The Optimal Study On Heat Well Structure Based On The Extremum Entransy Dissipation Principle

Modern Burning Unit(MBU)is a new kind of premixing burner fully using radiant energy.In order to make it for civil requirement,the thesis did research by theory,experiment and numerical simulation.Using thermal efficiency,absorbing heat quantity and distribution of heat flux as evaluating indexes,opening range,opening angle and opening diameter of burning tube and structural size and flow field characteristics of heat well were analysed to the influence on coupled heat transfer of radiation and convection.Finally,a procedure written by MATLAB was given to optimize the structure of heat well to guide engineering.The entransy balance equation on isothermal diffused gray body opening system with participating mediums was obtained for theory and was applyed to structural optimization of modern burning unit.The results showed that thermal efficiency decreased with the increase of reradiation surface opening width and vertical distance between burning tube and gas outlet,and increased with the increase of heat well opening width and that reradiation surface temperature increased with the increase of vertical distance between burning tube and gas outlet and decreased with the increase of reradiation surface opening width and heat well opening width.It also pointed out that heat well opening width was the key parameter of affecting the performance of modern burning unit and that heat transfer quantity caused by gas could not be ignored.An experiment for fuel consumption rate,distribution of heat well temperature,outlet gas temperature,outlet gas ingredient,burning performance and verification of thermal efficiency was carried out.When fuel consumption rate arrived at 0.6435 kg/h,the device was in state of flameless combustion.Also,reradiation surface temperature and thermal efficiency were compared to those of theoretical calculation.The results showed that relative error was less than 8 %,thus proving the rationality of theoretical calculation.Through numerical simulation analysis of heat flux curve of pan,velocity and temperature field,the results showed that heat flux increased with the increase of opening range and opening angle,and first increased and then decreased with the increase of opening diameter.When opening diameter equaled to 6 mm,opening angle equaled to 240°and opening range was the highest,heat flux arrived at the maximum value,outlet gas temperature and entransy dissipation arrived at the minimum value and heat transfer performance was the best.Comparing heat flux of numerical simulation with that of theoretical calculation,the relative error was less than 8 %,proving rationality of condition setting and model choosing.