分离结构扰流柱的叶片通道流动与换热数值研究

应用-两方程模型对分离结构扰流柱的叶片内冷通道的换热与流动进行了三维数值模拟研究,扰流柱的布置按简单叉排方式。计算结果表明:在本文的参数范围内,与完整扰流柱相比,分离结构扰流柱的换热效果略有增强,而阻力系数随之增大,分离位置居中的扰流柱通道的换热效果最好。随着开缝厚度的增加,通道表面换热效果和流动阻力系数均先略有增大而后逐渐减小。     

Experimental Study of Unsteady Local Heat Transfer for Impinging Miniature Jet

An experimental study was performed to characterize local and average heat transfer coefficients on a horizontal disk impinged by a circular liquid jet. The radial distribution of local heat flux and surface temperature were determined under unsteady-state conditions. The inverse heat conduction problem was solved using the responses of sensors located inside the experimental disk. It was shown that the distribution of the surface heat flux and the surface temperature was dependent on the radial location and the time. The average Nusselt number was seen to be independent of the nozzle-to-heat exchange surface spacing. It increased with the Reynolds number and the nozzle diameter.     

微尺度流道相变传热特性的实验研究

为了探究微流道相变传热的特性,本文以去离子水为工质,对不同结构尺寸的铝制矩形流道中的相变传热特性进行了实验研究.结果表明:在本实验范围内,传热系数随流道尺寸减小而增大.传热系数随着热流密度的增加而增加.在同一热流密度下,随着干度的增大,传热系数变化不大.     

Constructal Optimization of Louver Fin Channels Subjected to Heat Transfer Rate Maximization and Pressure Loss Minimization

To obtain better fluid mixing and higher heat transfer rate in the low Reynolds number regime, various types of fins have been employed for electronic cooling applications. However, previous works showed that there are no remarkable differences in the thermal performance of a straight-plate and a channel with louvered-fins when the Reynolds number is low or moderate. In this paper, the Constructal law is applied to optimize the geometry of a channel with louvered-fins, where the objective is to maximize the total heat transfer rate and minimize the pressure loss. The selected domain has three degrees of freedom; the louver angle ratio, the louver pitch ratio, and the inlet louver length to outlet louver length ratio. The results showed that the effect of louver on the louver pitch ratio and the inlet louver length to outlet louver length ratio. There is a minimum value for the louver pitch ratio and below this value the vortices upstream of the turnaround louver block the distance between louvers and so decreases the flow efficiency. A comparison between results and previous experimental studies indicated that the channel optimized by constructal law is considerably superior compared to the standard channel in low Reynolds number regime.     

螺旋折流板管壳式换热器壳程传热性能及压降的研究

本文对螺旋折流板换热器和传统的弓形折流板换热器进行了壳程传热性能和壳程的阻力的对比,同时通过实验方法对25°、40°螺旋角的螺旋折流板和弓形折流板换热器进行了壳程传热性能和壳程阻力的研究,得出螺旋折流板换热器的螺旋流动强化了传热,螺旋折流板换热器的壳程阻力比弓形折流板换热器的壳程阻力小。     

低气压下翅片管换热器空气侧换热特性的实验研究

为研究低气压环境下翅片管换热器空气侧的换热特性,对不同气压环境下空气侧流速和翅片间距对平翅片管换热器空气侧换热特性的影响进行了实验分析。实验环境气压范围为40～100 kPa,换热器迎面风速为1.0～3.5 m/s,翅片间距2～3 mm。研究表明:实验工况下环境气压40 kPa时空气侧传热因子仅为常压下的30.42%～46.41%;低气压环境空气侧流速和翅片间距对空气侧换热的影响趋势与常压数据基本保持一致;不改变换热器结构,环境气压的变化仅影响空气物性,而对空气的流动状态的影响不大;翅片间距影响随Re的减小和环境气压的降低而减弱,两种翅片间距模型空气侧传热因子平均差异在环境气压为100 kPa时为12.07%,40 kPa时缩小为3.00%。     

泄流槽式螺旋折流板换热器传热系数与压降实验研究

以螺旋角25°为例,研究了泄流槽式螺旋折流板换热器传热系数与压降的变化,并给出了泄流槽螺式旋折流板换热器的传热系数与压降相关的计算公式。该结果可为系统仿真和泄流槽式螺旋折流板换热器的设计计算提供借鉴。     

Pressure Loss and Heat Transfer Through Heat Sinks Produced by Selective Laser Melting

