| The 2D and 3D numerical simulations of flow and heat transfer for different media(water,nano-fluid)in annular microchannel were conducted.The simulation reliability was verified via comparing the simulation results with those of experiments.For a length of 100mm annular microchannel,with different annular clearance size of 0.5mm,1.0mm,2.0mm,3.0mm,5.0mm and 10.0mm,the 2D and 3D simulation results show that,the friction factor and the Nusselt Number increase with the increase of the annular clearance size.The heat transfer efficiency rises sharply with the decrease of the annular clearance size,and proves the micro size can enhance the heat transfer.For an annular clearance size of 0.5mm annular microchannel,with different length of 100mm,200mm,300mm,400mm,500mm and 600mm,both 2D and 3D simulation results prove that,the friction factor goes up,while The Nusselt Number declines slightly with the increase of the length.The heat transfer efficiency decreases sharply with the increase of the length.For the annular microchannel with 0.5mm clearance size and 100mm in length,the simulation results reveal that the heat transfer efficiency raises with the increase of the hot/cooling water flow rate,a lower cooling water temperature and a higher hot water temperature.The math equations for the friction factor with Reynolds number were obtained,and the equations for the Nusselt number with Reynolds number and Prandtl number were established.For the annular microchannel with 0.5mm clearance size and 100mm in length,the flow media is the nanofluid of 0～4.0%(v/v)Al2O3-H2O.The simulation results show that,the friction factor and the Nusselt Number rise with the rise of volume ratio of the nano Al2O3.While the heat transfer efficiency goes up then down with the rise of volume ratio of the nano Al2O3,and a maximum value for the heat transfer efficiency exists at the 1.0%(v/v)of the nano Al2O3.The nano particle enhances the heat transfer efficiency increasing a sequence of non-metal,water,and metal. |
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