New Transient Hot-Bridge Sensor to Measure Thermal Conductivity, Thermal Diffusivity, and Volumetric Specific Heat

A high sensitivity thermoelectric sensor to measure all relevant thermal transport properties has been developed. This so-called transient hot bridge (THB) decidedly improves the state of the art for transient measurements of the thermal conductivity, thermal diffusivity, and volumetric specific heat. The new sensor is realized as a printed circuit foil of nickel between two polyimide sheets. Its layout consists of four identical strips arranged in parallel and connected for an equal-ratio Wheatstone bridge. At uniform temperature, the bridge is inherently balanced, i.e., no nulling is required prior to a run. An electric current makes the unequally spaced strips establish an inhomogeneous temperature profile that turns the bridge into an unbalanced condition. From then on, the THB produces an offset-free output signal of high sensitivity as a measure of the properties mentioned of the surrounding specimen. The signal is virtually free of thermal emf’s because no external bridge resistors are needed. Each single strip is meander-shaped to give it a higher resistivity and, additionally, segmented into a long and short part to compensate for the end effect. The THB closely meets the specific requirements of industry and research institutes for an easy to handle and accurate low cost sensor. As the key component of an instrument, it allows rapid thermal-conductivity measurements on solid and fluid specimens from 0.02 to 100 W· m⁻¹·K⁻¹ at temperatures up to 250°C. Measurements on some reference materials and thermal insulations are presented. These verify the preliminary estimated uncertainty of 2% in thermal conductivity.     

Thermal Transport Properties of Water and Ice from One Single Experiment

For the first time, the transient hot wire (THW) and the transient hot strip (THS) techniques were used to measure the thermal conductivity and thermal diffusivity of ice and the thermal conductivity of liquid water simultaneously in one run. With the additional knowledge of the thermal diffusivity of water from a subsequent single-phase run, the latent heat of melting can be determined as well as the time dependent position of the interface between both phases during an experiment. The results of the dual-phase measurements are compared with those obtained in the single-phase experiments using the same simple setup. The composite THS and THW signals are interpreted based on the underlying phase-change-theory of Stefan and Neumann, as outlined briefly in the text.     

Transient Hot Wire (THW) Method: Uncertainty Assessment

The standard method for measuring thermal transport properties of dielectric solids such as ceramics and refractories is the transient hot wire (THW) technique. In its simplest arrangement, a thin wire is embedded between two sample halves, where it acts simultaneously as a resistive heat source and a thermometer. From its temperature signal, the thermal conductivity and the thermal diffusivity of the dielectric can be derived. Up to now, there is no uncertainty assessment for this technique strictly following the ISO Guide to the Expression of Uncertainty in Measurement. Here we analyze the ISO standard uncertainty of the THW technique in the same way as in a previous paper on the uncertainty of the closely related transient hot strip (THS) technique. The two papers provide a comprehensive comparison of the most important advantages and disadvantages of these two transient techniques. The results obtained here for the uncertainty (5.8% for the thermal conductivity and 30% for the thermal diffusivity) are nearly the same as those for the THS method. Experiments on a Pyrex standard-reference sample confirm the results.     

Measurements of the Thermal Effusivity of a Drop-Size Liquid Using the Pulse Transient Hot-Strip Technique

The thermal effusivity of drop-size liquids was measured by the pulse transient hot-strip technique. A strip sensor, used as a thermometer and heat source, is deposited on a smooth surface of an electrically insulating background material – onto which an insulating liquid sample is applied, completely covering the strip probe. Experiments can be made controlling the thermal penetration depth to within some 10 μm of the liquid sample – here demonstrated by measuring a drop of water at about 1% uncertainty. Measurements were made on water and a series of silicone oils (kinematic viscosity from 5 to 50 cSt; 1 cSt = 10⁻⁶ m²· s⁻¹) in microgravity conditions using a 10 m drop tower (10⁻³ g, 1.4 s), to investigate if any potential natural convection in the liquid at normal gravity condition is present, influencing the results. However, no such influence was observed. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

A Quasi-Steady State Technique to Measure the Thermal Conductivity

A new method is developed for the measurement of thermal conductivity. It combines characteristic advantages of steady-state and transient techniques but avoids major drawbacks of both these classes of methods. On the basis of a simple transient hot wire (THW) or transient hot-strip (THS) arrangement, a direct indicating thermal-conductivity meter is realized by adding only one temperature sensor. After a short settling time during which all transients die out, the instrument operates under quasi-steady state conditions. No guard heaters are required because outer boundaries are free to change with time. The instrument's uncertainty is provisionally estimated to be 3%.     

