Research On Liquid Film Flow And Evaporative Heat Transfer On The Bionic Surface Inspired By Dog’s Tongue

In recent years the evaporate heat transfer of liquid film is a highly efficient heattransfer technique, whose unique advantages are low flow rate, low temperaturedifference, high heat and mass transfer coefficient, simple structure and low energyconsumption and so on. It is focused on in the traditional industries and the high andnew-tech areas of the enhancement of heat transfer.Based on the characteristics of liquid film evaporative heat transfer, this papercarried out the bionic research of microstructure surface inspired by the dog’s tongue.According to the morphology and size parameters, this paper proposed a new type ofbionic micro-scale structure surface. The liquid film flow and evaporative heattransfer performance on the bionic surface were investigated by the method of thenumerical simulations and the experiments.First, the microstructure surface of the dog’s tongue was observed and measuredby laser scanning confocal microscope and Axio Scope A1. Then the information ofbiological surface was extracted to set up the physical model of the bionic surface,and to process the test samples of bionic surface.Compared with liquid film flow on the smooth surface, the effects of the bionicmicrostructures to liquid film were analysed by the numerical simulations. Thedistance of the liquid film flow on the bionic surface is a little shorter than that on thesmooth surface within the same time. The liquid film flow is hindered by the bionicmicrostructures, which lead to the result that the velocity of liquid film flow on thebionic surface is smaller than that on the smooth surface at the direction of flow. Asthe liquid film flow on the bionic surface, regularly strong votex was formed at the downstream. This corrugated disturbance was gradually spread out the upstream ofliquid film with the change of time. The bionic microstructures with staggered andoverlapped arrangement, make liquid film formed disturbance in the front row of thebionic microstructures, which contacted the behind row of the bionic microstructuresbefore not disappearing. These reiterative disturbance for the bottom boundary layerof liquid film formed vortex at the back of the microstructure, promotes the heat andmass transfer performance of the liquid film.The evaporative heat transfer performance of liquid film flowing on the bionicsurface was analysed by numerical simulation. The effects of the different structureson the plates and distribution modes on heat transfer performance were compared, andthe evaporative heat mechanism of liquid film on the bionic surface was elementaryrevealedas well. The bionic microstructure units not only can to increase the heattransfer area but also can generate obvious disturbance toliquid film flow. This is thereason of the heat transfer enhancement of the bionic surfaces. Meanwhile, theconvection generated by gas and liquid also promoted the heat transfer to a certainextent with the increase of water vapor.Finally, the experiments of liquid film evaporative heat transfer were carried outon the bionic surface and on the smooth surface. The liquid film evaporative heattransfer coefficients of the bionic surface and the smooth surface were measured. Theliquid film evaporative heat transfer coefficients of both surfaces were compared inthe thesis. The effects of the temperature, flux and surface structure on the liquid filmevaporative heat transfer were analysed as well. The results show that the liquid filmevaporative heat transfer coefficients of the bionic surface are increased by17.3%than that of the smooth surface with the same flow rate and temperature.