水平环形两相流的局域液体速度测量
Two-phase annular flow is commonly used in both commercial and industrial heat transfer however, we do not yet possess a thorough understanding of the nature of the fluid. Most analytical annular two-phase models are based on a relationship between theliquid film thickness, liquid film mass flux, and the axial pressure gradient or interfacialshear stress. The film thickness calculated from these models can then be utilized todetermine the heat transfer coefficient of the flow. Although they are specific to certainflow regimes and fluids, empirical models remain more accurate than these analyticalmodels. The key to understanding these flows lies with the liquid film. Therefore, tobetter understand the pressure drop and heat transfer of annular two-phase flow, thisstudy involves the development of local, liquid velocity measurement techniques andtheir application to horizontal, wavy-annular two-phase flow.Two techniques, Bubble Streak Tracking (BST) and Thin Film Particle ImageVelocimetry (TFPIV), have been developed in this study. Utilizing naturally occurringbubbles within the liquid film, the BST technique determines the liquid velocity bymeasuring reflected light streaks from the bubbles. A three-colored LED array createsdirectionally unambiguous streaks, while a strobe illuminates interfacial features thataffect the liquid velocity. The TFPIV technique applies a typical micro-PIV system to amacroscopic flow with the addition of a non-trivial image processing algorithm. Thisalgorithm successfully overcomes the image noise that occurs when applying PIV to atwo-phase, thin film. Although difficulties arise when processing the BST data, theresults of the BST and TFPIV methods are comparable, making BST an economicalalternative to TFPIV for calculating liquid film velocities.