The Research Of Flow Drag Reductionand Heat Transfer Enhancement Based On Super-hydrophobic Material

Micro-channel have the advantages of high heat transfer efficiency and compactstructure, etc. Super-hydrophobic surface have the function of reducing the flowing dragbecause of slippage, and according to the characters of hydrophobic surface, it has a certaineffect of enhance heat transfer at the same time. In recent years, super-hydrophobicmaterials also gradually received attention in scientific research of the micro-nano scaleflow, Therefore, combined with the super-hydrophobic surface and micro-channel, namely,decorate super-hydrophobic materials in the micro-channel surface. It can both enhanceheat transfer and reduce the flowing drag.According to the features of super-hydrophobic surface, derivate the relationship ofcontact angle and the slip velocity, and correct the formula of wall shear stress. Setting thewall slippage boundary and building the mathematical model of super hydrophobic microcircular channel and super hydrophobic micro rectangular channel. Simulate single-phaseflow and heat transfer. Getting the pressure drop through the channel and wall shear stressand verified by the deduced theoretical formula. Found that the deviation between thesimulation results and the theoretical results is little. It illustrated that the method of correctthe formula of wall shear stress to simulate the slip boundary as a starting point to a generalmode and have more universal, though it is different from the commonly method in theliteratures.Derivate the formula of slip length. Analysis of different diameter, inlet velocity andcontact angle to flow and heat transfer in circular micro-channel, and different equivalentdiameter, inlet velocity, contact angle and aspect ratio in rectangular micro-channel.Contrast the flow and heat transfer effect of bottom slip and both top and bottom slip in therectangular micro-channel. Compare the similarities and differences of simulation resultsbetween velocity inlet boundary and periodic boundary condition. Numerous studies haveshown that decorate longitudinal vortex generator within the channel can enhance the heattransfer. Based on this, we arrange longitudinal vortex generators in large scale narrowrectangular super-hydrophobic channel, and observe the effect of flow drag reduction andheat transfer enhancement. Research show that, both circular channel and rectangular channel, the comprehensiveenergy-saving effect of micro-channel is better than large channel. Super-hydrophobicchannel flow drag reduced apparently, and with the increase of apparent contact angle,hydrophobic become stronger, and the flow drag deduction and heat transfer efficiency hasmore enhancement. Rectangular channel aspect ratio have great impact on flow and heattransfer. Double side slip channel has better energy saving. Get the circularsuper-hydrophobic with160°contact angle micro-channel, and rectangular micro-channelwhich arranged longitudinal vortex generators and aspect ratio is20with double sidesuper-hydrophobic surface of the contact angle is160°is the optimal simulation results.