Comparative Calibration of Heat Flux Sensors in Two Blackbody Facilities

This paper presents the results of heat flux sensor calibrations in two blackbody facilities: the 25 mm variable temperature blackbody (VTBB) primary facility and a recently developed 51 mm aperture spherical blackbody (SPBB) facility. Three Schmidt-Boelter gages and a Gardon gage were calibrated with reference to an electrical substitution radiometer in the VTBB. One of the Schmidt-Boelter gages thus calibrated was used as a reference standard to calibrate other gages in the SPBB. Comparison of the Schmidt-Boelter gages calibrations in the SPBB and the VTBB agreed within the measurement uncertainties. For the Gardon gage, the measured responsivity in the SPBB showed a gradual decrease with increasing distance from the aperture. When the gage was located close to the aperture, a distance less than the aperture radius, the responsivity in the SPBB agreed with VTBB measurements. At a distance of about three times the aperture radius, the responsivity showed a decrease of about 4 %. This is probably due to higher convection loss from the Gardon gage surface compared to the Schmidt-Boelter sensor.     

Transfer Calibration Validation Tests on a Heat Flux Sensor in the 51 mm High-Temperature Blackbody

Facilities and techniques to characterize heat flux sensors are under development at the National Institute of Standards and Technology. As a part of this effort, a large aperture high-temperature blackbody was commissioned recently. The graphite tube blackbody, heated electrically, has a cavity diameter of 51 mm and can operate up to a maximum temperature of 2773 K. A closed-loop cooling system using a water-to-water heat exchanger cools electrodes and the outer reflecting shield. This paper describes the newly developed blackbody facility and the validation tests conducted using a reference standard Schmidt-Boelter heat flux sensor. The transfer calibration results obtained on the Schmidt-Boelter sensor agreed with the previous data within the experimental uncertainty limits.     

利用平板炉校准辐射热流计时角系数影响的分析

平板炉用于校准辐射热流计。标准辐射热流计和被校辐射热流计分别放置在石墨平板两侧,且角系数保持一致。辐射热流计受热感应面对平板的角系数,可认为是圆盘对与它平行的矩形的角系数,并以此进行计算。本文分析了辐射热流计至平板的距离、受热感应面面积对角系数的影响。     

Numerical Analysis of a Radiant Heat Flux Calibration System

Heat flux gauges are one of the devices that are used to determine the heat loads to which high-speed aerospace structures are subjected during flight. Prior to installation, these gauges are calibrated. The calibration system must be well understood if the heat flux gauges are to provide useful data during flight tests. A pseudo three-dimensional model of the radiant heat flux gauge calibration system was developed. The radiant heat flux gauge calibration system consists of a graphite plate heater and a circular foil heat flux gauge. The numerical model simulates the combined convection, radiation, and mass loss by chemical reaction on the graphite plate surface. It can be used to identify errors due to heater element erosion, and the deviations in the predicted heat fluxes due to uncertainties in various physical parameters of the system. A fourth-order finite difference scheme is used to solve the steady-state governing equations and to determine the temperature distribution in the gauge and the graphite plate, the incident heat flux on the gauge face, and the flat plate erosion. Initial gauge heat flux predictions from the model are found to be within ±5% of experimental results.     

入腔法校准辐射热流计入腔位置的确定

介绍了辐射热流计的校准方法,并详细说明了入腔法校准辐射热流计的装置和原理。校准是在黑体腔直径50 mm的钠管炉和高温黑体辐射源上进行的。所采用的热流计为水冷圆箔式热流计。建立了等效腔体模型用以计算有效发射率。理论计算和试验结果均表明入腔最佳位置在热流计距黑体腔底面1倍黑体腔直径处。     

A Summary of Heat-Flux Sensor Calibration Data

This paper presents a statistical evaluation of the responsivity data on a number of heat-flux sensors, calibrated using an electrical substitution radiometer as a transfer standard up to 5 W·cm⁻². The sensors, furnished by the customers, were of circular-foil or thermopile type. Comparison of the NIST and the customer measured responsivity values showed that the measurements agree within 3 % for more than half the number of sensors tested, so far. Considering the variation in the customer calibration techniques and the wide measuring range of the sensors used in the calibration, the agreement is encouraging.     

