Analysis Of Entropy Generation In Micro Combustion

With the rapid miniaturization of micro electromechanical systems,fuel cells have become increasingly difficult to meet their needs for energy nowadays.High-efficient and clean energy have become the focus of many scholars'research.Micro thermal photovoltaic system has also attracted lots of attention for its high energy density,non-polluting,portable and other advantages.As one of the most important components in the micro-thermal photovoltaic system,the efficiency of the micro-combustor determines the efficiency of the system.The micro combustor still has many problems and challenges due to its large surface area to volume ratio,such as unstable combustion inside the combustor and short flame residence time,which is easy to extinguish.In this paper,a micro-combustor is optimized.Combustion performance has been improved by changing the structure,the material of the combustor and mass-flow rate of the fuel.Combined with numerical simulation and analysis of entropy generation,the combustion characteristics and energy changes inside the combustor are further described in detail.Many researches have been carried out.?1?Numerical simulation and experiments on the combustors with different steps length have been carried out.The temperature and OH radical distribution in the combustor,wall temperature distribution and mean temperature of outer wall haven been analyzed.It can be concluded that the presence of the step has a positive effect on the combustion performance.The combustion situation inside the micro combustor with a step is more stable and its efficiency,which is higher than the combustion inside the combustor without a step.A comparative analysis of the effects of the step lengths?2mm,3mm,4mm,5mm and 7mm?of different micro-combustors on the entropy generation in the combustors have been carried out.It can be found that the entropy generation in the combustor was inversely proportional to the internal combustion performance.When the step of the micro-combustor is 4mm,the total entropy increase rate inside the combustor is only 0.0017W/K and the internal combustion is the most stable.?2?Using a micro combustor with a 4mm long step as a model,different porous media materials,combustor materials and mass flow rates(7.50×10^-7kg/s,9.38×10^-7kg/s and 1.13×10^-6kg/s were studied)have been studied for the combustion performance inside the micro combustor.Studies have shown that Si C and Al₂O₃ are suitable materials for porous media and micro-combustors,respectively.The larger mass-flow rate of hydrogen promotes a more intense chemical reaction and also increases the total entropy generation rate inside the combustor.Therefore,within a certain range,a larger hydrogen mass-flow rate would improve the stability of the combustor.?3?Based on the application of the micro thermoelectric system,the effects of the angle of the step,the porosity of the porous medium and the wall thickness of the micro-combustor on the power generation efficiency of the micro thermoelectric system were studied.It is obtained from the research that when the inlet angle of the micro-combustor is 45 degrees,the flow velocity is 6m/s,the internal and external flow fields are filled with porous media with porosity of 0.60 and 0.90,respectively,and the wall thickness of the combustor is 0.5mm.The maximum output power of the battery is 1.32W,and the efficiency of power generation in the system is up to 1.96%.