Jet Impingement Cooling of a Hot Moving Steel Plate: An Experimental Study

In the current study, a hot moving steel plate of 6 mm thickness with an initial temperature of 900°C has been considered for jet impingement cooling. The experiment has been designed with the help of Design of Expert software to optimize the process parameters based on the highest cooling rate. The various subsurface transient temperature histories have been measured during the cooling process. The surface heat flux and surface temperature were calculated with the help of a commercial inverse heat transfer solver called INTEMP. The experimental result has been presented in terms of cooling rate and critical heat flux.     

Enhancement of Cooling Rate for a Hot Steel Plate using Air-Atomized Spray with Surfactant-Added Water

The objective of the current research deals with the experimental study of an air-atomized spray with surfactant-added water, cooling a 12-mm-thick AISI-1020 stationary steel plate at three different initial surface temperatures (400°C, 600°C, and 900°C). Furthermore, the effects of surfactant concentration and airflow rate on the cooling rate have been investigated. The surface heat flux and surface temperature show a significant improvement in cooling for all three cases of initial surface temperatures when the air-atomized spray was used with surfactant-added water.     

R600a喷雾冷却系统换热过程

以R600a压力式封闭系统喷雾冷却过程为研究对象,对其换热过程进行分析。对液滴撞击热面后的状态进行建模,分析了其运动状态。通过忽略液膜的对流换热,引入韦伯数来简化并修正雾滴与热源表面的对流换热系数关联式;借鉴二次成核理论,通过单位时间内,单位面积上覆盖的雾滴数量对核态沸腾换热系数关联式修正。通过上述分析,以对流换热和核态沸腾换热两种机理为中心,建立了新的换热系数关联式。通过与其他文献的关联式、实验测量值进行比较、不同工质进行比较、不同实验系统比较,发现该式预测值和实验测量值偏差在20%以内,能够很好地预测压力式封闭系统喷雾冷却过程的换热系数。     

蒸发性对燃油瞬态喷雾撞击壁面的动态传热影响

直喷发动机燃油喷雾撞击壁面形成油膜,导致燃烧效率降低,颗粒物排放增加.伴随撞壁的动态传热过程对油膜蒸发具有重要影响.本文针对正戊烷、甲醇、甲醇-汽油混合燃料瞬态喷雾撞击壁面,研究了不同条件下蒸发性对燃油瞬态喷雾撞击壁面动态传热影响.结果表明,提高喷油温度可促进燃油雾化,增大喷油压力或降低喷油距离可提高液滴撞壁强度,缩短...     

喷雾冷却相变传热的建模与模拟计算

喷雾冷却是一种高效的热控技术,为了探索形成完善的喷雾冷却技术设计流程,文章开展了喷雾冷却传热过程的建模研究.针对喷雾冷却传热过程的模拟计算,基于喷雾冷却相变传热的4个传热机制:液膜对流传热、池沸腾传热、二次气泡沸腾传热、二次气泡高频化机制,利用Monte Carlo方法描述了不同粒径与速率分布的液滴撞击液膜并生成二次气...     

小温差喷雾碰壁蒸发的实验研究

本文对小温差下垂直平面的喷雾碰壁蒸发传热特性进行了实验研究,研究了喷嘴在不同的流量和喷距下热流密度、壁温和换热系数之间的关系.实验中,测量范围还扩展到无沸腾区域.实验发现,在常压下,水雾在加热表面开始沸腾的过热度约为10℃,这时的沸腾换热系数将急剧增大,壁温上升的斜率显著下降.本文的研究结果对新型蒸发器的开发有指导作用.     

Experimental Investigation Of Spray Cooling Heat Transfer On Straight Fin Surface Under Acceleration Conditions

A spray cooling heat transfer experiment on straight fin surface under acceleration conditions was conducted to investigate the effects of acceleration, flow rate, and nozzle height. The results show that the acceleration can improve the heat transfer performance in a limited way. In addition, whether in the acceleration or stationary condition, the flow rate as well as the nozzle height has the same impact on the spray cooling performance. It is also observed that the surface temperature can influence the effect of flow rate on spray cooling performance, and the cooling performance becomes worse with the increase of nozzle height.     

