调制光热辐射法测量块体和涂层的高温热物理性质
Measurement of High-temperature Thermophysical Properties of Bulk and Coatings Using Modulated Photothermal Radiometry
摘要：
本文介绍了采用调制光热辐射测量（MPR）方法测量块体和涂层高温热导率的仪器开发，其中样品由强度调制激光加热以探测样品的不同层。虽然MPR以前已经建立，但大多数以前的研究仅关注室温下的测量。MPR在高温下测量大块和涂层材料方面尚未得到很好的研究，这对于许多应用越来越重要，例如聚光太阳能发电（CSP）厂和核反应堆中使用的材料。MPR是一种非接触式技术，它利用样品的固有热辐射进行测温，这有利于在高温和恶劣环境下的测量。作者设计并使用了一个样品架，适用于高达973 K的高温测量，样品内具有良好的温度均匀性。通过测量具有已知热导率的散装材料来验证高温MPR设置。通过调节激光加热束的频率和热穿透深度，将该装置和技术扩展到各种基底上10 ~ 50 μm厚的黑色太阳吸收涂层的测量。研究表明，典型的太阳能吸收涂层的导热系数为0.4 ~ 0.8 W m-1 K-1，表明在高太阳辐射通量下，涂层内可能存在较大的温降，例如CSP电站的中心太阳能塔超过1000个太阳。
英文摘要：
This paper presents the development of instrumentation for the measurement of high-temperature thermal conductivity of bulk and coatings using a modulated photothermal radiometry (MPR) method, where a sample is heated by an intensity-modulated laser to probe into different layers of the sample. While MPR has been previously established, most of the previous studies only focus on the measurement at room temperature. The MPR has not been well studied for measurements of bulk and coating materials at high temperatures, which are increasingly important for a multitude of applications, such as materials used in the concentrating solar power (CSP) plants and the nuclear reactors. MPR is a non-contact technique that utilizes the intrinsic thermal emission from the specimens for thermometry, which is favorable for measurements at high temperatures in harsh environment. The authors designed and utilized a sample holder suitable for high temperature measurement up to 973 K with good temperature uniformity within the sample. The high-temperature MPR setup was validated by measuring bulk materials with known thermal conductivity. The setup and technique were then extended to the measurement of black solar-absorbing coatings of 10 to 50 μm thick on various substrates by modulating the frequency of the laser heating beam and the thermal penetration depth. The studies showed that thermal conductivities of typical solar-absorbing coatings are 0.4 ~ 0.8 W m-1 K-1, indicating a possibly large temperature drop within the coating under high solar irradiation flux, such as over 1000-sun for central solar towers in CSP plants.
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