共查询到20条相似文献,搜索用时 0 毫秒
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Subcooled flow boiling heat transfer experiments were performed with water and ethylene glycol/water mixtures at five flow velocities and four fluid inlet temperatures. Both turbulent flow and laminar flow were tested in a special test facility with its experimental test section heated from the bottom surface only. Boiling curves and subcooled flow boiling heat transfer coefficients of the tested fluids were determined from the experimental measurements. Predictive correlations of the subcooled flow boiling heat transfer coefficients were developed based on the experimental data. Comparisons are presented of wall temperatures between the experimental measurements and the correlation predictions. 相似文献
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Visualization experiments in upward forced convective nucleate boiling flows were carried out. The bubble growth and collapse have been measured using high-speed photography technique with distilled water under atmospheric pressure. The experiments show that the bubbles depart from nucleating sites shortly after nucleation and slide along the heater surface. The bubbles grow while sliding, attain a maximum size, then lift from the surface sometime during condensation, and quickly vanish in the bulk liquid. Parametric studies show that bubble diameter and departure frequency increases with an increase in heat flux, a decrease in subcooling, and a decrease in mass flux. 相似文献
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Experimental Investigation of Subcooled Vertical Upward Flow Boiling in a Narrow Rectangular Channel
Accurate models for the onset of nucleate boiling, density of active nucleation sites (Na), bubble departure size (Dd), and departure frequency (fd) are essential to the success of computational fluid dynamics analysis of two-phase thermal-hydraulics involving subcooled flow boiling in nuclear reactor systems. This work presents an experimental study of subcooled flow boiling in a vertical upward narrow rectangular channel that mimics the flow passage in the plate fuel assembly of boiling water reactors. The experiments are conducted over a range of mass flux (G = 122–657 kg/m2s), inlet subcooling (ΔTsub = 4.7–33.3?C), and heat flux (q″ = 1.7–28.9 W/cm2). Based on the experimental data, empirical correlations are developed for the prediction of onset of nucleate boiling, Na, Dd, and fd for given flow conditions. These correlations are valid in the nucleate boiling regime when the wall superheat is less than 12°C and can be incorporated in the computational fluid dynamics codes to enable more precise simulation of subcooled flow boiling heat transfer and two-phase flow in nuclear energy applications. 相似文献
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In this study, the effects of surface roughness, fluid velocity, and surface inclination on hot spot subcooled flow boiling are investigated experimentally. The experimental set-up consists of a circular heater that is placed on the lower wall of a channel. Based on the experimental data, two new independent empirical correlations are presented. The experimental results show that by increasing the surface roughness and fluid velocity, the surface heat fluxes increase. Inclination of the surface in either direction yields a higher heat transfer coefficient in comparison to its horizontal position when the surface is smooth and lower for the rough surface. 相似文献
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本文设计了一个可视化微小平直流道,利用摄影装置观察记录了液态水通过平板内部直径70μm的微孔在水平平板表面上形成液滴并成长直至脱离的过程,分析了不同流道高度条件下接触角之差与液滴高度和通道内流动空气的雷诺数的关系,并且进一步讨论了平板表面特性对液滴脱离高度和接触角之差的影响. 相似文献
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Flow boiling pressure drop and flow instabilities of Ω-shaped reentrant copper micro-channels were experimentally explored. Tests were conducted in deionized water and ethanol at inlet subcoolings of 10°C and 40°C, mass fluxes of 125–300 kg/m2·s, and a wide range of heat fluxes and exit vapor qualities. The operational parameters effects, i.e., heat flux, mass flux, inlet subcooling, and coolants, on pressure drop and flow instabilities were systematically explored. The two-phase pressure drop of reentrant micro-channels were found to generally increase monotonically with increasing heat fluxes and exit vapor qualities. Nevertheless, the roles of mass flux and inlet subcooling were dependent on the test coolant. 相似文献
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A closed-loop two-phase mini-channel-based heat sink driven by a micro-gear pump was developed in this work. Using water as an example, experiments were performed in two micro-channel heat sinks under the conditions of initial pressure of Pin = 34–113 kPa, mass velocity of G = 19–468 kg/m2s, outlet quality of xe,out = ?14–66%, and heat flux of q″ = 0–230 W/cm2, which covered single-phase flow, subcooled flow boiling, and saturated flow boiling regions. The results showed distinctive differences between the subcooled and saturated boiling regime and revealed that the influence of the system pressure. The experimental data were also compared to a boiling mechanism demarcation map and assessed against some empirical correlations, which suggests some uniqueness of the current heat sink associated with flow boiling at the mesoscale. 相似文献
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The present work is an experimental investigation of the incipient boiling of R134a inside a circular glass minichannel mounted horizontally and equipped with a series of transparent indium tin oxide heaters. The effects of heat flux input levels and refrigerant mass fluxes on the onset nucleate boiling process and on the saturated boiling heat transfer rate are quantitatively explored. The flow pattern visualizations, carried on by means of a high-speed camera, show that the nucleation process is oddly non-uniform: the first vapor bubbles are always generated on the upper side of the tube and lead to a first wall temperature drop. A further increase in the heat flux values results in an increased wall superheat until bubble nucleation also originates on the lower side of the tube, causing a second wall temperature drop. Finally, at higher heat input levels, the boiling process becomes uniformly distributed on the inner tube surface. This phenomenon occurred also after a 180° rotation of the glass tube, and, after a critical analysis of the potential origins, it remains presently unexplained. An evaluation of heat transfer coefficients for low vapor quality regimes is finally presented. 相似文献
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In this article, an experimental investigation is performed to measure the boiling heat transfer coefficient of water flow in a microchannel with a hydraulic diameter of 500 μm. Experimental tests are conducted with heat fluxes ranging from 100 to 400 kW/m2, vapor quality from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/m2s. Also, this study has modified the liquid Froude number to present a flow pattern transition toward an annular flow. Experimental results show that the flow boiling heat transfer coefficient is not dependent on mass flux and vapor quality but on heat flux to a certain degree. The measured heat transfer coefficient is compared with a few available correlations proposed for macroscales, and it is found that previous correlations have overestimated the flow boiling heat transfer coefficient for the test conditions considered in this work. This article proposes a new correlation model regarding the boiling heat transfer coefficient in mini- and microchannels using boiling number, Reynolds number, and modified Froude number. 相似文献