Measurements Of The Thermal Dissipation Rate In Horizontal Convection

In this paper,the thermal dissipation rate is measured in horizontal convection.Then we report the spatial distribution of the normalized thermal dissipation rate εN(r).And we find the local thermal dissipation rate εN(r)dependence of Ra numbers.Besides,statistical analysis of the measured fluctuation of εN(r)help us understand the plume in horizontal convection.In this paper,the horizontal convection system has a dimension ratio,L:W:H=1:1:1.The surface of heating plate and cold plate is a 100 × 100 mm square which has stationary temperature.In this measurement,a kind of temperature gradient probe is designed to measure εN(r),consist of four 0.36 mm diameter thermistors which are arranged in a rectangular coordinate.The separation of the thermistors is 0.8±0.1mm.The Prandtl numberPr = 5.4is constant.And the Rayleigh number Ra in this paper is 4.9×1011～8.2×l0-11.According to GL theory,thermal dissipation rate contains two contributions:one is mean thermal dissipation rate εm(r),coming from the mean temperature gradient;another is εf(r),generated by fluctuation which is effected by plume.The spatial distribution ofεm(r)report that εm(r)mainly comes from thermal boundary layers,both on the heating plate and the cold plate.And εm(r)will decreases with increasing vertical heights;εf(r)is dominated by the thermal boundary layers and the higher mixing region beyond the heating plate,reflecting the existence of thermal plume.And it will also decrease with increasing vertical heights.In bulk region,far away from the thermal boundary layers,the flow is laminar.The probability density distribution of temperature fluctuation δT,temperature gradient dT/dxi and εf(r)help us understand the development of plume in horizontal convection.Horizontal convection has unsteady turbulent state in mixing region,close to the thermal boundary layers.Besides,we get εN(r)dependence of varying Ra numbers.εm(r)will increase with increasing Ra numbers,both in the region of the heating plate and the cold plate.And εf(r)will decrease with increasing Ra numbers.