Quasi-Steady State Method: Uncertainty Assessment

The newly developed quasi-steady state (QSS) method to measure the thermal conductivity combines characteristic advantages of transient and steady-state techniques but avoids their major drawbacks. Based upon a transient hot strip setup, the QSS technique can be realized by adding only two temperature sensors at different radial distances from the strip. After a short settling time, the QSS output signal which is the measure for the thermal conductivity is constant in time as it is for steady-state instruments. Moreover, in contrast to transient techniques, the QSS signal is not altered by homogeneous boundary conditions. Thus, there is no need to locate a time window as has to be done with the transient hot wire or transient hot strip techniques. This paper describes the assessment of the QSS standard uncertainty of thermal conductivity according to the corresponding ISO Guide. As has already been done in previous papers on the uncertainty of the transient hot wire and transient hot strip techniques, first, the most significant sources of error are analyzed and numerically evaluated. Then the results are combined to yield an estimated overall uncertainty of 3.8%. Simultaneously, the present assessment is used as an aid in planning an experiment and in designing a QSS sensor to achieve minimal uncertainty. Such a sensor is used to verify the above mentioned standard uncertainty from a run on the candidate reference material polymethyl methacrylate.     

A new method for the evaluation of thermal conductivity and thermal diffusivity from transient hot strip measurements

The standard straight-line fit to data of a transient hot strip (THS) experiment to determine the thermal conductivity and thermal diffusivitya suffers from two major drawbacks: First, due to the statistical nature of the estimation procedure, there is no relation between the uncertainty of the measured value on one hand and the transport properties obtained on the other. Second, in order to account for he heat capacity of the strip and outer boundary conditions, two intervals of the plot must he rejected before analyzing it. So far, these intervals are selected arbitrarily. We now treat the THS working equation as a function of the four parameters concerned. a.U ₀ (initial voltage), andt ₀ (time delay). Chi-square fittings. following the Levenberg-Marquardt algorithm. are performed separately for several overlapping time intervals of the entire plot to find and a with minimal standard deviation. In the course of subsequent iterations an individual weighting factor is applied to each point to account for systematic errors. This procedure yields the "best" values of anda along with their individual errors. comprising the systematic and the statistical errors. Experimental results on Pyrex glass 7740 were taken to verify the new procedure.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder. Colorado, U.S.A.     

隔热条的轴钉应力开裂试验方法

隔热条是隔热铝合金建筑型材的关键部件,可用轴钉应力试验考察其在加工和使用过程中的适应性,选用切削液-清洗液联合浸泡法和清洗液浸泡法两种方法对隔热条进行了轴钉应力测试,并对比了方法的不同。结果显示:试样均未出现开裂现象,表明新版标准GB 5237.6-2012中规定使用更严格的方法(GB/T 23615.1-2009中规定的方法)来考察隔热条的耐轴钉应力开裂性是可行的。     

The Thermal Conductivity, Thermal Diffusivity and Isobaric Heat Capacity of Toluene and Argon

This paper presents absolute measurements for the thermal conductivity and thermal diffusivity of toluene obtained with a transient hot-wire instrument employing coated wires over the density interval of 735 to 870 kgm^–3. A new expression for the influence of the wire coating is presented, and an examination of the importance of a nonuniform wire radius is verified with measurements on argon from 296 to 323 K at pressures to 61 MPa. Four isotherms were measured in toluene between 296 and 423 K at pressures to 35 MPa. The measurements have an uncertainty of less than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. Isobaric heat capacity results, derived from the measured values of thermal conductivity and thermal diffusivity, using a density determined from an equation of state, have an uncertainty of ±3% after taking into account the uncertainty of the applied equation of state. The measurements demonstrate that isobaric specific heat determinations can be obtained successfully with the transient hot wire technique over a wide range of fluid states provided density values are available.     

Measurement of the Thermal Diffusivity of Solids with an Axisymmetrically Positioned Source of Heat Pulse

The pulse method of measurement of the thermal diffusivity of cylindrical samples is considered: an optimum version of normalization of the geometric parameters of a heat pulse, the thicknesses of a cylinder to the radius, and significance of the length of a heat pulse are discussed. The method is realized on an automated experimental setup with simultaneous recording of a thermal signal and the shape and length of a laser pulse. Nonlinear effects are eliminated by decreasing the energy density on the front surface of the sample. The setup presented allows measurement of the thermal diffusivity within a wide range of its values with an error not exceeding 5%. The obtained results of the determination of the thermal diffusivity of Al, Cu, and Fe are presented in comparison with the literature data.     

