Characteristics of Heat Transfer Control on Offset-type Turbulent Impinging Jet

热能应该留给下一代。偏置式冲击射流是改善和增强局部传热或传质的典型方法。在实际应用中，喷嘴在相对狭窄的密闭壁面空间中的位置是影响设备紧凑性的重要因素。1992年，以空气为工作流体，对斜向湍流撞击射流的传热特性进行了实验研究。喷嘴直径为30 mm，喷嘴与撞击面之间的距离为30 mm。密闭壁设置在喷嘴的同一水平面上。倾斜角度分别为45、60、90⋯⋯。撞击截面由透明亚克力板、热敏液晶片和厚度为20 μ m的不锈钢箔组成，CCD相机镜头前依次安装三种滤光片。将热敏液晶的彩色图像转换为电信号。一个像素的大小为0.5-1mm的正方形。校准颜色和温度之间的关系，以确定精度和分辨率。在给定温度下，液晶的散射反射光通过滤光片被分为三种颜色（红、绿、蓝）。在每个像素处获取各分量的亮度作为图像数据。用包含相对亮度的回归方程估计温度。利用详细的温度分布，求解受热截面的三维热传导方程，对局部热流进行局部补偿。结果表明，局部Nusselt数呈现峰移和高原特征。低雷诺数时，局部热流密度的影响显著，约占均匀热流密度的6-17%。1993年，用热风速仪研究了斜向湍流撞击射流的流动特性。在不加热条件下测量了截面上的速度和湍流强度。探头逆流放置，平行于撞击面。结果表明，喷嘴喷出的射流沿周围的静止流体向下滚动并撞击平面。在小流区，气流的滚降和撞击面附近湍流的放大促进了局部换热。这些流动参数（速度和波动强度）的梯度似乎与它们的绝对值一样影响局部换热强化。速度波动功率谱中影响换热性能的最优频率为80 ~ 300 Hz，且与雷诺数有关。这些结果将作为基础数据应用于实际设备。少

Thermal energy should be saved to the next generation. Offset-type impinging jet is a representative method to improve and augment the local heat transfer or mass transfer. In practical applications, the attitude of the nozzle in comparatively narrow space with confined wall is an important factor including the compactness of the facility.In 1992, the heat transfer characteristics of an oblique turbulent impinging jet were performed experimetaly by using air as a working fluid. The nozzle diameter was 30 mm and also the distance between the nozzle and the impingement surface 30 mm. The confined wall was set at the same level of the nozzle. The inclined angle was 45ﾟ, 60ﾟ and 90ﾟ. The impingement section was composed of an transparent acrylic plate, the thermosensitive liquid crystal sheet and the stainless steel foil whose thickness was 20 mu m. Three kinds of optical filters were mounted one after another in front of the lens of the CCD camera. The color image of thermosensitive liqui … More d crystal was converted into an electric signal. The size of one pixel was 0.5-1mm square. The relationship between color and temperature was calibrated to determine the accuary and resolution. The scatterd reflected light from the liquid crystal at a given temperature was divided into three components (Red, Green, Blue) of color by optical filters. The brightness of each component was obtained at each pixel as the image data. The temperature was estimated by the regression equation including the relative brightness. The local heat flux was compensated locally by using the detailed temperature distribution and solving the three-dimensional thermal conduction equation in the heated section. According to the results, the local Nusselt number showed the peak shift and the plateau. The effect of the local heat flux is remarkable at low Reynolds number and amounts to 6-17% of uniform flux.In 1993, the flow characteristics of an oblique turbulent impinging jet were carried out by using a thermoanemometer. The velocity and turbulent intensity across the section were measured in unheated condition. The probe was set against the flow and parallel to the impingement surface. According to the results, the jet from the nozzle rolled down the sorrounding stationary fluid and impinged the flat surface. The rolling down of the flow and the amplification of turbulence near the impingement surface were performed at the minor flow region and promoted the local heat transfer. The gradient of these flow parameters (velocity and fluctuation intensity) seem to affect the local heat transfer enhancement as their absolute vaues do. The superior frequency in power spectrum of velocity fluctuation affecting heat transfer improvement was from 80 to 300 Hz and depended on Reynolds number.These results will be applied in the practical facility as the basic data. Less