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Spray cooling characteristics of water and R-134a.
喷雾冷却水和r - 134 a的特征。
Part II: transient cooling
第二部分:瞬态冷却
Abstract
文摘
Spray cooling of a hot surface was investigated in the second of two papers to determine the effect of mass flux, Weber number, and degree of subcooling on two different working fluids such as pure water and R-134a. Full cone circular sprays were used to cool a circular surface of diameter 80mm with an initial temperature about 250/70C for pure water/R-134a, respectively. Both the transient liquid crystal technique (only for R-134a) and thermocouple wire temperature measurements were conducted. Cooling curves were obtained in a wide range of the above-mentioned parameters.
喷雾冷却的热表面在第二两篇论文的研究来确定质量流量的影响,韦伯数和低温冷却度在两个不同的工作液体如纯水和r - 134 a。完整的锥循环使用了喷雾冷却循环表面直径80毫米,最初对250/70C温度纯水/ r - 134 a,分别。瞬态液晶技术(只对r - 134 a)和热电偶线温度进行了测量。冷却曲线得到广泛的上述参数
1. Introduction
1。介绍
There has been an increased demand for new technique capable of removing high heat fluxes and such demands will continue to increase in the future. Among these techniques, spray cooling is one of the most notable methods to remove high heat fluxes. Applications exist in a wide range of industrial processes including rapid cooling and quenching in metal foundries, emergency of core cooling systems, cooling of microelectronics and ice chiller in air-conditioning systems. Most relevant studies[1,2] have been examined in Part I of this study. However, there seems only few papers to deal with the transient spray cooling. Most recently, Cui et al. [3] experimentally studied the effect of dissolving salts in water sprays used for quenching a hot surface. Both transient temperature distribution and surface heat flux were calculated. It is found that some dissolving salts would increase nucleate boiling heat transfer, but had little effect on transition boiling. Bernardin et al. [4] recorded the impact behavior of water droplets on a hot aluminum surface using a high speed photographic technique.It was found that droplet velocity and surface temperature were two important parameters governing
the impact behavior and ensuring heat transfer. Part I of this study addressed steady state boiling experiments during the spray cooling. This study, Part II, presents the results of liquid sprays of both water and R-134a during transient cooling. Prior to spray cooling, the test surface was initially heated to a constant temperature of 240C and 60C for water and R-134a, respectively. Cooling curves were obtained for different spray mass flux, Weber number, degree of superheat and degree of subcooling. The transient experiments in this work would provide necessary information and heat transfer characteristics through the film, transition and boiling regimes. The emphasis of this work is primary transient experimental and the objectives
were to tain temperature for pure water and R134a. It was possible to estimate the heat flux either using Fouriers law of heat conduction [5] or the sequential function specifi-cation method to solve one-dimensional inverse problem[3]. Both methods were used and compared for double check. The present surface heat flux calculation was found to within ±12%. The transient experiments using the present heater designed can provide the heat transfer characteristics throughout the film, transition, nucleate,and forced convection and evaporation regions. The critical as well as minimum heat flux (CHF and MHF)
