Numerical Simulation Of Hydrophobic Coating In Rectangle Channeland Discrete Inclined Ribs In Tube

Vortex generator has been widely used,but it usually result in substantiallyincreased pressure drops for the heat transfer enhancement.This paper obtains fromchanging wall condition to seek method to enhance heat transfer with reducing flowresistance.Super-hydrophobic surface has the characteristics of the flow drag reduction,wecombine vortex generator and super-hydrophobic surface and use turbulence model andlarge eddy simulation to explore the flow and heat transfer characteristics in a rectangularchannel.The result shows that the super-hydrophobic surface can enhance heat transfer inlaminar flow region,but reduce heat transfer in turbulent flow,because the surface effectsthe vortex structure and reduces the number of vortex near wall,the center of vortexstructure moves up so that the heat transfer effect is reduced.In both condition thedecrease of the fluid resistance is very significant,this obviously enhances the integratedheat transfer effect.With the increase of super-hydrophobic surface,flow resistance stillreduces and the heat transfer effect has only a little reduction,so that makes the integratedheat transfer effect enhanced.For circular channels,the tube itself can induce multi-longitudinal vortex,weanalyzes the characteristics of flow and heat transfer in four kinds of discrete inclinedribs tube when the flow velocity ranges from0.5m/s to2.5m/s.When the fluid flowsthrough the inclined ribs,the front and rear vortices appear around the ribs,main vorticesafter the ribs are generated in the tube,the flow process has no dead area and the ribsmakes the area of heat transfer larger.When the fluid flows through a row of inclinedribs,there will be12vortices generated after the ribs,they all together destroy theboundary layer to enhance heat transfer.The best integrated heat transfer effect occurs inthe arrangement of C with the rib height of0.25mm,and the integrated heat transfer effectenhances with the increasing of the number of rib rows,the integrated heat transfer effectincreases with the increasing of the rib pitches,and then decreases.It is the largest with12rows and12mm rib pitch.