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Jun Zhang 《中国化学工程学报》2015,23(9):1453-1459
Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as wel as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The sim-ulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence. 相似文献
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Heat transfer characteristics are studied for gas carrying evaporation with fluidized solid particles in a vertical rectangular conduit. Experimental results show that heat transfer of gas carrying evaporation is enhanced and the superheat of liquid in contact with heating surface lowers remarkably by introducing solid particles. Nucleate boiling on the heating surface is suppressed to a considerable degree. The mechanism of heat transfer enhancement by fluidized solid particles is analyzed with the consideration of collisions of solid particles with the boiling vapor bubbles. 相似文献
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An experimental study has been carried out to investigate systematically the effects of acoustic cavitation parameters and fluid subcooling on boiling of acetone around a horizontal circular tube. The experimental results show that acoustic cavitation enhanced remarkably the boiling heat transfer and decreased the incipient boiling superheat and that cavitation bubbles effect on boiling heat transfer reduced with cavitation distance. For boiling curves in a form of h-q“, elevated cavitation distance shift nucleate boiling curves to the right of the corresponding ordinary pool boiling curve. The associated mechanism of heat transfer enhancement is analyzed with the consideration of cavitation bubble influence on vapor embryo. 相似文献
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An experimental study has been carried out to investigate systematically the effects of acoustic cavi-tation parameters and fluid subcooling on boiling of acetone around a horizontal circular tube. The experimental results show that acoustic cavitation enhanced remarkably the boiling heat transfer and decreased the incipient boiling superheat and that cavitation bubbles effect on boiling heat transfer reduced with cavitation distance. For boiling curves in a form of h-q", elevated cavitation distance shift nucleate boiling curves to the right of the corresponding ordinary pool boiling curve. The associated mechanism of heat transfer enhancement is analyzed with the consideration of cavitation bubble influence on vapor embryo. 相似文献
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Gas phase polymerization of butadiene by neodymium catalyst was modeled. The effects of mass and heat transfer resistances in the external boundary layer and within particles, sorption of butadiene in polybutadiene,and deactivation of active sites on polymer particle growth and morphology were studied. Simulation results show that the effects of intraparticle mass and heat transfer resistances on the growth rate of polymer particles are insignificant, and that there is no significant effect of mass transfer resistance on the morphology of polymer particles.The simulation results were compared with the experimental results. 相似文献
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The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct current (DC) electric field with bubbles attached to the orifice. The air bubbles were slowly generated in the transformer oil pool at different orifices, so that the effect of flow on bubble shape was eliminated. The results showed that the bubbles were elongated and the departure volume decreased when the electric field was intensified. The major and minor axes, aspect ratio and departure volume increased with increasing the orifice diameter. Both the electric field and orifice size have great influence on bubble behavior. The bubble deformation was also simulated to compare with the experimental results. The numerical and experimental data qualitatively agree with each other. 相似文献
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This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three chemical vapor deposition (CVD) reactors. A two-dimensional model for the gas flow, heat transfer, and mass transfer was coupled to the gas-phase reaction and surface reaction mechanism for the deposition of polycrystalline silicon from trichlorosilane (TCS)-hydrogen system. The model was verified by comparing the simulated growth rate with the experimental and numerical data in the open literature. Computed results in the reactors indicate that the deposition characteristics are closely related to the momentum, thermal and mass boundary layer thickness. To yield higher deposition rate, there should be higher concentration of TCS gas on the substrate, and there should also be thinner boundary layer of HCl gas so that HCl gas could be pushed away from the surface of the substrate immediately. 相似文献