can also be obtained. Relevant uncertainty estimateswere listed in Table
1有新技术的需求增加，能够去除高热通量，这种需求将继续增加在未来。在这些技术中，喷雾冷却是一个最显着的方法，以除去高的热通量。应用范围广泛的工业过程，包括快速冷却和淬火的金属铸造厂，紧急的核心冷却系统，冷却微电子和冰冷却器的空调系统。最相关的研究[1,2]已在本研究的第一部分。然而，似乎只有少数文件处理瞬态喷雾冷却。最近，崔等。【3】实验研究了溶解盐在水热表面淬火中的作用。瞬态温度分布和表面热通量进行了计算。发现某些溶解盐会增加核态沸腾传热，但对过渡沸腾影响不大。伯纳丁等。[ 4 ]利用高速摄影技术记录了水滴在热铝表面的冲击行为，发现液滴速度和表面温度是控制铝表面的两个重要参数冲击行为与保证传热。第一部分研究了喷雾冷却过程中的稳态沸腾实验。本研究的第二部分，介绍了水和R-134a的液体喷雾剂的结果在短暂的冷却。喷雾冷却之前，测试表面最初被加热到240℃、60℃的恒定温度的水和R-134a，分别。冷却曲线获得不同的喷雾流量、Weber数，对过冷过热和程度。在这项工作中的瞬态实验将提供必要的信息和传热特性，通过电影，过渡和沸腾制度。这项工作的重点是初级瞬态实验和目标是那纯净水和R134a的温度。它是可能的估计的热通量使用傅里叶热传导定律[ 5 ]或顺序功能规范方法求解一维逆问题[ 3 ]。这两种方法的使用和比较双检查。目前的地表热流计算值在12%以内。使用本加热器设计的瞬态实验可以提供整个膜，过渡，核，和强制对流和蒸发区域的传热特性。临界以及最小的热通量（CHF和MHF）
也可以得到。相关的不确定性均列于表1。
2. Experimental
2。实验
For heat transfer measurements, TLC (only for R- 134a) and traditional thermocouple measurements were both conducted. However, due to the transient nature, the test surface was made from a very thin (0.5lm) Pt sputtered circular surface as stated in Part I of this paper to ensure isothermal conditions throughout the disk at every instant during the experiments.
传热测量，薄层色谱（仅用于R 134a）和传统的热电偶测量了。然而，由于瞬态性质，测试表面是由一个非常薄的（0.5lm）铂溅射圆形表面正如本文第一部分以确保等温条件下在每一时刻盘在实验。
2.1. Heater design and temperature measurements
2.1。加热器设计和温度测量
In addition to the heater design mentioned in Part I, the disk surface was also measured by three type K thermocouples with a diameter of 0.3mm bonded to the disk underside in sequential manner along the center line as shown in Fig. 1. High thermal conductivity paste (alumina/silica, k = 8.4W/mC) was applied to the thermocouples to warrant good contact between the copper substrate and the thermocouple bead. Heat conduction within the copper disk was high enough to give an almost uniform temperature profile along its centerline ( 6 1C). The transient temperature data were recorded every 20ms until the disk temperature fell below a cer C17-10) of thickness of the order of 0.2lm. Careful attention was paid to avoid influences due to the characteristic roughness of the TLC surface and black paint on the results. Meanwhile, thermophysical properties effect of the TLC were kept minimum and the uncertainty was estimated < ± 3%. Besides, a CCD camera, a frame grabber interface associated with Pentium III PC was used to analyze the color changes using a commercial image processing software (LCIA, Taiwan Pitot Co.) The image processing system maps the test section into 512 • 492 pixels (NTSC) locations and monitors each location individually for color change. Since the re- distribution that is high in the yellow–green range. In order to reduce the UV radiation damage to transient liquid crystal, a spectrum EB-74 UV sleeve filter was used to obtain 100% UV blockage. A lens with an extended view angle of 70 was implement with the present CCD camera to minimize angle effects and to achieve uniform illumination intensity throughout the domain measured.