Heat removal from electronic packages is often assisted with the use of heat sinks whose heat transfer surfaces come in a variety of forms such as cylindrical pins, flat fins, and corrugated sheet. These conventional designs are manufactured by traditional methods such as forging, machining, casting, stamping and bending, or a combination of processes. This article introduces a novel manufacturing technique, selective laser melting (SLM), and demonstrates its ability to fabricate new designs of heat sink that have not previously been considered, primarily due to their geometric complexity. Three novel finned structures have been manufactured and their thermal and fluid flow characteristics have been determined experimentally. The three heat sinks demonstrate selective laser melting's ability to produce fine detail and consist of a staggered elliptical array, an elliptical array where the pins are angled in a direction perpendicular to the flow, and a densely packed diamond array. The novel heat sink designs were compared to a cylindrical pin array manufactured using the SLM process as well as with pin fin data from the literature. The heat sinks produced by the SLM method have been shown to have superior performance to that of the conventional heat sinks. Although the angled elliptical fins transmit similar amounts of heat to the cylindrical pin fins across the range of air flow rates considered, they incur a lower pressure loss. The densely packed diamond array not only transfers 60% more heat than the cylindrical array, but does so with a lower pressure drop across it.     

Experimental Investigation of Heat Transfer in Microchannel with Inlet Cavitation Structure

Heat transfer of R134 a through the microchannel with an inlet reentrant cavitation structure was investigated for high flux thermal management of electronic devices.The cavitating flow patterns,pressure,and heat transfer characteristics were studied in the range of effective heat fluxes from 0 to 138.4 W/cm2 with mass flow velocities from 2.12 to 5.23 m/s.A stable and ideal starting point of two phase flow and heat transfer was commendably provided by the inlet cavitation orifice.There existed an axis deviation liquid jet after the micro-orifice.The refrigeration vapor was generated from the cavitation structure but liquidized at the downstream of the channel.The wall temperature along flow orientation presented an opposite trend under the test states with or without heat input.The cavitation structure can significantly suppress the flow oscillation in microchannels and the outlet pressure fluctuation reduced about 72%compared with the fluctuation at the entrance.The heat transfer coefficient had been distinctly impacted by heat flux at lower heat input and then maintained the value nearly constant of 11.0 W/(cm²·K)with the critical heat flux of 88.4 W/cm2.     

Heat Transfer and Pressure Loss in Combined Plain and Diagonally Finned Heating Surfaces

This paper presents the results of model investigation of the heat transfer in plain and combined plain and diagonally finned convective tube banks. A heat and mass transfer analogy, by means of a naphthalene sublimation technique, is used. The effect of tube bank arrangement on heat transfer coefficients and flow resistance is discussed. The results show an increase of Nusselt numbers in comparison to those obtained for plain tube arrangements; however, a significantly higher flow resistance accompanies this increase.     

Forced Convection Heat Transfer in Porous Structure: Effect of Morphology on Pressure Drop and Heat Transfer Coefficient

A light-weight structure with sufficient mechanical strength and heat transfer performance is increasingly required for some thermal management issues. The porous structure with the skeleton supporting the ambient stress and the pores holding the flowing fluid is considered very promising, attracting significant scientific and industrial interest over the past few decades. However, due to complicated morphology of the porous matrices and thereby various performance of the pressure drop and heat transfer coefficients(HTC), the comprehensive comparison and evaluation between different structures are largely unclear. In this work, recent researches on the efforts of forced convection heat transfer in light-weight porous structure are reviewed; special interest is placed in the open-cell foam, lattice-frame, structured packed bed, and wire-woven structures. Their experimental apparatus, morphological of the porous structures, effect of morphology on pressure drop and HTC, and further applications are discussed. The new method which measure morphology accurately should be paid more attention to develop more accuracy correlation. Also, the most research focused on low Reynolds number and existing structure, while very few researchers investigated the property of forced convection heat transfer in high velocity region and developed new porous structure.     

Experimental Analysis of the Effects of Particulate Fouling on Heat Exchanger Heat Transfer and Air-Side Pressure Drop for a Hybrid Dry Cooler