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A series of positive electrodes for Ni/MH battery were fabricated by addition of CoO.The morphology and microstructure of the electrodes were examined by SEM and EDS, and electrochemical behavior was investigated in three-compartment appliances at room temperature.The electrochemical performance of the positive electrodes with CoO was improved. Under the same charge-discharge cycle, the electrodes with CoO showed higher specific capacity, lower charge mean voltage and higher discharge mean voltage. But further increasing the content of CoO in the electrodes contributed negative effect on the overall performance. Addition of 8% (mass) CoO was suggested to be a suitable content for the positive electrode. 相似文献
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Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investigated the overall heat transfer performance and friction factor in ribbed and ribbed-grooved channels with rib angle of 30°.The experimental results show that the overall thermo-hydraulic performance for ribbed-grooved channel is increased by 10%-13.6% when compared to ribbed channel.The investigation on the effects of different rib angles and rib pitches on heat transfer characteristics and friction factor in ribbed-grooved channel was carried out using Fluent with SST(shear-stress transport) k-ω turbulence model.The numerical results indicate that the case for rib angle of 45° shows the best overall thermo-hydraulic performance,about 18%-36% higher than the case for rib angle of 0°.In addition,the flow patterns and local heat transfer characteristics for ribbed and ribbed-grooved channels based on the numerical simulation were also analyzed to reveal the mechanism of heat transfer enhancement. 相似文献
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The distributions of thermal resistance in viscous sublayer,buffer region and turbulent core region,local flow resistance and local heat transfer characteristics at different locations downstream of the twisted-tape element were numerically studied in a converging-diverging tube inserted with spaced twisted-tape element by analyzing the attenuation of self-sustaining swirl flow.The results showed that the local performance was poor as thermal resistance was too concentrated in its distribution for a particular region.The more uniform the distribution of thermal resistance,the better the local performance.The local performance reached its best when the fluid just left the spaced twisted-tape,in which the flow resistance dropped substantially but the enhancement of heat transfer was still significant.The self-sustaining flow was maintained at a long distance.The best performance was at the length of 36.85 times the diameter,increasing by 6.8% compared with a converging-diverging tube. 相似文献
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The effect of a radial d.c. electric field on nucleate boiling heat transfer was investigated experimentally using a single-tube shell/tube heat exchanger. A dielectric liquid (Freon R. 114) was used in the shell and the tube was heated by circulating water through it.
It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis.
It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application 相似文献
It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis.
It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application 相似文献
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电场分布对R123沸腾换热的影响 总被引:1,自引:0,他引:1
采用6种不同电极布置方式,进行了不同电势和热流密度下的R123池沸腾换热的试验研究。通过数值分析,计算了不同电极布置下换热面上的电场强度及分布。不同的电极布置,会导致换热面上电场强度和电场均匀性两方面的变化。结合试验和电场分布的计算结果,分析了电场均匀性、电场强度、热流密度与沸腾换热效果之间的关系。结果表明,在低热流密度下,电场分布对沸腾换热影响较大;而在高热流密度下,影响较小。电水动力学(EHD)强化换热效果是电场强度和电场均匀性综合作用的结果。 相似文献
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提出了颗粒碰撞壁面过程中颗粒打破边界层和颗粒与壁面导热的强化传热模型,以分析气固两相流中颗粒强化对流传热的机理,通过模型计算研究了风速、颗粒浓度和粒径等因素对颗粒在壁面的停留特性、颗粒在边界层的扰动及对导热和边界层破坏两种强化机制传热比重的影响.以气固两相流横掠圆管的传热过程为例进行计算,计算与实验结果一致,并获得了具有实用价值的关联计算式. 相似文献
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将一圆筒柱面电极布置在换热器入口管道处,并与高压电源正极连接,研究圆筒电极形成的非匀强电场对实验段换热表面CaCO3污垢沉积的影响。作为对比,同时分析了平行板电极(匀强电场)作用下CaCO3污垢沉积行为。结果表明,施加平行电极与圆筒电极均可抑制换热表面CaCO3污垢的沉积,抑垢率随施加电压(0~5000 V)的增加呈现先升高后降低的变化趋势。当施加平行电极时,最佳抑垢电压值为1000 V,最佳抑垢率为 73.27%。当施加圆筒电极时,最佳抑垢电压为500 V,最佳抑垢率为83%。因此,施加圆筒电极具有更好的抑垢效果,同时最佳抑垢电压更低,可降低电的消耗。此外,在无电场作用时,换热表面CaCO3晶体主要为树枝状文石结构,当施加圆筒或平行电极时,CaCO3晶体主要为块状方解石结构。 相似文献