除了加热器设计在第一部分中提到的，盘面也由三K型热电偶用直径0.3mm保税沿中心线如图1所示的顺序的方式下测量盘。高导热膏（氧化铝/氧化硅，K = 8.4w/m C）应用于热电偶令铜基板和热电偶珠之间的良好接触。铜磁盘内的热传导足够高，使其中心线（6 C C）几乎均匀的温度分布。瞬态温度数据进行记录，每20ms到磁盘的温度低于一定c17-10）对0.2lm级厚度。仔细注意，以避免由于TLC表面和黑色涂料的结果的特性粗糙度的影响。同时，薄层色谱的热物性效应保持最小，不确定度估计为＜3%。此外，CCD相机，与奔腾III PC相关的图像采集卡接口是使用商业图像处理软件对颜色的变化（LCIA，台湾总公司）的图像处理系统图试验段为512•492像素（NTSC）每个位置分别为颜色变化的位置和显示器。由于重新分配，是在黄绿色范围高。为了减少紫外线辐射损伤的瞬态液晶，频谱eb-74 UV滤筒采用100%紫外线阻挡。一个镜头的扩展视角为70实现与目前的CCD相机，以尽量减少角度的影响，并实现均匀的照明强度整个域测量。
2.2. Transient liquid crystal measurement
2.2。瞬态液晶测量
The experimental apparatus includes a flow circuit, thermochromatic liquid crystal imaging test section, and instruments, which is schematically shown in Fig. 2. A scanning electron microscope (SEM) image of the Pt surface is depicted in Fig. 3(a) and (b). With different magnification, the surface condition seen is different even under a same power applied (=10.0 kV). The crack with island-like porous nano/micro structure was clearly noted for •100,000 photograph; while for •60,000 more larger islands without a crack were found. A Panasonic CCD camera (model: AVC597NIF36) with a light source directly facing the nozzle exit, and mounted on a vertical stationary post was used with a maximum speed of 3 frames/s in NTSC format to record the color change of the liquid crystal coating as the liquid spray impinged onto the test surface.
实验装置包括一个流电路、液晶显示成像测试部分和仪器，这是示意性地示于图2。图3（a）和（b）中描述了Pt表面的扫描电子显微镜（SEM）图像。不同的倍率，看到的表面条件是不同的，即使在相同的功率施加（= 10千伏）。岛状多孔纳米/微结构的裂缝清楚地注意到：100000照片，而更大的岛屿没有裂纹被发现的60000。松下CCD相机（型号：avc597nif36）直接面对喷嘴出口的光源，并安装在垂直固定后采用3帧/秒的NTSC格式记录液晶涂层颜色变化为液体喷雾撞击到试样表面的最大速度
The time of color change of the liquid crystal driving a transient test is measured by a Panasonic 1/400 color CCD image senor and a computer vision system. The test surface is airsprayed with black background paints first and then liquid crystal (Hallcrest, BM/R18C5W/flected light from liquid crystal is dependent on the spectral intensity of the incident light and contains a peak value whose wavelength inversely depends on the temperature [6], the test chamber is shielded from room light and room air currents using thick black felt curtain covered in such way that the test surface only receives incident light emitted from the light source mounted inside the CCD.
对液晶驱动瞬态测试颜色变化的时间是由松下1／400彩色CCD图像传感器和计算机视觉测量系统。测试表面airsprayed背景为黑色颜料先液晶（hallcrest，BM / r18c5w /反映光从液晶依赖于入射光的光谱强度和峰值波长成反比的包含温度有关[ 6 ]，试验室屏蔽室光和室内空气流用厚厚的黑毡帘覆盖在测试表面只接收从光源发出的入射光安装在CCD这样的方式。
The light source used for this series of tests is a standard 60mm Taiwan Concept cool white fluorescent lamp (13W NB4210-60mm). The typical cool white fluorescent has a color temperature of 4100K and a spectral Once, for instance, Ti (up to 32C), T1 ( 14C), and the corresponding time (t) required to change the coated-surface color to green are known, the heat transfer coefficient h can be estimated from Eq. (2). The green color of the liquid crystal shows the largest light intensity, which is a reference point that conventionally uses. Noting that in Eq. (2), the original T1 is a constant. However, in the present study, T1 is time-dependent and increases as the time (t) increases which can be simulated as a series of step functions. Applying the Duhamels superposition principle, Eq. (2) can be rewritten in the following where DT1 and sj are the temperature and time step changes from the recorder readout. Since the time duration is too short to make the heat transport to the plexiglass plate, this assesses the assump
用于这一系列的测试光源是一个标准的60mm台湾概念冷白色荧光灯（13W nb4210-60mm）。典型的冷白荧光灯有一个4100k色温和光谱一次，例如，Ti（32 C），T1（14 C），和相应的时间（t）的需要来改变表面颜色绿色是已知的，传热系数h可以估计从式（2）。液晶的绿色显示最大的光强度，这是一个参考点，通常使用。注意到，在EQ（2）中，原来的T1是常数。然而，在本研究中，T1是随时间变化的和增加的时间（t）的增加，这可以被模拟为一系列的阶跃函数。应用Duhamel叠加原理，Eq.（2）可在1和SJ是从录音机读出温度和时间步长的变化如下重写。由于时间太短，使热量传递到有机玻璃板、评估假设
2.3. Analysis of liquid crystal thermography and experimental procedure
2.3。热成像和experimental2.3液晶分析。液晶热像分析与实验程序
