Forced Convection Phase-Change Heat Transfer with StreamwiseCurvature and Two-Phase Approach Flow

本项目主要是一个小区域强制对流沸腾换热到通道流的实验研究。结果的应用在于必须冷却小而高热流区的设备设计：用于光刻和医学的x射线源，微波速调管，激光器，微电子和光学器件，燃气轮机，聚变反应堆仪表和第一壁，高速飞机前缘表面和材料加工中的淬火。理论或科学价值在于描述热边界层和气泡边界层厚度相对于通道尺寸较小的情况下的沸腾行为。需要记录的影响有：加热长度、体速度、过冷度、压力、流体类型、被加热壁面的流向曲率和接近被加热表面的流体的空隙率。该计划首先完成正在进行的壁面凹曲率对过冷流沸腾特性影响的研究。在这项研究中，所有的空隙都被限制在非常靠近受热表面的地方。下一阶段和研究的主要部分是接近受热区域的流动是处于热力学平衡的蒸汽和液体的两相混合物。在本研究中，将研究直流道和凹凸弯曲流道内流动中接近流动、空隙率和两相流型的影响。在凹曲率下，通过弯曲流动中建立的横流压力梯度，空隙迅速从加热壁面转移出去。这种影响目前正在研究的情况下，接近的流动是一个过冷的液体。当进入流是两相混合物时，将会看到更大的好处，因为在直流和弯曲流之间，从核沸腾（DNB）出发点的热流密度将会大幅增加。一旦特征和描述，这可以在上述工程系统的冷却方案的设计资本化。

This project is predominantly an experimental study of forced convection boiling heat transfer from small regions to a channel flow. Application of the results lie in the design of equipment where small, high-heat-flux regions must be cooled: x-ray sources for lithography and medicine, microwave klystrons, lasers, microelectronic and optical devices, gas turbines, fusion reactor instrumentation and first walls, high-speed aircraft leading surfaces and quenching in materials processing. Theoretical or scientific value lies in the description of the boiling behavior in situations where the thermal boundary layer and bubble boundary layer thicknesses are small relative to the channel size. Effects to be documented are: heating length, bulk velocity, subcooling, pressure, fluid type, streamwise curvature of the heated wall and the void fraction of the flow approaching the heated surface. The program begins by completing an ongoing study on the effect of wall concave curvature on subcooled flow boiling characteristics. In this study, all the voids are constrained to very near the heated surface. The next phase and the main portion of the study is one where the flow approaching the heated region is a two-phase mixture of vapor and liquid in thermodynamic equilibrium. In this study, the effect of approach flow void fraction and two-phase flow regime will be investigated in flow within straight channels and within concave-curved channels. With concave curvature, voids are rapidly transported away from the heated wall by the cross-stream pressure gradient established in the curved flow. This effect is presently being investigated for a situation where the approaching flow is a subcooled liquid. The continuation project will characterize the stronger benefit that will be seen when the entry flow is a two-phase mixture in that there will be a substantial increase, between straight flow and curved flow, of the heat flux at the point of departure from nucleate boiling (DNB). Once characterized and described, this can be capitalized upon in the design of cooling schemes for the above engineering systems.