Measurements Of The Heat Transfer And Temperature Profiles In Horizontal Convection With Large Rayleigh Numbers

The convection phenomenon resulting from the horizontal temperature difference is widespread in the nature.In order to investigate this complex natural phenomenon,a simplified horizontal convection model is proposed.Horizontal convection,where the heat source and the cold source are at the same horizontal level,is different from Rayleigh-Bénard convection with the different horizontal levels.In this experiment,the horizontal convection flow is driven by a constant-temperature hot plate and a constant-temperature cold plate,and the plates are placed at the two ends of the bottom of the horizontal convection cell.In the previous experiments of horizontal convection,Rayleigh number（Ra）was less than 10¹².In order to investigate the characteristics of horizontal convection under large Ra,the experimental measurements were carried out in an experimental apparatus with an aspect ratio of 10 and a length of 2 m,which can extend Ra to a larger range(2.75×10¹² - 1.25×10¹³).In the paper,the heat transfer and temperature profiles in horizontal convection were measured under large Ra.It is found that the temperature profiles above the cold source have self-similar characteristics after the normalization under different Ra.The temperature structures can be described by the modified Prandtl-Blasius model.The dimensionless temperature profiles above the heat source gradually change as Ra increases.This structural variation means a change in the flow state in the system.The heat transfer of the horizontal convection system also has a state transition,and the scale between Nusselt number（Nu）and Ra gradually decreases from 1/4 to 1/5.The variations of temperature profiles above the heat source and heat transfer indicate a change in the state of the system.The ellipse model is also used to calculate the velocity by measuring the temperature in the flow field.Based o n this method,Reynolds number Re U and Re V are obtained.When Ra < 10¹²,Re U and Re V are below the 2/5 scale line.When Ra is gradually increased,the scale between Re and Ra increases to 2/5.This is consistent with the theoretical predictions.The experiments show that the temperature structures,heat transfer and Re at large Ra are no longer the same as that at small Ra.