微尺度水平管内沸腾换热特性研究

对不同质量分数下非共沸混合工质(R134a/R32)在微尺度管道内的流动沸腾换热特性进行了比较和分析,阐述了热流密度、质量流量和质量干度对换热的影响。结果表明:热流密度对换热的影响随着质量流量的增加而愈加明显;在质量分数为75%/25%和65%/35%时,换热系数随着质量流量的增大而增大;而质量分数为85%/15%时,换热系数随质量流量的变化先增加后减小;随着质量干度的增加,换热系数在各质量分数下基本上都呈上升趋势。     

An Experimental Investigation of Liquid Jet Impingement and Single-Phase Spray Cooling Using Polyalphaolefin

Experiments on triangular and rectangular array jet impingement and single-phase spray cooling have been performed to determine the effect of both cooling techniques on heat transfer coefficient (h) and the coolant mass flux required for a given cooling load. Experiments were performed with circular orifices and nozzles for different H/D values from 1.5 to 26 and Reynolds number range of 219 to 837, which is quite lower than the ranges employed in widely used correlations. The coolant used was polyalphaolefin. The experiments simulated the boundary condition produced at the surface of the stator of a high power low-density generator or motor. For the custom fabricated orifices, commercial nozzles, and conditions used in this study, both cooling configurations showed enhancement of heat transfer coefficient as H/D increases to a certain limit after which it starts to decrease. The heat transfer coefficient always increases with Reynolds number. In keeping with previous studies, single-phase spray cooling technique can provide the same heat transfer coefficient as jets at a slightly lower mass flux, but with much higher-pressure head. Special Nu_d correlations that account for the range of parameters and coolant studied in this work are derived.     

New Pool Boiling Heat Transfer in the Presence of Low-Frequency Vibrations Into a Vertical Cylindrical Heat Source

A vertical cylinder was applied as a heat source into a water pool; the vibrations were imposed into the heater with different heat fluxes, and the frequencies were adjusted at 10, 15, 20, and 25 Hz. An imaging system was employed to observe the produced bubbles around the cylindrical heat source. The results showed that the boiling heat transfer was enhanced under the vibrations with a shorter transient process, and the wall temperature also decreased. The best enhancement ratio was achieved at the frequency of 25 Hz and a heat flux value of 30 kW/m² as a consequence of imposed vibrations.     

Flow Boiling Heat Transfer in Micro-Channel Heat Sinks under Sub-Atmospheric Pressures

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 P_in = 34–113 kPa, mass velocity of G = 19–468 kg/m₂s, outlet quality of x_e,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.     

Study on Heat Transfer Performance of Skin Heat Exchanger

Cooling technology is facing new challenges with the increase of electronic equipment power onboard aircraft. The traditional heat sink based on high-altitude bleed air does not satisfy this increase of cooling demands. In this article, an air/air-type skin heat exchanger is studied for cooling aircraft electronic equipment. It uses outside high-altitude cold air rather than bleed air as a heat sink. This cooling technology can effectively remove the heat load of high-power electronic devices without greatly increasing aircraft performance penalty. To assess its high-altitude heat transfer performance, an experimental prototype was designed and made. Some experiments were conducted on a ground experimental test. The heat transfer criteria formulas were obtained for both the side air in the skin heat exchanger and its convective heat transfer coefficients. Based on these experimental analyses, the heat transfer performances of the skin heat exchanger in a high-altitude cruise condition are deduced when it is assumed to be installed at an unfavorable position and a favorable position, separately. This work tries to provide a technical support for its future onboard application.     

叶顶单一气膜孔位置传热特性的数值研究

本文采用数值模拟的方法对凹槽叶顶前缘气膜孔的位置进行了研究,通过改变前缘第一气膜孔位置来分析叶顶区传热。数值模拟结果表明,由于冷却气对该区域没有提供足够的保护,肩壁表面的平均绝热效率远低于凹槽底面,平均传热系数远高于凹槽底面。叶顶第一气膜孔向前缘移动使肩壁表面的平均传热系数先升高再降低,叶顶前缘低绝热冷却效率区逐渐消失...     

