Measurements Of Heat Transfer And Temperature Profiles In Horizontal Thermal Convection

We report on direct measurements of heat transfer and temperature profiles in horizontal convection(HC).The convection sample is a rectangular container with the dimension of L:W:H = 10:1:1,where L = 100 cm is the sample horizontal length.W and H are,respectively,the width and height of the HC sample.The motion of the internal fluid was purely driven by the temperature difference between two 10 cm-by-10 cm copper plates,which were placed separately at the two ends of the sample bottom.Except for the two thermal conducting copper plates,all other parts of the sample are adiabatic.We used de-ionized and de-gassed water at 35℃ as the working fluid,corresponding to Pr =4.8.The thermally driven force,as expressed by the dimensionless Rayleigh number,Ra,varying in the range of 6 ×1010≤Ra≤1012.In the HC sample,we measured the heat transfer through the square heating plate,as expressed by the dimensionless Nusselt number,Nu,as a function of the system control parameter Ra.Our results showed the scaling Nu=Nu0Ra1/4,which exceeds the classical Rossby scaling Nu～Ra1/5,and are in consistence with the recent results obtained from direct numerical simulation(DNS).In order to provide detailed information on the heat transfer in the 1/4 scaling region,we also study the temperature statistics and the temperature profiles.In the plume-dominated region,the temperature power spectrum P(f)～f-.4 over the frequency range 10-2<f<10-1,which agrees with the Bolgiano scaling.The mean temperature profile above the heating plate shows three features:a linear region,a broad minimum and a flat region,which is the first accurate division to the mean temperature profile from the experimental observations.We discussed that the PDF of temperature and temperature time derivative vary within or without the thermal boundary layer.