decay when covered with dust particles. In this paper, a visual experimental rig was established to investigate the effects of fin structures on particle deposition and air-side pressure drop. The fin types of test samples covered plain fins, wavy fins and louver fins, and the fin pitches ranged from 1.3 mm to 1.8 mm. The results show that, louver fins are most beneficial to particle deposition; the maximum particle deposition weight on wavy fins and louver fins increased by 25.6% and 52.8% respectively compared with that on plain fins, meanwhile the increment of pressure drop increased by 44.4% and 165.6% respectively. Small fin pitch can promote particle deposition and increase pressure drop; the maximum particle deposition weight on louver fins with fin pitch of 1.5 mm and 1.3 mm increased by 26.2% and 43.2% respectively compared with that on louver fin with fin pitch of 1.8 mm, meanwhile the increment of pressure drop increased by 24.1% and 49.4% respectively. The air-side pressure drop firstly increased then tended to be stable with the increase of particle deposition weight.关键词：fin-and-tube heat exchanger;particle deposition;pressure drop;fin structure;experimental investigation2788|3718|7发布时间：2024-07-18
- 摘要：The experiment rig of evaporative cooling heat exchanger is set up for experimental research and the environmental parameters were controlled in enthalpy difference laboratory in this paper. The influences of spray density, face velocity and environmental parameters on the performance of evaporative cooling heat exchanger were experimentally investigated. The optimal spray density and face velocity were found, which were 0.0314 kg/(m?s) and 3.22 m/s respectively. In addition, the heat transfer coefficient would decrease by 4.2% and the mass transfer coefficient would decrease by 9.3% when the wet bulb temperature was increased from 22 ℃ to 28 ℃; the heat transfer coefficient would increase by 10% and the mass transfer coefficient was increased by 13.7% with the relative humidity of inlet air decreasing from 85% to 55%.关键词：evaporative cooling heat exchanger;heat transfer coefficient;mass transfer coefficient;relative humidity;wet bulb temperature2352|2470|0发布时间：2024-07-18
- 摘要：Accurate calculation of refrigerant and oil properties is the foundation to numerical optimization of compressor. The physical properties calculation models of R32 saturation liquid, saturation gas, superheated gas and lubricating oil POE and PVE in the common range are developed based on explicit fitting of the given data. The properties of refrigerant and oil are then analyzed comparatively. These simple and reliable models can lead to shorter simulation time and higher accuracy. The maximum deviations of the predicted values of these models to experiment data are within 5%. These models can be supplied to calculate the mixture physical properties of R32 & POE and R32 & PVE.关键词：R32;POE oil;PVE oil;physical property;model2953|6296|4发布时间：2024-07-18
- 摘要：The tubes with special shape and surface are the most commonly used and effective methods to enhance the heat transfer. In this paper, the heat transfer coefficient correlation of gas side was experimentally put forward according to liquid drop tube heat exchanger for recovering waste heat of natural gas boiler. In different flue gas flow rate, the heat transfer performance and influencing factors of the round tube and drop tube were analyzed by changing the arrangement distance between the heat exchange tubes. Compared with the experimental data, it was proved that the experimental correlation can correctly reflect the characteristics of condensation heat transfer. The results showed that the pressure loss of the different flue gas through the liquid drop tube heat exchanger was smaller than that of the round tube, which is about 0.33~0.38 times of the round tube; the flue gas temperature drop was larger than that of the round tube; the temperature rise of the cooling water through the liquid drop tube heat exchanger was higher than that of the round tube; the convection heat transfer coefficient of the liquid drop tube heat exchanger was increased by about 7% than that of the round tube, indicating that the heat transfer performance of the liquid drop tube heat exchanger was better than the round. For the condensation heat transfer process, the liquid drop tube heat exchanger has the effect of heat transfer enhancement.关键词：drop tube;flue gas;condensation heat transfer;heat transfer performance2478|2318|0发布时间：2024-07-18