It is well known that significant fouling by particulate matter can have a deleterious effect on the performance of enhanced surface heat exchangers, and the same is true for hybrid heat exchangers. Hybrid heat exchangers are heat exchangers that are typically run in dry mode to reject heat. When the ambient conditions require more heat rejection than can be provided by sensible heat transfer, a water pump is turned on and water flows over the fins, and the evaporation of water provides a further cooling effect. Fouling in dry-mode operation is physically similar to that of air-cooled heat exchangers, but in evaporative mode the flow of the water over the coil eliminates the impact of fouling. A hybrid dry cooler heat exchanger of 60 cm × 60 cm frontal area has been installed in a well-instrumented wind tunnel to measure the heat exchanger's performance. Hot water flows through the coil to provide the load, and air flows over the coil to provide cooling. During evaporative mode operation another stream of water flows over the outside face of the coil, adhering mainly to the louvered fins. The louvered fins are specially designed for optimized water flow during wetting mode. The fins are made of aluminum, the tubes are copper, and protection against corrosion is realized by a special E-coating. This coil has been tested clean and fouled with ASHRAE standard dust, for both dry and wet operation. Results are presented for the air-side pressure drop and overall heat transfer conductance of the coil under all conditions for which 50% increases in air-side pressure drop are found under heavy fouling. The influence of fouling on heat transfer is small. Also, using the wetting water to wash the fouling off the coil is investigated and is found to be of some limited utility.     

蒸发冷却板式换热器的传热与阻力实验研究

通过对板式换热器传热的理论分析和在干工况、喷淋工况下的实验研究,得出板式换热器在喷淋情形下空气侧喷淋水量对强化对流传热系数的影响关系,进而拟合出喷淋情形下空气侧的对流传热系数的关联式。同时为了综合考虑由于喷淋造成的换热器性能的变化,还对喷淋前后空气侧的阻力变化进行了测试分析。     

超临界压力下倾斜上升内螺纹管传热特性的试验研究

在超临界压力下,对倾角α=19.5°的28.6×5.8(mm)倾斜上升内螺纹管内水的传热特性及管壁温度分布进行了试验研究。试验参数范围:p=23~28 MPa,质量流速G=600~1200 kg/(m2s),平均内壁热流密度q=300~600 kW/m2。试验结果表明:管内螺纹造成的漩流作用可减弱内螺纹管截面上自然对流的影响。倾斜内螺纹管壁温及传热系数沿周向分布不均匀性很小。壁面热负荷越大,壁温越高;提高质量流速可降低壁温。在高焓值区,压力越高,传热越强。此外,还提出了传热系数的计算公式以供工程设计参考。图6表1参11     

Experimental Study on Heat Transfer in Ducts with Winglet Disturbances

Heat transfer and friction characteristics for a new type of enhanced rectangular duct with winglets have been investigated experimentally. The results indicate that, in the range of Reynolds number from 5 2 10 3 to 4.7 2 10 4 , heat transfer performance of the enhanced duct with winglets is superior to the enhanced duct with transverse disturbances. Comparisons under the identical pumping power condition reveal that the Nusselt number ratio Nu/Nu o of the winglet duct to the smooth duct varies from 1.7 to 3.5, while this ratio is usually less than 1.5 for the enhanced ducts with transverse disturbances. For condition of same mass flow, the ratio Nu/Nu o of the winglet duct to the smooth duct varies between 2.7 and 6.0.     

冰浆传热与压降的研究进展

在固液两相冰浆在换热器中的传热和压降研究的现状和已取得的成果分析总结的基础上，介绍了所进行的直接接触式制冰的流动特性的研究成果，试验结果表明二元冰浆的摩擦阻力比纯水大，并随含冰率的变化呈非线性变化，但变化量不大，试验还测定了管道程度对二元冰浆流动阻力的影响。     

Heat Transfer Measurements inside Narrow Channels with Ribs and Trenches

Detailed heat transfer coefficient distributions are obtained for high aspect ratio (width/height = 12.5) duct with rib and trench enhancement features oriented normal to the coolant flow direction. A transient thermochromic liquid crystal technique has been used to experimentally measure heat transfer coefficients from which Nusselt numbers are calculated on the duct surface featuring heat transfer enhancement features. Reynolds number (calculated based on duct hydraulic diameter) ranging from 7100 to 22400 were experimentally investigated. Detailed measurements of heat transfer provided insight into the role of protruding ribs and trenches on the fluid dynamics in the duct. Experimentally obtained Nusselt numbers are normalized by Dittus-Boelter correlation for developed turbulent flow in circular duct. The triangular trenches provide heat transfer enhancement ratios up to 1.9 for low Reynolds numbers. The in-line rib configuration shows similar levels to the trench whereas staggered rib configuration provides heat transfer enhancement ratios up to 2.2 for a low Reynolds number of 7100.     

Numerical Study of Heat Transfer Augmentation of Viscous Flow in Corrugated Channels

Exact expressions are presented for the corrective terms for a one-dimensional fin temperature and heat lost when the insulated tip assumption is used for the case where the tip is maintained at a constant temperature. Both straight rectangular and uniformly thick annular fin geometries are discussed. Numerical examples are shown to highlight the considerable error in assuming an insulated tip condition.