Inhomogeneity Measurements of Long Thermocouples using a Short Movable Heating Zone

The thermoelectric inhomogeneity of wires is one of the main components of the measurement uncertainty when using thermocouples. During calibration, it is therefore important to determine how much the inhomogeneities affect the measurement result. Thermoelectric inhomogeneity is normally assessed by gradual, or step-wise, insertion of a thermocouple into a furnace or liquid bath. With this type of equipment, the length that can be scanned is typically limited to about half a meter. To assess thermoelectric inhomogeneity over greater lengths, it is necessary to adopt a different technique. Therefore, an apparatus with a short, movable heating zone has been set up and evaluated. The apparatus produces a short, well-defined heating zone that is moved along the thermocouple while both the measuring and reference junctions are kept at 0 °C. Heating is done by means of a hot-air fan that produces a temperature-controlled heating zone up to 700 °C. Two directionally controllable cold-air fans, one on each side of the heating zone, make it possible to vary the slopes of both temperature gradients of the heating zone. Two temperature gradients influence the thermocouple when performing measurements of inhomogeneity with this setup. The results are, therefore, not directly comparable to the results from measurements taken in a bath or furnace, where only one temperature gradient is present. The resulting curve obtained with the two gradients is approximately equivalent to the derivative of the curve obtained with one gradient. It is possible to convert the two-gradient curve to a single-gradient curve by numerical integration, as shown in this work. Comparisons with inhomogeneity measurements obtained using salt baths show good agreement with the calculated results.     

Implementation of a Water Heat Pipe at CETIAT

CETIAT’s calibration laboratory, accredited by COFRAC, is a secondary thermometry laboratory. It uses overflow and stirred calibration baths \((\hbox {from} -\,80\,{^{\circ }}\hbox {C} \hbox { up } \hbox { to } +\,215\,{^{\circ }}\hbox {C})\), dry blocks and furnaces \((\hbox {from } +\,100\,{^{\circ }}\hbox {C} \hbox { up } \hbox { to } +\,1050\,{^{\circ }}\hbox {C})\) and thermostatic chambers \((\hbox {from } -\,30\,{^{\circ }}\hbox {C} \hbox { up } \hbox { to } +\,160\,{^{\circ }}\hbox {C})\). Typical calibration uncertainties that can be reached for platinum resistance thermometers in a thermostatic bath are between \(0.03\,{^{\circ }}\hbox {C}\) and \(0.06\,{^{\circ }}\hbox {C}\). In order to improve its calibration capabilities, CETIAT is working on the implementation of a gas-controlled heat pipe (GCHP) temperature generator, used for industrial sensor calibrations. This article presents the results obtained during the characterization of water GCHP for industrial applications. This is a new approach to the use of a heat pipe as a temperature generator for industrial sensor calibrations. The objective of this work is to improve measurement uncertainties and daily productivity. Indeed, as has been shown in many studies (Dunn and Reay in Heat Pipes, Pergamon Press, Oxford, 1976; Merlone et al. 2012), the temperature of the system is pressure dependent and the response time, in temperature, follows the pressure accordingly. Thanks to this generator, it is possible to perform faster calibrations with smaller uncertainties. In collaboration with INRiM, the GCHP developed at CETIAT works with water and covers a temperature range from \(+\,30\,{^{\circ }}\hbox {C}\) up to \(+\,150\,{^{\circ }}\hbox {C}\). This device includes some improvements such as a removable cover, which allows us to have different sets of thermometric wells adjustable according to the probe to be calibrated, and a pressure controller based on a temperature sensor. This article presents the metrological characterization in terms of homogeneity and stability in temperature. A rough investigation of the response time of the system is also presented in order to evaluate the time for reaching thermal equilibrium. The results obtained in this study concern stability and thermal homogeneity. The homogeneity on 200 mm is better than 5 mK and with a calibration uncertainty reduced by a factor of three.     

The Combined Use of a Gas-Controlled Heat Pipe and a Copper Point to Improve the Calibration of Thermocouples up to 1100 ˚C