New Vacuum Blackbody Cavity for Heat Flux Meter Calibration

In the field of thermal radiation measurements, blackbody cavities are commonly used as reference standards for the calibration of heat flux meters. Applying the energy balance equation to the closed system including the cavity and the sensor, it is possible to predict the heat flux density absorbed by the heat flux meter. Calibration procedures developed at Laboratoire National de Métrologie et d’Essais (LNE) in recent years have allowed us to propose practical solutions for heat flux meters working below 100 kW · m⁻². The best relative uncertainties (k = 2) over the range of (10–100) kW · m⁻² vary from 1.7 % to 3 %. During previous studies, three major facilities were constructed, each one with the objective to respond to different technical problems considering the measuring principle of these heat flux sensors. Following this approach, the sensitivity of these meters to radiation, the sensitivity to radiation and convection, and also the influence of the size of the source or of the positioning of the sensor (horizontally, vertically, etc.) have been investigated. As an outcome of this recent experience, a new vacuum blackbody cavity has been set up. As well as the possibility to calibrate at very low irradiance, there are also some substantive improvements in heating, thermal performance, and calibration methodology. After a summary of the state of the art of calibration methods and their limits, the article presents the preliminary results of the characterization obtained with this new facility for which the objective is to reduce the uncertainties by at least a factor of two for heat flux densities lower than 20 kW · m⁻².     

温度传感器辐射修正校准的准确牲研究

为了确定温度传感器辐射修正校准的准确性,需要对温度传感器辐射修正校准结果进行对比及不确定度分析.本文介绍了在热校准风洞中进行温度传感器辐射修正校准的结果,并做了对比研究和不确定度分析.     

Uncertainty of the Calibration of Paired Temperature Sensors for Heat Meters

In heat meters, the temperatures of the incoming and the outgoing water are measured with calibrated platinum resistance thermometers. They are subject to legal metrology and the requirements for the uncertainty associated with the temperature difference are specified in national and regional standards. It is difficult to calculate this uncertainty, since it depends on the characteristics of both sensors and correlation needs to be considered. Causes of that correlation include calibration in the same facility, losses due to heat conduction, and common electrical measurements. Therefore, an analytical calculation of the temperature difference and the associated uncertainty is quite complicated, requiring several steps, corrections, and approximations. Monte Carlo techniques avoid these difficulties by simulating the calibration of both sensors simultaneously. As expected, the correlation reduces the uncertainty associated with the temperature difference indicated by the sensor pair considerably. Monte Carlo simulation and analytical calculations are briefly described and their results are compared.     

热管恒温槽校准工业用短型温度计的可行性研究

在(200~500)℃范围内,热管恒温槽是一种替代油槽和盐槽的清洁恒温源。受传热效率的限制,热管恒温槽在校准短型温度计时会产生较大的偏差。本文从传热学角度分析了短型温度计校准中偏差产生的原因。分析证明,在校准过程中,通过增大接触面积,提高换热系数的方式可以有效强化传热,减小因传热造成的偏差。实验表明,通过增加辅助金属环的方式能够有效提高传热效率,提高测量准确度,降低对被测温度计浸没深度的要求,完成工业用短型温度计的校准。     

热能表配对温度传感器的使用与检定

热能表作为一种新型的热量计量仪表，目前在我国的研究与应用日益受到关注。本文对热能表的配对温度传感器进行了详细的阐述和分析，介绍了有关的检定设备和检定方法。     

多孔泡沫金属中指数规律变热流平板表面的层流对流传热分析

采用Brinkman-Forchheimer-extended Darcy流动模型和局部非热平衡传热模型(双温度模型),对指数规律变热流密度条件下的多孔泡沫金属中平板表面的层流对流传热进行了分析,并得出了平板表面的热边界层的厚度和局部的对流传热系数的表达式。结果发现:平板表面的热边界层的厚度发展沿流动方向逐渐增大,但是增大的趋势由迅速趋向平缓;局部对流传热系数沿流动方向逐渐减小,而后趋于稳定。最后推导出了局部的对流传热Nusselt数的准则方程。     

