【作者】 唐爱坤；

【导师】 薛宏； 潘剑锋；

【作者基本信息】 江苏大学 ， 工程热物理， 2011， 博士

【摘要】 在微加工技术强有力的推动下,微型机械和机电产品的研发获得持续的突破,但其动力供给部分却未能获得大的进展,致使完整微机电系统过大过重或者不能长时间工作,这也成为MEMS发展的瓶颈。近年来,一些基于燃烧的微型动力装置由于具有能量密度高、工作时间长、体积小等优点,有望很好地解决这一问题,其能量密度被认为能够突破100kW/kg,因而受到世界范围内的普遍关注,并成为了各国科研竞争的焦点之一。微热光电系统是一种典型的微动力装置,它利用碳氢燃料在微燃烧器内燃烧产生的热能对燃烧室壁面进行加热,高温壁面辐射出的能量足够高的光子撞击低频带隙光电池产生电能。同其它的微动力装置相比,该系统最大的优点在于无运动部件、制造装配相对容易。本文对圆柱结构微热光电系统进行了结构改进,给出了新型平行板结构的模块化微热光电系统的设计方案,并通过数值分析的方法,开展了较系统的研究工作,取得了一些具有学术意义和实用价值的研究成果：(1)针对新型平行板结构的微热光电系统,分析了能量转换的各个环节,包括燃烧器中流动、传热以及燃烧的耦合过程、燃烧器壁面的辐射过程以及光电转换过程。在考虑辐射壁面温度分布不均匀性的前提下,结合Fluent和Matlab软件构建了一个从燃料化学能输入到电能输出的三维整体能量转换计算模型,并结合初步实验的测试结果对模型的正确性进行了验证。(2)以采用圆形喷口微燃烧器、无过滤器的系统作为研究对象,通过改变系统中辐射壁面与电池的距离、电池种类、光电池以及辐射表面工作温度等关键参数对系统的工作表现进行了一系列的计算,得出这些参数对系统性能的影响规律,从而为平板式系统的进一步优化设计提供出合理的参考依据。(3)鉴于辐射壁面温度分布对系统工作性能的重要影响,针对平行板微通道内的燃烧过程进行了大量模拟计算,提出了将圆形喷口改进成细长的方形喷口、适当减小燃烧通道的宽度等改善微尺度燃烧过程的措施,并通过燃烧过程的影响因素分析和计算,得出了混合气流量1500mL/min、通道高度0.6mm等平板式燃烧器合理的运行参数；随后,设计了内部带有多孔介质、内壁面催化以及入口设置稳流凸台等三种优化的燃烧器结构形式以及新型带有预热通道的平板式微燃烧器,分析了采用这些优化结构后的燃烧性能和壁面温度分布特征,并对比了它们对于提高系统工作性能所带来的积极作用,其中入口稳流凸台的设置可使系统在1500mL/min的混合气流量下获得了1.12%的整体效率,这可在一般矩形喷口燃烧器基础上提高33.9%。(4)为进一步提高装置的能量转化效率,在系统中设置了一维Si/SiO2光子晶体滤波器,以实现对不可用辐射能的回收利用。根据光学薄膜的设计理论以及传输矩阵的方法,获取了该类型滤波器的基本设计结构及对应的光学特性,并针对基本结构第一反射带宽度过窄的缺点,作出了相应的改进设计。系统整体计算的结果表明,过滤器的使用可在有效缓解电池冷却负荷的同时,通过提高辐射壁面的温度以达到提升系统输出性能的效果。在1500mL/min的混合气流量下,采用改进结构过滤器的系统功率输出达到了5.46W,其效率为2.6%,比采用基本结构过滤器时提高了5.7%。(5)微动力系统并不仅仅是常规尺度原型的简单缩小,不同装置都应该有其尺度上的极限,但很少有学者针对整体装置的尺度极限展开相关研究。本文的最后,针对平板式的微热光电系统,在考虑部件强度以及制造难度的基础上,结合文献资料、前期的微燃烧实验以及光电池冷却计算分析等,确定出一个完整的能量转换单元的极限尺寸为10mm×8mm×2.5mm,在1500mL/min的混合气流量下单元的功率密度达到了17.55W/cm3,这个数据充分彰显出平板式微热光电系统充当MEMS动力源的优势所在。本文的工作为微热光电系统的合理开发以及工作性能的正确评价提供了一条可行的研究思路,论文中提出的研究方法和得出的结论对于其它微动力系统的开发也有一定的参考价值。更多还原

