【作者】 李艳霞；

【导师】 刘中良；

【作者基本信息】 北京工业大学 ， 热能工程， 2012， 博士

【摘要】 近年来随着微电子机械系统的迅速发展，各种微小型设备对能量供给系统的要求越来越高，化学电池已逐渐不能满足其要求。因碳氢燃料具有较高的能量密度（大约是锂电池的100倍）、成本低和环保等优势，基于碳氢燃料燃烧的微型能量系统作为微小型设备的动力源具有广阔的发展前景，越来越受到人们的关注。但当燃烧器缩小到微尺度以后，其表面散热损失的影响急剧加大，燃料在有限空间内的点火和稳定燃烧变得异常困难，能否有效解决这些问题直接制约着燃料型微小能量系统的应用与快速发展。通过对国内外相关研究内容的调研发现，人们对微小尺度下固体壁-化学反应-对流换热-质量传递-固体壁导热之间的相互耦合与作用机制还缺乏深入透彻的认识，因此本文借助数值模拟研究和无量纲理论分析对狭小空间内的均相燃烧和传热过程进行了研究，并借助实验方法对微小空间中的催化燃烧与传热特性的影响因素进行了初步探索。本文的工作及主要成果如下：从固体壁对燃烧过程的影响作用着手，通过添加和优化流道内的固体插件（肋片），数值模拟研究了含有肋片和不含有肋片的固体壁对微小尺度空间内燃烧、流动及传热过程的影响规律。建立了包含固体壁在内的物理与数学模型，在充分验证模型准确性的基础上，分析了物理参数和几何参数对微小空间内燃烧、流动和传热传质特性的影响。结果发现，随着入口速度和通道间距的增加，火焰前沿的位置不断的向流体流动的下游移动，当流速较大时就会造成燃烧中脱火现象的发生。为了改善微细管道中的燃烧稳定性，本文建立了微细管道燃烧器和扁平矩形管道燃烧器中带有肋片的燃烧模型，研究了带有肋片的固体壁对小空间内预混气体燃烧、流动和传热特性的影响。结果发现在微细管道内增加纵向肋片，能够促使燃料燃烧放出的热量更有效的向上游移动，更好的预热未燃气体，防止吹熄现象的发生；在微尺度矩形通道中添加纵向肋片却没有达到改善燃烧稳定性的目的，然而在微尺度矩形通道中设置横向肋片后延缓了预混流体在通道燃烧器内的化学反应时间，火焰温度得到提升而下游区域烟气的温度有所下降，更有利于燃料的稳定燃烧。通过改变流道形状并合理布置固体壁，数值模拟研究了微小Swiss-roll燃烧器中预混气体入口速度、混合气体当量比和通道壁厚3项因素对燃烧、流动和传热传质过程的影响规律。建立具有逆向对流换热通道的Swiss-roll燃烧器内的甲烷/空气燃烧模型，研究找到了影响火焰位置的关键因素，发现由于过量的预热效应，燃料只有在很窄的速度和当量比变化范围之内火焰位置才能稳定在燃烧器的中心位置。流体流速较高时，流体与壁面之间的对流换热强度很大，高温烟气的热量通过间隔壁有效传递给了未然预混气体，即使甲烷含量非常稀薄的时候也能维持燃烧的持续反应，且火焰始终停留在反应物通道的第一个拐角处；流体流速较低时，甲烷/空气只有在很窄的当量比变化范围内Swiss-roll燃烧器内的燃烧才能维持链式反应（入口速度v0=1m/s时当量比变化范围在0.8～1.2之间，入口速度v0=0.5m/s时当量比仅在1.0时）。使用无量纲分析方法对一维的具有对流换热通道的燃烧器中燃烧与传热过程进行了理论分析。假设燃烧反应区等同于一个WSR反应器；假设中间隔板两侧与气体的对流换热系数和燃烧器外壁面对环境散热的对流换热系数为常数；假设间隔壁“无线薄”；忽略间隔壁的两个端面与周围环境的对流换热；忽略入口效应对换热系数的影响。分析得到了H=0且Bi→∞，H=0且Bi有限，H有限且Bi→∞，H有限且Bi有限四种情况时燃烧器中的间隔壁温度、反应物流体（冷流体）温度和产生物流体（热流体）温度沿着无量纲长度L方向上的变化曲线，以及WSR反应器出口温度(1)随着无量纲质量流量M值的变化趋势。采用阳极氧化方法和浸渍法制备了适合狭小空间的Pt-Al2O3催化剂，设计并加工了微尺度燃烧器，并利用催化燃烧测试实验系统进行了氢气在Pt-Al2O3催化剂表面的低温催化燃烧特性测试实验。实验研究了不同气体流量和当量比的H2/Air预混气体在微小尺度燃烧器内的无焰催化反应，当量比1.0时336ml/min的预混气体的催化放热反应使燃烧器平均壁面温度达到490K，并随着流量的降低，燃烧器壁面平均温度也逐渐降低；在改变预混气体中空气与燃料的化学当量的过程中，随着当量比从0.8到1.2的不断增大，燃烧器的外壁面温度先是不断上升直至达到一定的温度而基本保持不再变化。更多还原

