Experimental Study On Direct Contact Heat Transfer In Bubble Column

Since the direct contact heat exchange has no heat exchange wall surface,it has the advantages of simple structure,less fouling,high heat transfer coefficient and fast heat exchange rate compared with the wall-in heat exchanger.In this paper,the heat transfer characteristics of paraffin,binary and ternary nitrate molten salt in direct contact heat exchange with air were studied by experiments.Then,based on the law summarized by the experimental data,the dynamic response law of the tower solar thermal power generation with heat storage system under typical day and meteorological conditions is simulated by gPROMS simulation programs.Firstly,a direct contact heat exchange experimental system was built.The experimental device was made up of a vertically fixed 316 L stainless steel tube with an inner diameter of 98 mm and a height of 1100 mm.A gas distributor was fixed in the experimental device to divide the experimental device into upper and lower parts.Then,the air exchanges heat with the high temperature liquid in the upper portion after through the gas distributor.During the experiment,an 8-way temperature inspection instrument was used to collect and record the temperature at different heights of the gas-liquid two phases.The effects of superficial gas velocity,gas-liquid temperature difference,static liquid height,gas distributor pore size and other parameters on the heat transfer characteristics of direct contact heat transfer between high temperature medium and air were investigated.Under the experimental conditions,the air has completed the heat exchange process at a height of 5 mm above distributor.As the superficial gas velocity increases,the volume heat transfer coefficient and gas holdup rate increase.For gas holdup,the growth rate is faster at lower superficial gas velocity;under the experimental conditions,increasing the static liquid height will only result in a decrease in volumetric heat transfer coefficient and gas holdup.The effect of the pore size of the gas distributor and gas-liquid temperature difference on the volumetric heat transfer coefficient is not obvious.According to the experimental results,the empirical correlation of the volume Nusselt number of the paraffin wax and the nitrate molten salt in direct heat contact with air was obtained.Secondly,the flow model of the bubble column in direct contact heat exchange was studied quartz column.The direct contact heat exchange process between the molten salt and the air in the quartz column was studied by infrared temperature measurement.Based on the previous work of other researchers,a method for calculating the temperature difference of direct heat transfer was proposed.Finally,a one-dimensional dynamic mathematical model of the tower solar thermal power station(CSP)system was established.The gPROMS software was used to simulate the dynamic response of the CSP system in the CSP system using the heat storage system during the summer typical day and the fluctuation of the meteorological conditions.The simulation results show that the heat storage system has a significant buffer effect on the impact of meteorological conditions on the CSP system.