【Abstract】 With the powerful impulse of micro-machining technology, persistent breakthroughs have been obtained on the development of micro-machinery and electromechanical products. However, no remarkable progress has been obtained in its power supply part, which makes the complete system too big and heavy or can not woking for long time, so this problem has become the bottleneck of MEMS development. In recent years, due to the advantages of high energy density and long working time as so as small volume, several micro power generators which based on combustion are expected to well solve this problem. Their energy densities are supposed to exceed 100kW/kg, so have aroused public concern around the world and are becoming one of the focus in the scientific research competition.As one kind of typical power generating machine, micro-thermophotovoltaic system utilize thermal energy to heat the outer surface of combustor which coming from combustion of hydrocarbon fuels in the micro-combustor, and electricity can be generated when the sufficiently higher-energy photon reaches PV cells. Compared to other power generating machines, its greatest advantages are including no moving components and relatively easy to manufacture and assemble.By modifing the structure of previous cylindrical combustor system, a novel modular micro-thermophotovoltaic system with plane cell structure is proposed in this paper. Systematic research have been carried out through numerical analysis, and some achievements with scientific significance and values have been acquired:(1) Each links of energy conversion is analysed for the new plane cell type micro-thermophotovoltaic system, which including flow, heat transfer and combustion coupling process, radiation process of combustor’s outer wall and photoelectric transformation process. Then, on the premise of non-uniformity of wall temperature distribution, a three-dimensional energy transition computational model is constructed through combining the softwares of Fluent and Matlab which describes the whole transition process of chemical energy to electricity, and the accuracy of model has been verified by preliminary experiment results. (2) The system adopting round nozzle combustor and without filter is taken as study object, by changing distance between radiation wall and PV cell, cell types, working temperature of radiation surface and cell, a variety of preliminary calculations about system performance are maken. According to the analysis of calculation results, some basic conditions for system operation are obtained which can provide reasonable references for the further optimal design of plane cell system.(3) Considering the significance of radiation wall temperature distribution to the system working performance, a great amount of simulations about combustion in the plane cell microchannel are done in the following study. Firstly, measures of improving microscale combustion are presented such as replacing the round nozzle with elongated rectangular nozzle, approximately decreasing width of combustion channel. By further analyzing the effect factors in the combustion process, suitable operating parameters for plane cell combustor such as mixture flux 1500mL/min and channel height 0.6mm are gained. Then, three optimized combustor structures namely porous media in the combustion channel, catalysis on inside walls, convex blocks for steady flow at the inlet and another new plane cell micro-combustor with preheating channels are designed. Combustion characteristics and wall temperature distribution of these optimized structures are analyzed, and the active effects of improving the system working performance are contrasted. Among these four structures, an overall efficiency 1.12% can be realized by using inlet convex blocks for steady flow at mixture flux 1500mL/min, which is 33.9% higher than the original combustor with rectangular nozzle.(4) To further increase the energy conversion efficiency, a one-dimension Si/SiO2 photonic crystal filter is set in the system to ensure recycle of unavailable radiation energy. The basic structure design and corresponding optical characteristics are obtained through optical thin film theory and transmission matrix method, and a improved design is done according to the narrower first reflection band of basic structure. Calculation results show that the using of filter can effectively lower the burden of cell cooling, while at the same time boost the temperature of radiation wall so as to raise system output performance. System output power density and total efficiency reaches 5.46W and 2.6% when using the improved structure filter at mixture flux 1500mL/min, which is 5.7% higher than the result of using basic structure filter.(5) Micro power system is not merely minification of their conventional scale prototype, and each device should has its dimension limits, but few scholar have undertaken related study on the whole device’s miniaturization limitations. In the end of this paper, the minimum dimension of one energy transition cell in the plane cell micro thermophotovoltaic system is determined by considering parts strength and manufacture difficulty and combining related reference, micro combustion experiment and calculation analysis of PV cell cooling, the whole size of energy transition cell is 10mm X 8mm X 2.5mm.The power density is up to 17.55W/cm3 when the mixture flux is 1500mL/min, which fully demonstrates the advantages of plane cell micro-thermophotovoltaic system as the power sources of MEMS.This work provides a practicable research thought to rationally develop and correctly evaluate of working performance for micro-thermophotovoltaic system. However, the methods and conclusions presented in this paper can also be applied to other power systems.更多还原