The local heat transfer coefficient over the target wall can be obtained by assuming one-dimensional transient conduction over a semi-infinite solid wall with the initial and boundary conditions on the liquid crystal coated surfaces are This gives the dimensionless wall temperature response as follows:
局部传热系数在靶面可以通过假设一维瞬态传导在半无限大固体壁面与初始和边界上的液晶表面条件给出了无量纲壁温度响应得出：
dimensioned matrix of red, green, and blue values. The image size is 320 • 240 • 3 (ffi0.22MB). Image processing begins with a captured image for the entire target walls which is 320 • 240 pixels. During the experiments, the image processing system records the time for the color change to green for the entire surface. Finally, the time and temperature are logged in a computer program to obtain the local heat transfer coefficient. Spray parameters used are the same in Part I of this paper. The operating and test conditions can be also found in Part I of the paper. The test surface was cleaned prior to each measurement by washing it first with acetone and, then cleaning it with distilled water. It was heated to 70C (R-134a) and 250C (water) by regulating the power to the heaters. Then the liquid supply pump was switched on. Once the nozzle pressure reached a steady value, the power to the heaters was turned off and remove the plastic plate shield simultaneously to allow liquid spray from the nozzle to quench the test surface. It usually takes 0 470 s, depending on spray parameters, to cool the test surface from 70C (R-134a)/250C (water) to 15C (R-134a)/80C (water). Temperatures measured by thermocouples were continuously recorded by a data acquisition system. TLC measurements were simultaneously conducted. In addition, boiling phenomena photographs at selected conditions were taken as stated earlier.
红、绿、蓝值的尺寸矩阵。图像的大小是320•240•3（ffi0.22mb）。图像处理开始与捕获的图像为整个目标墙是320 - 240像素。在实验过程中，图像处理系统记录的颜色变化的时间为整个表面的绿色。最后，在计算机程序中记录的时间和温度，以获得局部传热系数。在本文的第一部分中使用的喷雾参数是相同的。的操作和测试条件，也可以发现在第一部分的文件。测试表面清洗之前，每次测量，首先用丙酮清洗，然后用蒸馏水清洗它。它被加热到70 C（R）和250（水）通过调节电加热器。然后接通液体供应泵。一旦喷嘴压力达到稳定值，加热器的功率被关闭，并同时删除塑料板屏蔽，允许从喷嘴的液体喷射淬火的测试表面。它通常需要0 470秒，这取决于喷雾参数、冷却试验表面从70 C（R-134a）/ 250（水）15 C（R-134a）/ 80 C（水）。热电偶测量的温度连续记录的数据采集系统。同时进行TLC测量。此外，沸点现象在选定的条件下拍摄的照片，如前面所述。
dimensi3. Results and discussion
dimensi3。结果与讨论
As one may know, the surface temperature of the test surface is the most important parameter in quenching and is used to define the four distinct heat transfer regimes of the boiling curve: (1) film boiling (2) transition boiling, (3) nucleate boiling, and (4) single phase liquid cooling. The boiling curve has found in most boiling studies as part I of this paper did. While, for quenching studies, the temperature as well as surface heat flux vs. time/or cooling curve shown in Fig. 4 are frequently encountered. In Fig. 4, the common encountered film boiling regime persists from elevated surface temperature down to a lower limit used to be referred to minimum heat flux (MHF) or Leidenfrost point (indicated by arrows) below which the transition boiling occurs. As the surface temperature decreases from Leidenfrost in the transition boiling regime (e.g. 25C < Tw < 50C, at We = 152), the heat transfer rate increases as more efficient surface wetting and boiling occur. At the lower temperature boundary of the transition boiling regime, where the entire surface becomes available for wetting and heat transfer rate reaches a maximum (so called CHF). This maximum heat flux can be seen from the steepest portion (or inflection point indicated by arrows) of the cooling curves in Fig. 4. Below CHF (e.g. q00 2.4 • 104 W/m2 at We = 152 and DTsub = 4C)the heat transfer rate in nucleate boiling (e.g. 20C < Tw < 25C at We = 152) decreases with decreasing surface temperature. The lower temperature boundary of the nucleate boiling is determined by the minimum wall superheat (e.g. Tw 6 20C at We = 152) required to sustain vapor bubble nucleation and growth within the impinging droplets. The film evaporation/or single phase forced convection would exist below the boundary (e.g. q00 6 2 • 103 W/m2 at We = 152 and DTsub = 4C).
