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.     

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.     

涡轮叶顶冷却布置对叶顶传热冷却性能的影响

本文采用数值模拟的方法,对比分析了1+1/2对转涡轮四种不同的叶顶冷却布置方案对叶顶传热、冷却性能以及气动特性的影响。四种布置方案分别是:靠近压力面垂直叶顶方向、靠近压力面且与叶顶有30°出射角、中弧线位置垂直叶顶方向、中弧线位置有30°出射角。研究表明,气膜孔沿压力面布置与气膜孔沿中弧线布置相比可以降低叶顶传热系数;由于气膜孔倾斜布置气膜射流动量降低,且削弱了肾形涡的影响,气膜的侧向覆盖范围增大。因此气膜孔靠近压力面布置可以提高气膜冷却效率;气膜孔靠近压力面且有30°出射角比垂直布置叶顶热负荷减少2.7%。另外,气膜孔靠近压力面布置可以降低主流的泄漏流量,有利于减小泄漏损失和提高涡轮效率。     

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.     

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...     

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。     

雾化喷射冷却的机理及模型研究

雾化喷射冷却的换热机理十分复杂,目前其研究还很不成熟。本文从喷射雾滴的特性参数出发,以被冷却表面上形成的喷射液膜为对象,考虑了冷却液体向环境的散热,建立质量、能量守恒方程,得到半经验半解析的雾化喷射换热模型。其中,本文提出真换热系数和显换热系数的概念,认为显换热系数受空间散热影响,而真换热系数只与喷雾动量有关。最后设计了雾化喷射局部换热实验,对模型进行检验,结果表明,该模型能够较好地符合实验所得的换热系数及加热面表面温度沿喷射半径的分布趋势。     

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...     

带气膜孔内部冷却通道的流动传热特性

燃气轮机高温透平内部冷却通道中弯头、肋片和气膜孔之间存在着复杂的交互作用。本文采用瞬态液晶技术对光滑通道、无抽吸的带肋通道和有气膜孔抽吸的带肋通道的表面传热分布和沿程压力损失进行了详细测量,同时采用RANS数值模拟方法研究其流场特性。结果表明180°弯头产生的大分离是压力损失的主要因素,45°斜肋片产生的螺旋形流动在弯头与大分离交互作用明显,气膜孔抽吸破坏孔附近边界层使得肋间传热而相对集中于孔附近。在13%抽吸量条件下,气膜孔抽吸降低U型通道中压力损失约20%,同时保持传热强化程度与无抽吸工况相同。     

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.     

喷雾冷却换热机理和影响换热性能的因素

基于目前国内外相关研究结果,分析了喷雾冷却的传热特性,阐述了喷雾冷却换热机理,给出了强化方法,研究了影响换热性能的因素,并给出一些理论临界热流密度（CHF）模型。最后结合高功率激光器件的散热需求,提出了喷雾冷却的发展方向。     

Experimental heat transfer study of beef carcasses chilled by mist sprays

Experimental studies were conducted on the chilling of beef carcasses by mist sprays to investigate the effect spray droplet size and Weber number have on the heat transfer and carcass weight loss during spray chilling. Experiments were conducted on 16 beef carcass halves. Half were conventionally chilled by the circulating air in the meat chiller, while the others were chilled by water mist. Tests reveal that spray heat transfer increases with the increase in the spray mass flux. Beef carcasses chilled by mist spray also show a reduction in carcass weight loss with the increase in the spray Weber number.     

喷雾冷却换热机理和影响换热性能的因素

 基于目前国内外相关研究结果,分析了喷雾冷却的传热特性,阐述了喷雾冷却换热机理,给出了强化方法,研究了影响换热性能的因素,并给出一些理论临界热流密度（CHF）模型。最后结合高功率激光器件的散热需求,提出了喷雾冷却的发展方向。     

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。     

Heat Transfer from a Hot Moving Steel Plate by Air-Atomized Spray Impingement

Air-atomized spray cooling of a hot moving AISI 304 steel plate of 6 mm thickness has been investigated experimentally by varying water flow rate and plate velocity at a fixed nozzle-to-plate distance. It is found that the heat transfer coefficient is a non-linear function of surface temperature. The result shows that the cooling rate increases with an increase in the water flow rate. The highest cooling rate has been found for the static plate, whereas for a moving plate, an increasing cooling rate trend has been observed with increasing plate velocity.     

