Structural Optimization And Characteristic Research Of Immersion Tube Of Submerged Combustion Evaporator

Immersion combustion evaporation technology is a new combustion technology that uses high temperature gas as a heat source to directly exchange heat with liquid.There is no fixed heat exchange wall,which makes the evaporator suitable for processing liquids that are prone to scaling;Compared with traditional evaporation technology,it has the advantages of high thermal efficiency and low pollutant emission,which meets the current needs of energy conservation and environmental protection.Rapid changes in pressure in the combustion chamber due to liquid level fluctuations due to rising bubbles,In this paper,aiming at stabilizing the back pressure fluctuation of the combustion chamber and improving the heat transfer performance of the evaporator,the submerged tube structure of the submerged combustion evaporator is optimized and improved.Using the research method combining numerical simulation and experiment,under the conditions of different immersion pipe inlet flow velocity and different immersion depth,the influence of immersion pipe structure on the back pressure fluctuation characteristics and heat transfer performance of the combustion chamber was studied.The corresponding physical model is established,the RNG k-ε turbulence model and the VOF multiphase flow model are used to conduct cold numerical simulation of the gasliquid two-phase turbulent flow in the submerged combustion evaporator.The results are as follows:（1）When the inlet velocity of the immersion tube increases,the fluctuation range of the back pressure of the combustion chamber increases;the average velocity of the section increases first and then remains unchanged with the increase of the inlet velocity.When the flow velocity is lower than 0.4437m/s,the immersion depth increases and the pressure fluctuation weakens;when the flow velocity is higher than 0.7369m/s,the pressure fluctuation increases with the increase of the immersion depth.（2）The addition of perforated plates can effectively reduce the pressure fluctuation range of the combustion chamber and increase the heat exchange area to achieve the purpose of strengthening heat exchange.（3）When the flow rate is lower than 0.4437m/s,the effect of the pore size on the pressure fluctuation amplitude is not obvious;when the flow rate is higher than0.7369m/s,the perforated plate with a pore size of 10 mm has the best pressure stabilization effect,followed by 7mm,5mm,and 16 mm,the porous plate with a pore size of 13 mm has the weakest stabilization effect on the back pressure fluctuation,and the difference between the two fluctuations can reach 23.3%.（4）Combined with the mathematical model of the size of the bubbles after detachment,the bubble floating mechanism and the two-phase heat and mass transfer model,it is concluded that the pore size has little effect on the residence time of the flue gas under the research conditions;the size of the high-quality heat exchange area is defined as the evaluation of the heat exchange performance of the evaporator.When the flow rate is low,the difference in the high-quality heat exchange area provided by different apertures is not obvious;when the flow rate is higher than 0.7396m/s,the perforated plate with the aperture of 7mm can provide the largest high-quality heat exchange area,followed by 10 mm,5mm,and 13 mm.The minimum is 16 mm.The surface area of the bubbles formed after the airflow passed through the porous plate with a pore size of 7 mm was 35.64% higher than that of 16 mm,indicating that the 7 mm pore size porous plate had the most significant enhancement of heat exchange.According to the dimensions of the evaporator geometry,a submerged combustion evaporator was fabricated and a test rig was built.Cold state and hot state experiments were carried out on four immersion tube structures of straight tube type,orifice plate type,circulating retaining ring type and orifice plate type with circulating retaining ring,respectively.Experimental results show that:（1）The average value of the pressure experiment at different immersion depths is3.3% higher than the simulated average value,and the average pressure fluctuation amplitude is 43.2% higher than the simulated value.（2）The addition of a circulating baffle ring can generate a directional circulating flow in the water body,and its voltage stabilization effect becomes more and more significant with the increase of the flow rate.（3）Under the experimental conditions,the pressure fluctuation amplitude of the perforated plate structure with the circulating baffle ring is 18.13% lower than that of the perforated plate structure,and 23.38% lower than that of the circulating baffle ring structure.In the heating experiment,the combined structure of the perforated plate and the circulating retaining ring has the fastest heating speed.It is shown that the perforated plate structure with the circulating retaining ring has the best voltage stabilization effect and heat transfer performance,and is the optimal submersible tube structure in this study.