Characteristics of heat transfer and homogeneous nucleation process during quenching high temperature surface with an impinging water jet

对冲击水射流下的换热特性和均匀成核进行了实验研究。实验条件为：射流速度3~15m/S，液体温度20~95℃，射流直径2~3 mm，初块温度2 5~6 0 0℃。采用铜、黄铜和碳钢三种不同的材料作为试块，当块体温度高于莱登弗罗斯特温度时，液体冷却时，表面温度高于液体过热度热力学极限的情况下，表面温度是否有足够的冷却能力，很大程度上取决于表面温度是否超过液体过热度的热力学极限。当冷却表面的温度高于液体过热度的热力学极限，且有足够的液体冷却能力时，可在很短的时间内交替重复干湿条件，使表面温度逐渐下降。当…当表面温度低于液体过热度的热力学极限时，表面有一个稳定的润湿区域，即在撞击射流区中心附近，但湿润区域不会扩展到受热表面。这种情况一直持续到表面温度达到表面温度。我们将这一持续时间定义为驻留时间t^*，然后可以确定驻留时间的表面温度Tw^*。滞留时间和表面温度可以用下列方程来预测：(1)(2)在滞留时间之后，湿润区域开始扩大，覆盖整个表面。我们可以弄清楚表面温度和表面热流是如何随着湿润区域的移动而变化的。例如，我们可以指出最大热流Q&lt；max&gt；出现在润湿区内的位置，并可以用以下公式估算最大热流：(3)p、c和λ分别是密度、热容和导热系数，Q_c是冲击射流稳定冷却下的临界热流密度。较少

An experimental study has been made of heat transfer characteristics and homogeneous nucleation with an impinging water jet. The experimental condition is varied from jet velocity of 3 to 15 m/s, liquid temperature of 20 to 95 ℃, jet diameter of 2 and 3 mm, and initial block temperature of 250 to 600 ℃. Three different materials of copper, brass and carbon steel are employed as tested block.When the block temperature higher than Leidenfrost temperature is cooled by liquid, condition whether an occurrence of wetting high temperature surface appears or not, strongly depends on whether in the case that the surface temperature is kept higher than the thermodynamic limit of liquid superheat the cooling capacity is enough or not. For the case of cooling the surface higher than the thermodynamic limit of liquid superheat and enough cooling capacity of liquid, the wet and dry conditions are alternatively repeated at very short time during which the surface temperature gradually goes down. When … More the surface temperature becomes lower than the thermodynamic limit of liquid superheat, a stable wetting is confirmed on a limited area of the surface, namely near the center of impinging jet zone, but the wetted area never expand over the heated surface. This condition is lasting until the surface temperature reaches a surface temperature. We define this lasting time as a resident time, t^*, and then can determine the surface temperature, Tw^*, at the resident time. The resident time and the surface temperature can be predicted by the following equations,(1)(2)After the resident time, the wetted area starts expanding to cover the entire surface. We can clarify how the surface temperature and surface heat flux change with moving the wetted area. For example, we can point out the position at which the maximum heat flux, q_<max>, appears within the wetted zone and can estimate the maximum heat flux by the following equation ;(3)where p, c and λ are density, heat capacity and thermal conductivity, respectively and q_c is critical heat flux under the steady cooling with impinging jet. Less