自然循环预冷和低温热管耦合系统的初步实验研究

介绍的高效低温传热方法主要包括 :自然循环冷却法和基于自然循环预冷及低温热管的高效低温冷却方法。自然循环冷却法的特点是在大温差条件下实现物体的快速冷却。一旦被冷却物体到达或接近低温液体的温度 ,将产生循环动力不足的情况 ,必须采用诸如气体引射或容器自增压等方法加以解决。而低温热管的特点在于能在小温差条件下 ,传递大量的热能。文中将自然循环预冷法及低温热管技术有机结合 ,综合自然循环和低温热管的优点 ,取长补短 ,既可以在很短的时间内使被冷却物体的温度降低下来 ,又可以保证被冷却物体的温度波动较小。文中还详细给出了基于自然循环预冷及低温热管的高效低温传热单元的设计及试验结果     

SPRAY COOLING OF HIGH TEMPERATURE METALS USING HIGH MASS FLUX INDUSTRIAL NOZZLES

Systematic experiments were conducted for the spray cooling of high-temperature stainless steel using three different types of industrial sprays: full cone and flat hydraulic nozzles and a flat air-mist nozzle. In the present study, a wide range of mass flux (1.5–30 kg/m²sec) is covered, which has never been thoroughly investigated before. Orientations with respect to gravity and spray angle were also explored.

The data have been analyzed and correlated. The results of this study will be important to the product quality control in industries by providing a good estimation of heat flux at different mass flux, spray types, and surface temperatures, especially for spray cooling of stainless steel and other metals with similar thermal properties.     

Experimental Investigation of the Effect of Multiple Synthetic Jets on Heat Transfer and Pressure Loss in Minichannels

Synthetic jets can enhance thermal performance by creating wall impingement, disrupting boundary layers, and enhancing mixing within a minichannel. This study investigates using multiple synthetic jets along the length of minichannels with an aqueous–glycol mixture. Using synthetic jets, an average heat transfer coefficient increase up to 81% was demonstrated. It was also shown that pressure loss can be reduced by 78% while maintaining equivalent heat transfer performance. The effects of momentum ratio, frequency, and bulk Graetz number on heat transfer and pressure loss is presented along with an empirical correlation that predicts the heat transfer enhancement.     

R1336mzz闪蒸喷雾冷却传热特性的实验研究

闪蒸喷雾冷却是高热流密度电子器件有效的散热技术之一.本研究采用新型工质R1336mzz,建立了一个闭式闪蒸喷雾冷却实验平台,研究了喷雾流量和入口温度等影响因素对其传热特性的影响.实验结果表明,闪蒸喷雾冷却的传热性能随流量的增加先增大后减小,在流量为1.4 L/min时,获得最佳的传热性能,临界热流密度最高可达349 W...     

声波作用下铜球传热特性实验*

针对频率为500 Hz～3000 Hz和声压级为110 d B～133 d B的声场作用对铜球在空气中自然冷却的传热特性的影响,通过热电偶测温的方法,分析铜球温度梯度的分布与声场声压级、频率以及铜球直径的关系。结果表面,当频率f一定时,随着声压级的增加,铜球的传热效果得到明显增强,对于直径为5 mm的铜球,在133 d B声场中传热系数最大增加了25%。当声压级一定时,在频率范围中存在某一频率,此时铜球的传热系数最大,此特殊频率随着声压级的增大而增大。当铜球的直径为5 mm时,可以在低频段观测到声流效应的影响,而当铜球的直径为10 mm、15mm时,很难在低频段辨别出声流效应的影响。所得结论为声波应用于电站锅炉中,强化煤颗粒燃烧提供了依据。