共查询到20条相似文献,搜索用时 15 毫秒
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Forced convection heat transfer from a helically coiled heat exchanger embedded in a packed bed of spherical glass particles was investigated experimentally. With dry air at ambient pressure and temperature as a flowing fluid, the effect of particle size, helically coiled heat exchanger diameter, and position was studied for a wide range of Reynolds numbers. It was found that the particle diameter, the helically coiled heat exchanger diameter and position, and the air velocity are of great influence on the convective heat transfer between the helically coiled heat exchanger and air. Results indicated that the heat transfer coefficient increased with increasing the air velocity, increasing helically coiled heat exchanger diameter, and decreasing the particle size. The highest heat transfer coefficients were obtained with the packed-bed particle size of 16 mm and heat exchanger coil diameter of 9.525 mm (1/4 inch) at a Reynolds number range of 1,536 to 4,134 for all used coil positions in the conducted tests. A dimensionless correlation was proposed for Nusselt number as a function of Reynolds number, particle size, coil size, and coil position. 相似文献
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自然循环型气液固三相流载气蒸发传热的实验研究 总被引:1,自引:0,他引:1
符号表Cs固体颗粒在液体中的含量vol.%dp固体颗粒直径mmde实验段当量直径mmh表面传热系数kw/m2Kk液体导热率W/mKq热通量kw/m2r液体汽化潜热kJ/kgTw加热壁面温度℃ug载气表现速度mm/sul循环液速m/sρg载气的密度kg/m3ρl液体的密度kg/m3ρs固体颗粒的密度kg/m3μg气相粘度mPa·sμl液相粘度mPa·sBo沸腾准数Nu努塞尔准数Reg载气雷诺数Rel液体雷诺数沸腾与蒸发装置内换热壁面上的结垢与结疤是降低换热效率的重要因素之一。换热装置的防垢抗垢一直受到重视。近年来,一些研究者将固体颗粒引入换热器的加热管内,形成流化床换热… 相似文献
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对空冷翅片式和水冷光管式两种冷凝器进行了数值模拟,模拟了不同结构、不同对流换热系数、不同流速下氨液的冷凝量。结果表明:冷凝器管内热阻比管外热阻对氨气的冷凝影响更大;管径一定时,氨液冷凝量随入口速度的的增大而减小,当速度增加到某一值时,冷凝量基本不发生变化,对空冷翅片式冷凝器该速度为0.15m/s,水冷光管式为0.2m/s。 相似文献
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Heat transfer augmentation due to turbulence in the gaseous flow of a gas-solid fluidized bed is analyzed. Since the heat transfer in such beds is enhanced by various mechanisms, each mechanism's contribution can only be separately evaluated using special means. Therefore, we employed a new mass transfer measurement technique to measure the contribution of the turbulence induced by particle motion on the total heat transfer occurring around a horizontal test cylinder immersed in a fluidized bed. Results indicate that the mass transfer, i.e., analogous to convective heat transfer to or from the gaseous flow, is enhanced by the turbulence produced from particle motion on the front side of the cylinder surface, but that other heat transfer mechanisms besides turbulence contribute to the heat transfer augmentation taking place on the cylinder side walls and back-side surface. 相似文献
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This article presents the research on the air–water system flowing in a pipe section with electrical heating with a wire-mesh bed inside it. The heat flux was determined and so was the convective heat transfer coefficient for the two-phase flow through a pipe length that had been completely or partially filled with the wire-mesh packing. The packing level was found to strongly affect the heat transfer potential. Also, the dominant role was identified for a liquid in the heat exchange process under two-phase gas–liquid flow through the wire-mesh packing. 相似文献
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High-speed visualization of adiabatic flow and heat transfer rate determination for constant wall heat flux conditions were performed to study the flow and heat transfer behavior of non-boiling, gas–liquid two-phase vertical upward flow in a 2.00 mm-diameter tube. Liquids of different volatilities, including water, ethylene glycol, and hexadecane, were employed to investigate the roles of convective heat transfer and evaporation for a wide range of flow conditions encompassing Taylor, slug-annular, and annular flow regimes. The heat transfer rate is found to depend strongly on the flow regime. Significant evaporative cooling was observed for the volatile system at high gas flow rates. A heat transfer enhancement up to fivefold over that for the liquid-only flow was observed in the annular flow regime. 相似文献
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Irma Welling 《实验传热》2013,26(1):7-19
This article describes an experimental study of natural convection around a horizontal square plate and a vertical cylinder, and provides data for the velocity and temperature profiles around representative heat sources of high heating capacity. From the measured velocity and temperature distributions, enthalpy fluxes, average convective heat transfer coefficients, and volume flow rates were derived for the plate and cylinder heat sources. New relationships between volume flow rate and distance above the plate and cylinder are presented. 相似文献
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The morphological instability of solidification is analytically studied in the presence of an anisotropic and heterogeneous
phase transition zone with allowance for a liquid flow and convective heat-andmass transfer in this two-phase zone. The mechanism
of breaking the stability of solidification is considered; it consists in a convective heat and impurity transfer during a
liquid flow along channels in the phase transition zone. The morphological instability is subjected to linear analysis with
allowance for a liquid flow in the liquid phase of the system, impurity diffusion in the two-phase zone, and the dependence
of the transfer coefficients on the phase composition. The perturbation evolution parameter is determined for an anisotropic
and heterogeneous two-phase zone, and neutral stability curves of the process are obtained. It is shown that taking into account
impurity diffusion and an increase in the heterogeneity of the phase transition zone broaden the instability region and that
a decrease in the anisotropy narrows this region. A new criterion of convective morphological instability of solidification
with a two-phase zone is found, and it substantially broadens the instability region when the liquid flow velocity increases. 相似文献