The calibration of platinum-based thermocouples from 420 °C to 1,100 ˚C is currently carried out at INRIM making use of two different apparatus: for temperatures below 930 ˚C, a potassium gas-controlled heat pipe (GCHP) is used, whereas a metal-block furnace is adopted for higher temperatures. The standard uncertainty of the reference temperature obtained in the lower temperature range is almost one order of magnitude better than in the higher temperature range. A sealed copper cell was investigated to see if it could be used to calibrate thermocouples above 930 ˚C with a lower uncertainty than our current procedures allowed. The cell was characterized with Type S and Pt/Pd thermocouples and with an HTPRT. The freezing plateaux were flat within 0.01 ˚C and lasted up to 1 h with a repeatability of 0.02 ˚C. The temperature of the cell was determined with a standard uncertainty of 0.04 ˚C. Hence, the copper cell was found to be superior to the comparator furnace for the calibration of platinum-based thermocouples because of the significant decrease in the uncertainty that it provides. An analysis was also carried out on the calibration of Pt/Pd thermocouples, and it was found that the combined use of the potassium GCHP and the Cu fixed-point cell is adequate to exploit the potential of these sensors in the range from 420 °C to 1,084 °C. A comparison with a fixed-point calibration was also made which gave rise to agreement within 0.07 ˚C between the two approaches.     

Overcoming Inhomogeneity and Hysteresis Limitations of Type R Thermocouples in an International Comparison

Type R thermocouples are widely used and convenient high-temperature transfer standards; however, the achievable accuracy is limited by the effects of inhomogeneity and hysteresis. In this article, we summarize the results of the recent international comparison APMP-T-S1-04 and discuss the results of the thermoelectric scanning, spatially resolved over the length of the thermocouples. The thermoelectric signatures show both reversible (hysteresis) and irreversible inhomogeneities introduced by the calibration processes used by the participants. The results demonstrate that although the reversible hysteresis of Type R thermocouples limits their performance as a transfer standard in thermometry, this can be managed by appropriate design of the comparison protocol. By performing all calibrations from lower to higher temperatures from an initial 450°C anneal state, a pilot laboratory reproducibility of typically 0.03°C (k = 2) and a reference value uncertainty of 0.03–0.06°C (at k = 2) over 0–1,100°C were achieved. This allowed statistically significant testing of the calibration capabilities of all the participants.     

热管传热性能的评价方法及其测试装置

热管是一种利用工质相变进行热量传递的高效传热元件。文中介绍了一种等效的评价热管传热性能的方法即管内等效对流换热系数法。此外 ,还介绍了等效对流换热系数法测量装置。利用该装置还可研究不同的充液率、不同成分的工质以及倾角对热管传热性能的影响 ,从而研制出高效传热性能的热管     

钠热管炉复现铝凝固点

介绍了利用钠热管炉复现铝凝固点的连续热流密度法.在凝同曲线达到最高值后约3 h,凝固温度下降小于0.6 mK.同时,在高精度复现铝凝固点时,必须在同定点容器内形成内液固界面和外液固界面.当内液固界面破损时,所复现的铝凝固温坪出现波动.此外,往温度计阱重新插入室温的石英玻璃管进行诱导,非常有助于延缓波动的再次发生.     

Assessment of Temperature Measurements Using Thermocouples at NIS-Egypt

Thermocouples are increasingly used in industry and research. For many industrial heating processes, particularly those carried out at high temperatures, a thermocouple is the most convenient and simple instrument for temperature measurement. In some instances, it is the only feasible method. The aim of this study is to select and recommend the best thermocouples from both base and noble metals to users in industrial and scientific institutions. Different types of thermocouples and calibration methods are described. From this work, the Nicrosil–Nisil thermocouple has been proposed as the best base metal thermocouple and the Au/Pt thermocouple is the most recommended as a substandard up to 1,000 °C.     

浅析地表水水源热泵换热器盘管管材选用

首先介绍了水源热泵的工作原理和地表水水源热泵换热器盘管的安装形状。详细说明了地表水水源热泵换热器盘管对管材的性能要求,列举了几种常用给水塑料管材和金属管材并说明它们的技术性能,最后采用模糊综合评判方法对各种管材相对主要性能因素进行评判比较,选择出最优管材,江河水源热泵换热器盘管若采用线圈状安装形式,建议选用HDPE管;若采用U形状安装形式,建议选用铜管。     

基于水蒸发潜热的热管空调设计与性能研究

本文提出了创造低压环境使水大量蒸发,利用水的蒸发潜热制冷的方案,设计并搭建了热管空调系统实验台,测试了30～85℃工况下负压蒸发热管空调的工作性能,利用COMSOL Multiphysics建立流体传热模型分析内部换热情况.在40℃下实验台的设计指标EER为2.1,制冷量为298 W.实验结果表明:该系统在50～75℃...     

