Flow and Heat Transfer Characteristics of Hydrophobic and Hydrophilic Microchannel Flow

在层流范围内研究了疏水性和亲水性微通道内的单相和两相流动特性。疏水微通道由涂有硅酮的玻璃管制成。通过测量压降，发现在具有光滑疏水表面的管道中流动的脱气自来水没有发生减阻。利用显微镜和高速录像系统对氮气和自来水两相流进行了实验研究，测量了两相流的总压降和流型。当液体流量较小时，疏水微通道内的总压降比普通微通道高得多。该流型为小液段和小气段在管内流动，无液膜。液弹两端固体壁面上液体的分离和粘附，造成了比有液膜弹状流更大的阻力。同时，在亲水性表面中，预计难以出现液膜破裂。亲水性微通道两相流比疏水性微通道具有更好的减阻效果。然而，对于亲水性表面，在微通道内制备硬质光催化TiO_2涂层太困难。

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.