 可以知道，试验表面的表面温度是淬火过程中最重要的参数，用于定义沸腾曲线的四种不同的传热制度：（1）膜沸腾（2）过渡沸腾，（3）核沸腾，和（））单相液体冷却。沸点曲线已经发现，在大多数沸腾的研究，本文的第一部分。然而，淬火研究，温度，以及表面热通量与时间/ /或冷却曲线如图4所示经常遇到。在图4中，常遇到的薄膜沸腾持续升高表面温度下降到一个较低的限制使用被称为最小的热通量（MHF）或Leidenfrost点（箭头所指）下面的过渡沸腾时。随着表面温度降低莱顿弗罗斯特在沸腾的过渡政权（例如25℃＜台湾＜50 C，在我们= 152），传热率增加更有效的表面润湿和沸腾的发生。在较低的温度边界的过渡沸腾制度，其中整个表面变得润湿和传热速率达到最大值（所谓CHF）。从图4中的冷却曲线的最陡部分（箭头表示的拐点）可以看出这个最大热流。在CHF（例如q00 2.4•104 W/m2我们= 152和数据用户= 4°C）的传热速率在沸腾（例如20℃＜台湾＜25 C在我们= 152）降低表面温度降低。核沸腾的较低的温度边界是由最低壁过热（例如TW 6 20 C在我们= 152），以维持汽泡的成核和生长内的撞击液滴。薄膜蒸发或单相强制对流会存在下面的边界（例如q00 6 2•103 W/m2我们= 152和数据用户= 4 C）。
Based on the above physical heat transfer mechanism, the present results shown in Fig. 4(a) and (b) for two subcoolings are thus analyzed. For both cases with R-134a, elapsed time is about 240 s with different We. Generally, the Weber number effect can be clearly noted at D Tsub = 2C. Although, for DTsub = 4C, the effect seems still significant, the ranges influenced became less as compared to that for DTsub = 2C.
基于以上物理传热机理，如图4所示的结果（A）和（B）两subcoolings是这样分析。两例R-134a，运行时间约为240 s的不同我们。一般来说，韦伯数的影响可以清楚地注意到，在D = 2虽然TSUB，为数据用户= 4 C，效果似乎仍然显著，影响的范围越来越少相比，数据用户= 2。
Also shown in Fig. 4(a) and (b) are the surface (wall) heat flux distribution. For both cases the maximum surface heat flux occurred at about t = 100–125 s. The surface heat flux increases as We increases as one would expect. Within uncertainty in heat flux, there seems no significant difference for these two different subcoolings.
