Thermal Dissipation Field And Its Statistical Properties In Horizontal Convection

A study of the local thermal dissipation rate is carried out in horizontal convection.A temperature gradient probe consisting of four identical thermistors is made to measure the thermal dissipation rate εN(r)in the horizontal convection generation device filled with water.The measurements are conducted over varying Rayleigh numbers Ra and vertical positions r above the heating plate and the cooling plate.In the experiment,the temperature gradient probe consists of four thermistors with diameter of 0.36 mm.These four thermistors are arranged in Cartesian coordinates.The horizontal convection generation device is a rectangular container with dimension of L: W: H = 10: 1: 1.Its length,width and height are respectively 500 mm,50 mm and 50 mm.To ensure no heat transferred,the container is completely wrapped with insulation material and put into an incubator.The internal convection is purely generated by the temperature difference between two 50-mm-by-50-mm copper plates.They are placed at two ends on the floor of the container.In the study,the Prandtl number Pr is basically constant and the range of the Rayleigh number Ra is 2×1010～2×1011.According to the GL theory,thermal dissipation rate contains two contributions: one is εm(r),mainly affected by the mean temperature gradient;the other is εf(r),mainly resulting from the plume generated in the thermal boundary layer.It is found that in the Ra range studied εN(r)is mainly concentrated in the region within and near the boundary layer and the contribution stemming from the mean temperature gradient is dominant compared with the other generated by thermal plumes.The transition in horizontal convection can be revealed by the change of εN(r)with Ra in the study.The Ra dependence above the heating plate is given based on the experimental data and theoretical models are used to explain the Ra dependence above the cooling plate.The time series and the probability density functions of the data measured are also analyzed.The experiment provides the physical picture about the thermal dissipation field in horizontal convection.