太阳能高温热化学耦合相变反应器传热机理及性能研究

Solar high-temperature thermochemical process is a promising concept to produce hydrogen as well as basic chemical materials by concentrated solar energy. Due to a poor accuracy of solar radiation concentrating, the traditional two-cavity solar reactor commonly suffers from over-heating in solar radiation absorbing area, along of a sharp temperature gradient in reaction area because of lower reactant thermal conductivity, resulting in an invalidation or a low reaction efficiency of the reactor, respectively. In this project, a novel solar reactor, based on an innovative integration of phase-transition heat transfer, temperature leveling of heat pipe and flat plate heat pipe, will be developed. In this design, radial temperature gradient in radiation absorbing chamber and axial temperature gradient in reaction chamber will be lowered, thus to enhance thermochemical conversion efficiency and safety of the solar reactor. The flow, heat transfer and start-up limitation of high-temperature flat plate heat pipe absorber will be studied, and the effects of its characteristic parameters on heat and mass transfer performance will be investigated, to reveal its heat and mass transfer mechanism under multiphase flow state in the restricted spaces. The start-up characteristic and heat transfer limitation of the heat exchanger coupled of the flat plate heat pipe and the heat pipe, in consideration of extremely strong, heterogeneous, sudden changing solar radiation in the flat plate heat pipe area, as well as thermal conductivity of the medium and characteristic parameters of the heat pipe in cooling section, will be analyzed, and a heat transfer model will be established. Also a thermochemical model will be developed, considering the solar radiation, phase-transition heat transfer, thermal conduction, mass transfer, as well as chemical reaction coupling method under heterogeneous, unstable and high heat flux conditions. The thermochemical model will be studied theoretically and experimentally to investigate the heat and mass transfer, and reaction mechanism of the reactor. This project therefore aims to develop a novel high-temperature thermothemical reactor integrated with solar radiation absorption and reaction, and to reveal its reaction mechanism, under extremely strong, heterogeneous, sudden changing solar radiation and the presence of carbon and hydrogen elements. The innovation of this project lies in a novel conceptual design to improve the thermochemical efficiency and reactor safety of the solar high-temperature thermochemical process.

太阳能高温热化学转化（制氢或基础化工原料）是太阳能高温热利用的前沿课题。聚光精度差导致太阳能反应器吸热侧高温过热，产生失效；反应物导热系数低使反应侧温度梯度大，反应效率低。拟将热板和热管相变传热及均温性的特性移植到太阳能反应器中，降低吸热侧径向及反应侧轴向温度梯度，提高反应效率和可靠性。研究高温热板接收器流动、传热和启动极限，探索热板结构参数对工质流动和传热的影响，揭示受限空间内多相流耦合热质传递机理。分析热板-热管换热器在热板端极强复杂剧变辐射和冷端热管结构参数及导热介质条件下的启动特性和传热极限，并建立其传热模型。建立非均匀、非稳态和高热流密度下，耦合辐射、相变传热、导热、传质和反应过程的数学模型，对反应器传热、传质和反应机理进行模拟和实验验证。本项目旨在极强复杂剧变辐射及碳、氢存在的苛刻工况下，建立高温热化学耦合相变反应器，并揭示其反应机理，为提高反应效率和可靠性提供新思路。

针对现有太阳能反应器存在非均匀和不稳定高热流辐照下稳定性差以及反应区域温度梯度大的问题，结合热管原理，提出一种太阳能高温热化学耦合相变反应器。其核心部件为高温异型热管，由平板式蒸发段和多管式冷凝段耦合而成。采用理论与实验相结合的研究方法考察了其传热性能，并构建了反应器集热性能测试系统，测试和评估了反应器的集热性能。主要研究内容和结果如下：.对反应器进行设计，重点设计核心部件—高温异型热管。数值模拟考察了相关结构参数对反应器传热的影响以及高热流密度下的热承载能力，结果表明：反应腔内冷凝管的存在强化了传热，物料采用侧面切向进气和出气方式时传热性能较好；反应器的结构满足安全使用要求。.建立了一维稳态传热热阻模型，得到了热管结构参数和操作条件对热管传热性能的影响规律；构建了热管腔内蒸汽压降计算模型，获得了热管结构参数对热管腔内蒸汽压降的影响规律。.搭建了单根直通型和异型水-玻璃热管的可视化实验装置，研究了热管在不同操作条件下的相变传热行为，揭示了异型热管可视化启动规律：平板式蒸发段和多管式冷凝段的冷凝面表现出相似的蒸汽冷凝行为，且启动机理一致，板面传热效果略低于管。.实验考察了不同操作条件对高温异型热管传热的影响规律。结果表明：高温异型热管没有常规直通型热管的“平面前锋”启动现象，但管内连续蒸汽流移动速度与直通型在同一数量级；在不同操作条件下高温异型热管均可有效启动，且传热性能稳定，表现了良好的均温性和径向温度展平性能。.研制了一高热流密度聚光太阳能模拟器，经测试发现：在最大输出光强下模拟器辐照至直径210 mm焦平面上的光功率约为4.5 kW，平均热流密度达到130 kW/m2以上，满足设计要求。以此模拟器为光源，测试了反应器的传热性能，并进行了集热效率分析。结果表明：高温异型热管在30 min左右，且在连续变倾角下性能稳定；反应器具有较强的吸热和传热能力，其集热效率主要受冷却流量的制约，在大的冷却流量下高达50%以上；热损主要辐射损失。.对生物质高温热还原金属氧化物进行了热分析研究，获得了基本反应机理；研究表明ZnO/生物质的反应温度在1100℃左右，可用于太阳能高温热化学反应。.总之，高温异型热管具有将吸热面和冷凝面温度展平的优良特性；太阳能高温热化学耦合相变反应器集热效率高，均温性能好，可用于塔式或者碟式集热系统1000℃以上的高温接收器及热化学反应器。