倾角与冷却水温度对新型闭式重力热管换热器传热性能影响

本文以丙酮为工作流体,设计了一套新型重力热管换热器,该装置由五根底部连通的垂直蒸发管共用一根水平同心套管冷凝管构成。采用理论和实验相结合的研究方法,分析了装置的传热性能,并对其结构参数进行优化。研究了当倾斜角度为15°~90°、操作温度为40~80℃、冷却水温度为10~30℃时装置的传热性能。结果表明:新型重力热管换热器具有良好的等温性能及操作稳定性;当充液率为15%、倾斜角度为60°、冷却水温度为30℃时,换热器达到最佳工作状态;最大传热量可达1 700 W左右,此时平均热阻为0.042℃/W。     

Numerical Modeling of Heat and Mass Transfer in a Low-Temperature Heat Pipe

A mathematical model of heat and mass transfer in a low-temperature heat pipe has been formulated. Numerical modeling of the problem of heat and mass transfer has been carried out. The distributions of the velocities, the pressure, and the temperatures in the heat pipe have been obtained. The results can be employed in analyzing the efficiency and power of low-temperature heat pipes.     

Intercomparison of Copper Fixed-Point Cells by Using Pt/Pd Thermocouples

The objective of the EUROMET Project No. 844 in the field of thermometry was the intercomparison of the freezing temperatures of the copper fixed-point cells (t ₉₀ = 1084.62°C) of the participating laboratories by using Pt/Pd thermocouples. For most of the 13 participating laboratories, agreement of the freezing temperatures of the different copper fixed points within ±0.06 K was found. Furthermore, the results of the intercomparison show that Pt/Pd thermocouples are suitable for use as transfer standards for the dissemination of temperatures and to approximate the ITS-90, at least up to the freezing point of copper.     

Application of a Heat Hydraulic Accumulator to Thermal Stabilization of the Evaporation Zone of a Heat Pipe

The use of a heat hydraulic accumulator (HHA) for thermal stabilization of the evaporation zone of a heat pipe (HP) has been proposed. The experimental setup for investigation of the heat pipe with a heat hydraulic accumulator has been described. Results of the experiments on this assembly have been presented. It has been shown that the installed heat hydraulic accumulator allows thermal stabilization of the evaporation zone of the heat pipe to a precision of 1°C.     

钛制热管式换热器热管与管板连接工艺研究

针对承受较大内外压差的钛制热管式换热器的热管与管板连接工艺难题,设计了一种接头连接,并制定了具体的工艺规范,先采用脉冲TIG焊焊接热管管壳与套管,然后进行单个热管制备,最后采用真空电子束焊接工艺焊接套管与管板间环对接缝。依据工艺制备了样件,对焊接头进行了外观、无损、低倍金相、拉脱力检测,对样件整体进行了水压试验考核。结果表明,样件各项检测及试验满足相关标准要求,研究结果为高性能钛制热管式换热器的研制奠定了关键工艺基础。     

Calibration of Radiation Thermometry Fixed Points Using Au/Pt Thermocouples

At NMIA, radiation thermometers are calibrated by comparison with a number of reference radiation thermometers which are themselves calibrated using fixed-point cells on the ITS-90 temperature scale (In, Sn, Zn, Al, Ag, and Au). The suitability of NMIA fixed-point cells used for standard platinum resistance thermometers (SPRTs) is evaluated by the comparison of ensembles of cells at each fixed point, and by participation in the international BIPM Key-Comparisons K3 and K4. However, the NMIA fixed-point cells used for radiation thermometry are typically much smaller (only 110 mm in length) and the thermowell length immersed in the metal much shorter (85 mm) than those used for SPRTs. Further, the insulation at the front of the crucible needs to accommodate the F/10 viewing cone of the radiation thermometers, so significant temperature gradients exist near the top of the crucible. As a consequence, the conduction errors obtained using SPRTs are too large to be of practical use. A convenient methodology based on the use of a Au/Pt thermocouple, together with a protective tube assembly to reduce conduction errors, has been developed. This allows the convenient measurement of the phase transition temperature traceable, at the 30 mK level, to the fixed-point cells used at NMIA to realize and maintain the ITS-90 scale. As the measurements are made in situ, the temperature environment, and hence the geometry and formation of the liquid?Csolid interface during melting and freezing, are similar to that occurring when used with radiation thermometers. Results are presented for ITS-90 fixed points up to Ag, establishing formal traceability of radiation thermometry fixed-point cells to NMIA??s primary ITS-90 cells.     

青藏铁路冻土重力热管传热特性的研究

应用重力热管是解决青藏铁路建设中冻土路基冻融问题的一个较为实际的方法.本文通过分析重力热管的热阻网络,提出了重力热管的传热模型,并利用现有的热管内部传热的经验关系式,对不同倾角、不同管径以及不同冷凝管长度条件下的传热量进行模拟计算.