Numerical Investigations On Combustion And Enhancing Heat Transfer Characteristics Of Micro Combustor By An Internal Spiral Fin For Micro-thermophotovoltaic System

With the rapid development of micromechanical manufacturing technology,microelectro-mechanical systems are widely used in communication,military equipment,biomedical equipment,aerospace,and other applications.Currently,micro-electromechanical systems are mostly driven by a chemical battery,which brings a series of problems such as low energy density,high price,chemical pollution,and short running time.Micro-thermophotovoltaic systems,thanks to its advantage of simple structure and no moving component,has become a hot pot of research.As the core component of the micro-thermophotovoltaic systems,the micro combustor is the key factor affecting the output power.Based on this,combining the advantages of combustion stabilization and enhanced heat transfer technology,such as multi–channel and fin,a cylindrical micro combustor with spiral fin is proposed.The effect of spiral fin’s length L and pitch W on the combustion and heat transfer of micro combustor is investigated.The result shows that the longer the length L and the shorter the pitch W,the better the combustion and heat transfer characteristics and turbulence kinetic energy of micro combustor.However,the embedded spiral fins will increase the friction between the premixed gas and the combustor chamber.In order to reduce the pressure loss,based on the optimal structure of micro combustor with spiral fin(length L=14mm,pitch W=2.355mm),a novel design of the micro combustor with spiral fin opening is developed.The influence of hole size D and hole number B of the spiral fin on the pressure loss,temperature distribution and energy output,energy conversion efficiency and turbulent kinetic energy are numerically investigated.It’s illustrated that the increase of hole size D and hole number B is conducive to decreasing the pressure loss and improving the performance of micro combustor.When the inlet velocity is 8m/s and the opening size is 0.6mm,compared with micro combustor without spiral fin opening,the pressure loss of micro combustor with spiral fin opening numbers of 2,4 and 6 decreased by 54.43 Pa,121.73 Pa and178.33 Pa,respectively.But,the increase of hole size D and hole number B will reduce the mean outer wall temperature and temperature uniformity of the micro combustor,which has a negative influence on the heat transfer of micro combustor.In addition,it is found that the change of spiral fin structure parameters has a significant effect on the combustion and heat transfer of the micro combustor.Therefore,multi-factor analysis is conducted on the structural parameters of spiral fin.The method of Taguchi experimental design,Grey relational analysis and Analysis of variance are adopted to investigate the influence of spiral fin length L,spiral fin pitch W,spiral fin number B and spiral fin opening size D on the combustion and thermal performance of micro combustor embedded with spiral fin.According to the results of average grey relational grades,it is found that the factor with the largest effect is spiral fin length L,followed by spiral fin number B,spiral fin pitch W and spiral fin opening size D.Moreover,the result of variance analysis shows that the contribution of length(L),pitch(W),number(N)and opening size(D)to the comprehensive performance of micro combustor is 48.522%,18.613%,30.239% and 1.746%,respectively.In conclusion,the efficient way to optimize the micro combustor with spiral fin is to vary the spiral fin length L.