图4（a）和（b）所示的表面（壁）热流分布。对于这两种情况下，最大的表面热通量发生在约t = 100 - 125秒。表面热通量增加，我们增加，正如人们所期望的那样。在热通量的不确定性，看来这两种不同的subcoolings无显著差异。
Fig. 5(a) and (b) show the corresponding boiling curves of Fig. 4 at DTsub = 2 and 4C, respectively. It is clearly seen that the above- stated four regimes exist for both DTsub = 2C and 4C subcoolings. The effect of subcoolings on heat flux seems not noted due to a small difference between these two subcoolings. However, the effect on DTsat as compared both Fig. 5(a) and (b) can be stilled noted. In addition, the effect of Weber number is clearly noted again. The phenomenon associated was observed by Yoshida et al. [2] where they found, when We P 80, each droplet having impinged upon the heater surface was crashed to disintegrate into small fragments; while when We < 80, each droplet was subject to a deformation but it soon restored its spherical shape and then rebounded from the test surface. Generally, the boundaries to the boiling regimes, MHF and CHF, are nearly independent of spray We. However, the droplet dynamics and corresponding heat transfer mechanisms are different. In fact, the impact characteristics in each regime, such as droplet breakup, spreading rate, and film stability are strongly dependent on spray We. These behavior have been also reported in Bernardin et al. [4]. Based on Bernardin et al. [4], the present spray We tested belongs to intermediate (We 6 96) and high Weber numbers (We > 96)

图5（a）和（b）显示相应的沸腾曲线图4数据用户= 2和4，分别。可以清楚地看到，上面说四的政权都存在数据用户= 2 C和4 C。在热通量的影响似乎没有注意到subcoolings由于这些subcoolings之间的差异小。然而，效果都dtsat相比，图5（a）和（b）可以使注意。此外，韦伯数的影响再次明确指出。吉田等人观察到的现象相关。[ 2 ]，他们发现，当我们P 80，每个液滴具有影响加热器表面坠毁解体成碎片；而当我们＜80，每一滴是有变形但很快恢复了它的球面形状，然后从测试表面反弹。一般来说，在沸腾的制度边界，MHF和充血性心力衰竭，几乎是独立的喷我们。然而，液滴动态和相应的传热机制是不同的。事实上，在每个政权的冲击特性，如液滴破碎，扩散率，和膜的稳定性强烈依赖于喷雾我们。这些行为也被报道在伯纳丁等。[ 4 ]。基于伯纳丁等人。[ 4 ]，我们测试的本喷雾剂属于中间体（我们6个96）和高Weber数（我们> 96）
Fig. 6(a) and (b) show, on the other hand, pure water cooling performance at DTsub = 55C and 60C with three different We. The corresponding boiling curves (qCHF and qmin shown by arrows) were illustrated in Fig. 7(a) and (b), respectively. Generally, the above-mentioned four distinct heat transfer regime were again found as the same to R-134a cases. However, the starting temperature at which the transient experiment starts for pure water seems much higher, about 240C and it takes a relatively longer time, about 470 s for completion of a cooling process. Three Weber numbers were used for water and all are higher than those used for R-134a. In addition, the surface heat flux seems as expected much higher as compared to those of R-134a. For instance, the present cooling characteristics results in Fig. 7 for We = 80 has the maximum q ffi 1.0 • 105W/m2 at DTsat ffi 30C, while, for R-134a, at We = 96 the maximum q ffi 1.2 • 104 W/m2 . This is perhaps because, again, for We 6 80, as also evidenced by Yoshida et al. [2], liquid water droplet rebound phenomena occurs due to the predominant role of water surface tension and the bulk motion of vapor generated from the water droplets. Furthermore, due to a higher latent heat of water, the corresponding boiling curves shown in Figs. 5 and 7 look different in its magnitude. Even though, the present water result is still smaller than that (q = 4.7 • 105 W/m2 at We = 28) of Yoshida et al. [2], due to the different subcooling and spray volume flux as well as different heating surface and surface condition, in spite of the same trend found on boiling curves. In fact, also included in Fig. 7 is the data from Yoshida et al. [2] for different test surface. At DTsat = 30C and We = 33, q was found to be about 1.0 • 105 W/m2 for steady state experiments, which almost has the same value of the present result at We = 80. While, for transient results shown in Fig. 7, they are much higher as stated before.