- 摘要：To solve the problem that frosting leads to lower efficiency of the heat pump air conditioner for electric vehicle in the heating process, a new method of composite defrosting is proposed after analyzing the deficiency of the existing defrosting method.At the beginning of the defrosting, firstlyenter the bypass defrost stage. Then reverse cycle defrost stagetimelyaccording to the defrost state.An electric bus air conditioning system with a rated power 8.0 kW was transformed,and the comparative test was carried out in the simulated environment of the outdoor at (2±0.5) ℃, the indoor at (20±0.5) ℃ and the relative humidity of (80±5)%. The change of the compressor suction and discharge pressure, the outdoor heat exchanger temperature, indoor temperature and power consumption were measured. The experimental results indicated that, compared with the method of reverse cycle defrosting, the compressor shock of discharge and suction was reduced, the fluctuation of indoor temperature was decreased and energy consumption decreased by 8.13%; compared with the method of hot-gas bypass defrosting, the time of defrosting was decreased by 60 s and energy consumption decreased by 6.56%.关键词：defrosting;heat pump;electric vehicle2697|3525|4发布时间：2024-07-18
- 摘要：Based on the frosting and defrosting problems of cascade air source heat pumps (CASHPs) during heating operation in the cold area in winter, a novel thermal energy storage CASHP defrosting system with a thermal accumulator is proposed. The defrosting performances of thermal energy storage defrosting mode with intermittent heating and continuous heating were experimentally studied, and then the experimental results were compared with common used hot-gas bypass defrosting mode. It was found that in energy storage defrosting mode, the defrosting duration time and the energy consumption were reduced by 71.4%~77.6% and 65.1%~85.2% respectively compared with hot-gas bypass defrosting mode, and the system defrosting operation was more stable and reliable.关键词：air source heat pump;cascade cycle;defrosting;thermal accumulator15423|11957|10发布时间：2024-07-18
- 摘要：Experimental studies of indoor thermal environment and ventilation effectiveness were performed in a room with low temperature radiant ceiling heating system combined with mixing ventilation system and displacement ventilation system. The results show that when radiant ceiling surface temperature ranges from 25 to 29 ℃, supply air temperature ranges from 15 to 19 ℃ and supply air flow rate equals 4.2h-1, the distribution of indoor thermal environmental parameters are relatively uniform, the indoor vertical air temperature differences are less than 1℃ and ventilation effectiveness is approximately 1.0 when low temperature radiant ceiling heating system is integrated with mixing ventilation system. The distribution of indoor thermal environmental parameters are relatively non-uniform, and the indoor vertical air temperature differences are large and up to 4℃ and ventilation effectiveness is approximately 1.1 when low temperature radiant ceiling heating system is integrated with displacement ventilation system.关键词：radiant ceiling;mixing ventilation;displacement ventilation;indoor thermal environment;ventilation effectiveness2636|2615|4发布时间：2024-07-18
- 摘要：Parallel flow evaporator with louver fins for roof top bus air conditioner was designed to replace the fin-and-tube evaporators. The capacity of parallel flow evaporator was simulated and the fin parameters were optimized by the established simulation model. Two sets of samples were experimentally investigated to verify the simulation results. The experiment results show that little condensate water was seen during the experiments, and the evaporator with 4 flow paths is of better homogeneity in refrigerant distribution and 11.2% higher in heat transfer than that with 8 flow paths. The newly designed evaporator is 38% lighter, 57.6% less volume and 10.5% less refrigerant charge than the traditional fin-and-tube evaporator, and almost solved the two serious problems of the application of parallel flow evaporator in bus, i.e., the removal of condensate water and the uniform distribution of two-phase-flow refrigerant, which indicates that the newly designed evaporator has reached the requirement of industry and can be used to replace the traditional fin-and-tube evaporator.关键词：bus air-conditioner;louver fins;simulation;evaporator;parallel-flow heat exchanger2360|2338|2发布时间：2024-07-18
- 摘要：In this study, an ANN model for an experimental VS DX A/C system was developed to predict its outputs with an assumption that the indoor air states will not influence the relative value of system outputs. Steady state experiments under a fixed indoor air state were carried out in this study to obtain the operational characteristics of the system for training and testing the ANN model and the ANN model developed was validated through steady state experiments under the non-training indoor air state. The experimental results showed that the max errors of prediction in training, testing and validating were below 5% and the average errors were below 3%, suggesting that the ANN model developed was capable of predicting the system outputs with satisfactory accuracy at both training and non-training indoor air states.关键词：air-conditioning system;steady state ANN model;steady state experiment;direct expansion2291|2553|1发布时间：2024-07-18
