Experimental Study On The Effect Of Liquid Additives On Flow Pattern Of Bubble Pump

The pumpless lithium bromide refrigeration unit is a unit that replaces the traditional solution pump driven by high-grade electrical energy with a bubble pump driven by low-grade thermal energy to achieve refrigeration purposes.It not only effectively uses the waste heat of the ship and industrial waste heat,but also reduces high-grade energy—electricity consumption.For the bubble pump,the core component is the lift pipe.The conversion and phase change process between the gas-liquid two-phase flow pattern in the lift pipe will have a greater impact on the bubble pump's lifting efficiency.Liquid additives(also known as surfactants,such as n-octanol,etc.)will further affect the flow pattern in the lift pipe and the pumping process of the bubble pump by affecting the surface tension and other property parameters.In this thesis a bubble pump experimental platform was built and tested.Two-phase flow pattern was visualized and experimentally studied by using the controlled variable method in which different heating power,the concentration of the lithium bromide aqueous solution and the concentration of the liquid additive are as variables,while high-speed cameras and thermal imaging cameras are utilized as auxiliary instruments.In the experiment,six flow patterns including bubble flow,slug flow,plug flow,churn flow,annular flow and slug-annular flow were observed in the lift pipe of the bubble pump.Experiments were conducted to study the influence of the concentration of lithium bromide solution and additives on the flow pattern shape and flow velocity in the lift pipe,as well as the velocity conversion limits of bubble flow-slug flow-plug flow.It is found that the flow pattern velocity with low concentration solution is higher than that with high concentration solution,and the additives have a greater influence on the number and volume of the bubble flow and the slug flow.Reducing the solution concentration and adding surfactant will increase the conversion speed from bubble flow to slug flow,and reduce the conversion speed from slug flow to plug flow.The temperature distribution of the flow pattern in the lift pipe and the temperature change trend in the axial and radial directions were tested and analyzed.The change trend of the gas production rate of the generator with the solution concentration and the additive concentration is obtained by calculating the heat balance of the generator.It is found that there is a long cylindrical low-temperature wake area below the slug flow and a conical laminar temperature distribution above.There is a long conical low temperature wake area below the plug flow,and a semicircular temperature distribution above.The annular flow has a uniform laminar temperature distribution in the radial direction,and the slug-annular flow has an hourglass-shaped temperature distribution.In the axial direction,for the slug flow and plug flow the highest temperature is in the center of the bubble,the temperature above is higher than the temperature below.The temperature of the annular flow gradually decreases from bottom to top,and for the slug-annular flow,temperature at bottom is higher than the above,it is lowest at the intermediate liquid film.In the radial direction,the temperature trends of the four flow patterns are all parabolic.During the experiment of the bubble pump pumping,the appearance and disappearance of each flow pattern correspond to a certain pressure and temperature.By analyzing the change rule of the pressure of the bubble pump with time,the influence rules of different conditions or parameters(heating power,lithium bromide solution concentration,additive concentration)on the pumping time,the length of the intermittent section and the duration of the slug flow during the pumping process are obtained.The results of the study show that reducing the concentration of lithium bromide solution,increasing the heating power,and adding surfactant can advance the pumping time.and reduce the duration of the slug flow,however when the additive concentration exceeds 0.1%,there is a reverse trend.