国防地下工程数值模拟与内部热负荷计算

为计算国防地下工程内部热负荷,建立了国防地下工程壁面动态传热的数学模型,并应用FLUENT软件,基于有限容积法对其进行数值模拟,计算得出全年国防地下工程的壁面传热量以及内热源散热量,再综合人体散热量,即得到国防地下工程内部总的热负荷。计算结果表明,该方法可以较为准确地算出国防地下工程内部热负荷。     

热能表配对温度传感器的使用与检定

热能表作为一种新型的热量计量仪表,目前在我国的研究与应用日益受到关注。本文对热能表的配对温度传感器进行了详细的阐述和分析,介绍了有关的检定设备和检定方法。     

周期热流法测定金属导热系数

根据周期热流法的测试原理,采用理论分析、实验测定和数值仿真相结合的研究方法,设计了一套导热系数测试系统.利用先进的数据采集系统,通过自编程实现了数据的自动采集与处理.通过数值实验发现所需测试试样的最小长度远小于相关文献中的穿透深度.对几种试样进行了测试,发现导热系数最大误差不超过5%,经仿真修正后误差在3%以内.该测试系统具有简单、可行、数据可靠的特点.     

卫星红外特性及空间热流对其的影响

建立了完善的卫星温度场与红外特性的理论计算模型.首先根据卫星、地球和太阳的位置关系,计算了卫星接收的空间热流;其次利用有限元法求解瞬态热平衡方程,得到了卫星的表面温度分布;然后在3～6 μm和6～16μm波段分别计算了卫星作为点源时的红外辐射强度空间分布;最后比较了卫星、卫星本体和卫星太阳翼在红外双波段的辐射强度,并详细分析了空间热流对卫星红外特性的影响.文章的研究结果对于空间目标的红外探测与识别具有参考价值.     

High Temperature Superconductor THz Thermal Sensors and Coolers

High temperature Superconductors (HTSCs) are a good candidate for developing THz radiation sensors. They are easy to manufacture and operate in the convenient temperature range of 80–140 K. The speed of operation of a THz sensor need to be controlled by a fast dissipation of heat, by the electrons which act as the sensing element. There is recently a surge in the development of fast and efficient low dimensional thermoelectric, temperature control devices. They would be ideal for cooling of the sensor, over the temperature interval of operation of the HTSCs. Status of these cooling devices towards achieving low temperature self cooling is discussed in the paper. Some results of the modeling study, carried out by the author, in an HTSC hot electron thermal sensor (HETS) are presented.     

一种新研闭环大电流传感器校准装置

主要叙述闭环大电流传感器结构特点与工作原理,并对闭环大电流传感器校准现状进行分析。介绍了闭环大电流传感器校准装置研制解决的关键技术及装置组成、工作原理等。实验结果表明,该装置能够满足大电流传感器校准需要。     

La_2O_3弥散增强钨合金面对等离子体材料及其高热负荷性能

本论文通过粉末冶金方法制备La2O3弥散增强钨合金面对等离子体材料并对其进行了组织性能和电子束热负荷性能的分析。结果显示La2O3弥散增强相抑制钨粒子长大效果显著,而且使W-1wt.%La2O3合金材料的抗弯强度提高了约35.7%。同时,W-1wt.%La2O3也表现出较好的热负荷性能,能够承受6MW/m2热负荷功率密度;在更高热负荷条件下,较高的表面温度导致La2O3出现熔化及W-1wt.%La2O3合金材料表面出现微裂纹等损伤,因此面对等离子体材料直接水冷对延长材料使用寿命和提高热负荷性能是十分重要的。