Abstract

The transient temperature measurements and subsequent prediction of heat flux are prime requirements to quantify instantaneous heat transfer characteristics in short duration unsteady flow phenomena. Coaxial surface junction thermocouples (CSJT) are efficient laboratory tools that can cater both the requirements of measuring continuous as well as instantaneous temperatures. In addition, they have the capability of fast response behaviour for the measurement of transient temperature even in harsh environments. Ease of fabrication process, robustness and cost effectiveness are some of the advantages of CSJTs over its counterparts. The present investigations mainly focus on CSJT as a potential “heat flux sensor” for short duration experiments. For this purpose, an E-type probe (3.25 mm diameter and 10 mm long) was prepared in-house. The fabrication process involves intentional plastic deformation between the two metallic thermo-elements of the probe to achieve a sensing junction of 20 μm. The characterization and quality of the sensing surface is supported through Electron Discharge X-ray (EDX) and Field Emission Scanning Electron Microscope (FESEM) studies. The probe was exposed to a continuous wave laser source of known wattage (in the range of 0.2 W–0.5 W) which acts as a source for step heat load. Transient temperatures recorded from the probe are further processed for heat flux computation through analytical and numerical methods. As a term of inference during the test window of 0.4 s, it is observed that temperature as well as heat flux values have a nice match in trend as well as magnitude with an uncertainty band of ±5%.

中文翻译：

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同轴表面结点热探头通过基于激光的热通量评估进行瞬态测量的有效性

摘要

瞬态温度测量和热通量的后续预测是量化短时非稳态流动现象中瞬时传热特性的主要要求。同轴表面结热电偶（CSJT）是有效的实验室工具，可以满足测量连续和瞬时温度的要求。此外，即使在恶劣的环境下，它们也具有快速响应性能，可用于测量瞬态温度。相比JJT同类产品，CSJT的一些优势在于其易于制造，坚固耐用和具有成本效益。目前的研究主要集中在CSJT作为短期实验的潜在“热通量传感器”。为此目的，内部准备了E型探头（直径3.25 mm，长10 mm）。制造过程涉及探头的两个金属热元件之间的故意塑性变形，以实现20μm的传感结。通过电子放电X射线（EDX）和场发射扫描电子显微镜（FESEM）研究来支持传感表面的特性和质量。探头暴露于已知功率（在0.2 W–0.5 W范围内）的连续波激光源中，该激光源用作步进热负载。通过分析和数值方法进一步处理从探头记录的瞬态温度，以进行热通量计算。作为在0.4 s的测试窗口期间的推论术语，可以观察到温度和热通量值在趋势和幅值上都具有很好的匹配，不确定带为±5％。