Experimental Investigation of Heat Transfer Coefficient from the Impingement of a Slot Jet Using Conjugate Gradient Method with Adjoint Equation

The convective heat transfer coefficients resulting from a slot jet on a plane surface have been estimated by using the real measured temperatures in the plate and inverse method. In this study, the inverse method used the conjugate gradient method with an adjoint equation. Distributions of the local heat transfer coefficient on the impingement surface were determined for various Re and H/Dh. It was found the heat transfer coefficients generally tended to decrease with increasing separation distance and to increase with an increase in Reynolds number. This presented method is able to estimate the variation of the local Nusselt number with time.     

高功率固体激光器喷雾冷却技术

喷雾冷却作为一种解决高功率激光器散热需求的技术得到越来越多的关注。结合近几年的研究工作,综述了喷雾冷却技术的研究现状。针对高功率激光器的散热需求,主要从传热机理、影响因素、温度均匀性方面进行阐述,分析了存在的问题。提出将制冷系统和喷雾系统结合、R600a等制冷剂为冷却剂的冷却方案,设计了气助式制冷喷雾冷却系统,分析了适用于制冷喷雾冷却系统的工质,提出了喷雾冷却技术在高功率固体激光器散热中的发展方向。     

微通道换热公式应用于水和制冷剂适用性评价

水是微通道流动沸腾常用的换热工质,由于其饱和温度较大,目前的沸腾实验大多采用制冷剂替代.然而,水和制冷剂在物性参数上依然具有较大差异,应用于制冷剂的换热公式并不一定能有效应用于水.因此,本文收集1084个工质为水和1002个工质为制冷剂的实验数据,比较两者在无量纲数上的差异,并选取6个常用换热公式,比较其应用于两者的预...     

涡轮叶片前缘阵列冲击冷却流动及传热特性数值研究

本文采用SST湍流模型模拟了类前缘通道内蒸汽射流阵列冲击冷却的流动与传热特性,分析了雷诺数(Re=10000～50000)、孔径比(d/H=0.5～0.9)和孔间距比(S/H=2～6)对流动及传热性能的影响规律,得到了相应的传热和摩擦关联式。结果表明:在不同雷诺数下,d/H从0.5到0.9变化时,通道压力损失系数降低了76%～79%,靶面平均努塞尔数降低了45%～49%;S/H从2增至6时,通道压力损失系数增加了1.64～1.92倍,靶面平均努塞尔数增加了54%～64%;增大d/H、减小S/H可有效提高类前缘通道蒸汽冲击冷却的综合热力系数。本文研究结果可为未来先进燃气轮机高温涡轮叶片蒸汽冷却结构的设计提供参考和借鉴。     

Experimental Design and Methodology for Estimation of Local Heat Transfer Coefficient in Jet Impingement Using Transient Inverse Heat Conduction Problem

Abstract

This article aims to employ a two-dimensional inverse heat conduction technique in designing an experiment for accurately estimating the local convective heat transfer coefficient in slot jet impingement, given temperature measurements at some interior locations in the target plate. The method uses a sequential procedure together with the Beck function specification approach. Solution accuracy and experimental errors are examined using simulated temperature data. It is concluded that a good estimation of the space variable heat transfer coefficient can be made from the knowledge of the transient temperature recordings. The technique is used in a series of numerical experiments to provide the optimum experimental design for a slot jet impingement heat transfer investigation.     

微重力下微结构表面强化沸腾换热研究

为了提高航天器中电子器件的冷却效率,本文利用干式腐蚀方法形成方柱微结构,通过控制加热电流方法,在北京落塔进行了持续3.6 s有效微重力时间的过冷FC-72池沸腾强化换热实验研究。研究结果表明:相比光滑表面,方柱微结构表面利用其独立于重力水平的毛细作用力,显著地强化了微重力沸腾换热。     

Effect of Oxide Layer in the Ultra Fast Cooling of a Steel Plate

This study deals with the effect of oxide layer during ultra-fast cooling of a hot plain carbon steel plate. In the current research, the hot plain carbon steel plates were cooled from an initial surface temperature of 900°C by using air atomized spray at different air pressures. The heat transfer analysis illustrates that during high pressure air atomized spray cooling, the average surface temperature is almost unaffected by the presence of an oxide layer. For better understanding, the plain carbon steel cooling data have been compared with the data obtained during the cooling of a stainless-steel plate.