Flow and Heat Transfer Characteristics of Hydrophobic and Hydrophilic Microchannel Flow

在层流范围内，研究了疏水和亲水微通道中的单相和两相流动特性。该疏水微通道是由涂有硅胶的玻璃管制成的。通过测量压降发现，在疏水表面光滑的管道中流动的脱气自来水没有发生减阻作用。在氮气和自来水两相流中，利用显微镜和高速录像机测量了总压降和流型。在液体流量较小的情况下，疏水微通道内的总压降比正常通道大得多。这种流动模式是在无液膜的管道中流动的小液段和小气段。液弹两端固壁上液体的分离和粘连比液膜弹状流的阻力大。同时，在亲水表面，预计很难出现液膜破裂。与疏水通道相比，亲水微通道两相流具有更好的减阻效果。然而，要在微通道内制备一层硬质的光催化二氧化钛涂层以获得亲水性表面是非常困难的。

Characteristics of single and two-phase flow in hydrophobic and hydrophilic microchannels were investigated in the laminar flow range. The hydrophobic microchannel was made by a glass tube coated with a silicone. Drag reduction did not occur in degassed tap water flowing in pipes with the smooth hydrophobic surface by measuring the pressure drop. Experiments in two-phase flow (nitrogen and tap water) were carried out to measure the total pressure drop and the flow pattern by using a microscope and a high-speed VTR system. For small liquid flow rate, total pressure drop in the hydrophobic microchannel was much higher as compared with the normal channel. That flow pattern was small liquid and gas segments flowing in the pipe without liquid film. The separation and adhesion of the liquid on the solid wall at both ends of liquid slug, caused larger drag than the slug flow with liquid film. Meanwhile, in the hydrophilic surface, a bursting of liquid film is expected to be hard to arise. The hydrophilic microchannel two-phase flow is more expectative for a drag reduction than the hydrophobic channel. However, it was too difficult to make a hard photocatalytic TiO_2 coating inside of a microchannel for a hydrophilic surface.