Numerical Simulation Of Structure And Stability Optimization Of Submerged Combustion Unit

Improving energy efficiency and reducing combustion emissions needs higher requirements with the gradual depletion of energy in the world,the intensification of environmental degradation,and the further increase in human dependence and demand for energy.Considering that combustion is still the main way to obtain energy,it is necessary to solve problems in terms of developing efficient combustion technologies and equipment,rationally organizing the combustion process,and increasing the proportion of clean and efficient energy in energy consumption.As a new type of heating technology for gas-liquid two-phase direct contact heat transfer,immersion combustion is widely used because of its advantages of high thermal efficiency and low emissions.In the course of this research,first,numerical simulations under various working conditions are carried out for the unstable back pressure of the combustion chamber and the small heat exchange area.Second,the related cold experiments are carried out to optimize the structure of the immersion tube.Finally,a high-speed constant-pressure burner that can be used for submerged combustion is numerically simulated.The details are as follows.(1)Two solutions are proposed after the theoretical analysis of the causes of combustion instability during the immersion combustion process:(1)The structure of the immersion tube is optimized in order to reduce the back pressure fluctuation range of the combustion chamber.(2)A high-speed constant-pressure burner is used in submerged combustion devices,whose outlet pressure fluctuates within a certain range but can keep the combustion state in the combustion chamber unchanged.(2)The cold numerical simulation and experimental study of the two-phase flow state in the immersion combustion process under various working conditions are carried out,and the following conclusions are drawn.(1)The inlet pressure of submerged tube(burner back pressure)of submerged combustion heating equipment fluctuates ceaselessly,and its fluctuation range changes with the change of air inflow and immersion depth of submerged tube.(2)The immersion combustion equipment will have great back pressure and wide range of fluctuations at the starting moment,resulting in difficulty in ignition.The immersion depth can be reduced and the burner power can be reduced when the immersion combustion equipment is started.After the equipment is started,the immersion depth of the immersion tube and the combustion power of the burner can be adjusted gradually(3)When the perforated plate is not added,The air will directly float along the outer wall of the submerged tube due to the effect of buoyancy after being sprayed out of the submerged tube outlet,and theheated liquid cannot be sufficiently agitated.(4)As the air supply is increased,the air flow,which enters into the heated liquid from the nozzle of the immersion tube,will increases.When its rate reaches 83.12m3/h,the rigidity of the air flow will gradually appear,and the fluctuation range of the immersion tube inlet pressure will slowing shrieking.(5)With the gradual increase of the air intake and the immersion depth,the gas-liquid interface between the air and the heated liquid,high-quality heat transfer surface,and air retention can be significantly increased,which should have practical significance in enhancing heat transfer.(3)The structure of the immersion tube is optimized.A porous plate is provided at the periphery of the immersion tube outlet to divide the bubble into multiple small bubbles when it floats up,which can not only enhance the heat and mass transfer but also stabilize the back pressure of combustion chamber.When the immersion depth is300 mm and the air flow at the entrance of the immersion tube is 69.27m3/h,The numerical simulation results show that the addition of porous plates and the absence of porous plates can increase the gas-liquid junction area by about 250%,the high-quality heat exchange area by about 536%,and the retained air volume by about295%.The experimental results show that the addition of a porous plate can reduce the fluctuation of the pressure inlet of the immersion tube by about 51.3%.(4)A high-speed constant-pressure burner based on the clogging phenomenon of the Laval nozzle is used for numerical simulation calculations,and it is verified that the combustion state in the combustion chamber remains unchanged under different outlet pressure conditions of the burner.