The Experimental Research Of Boiling Heat Transfer With TiO₂Nanotubearrays Surface On Titanium

More and more heat transfer enhancement techniques are used in the industry,However, with the progress of science and technology, high integration, great heat flow,micro system put forward new requirements to heat transfer. It is imperative to exploit moreefficient heat transfer enhancement techniques. Thus, nano heat transfer enhancementtechnology arises as the times require, and soon become the hot area all over the world.TiO₂Nano-film surface with advantages of gas-sensitivity, humidity-sensitivity, dielectriceffect, photovoltaic effect, high catalytic activity are widely used in solar cell, self-cleaningmaterials, photocatalytic degradation and gas sensor, etc. TiO₂nanotube array film surfaceas a new form of TiO₂nano-film surfaces, which is ideal enhanced boiling heat transfersurface comparing with others, has the bigger specific surface area and better adsorptionproperty. Thus studying heat transfer enhancement of TiO₂nanotube array film surface isvaluable in engineering.Two kinds of TiO₂nanotube array film with different structure of tube arrays wereprepared respectively on the heat transfer surface of titanium heat exchanger plate and tubein inorganic and organic electrolytes via anodic oxidization. Taking deionized water asworking fluid, boiling heat transfer properties of nanotube array film surface （modifiedsurface） were studied in pool boiling and flow boiling respectively. The resultsdemonstrated that the boiling heat transfer coefficient of modified surfaces whether poolboiling and flow boiling were both higher than that of smooth, and the boiling heat transfercoefficient of modified surface （P1） prepared in organic electrolyte was higher than that ofmodified surface （P2） prepared in inorganic electrolyte. In the pool and flow boiling, theycould be increased80%¹10%and40%⁹0%times respectively, meanwhile, the flowpressure drops of modified surface and smooth surface were little difference, modifiedsurface didn’t significantly increase the pressure loss due to changes of surface morphology,and mass velocity had little effect on heat transfer enhancement of modified surfaces.Through observing with the CCD, we found that the bobble detachment radius ofmodified surface was smaller than that of smooth surface, and the bubble’s density anddetachment frequency became higher. It also reflect principle of modified surface enhancedboiling heat transfer, that many nano holes in film layer significantly improved the liquidboiling vaporization core number, consequently enhanced the efficiency of the boiling heat transfer.In this pape, using the least square method and revising coefficient of Gungor model’sinhibiting factor, we obtained pipe flow boiling heat transfer coefficient formula ofmodified surface, this formula were in good agreement with experimental data and the erroris within20%.