Effects Of Dimensions On The Fluid Flow And Mass Transfer Characteristics In Wavy-walled Tubes

With the development of technology and the short of energy, the high efficiency heat and mass transfer devices are paid much more attention. The enhancement of heat transfer performance especially in the plate or the tube heat exchangers could be realized by means of changing the wall shape of the employed channels. The relative studies pointed out that the flow separation easily appears in abnormity tubes; in comparison with the corresponding straight-walled tube, the mass transfer has been enhanced in the wavy-walled tubes; also the transfer enhancement mechanism is brought out. In this study, the effects of dimensions on the fluid flow and mass transfer characteristics in wavy-walled tubes will be investigated, and then the mass transfer enhancement under equal pumping power condition will be focused especially. The present study will provide a significant reference for the design of high efficient reactors and heat exchangers.The paper is divided into five chapters, the main contents are as follows:Above all, the previous work in this area has been reviewed. Many investigators devoted their efforts to study on the mechanical properties of channels with different wall shapes. The above studies had already treated the fluid flow and mass transfer characteristics in various channels and tubes, but the effects of dimensions on heat and mass transfer characteristics have been scarcely explored.In chapter2, the experimental apparatus, measurement techniques and principles used in the study are described. In order to investigate the combined effects of the wavelength and amplitude on the fluid flow and mass transfer characteristics, the wave factor Fw is defined. The measurements of mass transfer rate and flow patterns are performed by the electrochemical method and aluminum dust method, respectively.In chapter3, the experimental results are introduced. The results showed that the wavelength and amplitude of the wavy-walled tubes obviously affect the fluid flow and mass transfer characteristics. For the steady flow, with the increment of the wave factor Fw, the overall pressure drop increases and thus leads to an earlier shift of transitional flow to turbulence as well as a better mass transfer enhancement. Furthermore, mass transfer enhancement is compared with the corresponding straight-walled tube under equal pumping power condition. It is found that the greater mass transfer enhancement appears at the moderate Reynolds number. Based on the flow visualization results, the characteristics of the flow structures in wavy-walled tubes with different dimensions are displayed clearly. For the pulsatile flow, with the decrease of the wave factor Fw, the mass transfer enhancement E increases. The optimal Stopt is same at same Res in different wavy-walled tubes.In chapter4, the fluid flow in wavy-walled tubes and the corresponding straight-walled tube for steady flow is investigated numerically by FLUENT software, numerical results is agreement with experimental results.Finally, according to the experimental and numerical results, it is concluded that the optimum mass transfer enhancement could be obtained in the wavy-walled tube near the Fw=0.5.