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    基于多点聚焦的太阳能腔式吸热器热流密度均匀化研究

    Uniformization of heat flux in a solar cavity receiver via multi-point focusing

    • 摘要: 为解决腔式吸热器驱动生物质气化反应器时极易引发的局部过热的问题,通过光线追踪法建立了定日镜场与腔式吸热器间的光热转换的物理与数学模型,分析了单台定日镜在实时与定时追踪模式下的光学效率变化。同时,还对单点聚焦与多点分区聚焦策略下腔式吸热器集热面上的热流密度分布进行了对比分析。结果表明:在设定的100面定日镜、单面镜尺寸10 m×10 m、吸热器开口中心标高85 m、倾角25°、镜面反射率0.9并基于当地经纬度与时间参数计算DNI的边界条件下,采用分区多点聚焦后,集热面上的热流密度峰值由原本的380 kW/m2骤降至100 kW/m2,降幅超过70%,平均热流密度也锐减至原来的1/5,显著改善了热流密度过于集中的问题。在此基础上,针对高频追踪所导致的机械磨损与附加能耗问题,提出了定时追踪与多点聚焦相耦合的协同追踪策略。模拟表明:该策略不仅将定日镜场整体的光学效率折损严格控制在了±2%,还大幅降低了定日镜调整频次与附加能耗,并使得热流密度集中区域呈周期性变化。这种动态变化的聚光特性不仅能够有效平衡吸热器表面的热应力分布,还有助于降低静态热斑长期驻留所引发的局部热疲劳风险,为生物质气化系统的高效、长周期安全运行提供了保障。

       

      Abstract: To address the severe local overheating issue that occurs when a solar cavity receiver drives a biomass gasification reactor, this study establishes the physical and mathematical models of photothermal conversion between the heliostat field and the cavity receiver using the ray-tracing method. The variation in the optical efficiency of a single heliostat under real-time and timed tracking modes is analyzed. Meanwhile, the heat flux distributions on the absorbing surface of the cavity receiver under single-point focusing and multi-point zonal focusing strategies are compared. The results indicate that, under the boundary conditions adopted in this study, namely 100 heliostats, a single-heliostat size of 10 m × 10 m, a receiver aperture center elevation of 85 m, a receiver inclination angle of 25°, a mirror reflectivity of 0.9, and DNI calculated based on local longitude, latitude, and time parameters, by employing the multi-point zonal focusing strategy, the peak heat flux on the absorbing surface sharply drops from 380 kW/m2 to 100 kW/m2, achieving a reduction of over 70%. Concurrently, the average heat flux is reduced to one-fifth of its original value, significantly mitigating the issue of excessive heat flux concentration. On this basis, to alleviate the mechanical wear and additional energy consumption caused by high-frequency tracking, a synergistic tracking strategy coupling timed-tracking with multi-point focusing is proposed. Simulations demonstrate that this strategy not only strictly limits the overall optical efficiency penalty of the heliostat field to within ±2%, but also substantially reduces the adjustment frequency and additional energy consumption of the heliostats. Moreover, it induces a periodic variation in the localized high heat flux zones. This dynamically varying concentrating characteristic can not only effectively balance the thermal stress distribution across the receiver surface, but also help reduce the local thermal fatigue risk caused by the long-term residence of static hot spots, thus providing a strong guarantee for the efficient, long-term, and safe operation of the biomass gasification system.

       

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