图6（a）和（b）显示，另一方面，纯净水冷却性能数据用户= 55 C和60 C与三个不同的我们。相应的沸腾曲线（qCHF和Qmin箭头所示）是在图7（a）和（b），分别。一般来说，上述四种不同的传热机制被再次发现同样对R-134a的例。然而，起始温度的瞬态实验开始纯净水似乎高得多，约240 C，它需要一个相对较长的时间，约470秒的冷却过程完成。三用于水和韦伯数均高于用于R-134a。此外，地表热通量似乎想象的要高于R-134a。例如，目前的冷却特性的结果在图7中我们= 80具有最大Q FFI 1•105w /平方米在dtsat FFI 30 C，而对R-134a在我们= 96最大Q FFI 1.2•104 W/m2。这也许是因为，再次，为我们6个80，也证明了吉田等。【2】由于水表面张力的主要作用和水滴产生的水汽的体积运动，出现了液体水滴反弹现象。此外，由于较高的潜热的水，相应的沸腾曲线显示在无花果。5和7看起来其大小不同。即使，目前的水的结果仍然是小于（Q = 4.7 / 105米/平方米在我们= 28）的吉田等。[ 2 ]，由于不同的过冷度和喷雾流量以及不同的加热表面和表面状况，在沸腾曲线发现同样的趋势，尽管。事实上，也包括在图7是来自吉田等的数据。【2】针对不同的试验表面。在dtsat = 30 C和我们= 33，Q是1•105 W/m2稳态实验，几乎在我们= 80的结果相同的值。然而，对于图7所示的瞬态结果，它们比以前更高。
Fig. 8 shows the detailed heat transfer coefficients on the test surface for R-134a at three different Weber numbers at DTsub = 4C with an average h shown for each graph and its corresponding cooling time noted. The results are presented for a circular region over entire surface. The effect of increasing We is clearly seen and is to increase h (or h). Such phenomena is indicative of a consistency of heat transfer mechanism obtained in Part I and the former discussion (Part II) of this paper which includes boiling curves as well as cooling curves and h–q curves. The photographs for Fig. 8(a)–(c) correspond to a droplet Weber number of 50, 96 and 152 for R-134a. The droplet impact characteristics at We = 50 suggest that relative stable droplets where surface tension forces tend to overcome the breakup effects of inertia and pressure, which results in a relatively low heat transfer as shown in Fig. 8(a). As We increases to 96, it gives the momentum of the droplet, and results in the droplet spreading rate and extent of intact radial film spread to be about 60% greater as shown in Fig. 8(b) with red color than that in Fig. 8(a). At this stage, breakup of the liquid film is caused by liquid ejection and interfacial stabilities due to a plenty of vapor bubble formation as evidenced by Bernardin et al. [4] and Inada and Yang [7]. This behavior would create a series of larger liquid island-like (also globule-like) zones with a fine mist of small droplets mixed as shown in Fig. 8(b). At We = 152, excessive boiling and instabilities throughout the entire film were observed and this time the liquid film rapidly breaks up into a lager dispersion of very fine droplets as evidenced by the red color in which a full coverage of the entire region was found (see Fig. 8(c)). These results are very close to those of Kenning and Yan [8] of which a heat transfer coefficient of 1.6 • 103 6 h 6 2.3 • 103 W/m2 C was found for pool boiling heat transfer on a thin plate with liquid crystal thermography. All three Weber number results can be also observed and found in Part I of this paper for boiling visualization and nucleate boiling results.
