Cooling Characteristics of Hot Surface by Air-Water Mixture

对喷嘴和热转移实验的流动特性的测量已经在该区域低质量水流速的雾冷却中进行了性能。喷嘴和热转移表面之间的距离固定在520毫米处，穿过实验。在W=0.02-0.14 [kg/m^2 s]， the droplet diameter d=15-36 [<micrn>m]， the impinging vVelocity V=4-7.2 [m/s]， and temperature of the surface 100-600 [C]。理论分析也被传送到了以实验数据的援助为基础的热转移中，以区域相等的方式进行电影冲洗。由雾冷却引起的总热通量被认为是由辐射总和Q.来表达的。由空气qa和水滴q_w的蒸发造成的压力是估计的。通过辐射的热通量可以通过q_e计算<epsilon><alpha>（T_w ^4-T ^4）。“解放运动<epsilon>是由空气输送的实验决定的。”假定空气流动可以成为一个轴对称的laminar stagnation flow，热通量q_a = 5.4 Pr ^<0.4><lambda>a（D8 vi <nu>D8（T_w-T_a） was被发现。由于水滴蒸发的热通量，该模型中的水滴被部署在径向方向上的气流和运动所拖累，q_w = 2.15 X10 ^3<lambda>_vW（T_w-T_<sat>）的表达被保留。在分析中，它被认为是这样的：每个水滴漂浮在蒸汽机电影上，而没有与表面和热量接触，只能通过蒸汽机电影的行为转移到水滴上。它是通过对热通量进行分析来澄清的，即通过水滴蒸发的热通量可能会影响到水的质量速度，而不是D^<0.5>和V^<0.5>。总热通量根据本分析结果得出结论，该实验在250-600 [° C]的表面温度范围内计算。

Measurement of the flow characteristics of nozzles and the heat transfer experiment have been performed on fog cooling in the region of low mass velocity of water. Distance between the nozzle and the heat transfer surface was fixed at 520 [mm] throughout the experiments. The mass velocity of water lies in the range of W=0.02-0.14 [kg/m^2s], the droplet diameter d=15-36 [<micrn>m], the impinging velocity V=4-7.2 [m/s], and temperature of the surface 100-600 [゜C]. Theoretical analysis has been also carried out on the heat transfer in the region equivalent to film boiling with the aid of experimental data. Total heat flux by fog cooling is assumed to be expressed by the sum of radiation Q., forced convection by air qa and evaporation of the droplets q_w which are estimated independently. Heat flux by radiation can be calculated by q_e=<epsilon><alpha> (T_w^4-T ^4). The emissivity <epsilon> was determined by the experiment by air convection. Assuming that the air flow can be considered to be an axsymetric laminar stagnation flow, the expression of the heat flux q_a=5.4Pr^<0.4><lambda> a(D8vi<nu>D8(T_w-T_a) was obtained. For the heat flux by the evaporation of droplets, the model which the droplet is dragged by the air flow and moves in the radial direction was employed and the expression of q_w=2.15X10^3<lambda>_vW(T_w-T _<sat>) was obtained. In the analysis, it is assumed that each droplet floats on the vapor film without contact with the surface and the heat is transfered to the droplet only by conduction through the vapor film. It was made clear by the analysis that the heat flux by the droplet evaporation is proportional to the mass velocity of water, and inversely to d^<0.5> and V^<0.5>. The total heat flux calculated by this analysis agrees well with that by the experiment in the range of the surface temperature of 250-600 [゜C].