【Abstract】 With the rapid development of MEMS systems in recent years, the requirementof vast micro and small equipments for the energy supply system is getting higher andhigher. Whereas, the chemical batteries have been unable to meet their requirements.Due to hydrocarbon fuels having advantages of higher energy density (about100times that of lithium batteries), lower cost and more environmentally friendly,micro-energy system based on the combustion of hydrocarbon fuels as a power sourceof the micro device increasingly attract the people’s attention. But when the burner isreduced to the microscale, the impact of the surface heat loss to the enviromentalincreases sharply. The fuel ignition and stable combustion becomes extremelydifficult within the limited space. It will restrict the application and development ofmicro and small energy systems using hydrocarbon combustion if being able toeffectively solve these problems.By surveying the status of micro or small combustion in the domestic andforeign research field, the mutual coupling mechanism of solid wall-chemicalreaction-convection heat transfer-mass transfer-thermal conduction in micro or smallspace is not understood deeply and thorough. The homogeneous combustion and heattransfer process in micro space were studied with the numerical simulation andnon-dimensional theoretical analysis in this article. And the catalytic combustion heattransfer characteristics were experimental studied. The work and the main results areas follows:By adding and optimizing the solid plug in the flow channel (e.g. fins),Numerical simulations of premixed combustion in a micro scale rectanglechannel with or without fins were studied to investigate the effects of solid wallsto small-scale combustion, flow and heat transfer process. The physical andmathematical model containing solid walls was built and the accuracy was fullyverified. The effects of physical and geometrical parameters on combustion, flow, heatand mass transfer characteristics in a confined space were studied. The results showedthat: The inlet velocity and the channel gap have very important impacts on thelocation of the flame front. And the location of the flame front shifts downstreamalong the fluid flow with the increase of inlet velocity and channel gap. The blow outwill happen when the inlet velocity is large. In order to improve the combustion in thetenuous situation, the combustion models of a tiny tube or a flat chennel with finswere built. Through studing the effect of the walls with lengthways and transverse finson the combustion, flow and heat transfer characteristics in a small space, it could beconcluded that: the increasing of transverse fins in a small tube could carry more heat energy that fuel combustion released to upstream region and preheat the unburned gaseffectively and prevent the blow out phenomenon occurring. The combustion in amicro-scale rectangle channel could not be improved by adding lengthways fins alongthe inner walls. But the transverse fins on the inner walls postphone the reaction timefor pre-mixed fluid in the small channel. It promotes the combustion stably.By changing the shape of the flow channel, Numerical simulations of smallscale combustion in a Swiss-roll burner were undertook to investigate the effectsof gas inlet velocity, the mixture equivalence ratio and wall thickness on theprocess of combustion, flow, and heat and mass transfer. The methane/aircombustion model inside the small-scale Swiss-roll burner with a reverse convectiveheat transfer channel was established. The research results show that the key factorsaffecting the flame position is inlet velocity. The flame stabilized at the center of theburner only in a very narrow range because of excessive warm-up effect. When theinlet velocity is large, the wall heat conduction effect has been weakened by thestrength convective heat transfer along the fluid flow direction. The flame maintains asustained response and always stay at the first corner of reactant channel even if themethane concentration is very thin. When the inlet velocity is small, the methane/airmixture could maintain the chain reaction within the Swiss-roll burner only in verynarrow range (e.g. when inlet velocity v0=1m/s, the equivalence ratio ф=0.8~1.2orwhen the inlet velocity v0=0.5m/s, the equivalence ratio ф=1.0).The theoretical analysis of combustion and heat transfer processes in theone-dimensional burner with a convective heat transfer channel usingnon-dimensional analysis method was undertook. The analysis model assume that:the combustion reaction zone is equivalent to a WSR reactor. The convection heattransfer coefficient of between both sides of the middle partition and gas and betweenthe burner outer wall and the environment is a constant. The middle partition wall’sthickness is infinitely thin. The two ends of the interval wall are adiabatic. Theentrance effect on the heat transfer coefficient is ignored. The results shows the curvesof the interval wall temperature, the reactant temperature (cold fluid) and the resultanttemperature (hot fluid) along the dimensionless length L and the trend line of WSRreactor outlet temperature with the dimensionless mass flow rate M for these fourcases. They are H=0and Bi→∞, H=0and Bi≠0, H≠0and Bi→∞, H≠0and Bi≠0.The Pt-Al2O3catalysts suitable for small spaces were prepared using theanodic oxidation and impregnation method. A microscale combustor wasdesigned and fabricated. And the catalytic combustion of hydrogen on thePt-Al2O3catalyst surface at low temperature was experimental studied. Theeffects of mixture flow rate and the equivalence ratio of H2/Air premixed mixture onthe flameless catalytic reaction and heat transfer in the micro-scale burner were got.The average wall temperature of the catalytic reaction burner was about490K when the flow rate of1.0equivalence ratio mixture was336ml/min. The wall’s averagetemperature of the burner was gradually reduced with the flow rate reducing. Whenchanging the equivalence ratio of the premixed mixture, the outer wall temperature ofthe burner first increased until it reaches a certain temperature and remained thecertain value with the equivalence ratio increasing from0.8to1.2.更多还原