- 摘要：In this paper, the application feasibility of evaporative condenser in protective engineering is analyzed. The influence of air volume and water spraying density on heat and mass transfer performance was investigated in the experimental platform designed by the authors. It is found that refrigerating capacity and heat transfer capacity were almost unchanged, heat transfer capacity of unit air volume and total consumption were increased, and ECR was reduced, with the decrease of the air volume when spraying density was constant. Refrigerating capacity, energy consumption of compressor and ECR were changed in the same way with the spraying density under different air volume. The best air volume and spraying density are 2000 m3/h and 0.025 kg/(m?s).关键词：evaporative condenser;air volume;spraying density;heat transfer;protective engineering2121|2281|0发布时间：2024-07-18
- 摘要：The cold storage material of HCOONa?2H2O 21%+water 79% which have appropriate phase change temperature, large latent heat, large thermal conductivity and good stability was studied in this paper. Cold storage insulation boxes with two kinds of insulation layers have been produced, one is pure polyurethane foam (PU) and the other is vacuum insulation panel and polyurethane foam (VIP-PU). Cold storage agents were frozen in the low temperature refrigerator and then were put into the cold storage insulation boxes. Different quality of cold storage agents and different freezing temperature were studied. The results showed that the cold storage effect of the VIP-PU box is two times of the PU box. When the coolant quality is 15 kg and the freezing temperature is ﹣60 ℃, the VIP-PU cold storage box could maintain the temperature at ﹣10 ℃ for 13 hours, which has the optimal cold storage effect.关键词：composite phase change material;HCOONa•2H2O;cold storage insulation box;VIP-PU composite thermal insulation material2291|2935|13发布时间：2024-07-18
- 摘要：In order to improve the effect of cold storage in box with nano fluid, the low density sponge is used to adsorb nano particles and the thermophysical properties of the coolant is changed. The carrots are used as the experimental object in the experiments by orthogonal method. And the integral value of average temperature of the air in the box is taken as the index to compare the effect of cool storage. The influence of thickness of porous sponge (8 mm, 16 mm, 20 mm), mass fraction of nanofluids (0.1%, 0.15%, 0.2%), quality of cold storage materials for per kilogram of vegetables (0.429 kg, 0.5 kg, 0.571 kg), and pre-cooling temperature of vegetables (-1 ℃, 4 ℃ , 12 ℃) on the refrigeration effect in the incubator were explored. The results of the study are as follows: (1) the importance sequences of factors are pre-cooling temperature of vegetables, mass fraction of nanofluids, the quality of cold storage materials for per kilogram of vegetables, and the thickness of porous sponge; (2) with the increasing of the thickness of porous sponge, the mass fraction of nanofluids, and the quality of cold storage materials for per kilogram of vegetable, the effect of cooling storage will be better. The optimal pre-cooling temperature is 4 ℃ out of 12 ℃, 4 ℃, - 1 ℃; (3) the optimal combination of all the factors for the effect of cool storage is as following: the thickness of porous sponge of 20 mm, the mass fraction of 0.2%, the quality of cold storage materials for per kilogram of vegetable of 0.571 kg, and vegetables pre-cooling temperature of 4 ℃. But the porous sponge of 16 mm instead of 20 mm, and the mass fraction of nanofluids of 0.15% instead of 0.2% are suggested for economical reason. This experiment method and results provide a theoretical basis for further experiments and analysis.关键词：cold storage incubator;orthogonal test;influencing factors2049|2232|1发布时间：2024-07-18
- 摘要：The heat exchanger of the gas hydrate mud cooling system is very critical to the exploitation of gas hydrate. Based on the occurrence characteristics of gas hydrate, the study focused on the effect of different kinds of heat exchanger to the original gas hydrate sample acquired by drilling. Under the same conditions, the heat transfer efficiencies of coaxial heat exchanger and spiral heat exchanger with the same heat transfer area were measured and analyzed. By combining the experimental results with heat transfer calculation and numerical simulation, it indicated that the heat efficiency of spiral heat exchanger was higher than that of coaxial heat exchanger 70% when the conditions required by coring hydrate sample was achieved.关键词：natural gas hydrate;spiral plate heat exchanger;coefficient of heat transfer;numerical simulation2059|2169|0发布时间：2024-07-18
