An Experimental Study Of The Effects Of Prandtl Number On Heat Transfer And Flow Structure In Turbulent Rayleigh-bénard Convection

Many phenomena in nature and industrial production are related to turbulent heat convection,such as the flow in oceans due to temperature differences,the convection of the atmosphere due to solar radiation,and the convection present in heat exchange and heat sinks of many devices.The three dimensionless parameters of RayleighBénard convection are Rayleigh number(Ra),Prandtl number(Pr)and aspect ratio of convection cell().The study of this simplified model is of great significance for understanding natural thermal convection phenomena in application and lifeIn this paper,the effects of Pr on Rayleigh-Bénard convection are systematically studied in a cylindrical convection cell with 0.973 and cell diameter 29.0cm in horizontal direction.The Pr of the experiment was 9.40±0.02,7.00±0.02,5.42±0.01,4.34±0.01 and 3.58±0.01,respectively.The Ra was in the range of 2.63 10 and 3.89 10 respectively.The experiment focuses on two aspects:(1)the efficiency of turbulent heat transfer;(2)the flow structure of RB convection.In our experimental range of Ra and Pr,the scaling law of Nu for Ra are ? (6.,Pr has only little effect on system heat transfer in this range,as well,the NOB effect of water on heat transfer is less significant overall.As for the Re of LSC,Re satisfied a scaling law of 0)? (6..when Pr was in the range of 3.58 ? 9.40.Under the same Ra,Re decreases with the increase of Pr.The symmetry of probability density function(PDF)of temperature fluctuation was broken due to the passing plume near the wall,while the PDF shows a very symmetrical shape in the center of the cell.The change of Pr mainly affects only the tail of PDF.With the increase of Pr,the tail of PDF is warped up,but the difference gradually disappears with the increase of Ra.