Fluid Flow And Mass Transfer Characteristics In A Wavy-Walled Tube For Steady Flow

With the development of science and technology, the high efficiency heat and mass transfer devices with low power consumption are paid attention more and more. Flows in the periodically converging-diverging channels or tubes are present in numerous applications. The feature of these devices is that by utilizing the unsteady vortex motion generated from the forced or self-sustained oscillation, the required higher heat and mass transfer rates can be attained without turbulent flow. Many investigators have devoted their efforts to the studies on heat and mass transfer for flow in the above channels or tubes. However, the flow instability and the transport mechanism have not been clarified yet. The objective of the dissertation is on the base of previous investigators' results, by means of experiment and accessorial numerical simulation to find the optimum operating conditions and to describe the mechanism of flow instability, too. Main contents of this dissertation are as follows:In Chapter 1, the previous studies on fluid flow and heat and mass transfer characteristics in two-dimensional channels and axisymmetric tubes have been reviewed. These studies indicate that for the two-dimensional channels, the flow instability, which leads to the flow transition from laminar to turbulent flow, is triggered by periodical Tollmien-Schlichting wave. Moreover, the studies showed that the optimum transport enhancement could be obtained at medium Reynolds Number in the transitional flow regime, the mechanism of resonant enhancement can be used to explain this phenomenon. Based on the fact that the intermittent flow instability, such as puff and slug, occurs in the straight-walled tube with the circular cross section, it is expected that the flow instability is different between the wavy-walled tube and the wavy-walled channel.Chapter 2 introduced the experimental apparatus and various measurement techniques applied to the current study. The flow patterns are visualized mainly by the aluminum dust method and dye injection method. The stream-wise velocity profiles are obtained by the numerical simulation in laminar flow regime. Mass transfer rates and wall shear stresses are measured by the electrochemical method.Chapter 3 described the experimental results. First, according to the pressure drop experiment, the flow is divided into three regimes. Electrochemical experiment results show that the wall shear stress and the mass transfer rate increase with Reynolds Number, and there is a sudden increment in transitional flow regime, but the trend is different in each flow regime.Flow visualization result indicates that the intermittent instability is completely different from that of in the two-dimensional channel. This is the most important difference between the wavy-walled channel and the wavy-walled tube.Chapter 4 summarized the present results. It is concluded that the resonant mass transfer enhancement does not exist in the wavy-walled tube. Thus, the mass transfer enhancement in the wavy-walled tube for steady flow is found to strongly depend on the flow instability, i.e., the intermittent flow instability contributes to the sudden increase of mass transfer rate. Some possible extensions of the present work are also given.