金属浴石油产品铜片腐蚀检测仪器的研制

为解决传统液体浴腐蚀仪器试验恒温时间长、控温误差大的问题,设计了一种基于金属浴温控技术的石油产品铜片腐蚀测定器。该仪器主要用于测定部分石油产品在特定温度下,对金属铜的腐蚀程度。试验结果表明该仪器温场波动小、加热均匀、工作效率高,可在石油产品铜片腐蚀试验中广泛应用。     

Measurements of the Thermal Conductivity and Thermal Diffusivity of Polymer Melts with the Short-Hot-Wire Method

In this paper, the thermal conductivity and thermal diffusivity of four kinds of polymer melts were measured by using the transient short-hot-wire method. This method was developed from the hot-wire technique and is based on two-dimensional numerical solutions of unsteady heat conduction from a wire with the same length-to-diameter ratio and boundary conditions as those in the actual experiments. The present method is particularly suitable for measurements of molten polymers where natural convection effects can be ignored due to their high viscosities. The results have shown that the present method can be used to measure the thermal conductivity and thermal diffusivity of molten polymers within uncertainties of 3 and 6%, respectively. Further, the thermal conductivity and thermal diffusivity of solidified samples were also measured and discussed.     

A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids

A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, C_p, of the fluid, provided that the density is measured, or available through an equation of state.     

热敏CTP曝光参数中的斜排角度的设定及分析

使用适用于激光密排斜排热敏CTP的测控条,对国产热敏CTP的曝光参数中的激光密排斜排角度进行设定及研究,并分析了斜排角度对制版质量的影响。结果表明,激光密排斜排角度设置不正确,印版图文信息会发生扭曲、变形,影响制版质量。     

An Inverse Analysis to Estimate Relaxation Parameters and Thermal Diffusivity with a Universal Heat Conduction Equation1

This paper presents an inverse analysis for simultaneous estimation of relaxation parameters and thermal diffusivity with a universal heat conduction model by using temperature responses measured at the surface of a finite medium subjected to pulse heat fluxes. In the direct analysis, the temperature responses in a finite medium subjected to a pulse heat flux are derived by solving the universal heat conduction equation. The inverse analysis is performed by a nonlinear least-squares method for determining the two relaxation parameters and thermal diffusivity. Here, the nonlinear system of algebraic equations resulting from the sensitivity matrix is solved by the Levenberg–Marquardt iterative algorithm. The inverse analysis is utilized to estimate the relaxation parameters and the thermal diffusivity from the simulated experimental non-Fourier temperature response obtained by direct calculation.     

Model of Fractional Heat Conduction in a Thermoelastic Thin Slim Strip under Thermal Shock and Temperature-Dependent Thermal Conductivity

The present paper paper, we estimate the theory of thermoelasticity a thin slim strip under the variable thermal conductivity in the fractional-order form is solved. Thermal stress theory considering the equation of heat conduction based on the time-fractional derivative of Caputo of order α is applied to obtain a solution. We assumed that the strip surface is to be free from traction and impacted by a thermal shock. The transform of Laplace (LT) and numerical inversion techniques of Laplace were considered for solving the governing basic equations. The inverse of the LT was applied in a numerical manner considering the Fourier expansion technique. The numerical results for the physical variables were calculated numerically and displayed via graphs. The parameter of fractional order effect and variation of thermal conductivity on the displacement, stress, and temperature were investigated and compared with the results of previous studies. The results indicated the strong effect of the external parameters, especially the time-fractional derivative parameter on a thermoelastic thin slim strip phenomenon.     

瞬态热带恒功率法测量导热率

基于传统热桥法基本原理,提出了新的非对称结构模型--瞬态热带恒功率法用于测量材料的导热率。非对称结构模型将热源热带与温度传感热带电路彼此独立,消除了热带电阻自热以及环境温度变化带来的影响。通过短时间内快速测量恒流电路中两热带的电压差随时间的变化关系准确测量材料的导热率。依据此模型设计了热带加热片,建立了基于LabVIEW测试软件的实验装置自动测量平台,实验测量结果与参考材料导热率具有良好的一致性,相对偏差在3％左右,验证了该理论模型的有效性。     

Analysis of the Errors in Measuring the Thermal Characteristics of an Unbounded Plate by the Pulse Method

The errors in measuring the thermal diffusitivity and heat capacity by the pulse method are analyzed. The errors due to heat exchange, the finite dimensions of the plate and the length of the heat pulse, as well as distortions due to preliminary signal processing (filtering) are considered.     

Thermal Conductivity of Liquid Tin and Indium

The present paper reports new measurements of the thermal conductivity of liquid tin and indium. The measurements have been performed at atmospheric pressure in a range of temperatures from 450 to 750 K using a new experimental method based on the principle of the transient hot wire technique. The particular version of the technique employed for molten metals has been shown to have an accuracy in the measurement of the thermal conductivity of molten metals of ±2%. Ultimately, it is intended that the technique operate in a wide range of temperatures, from ambient up to 1200 K, and work is in progress to increase the working temperature and to extend the range of measurements. The results are compared with experimental data reported in the literature by other authors and with predictions of the Wiedemann and Franz law.