图8显示了详细的传热系数的测试表面的R-134a在三个不同的Weber数在数据用户= 4 C平均小时每个图及其对应的冷却时间注意。结果提出了一个圆形区域在整个表面。增加我们的效果是清楚地看到，并增加H（或H）。这种现象是表示在第一部分中获得的传热机制的一致性和前者的讨论（第二部分），本文包括沸腾曲线，以及冷却曲线和H - Q曲线。图8照片（一）–（C）对应于一个液滴韦伯数的50，96和152为R-134a。在我们= 50表明，相对稳定的液滴在表面张力会克服惯性和压力破裂的影响液滴冲击特性，结果在一个相对较低的热传递图8所示（一）。当我们增加到96，它给了液滴的势头，并导致在液滴扩散率和完整的径向膜扩散的程度约为60%，如图所示的图（b）与红色比图8（A）。在这个阶段，液体膜的破裂是由于液体喷射和界面的稳定性，由于大量的气泡形成，如伯纳丁等人证明。[ 4 ] Inada和杨[ 7 ]。这种行为会产生一系列更大的液岛状（也球状）带小水滴混合的细雾，如图8所示（b）。在我们= 152，过大的沸腾和整个膜的不稳定性进行观察，这一次的液体膜迅速分解成一个大的分散体的非常细的液滴证明的红色，其中一个完整的覆盖整个区域被发现（见图8（c））。这些结果是非常接近的认知和燕[ 8 ]，1.6 103 6 6 2.3•H•103 W/m2 C传热系数被发现的池沸腾换热与液晶板成像。所有三个韦伯数的结果也可以观察到，在本文的第一部分沸腾的可视化和核沸腾的结果
Finally, the present qmax = qCHF and qmin results were formulated in terms of the relevant variables. Theoretically, qmax can be calculated based on qmax ¼ m_ ðhfgþ CpDT subÞ to examine the accuracy of the present measurements. The deviation between qCHF (cooling and boiling curves; e.g. Figs. 4 and 6, 5 and 7) and qmax comes from the sources of different kinds of heat losses and all kinds measurement uncertainties. This result is shown in Figs. 9(a) and (b) for R-134a and water, respectively. It is found that the present deviation from the theoretical value is about 20%. This strongly suggests that an effective spray cooling was applied for both water and R-134a. Such results are similar to the previous study of Yoshida et al. [2] for water. On the other hand, qmin found from experiments (cooling and boiling curves; e.g., Figs. 4 and 6, 5 and 7) was compared with that of empirical correlation, qmin = Chfgqv(qg(ql qv)/ (ql + qv) 2 ) 0.25 where C = 0.09–0.18 [9] with a C = 0.11 found for the present study and the results seem good as the data were located on 45  diagonal line within ±10% band which is shown in Fig. 10.
最后，目前的Qmax = qCHF和Qmin的结果在相关的变量来描述。从理论上讲，最大尿流率可以基于最大尿流率¼m_ðHFGþCPDT子Þ审视目前的测量精度计算。之间的偏差（qCHF冷沸腾曲线如图。4、6、5和7）和尿流率来自各种来源和各种热损失的测量不确定度。这个结果显示在无花果。9（a）和（b）分别为R-134a和水。据发现，目前的偏离理论值约为20%。这有力地表明，一个有效的喷雾冷却水和R-134a的。这样的结果是相似的吉田等人的研究。[ 2 ]水。另一方面，从实验中发现（Qmin冷却沸腾曲线如图。4、6、5和7）与实证的相关性相比，Qmin = chfgqv（QG（QL QV）/（QL + QV）2）0.25，C = 0.09–0.18 [ 9 ]和C = 0.11发现的研究现状和效果很好的数据分别位于45对角线在±10%波段，如图10所示。
4. Conclusion
4。结论
A series of transient experiments which is different from Part I of this paper (steady state) was studied with an aid of TLC technique for liquid sprays of R-134a and water. Both cooling curves as well as the corresponding boiling curves were found. In addition, the MHF and CHF were also measured and compared with those of previous studies [2,9]. Detailed heat transfer distribution on a hot surface was firstly made possible to examine the effect of spray mass flux for R-134a and the data were also extracted to compare with thermocouple measurements. It was found on an average that they two in good agreement within ±10%.
一系列的瞬态实验的不同，本文的第一部分（稳态）与R-134a和水液喷洒薄层色谱技术援助研究。两个冷却曲线以及相应的沸腾曲线被发现。此外，美家和CHF也进行了测量，与以往的研究相比，[ 9 ]。详细的传热分布在热表面可能是首先对R-134a和数据喷射质量通量的影响进行提取与热电偶测量比较。结果发现，他们平均两人在10%以内有较好的一致性