Research On Thermal Performance And Flame Stability In Microtube Radiant Combustor

In the development process of micro-electro-mechanical system,the shortcomings of low energy density,high quality and short battery life of its energy supply components have become more and more prominent,which greatly limits the miniaturization and portability of electronic equipment and mechanical products.Micro thermophotovoltaic system based on hydrocarbon fuel combustion has significant advantages such as high energy density,small size,light weight,and long and stable energy supply time,which is a micro power system with good application prospect.The working principle of the micro thermophotovoltaic system is to use photovoltaic elements to convert the radiation energy from high-temperature wall of the micro radiant combustor into electric energy,but the current energy conversion efficiency of the micro thermophotovoltaic system is relatively low.In order to improve the energy conversion efficiency of this system,in the design process of the micro-combustor,it is usually necessary to increase the wall temperature level and temperature uniformity of the micro-combustor as much as possible,while ensuring the stable combustion of the fuel in the combustor.Therefore,the competition mechanism and collaborative optimization design between heat transfer and combustion in the microcombustor is a key scientific issue.This dissertation takes the microtube radiant combustor used in micro thermophotovoltaic system as the research object,aiming to improve the thermal performance and flame stability of the combustor.The coupled heat transfer and flame stability of hydrogen combustion in the microtube radiant combustor are studied by numerical simulations.The main research content includes the analysis and enhancement of heat transfer in the microtube radiant combustor,the stability analysis of swirling flame in the microtube radiant combustor,and the heat transfer performance analysis of the swirling microtube radiant combustor.A numerical model of coupled heat transfer of the microrube radiant combustor is establisehed.In view of the difficult problem of radiative heat transfer calculation in simulation process,the effects of two processing methods of weighted sum of gray gases(WSGG)model and different WSGG model parameters on the calculation reliability of radiative heat transfer are evaluated,providing a theoretical basis for practical application selection.Meanwhile,a micro-scale combustion experiment platform is built,and the numerical results are validated against the experimental data,indicating the reliability and accuracy of the numerical model.From the perspective of heat transfer,this dissertation clarifies the law of coupled heat transfer and enhances the heat transfer performance of the microtube radiant combustor.Firstly,the coupled heat transfer characteristics of the combustors with different channel diameters are studied,the heat flux distributions of the inner and outer walls are analyzed,and the influence of thermal radiation on the flame structure and wall temperature distribution is analyzed.Secondly,In order to strengthen the heat transfer performance of the microtube radiant combustor,a heat transfer enhancement measure with a convergingdiverging channel structure is proposed.This dissertation explores the influence of inlet velocity and solid wall materials(quartz,stainless,silicon carbide)on heat transfer performance,and reveals the enhanced heat transfer mechanism of the convergingdiverging channel.Finally,the influences of the throat position and throat diameter of the converging-diverging channel are analyzed,and the influence law of the structural parameters of the converging-diverging channel is obtained.Based on the concept of swirl-stabilized flame,a swirling microtube radiant combustor is developed and designed,and its internal swirling flame combustion characteristics and flame stability are studied.This dissertation investigates the influence of inlet velocity,equivalent ratio and solid wall material on combustion characteristics,and reveals the flame anchoring mechanism in the swirling microtube radiant combustor.It is found that the corner recirculation zone in the combustor is used to enhance the preheating effect and the inner recirculation zone is used to anchor the flame,thereby enhancing the stability of the flame.In addition,the blow-out limit of the combustor with different swirl blade angles under hydrogen lean combustion is obtained,and the flame anchoring and blow-out mechanism under different blade angles are revealed.Finally,based on the swirling microtube radiant combustor,the influences of combustion mode and structural parameters on the heat transfer performance are carried out.A comparative study of thermal performance in a swirling microtube radiant combustor with premixed combustion and non-premixed combustion at different inlet flow rates and equivalence ratios is carried out,which provides a reference for the selection of premixed and non-premixed combustion modes under different inlet conditions.In addition,the structural parameters in the swirling microtube radiant combustor that have a greater influence on the characteristics of recirculation zones are analyzed,and the influence rules of different structural parameters on the heat transfer performance of the combustor are obtained,which improves the heat transfer performace of this swirling microtube radiant combustor.