- 摘要：To meet the needs of efficient electronics cooling, a flat loop heat pipe (LHP) with novel evaporator structure was designed based on improving capillary pressure, decreasing flow resistance, enhancing heat transfer and reducing heat leakage. Compared with evaporator of conventional flat loop heat pipe, the novel evaporator replaced mechanical microchannels with biporous microchannels. Heat transfer performance of the LHP was investigated at the anti-gravity orientation. The experimental result showed that, the LHP can start-up quickly without any temperature overshoot and oscillation at the heat load of 20 W. Besides, the novel LHP was able to keep the highest temperature of the evaporator below 80℃, and the thermal resistance of LHP was only 0.15 K/W at the heat load of 200 W. The comparative experiments indicated that the novel design of evaporator can shorten the heat transfer route in the height direction, enhance evaporation/boiling heat transfer and further reduce heat leakage, thus improved the anti-gravity operating ability of LHP.关键词：loop heat pipe;anti-gravity experiment;evaporator;biporous2377|3910|4发布时间：2024-07-18
- 摘要：A portable cooling system for military electronic is developed to solve cooling problems under high temperature circumstance by integrating the micro efficient refrigeration components. The experimental results show that the refrigeration system has a cooling capacity of 300 W under the ambient temperature of 40 ℃ ，the intake air temperature is cooled to15 ℃. It effectively solves the cooling demand of the military portable devices under high temperature circumstance.关键词：electronic cooling;refrigerating capacity;integration2278|2733|4发布时间：2024-07-18
- 摘要：To experimentally investigate the hunting mechanism of superheated temperature of a variable refrigerant volume refrigeration system, the opening of electronic expansion valve, the capacity of chilled water and the outlet temperature of cooling water are changed. The results show that when the opening of electronic expansion valve is at 24.7 %-25.3 %, the humting amplitude of superheated temperature is less than 1 K. With the opening increasing (25.6%-26.2%), the humting amplitude is about 3 K. When the opening is at 26.5%-26.8%, the amplitude goes back to less than 1 K. Moreover, the change of heat transfer in evaporator is the primary cause to hunting of superheated temperature, and heating load and refrigerant mass flow are the important parameters for in-tube boiling heat transfer, and both of them should be considered in the investigation for hunting of superheated temperature. In addition, pressure ratio has greater effect on refrigerant mass flow. When the system is at the first stage of increasing pressure ratio, the mass flow rate of refrigerant also increases, and the surface coefficient of heat transfer sharply increases while superheated temperature decreases. When the pressure ratio is sequentially increasing, the mechanism of heat transfer keeps alternation between convective boiling of liquid film and heat transfer of superheated vapor. The mechanism of hunting of superheated temperature for closed-loop control of expansion valve-evaporator is more complicated, which should be focused in later research.关键词：electronic expansion valve;superheated temperature;hunting2281|3210|8发布时间：2024-07-18
- 摘要：The quality of biospecimens is a very important factor of evaluating a biobank. Cryopreservation may induce apoptosis and changes of gene expression in cells. In this research the apoptosis profiles were assessed by Flow Cytometry and the expression of RNAs related to apoptosis were estimated by Real-time fluorescent quantitative PCR (qPCR) in Hep-G2 cells after cryopreservation. The results showed that with the addition of 10% DMSO or no cryoprotectant during cryopreservation, the cryopreservation progress made some impact on apoptosis and the expression of RNAs related to apoptosis in Hep-G2 cells. During cryopreservation, the cells were all dead with no cryoprotectant, but more cells apoptosis occurred with 10% DMSO. The cells could be recovered to normal level when the cells were recultured for 24 h after cryopreservation.关键词：cryopreservation;apoptosis;flow cytometry;real-time fluorescent quantitative PCR2413|2240|1发布时间：2024-07-18
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