Submerged Combustion Gas Water Bath Heating Device Heat Transfer Performance Analysis And Numerical Simulation Research

The submerged burning natural gas heating device is relatively new and has the advantages of compact structure and high energy efficiency compared with the traditional water jacket heating method.This research group has developed the first submerged burning natural gas heating device in China and put it into use.During the actual operation of the device,the heat transfer effects of natural gas temperature rise,flue gas and water bath can achieve the designed objectives.However,the complexity of water bath flow and heat transfer brings great difficulty to the design in the calculation of heat transfer in the early heating device.In order to simplify the calculation process of heat transfer and improve the efficiency of heat transfer,this type of heating device is widely used.In this paper,theoretical analysis and numerical simulation of the heat transfer characteristics of water bath are carried out based on the actual operating data of the heating device,so as to provide reference for the research and development and design of the follow-up immersion combustion heating device in China.Firstly,this paper introduces the application background of the heating device,briefly introduces the domestic and foreign common natural gas heating technology,and summarizes the research status of the heat transfer of gas-liquid two-phase flow across the tube bundle similar to the heat transfer mechanism of the heating device.Finally,the critical evaporation temperature of the water bath 60? is selected as the design parameter of heat transfer,and the heat transfer process of the water bath in the heating device is theoretically analyzed and calculated,and the appropriate correlation formula is selected to obtain the design comprehensive heat transfer coefficient.It lays a theoretical foundation for the analysis of heat transfer characteristics of water bath in subsequent heating devices.Secondly,combined with the measured data of the heating device operating under different power stability,the temperature distribution characteristics of the heating device heat exchange system were analyzed,and the results showed that the flue gas has a good effect on the overall disturbance of the water bath,and the temperature distribution of each layer of the water bath is relatively close.The water bath has sufficient heat exchange,and the temperature of the flue gas discharge is lower than the temperature of the water bath,which indicates that the heat exchange structure of the heating device is arranged reasonably;as the operating power of the heating device increases,the disturbance of the water bath by the flue gas becomes more severe,and the stable temperature of the water bath and natural gas heat exchange The temperature difference will increase.Then,by theoretically calculating and analyzing the comprehensive heat transfer coefficient of the water bath,the degree of influence of the water bath temperature and the heated natural gas flow rate on the actual comprehensive heat transfer coefficient is clarified.The actual measured data is also used to calculate the convective heat transfer coefficients inside and outside the tube.The actual comprehensive heat transfer coefficient under the rateddesign conditions is calculated by data fitting.The calculation result is 1709.50 W /(? · K).Then calculate the water bath flow velocity value by inverse calculation of the actual convective heat transfer coefficient outside the tube,and fit the relationship between the power and the water bath flow rate.The water bath flow rate of the heating device at 200 kW is 0.59 m / s,which can be the same design.The structure type heat exchanger water bath flow velocity value provides a reference.Finally,the velocity field and temperature field distribution of the heating unit under different power operation are obtained by numerical simulation of computational fluid dynamics,which directly reflects the disturbance degree and heat transfer characteristics of the flue gas to the water bath.At the same time,a monitoring point is created in the heat exchange tube bundle area of the geometric model,and the water bath velocity obtained by reverse calculation of the above heat transfer is verified by using the properties of density to distinguish points and the average velocity of water at the monitoring point.