Hot-wire Instrument Research Articles

Thermal Conductivity of Liquid trans-1,2-Dichloroethene (R-1130(E)): Measurement and Modeling

The thermal conductivity of liquid trans-1,2-dichloroethene (R-1130(E)) was measured at temperatures ranging from 240 K to 340 K and pressures up to 25 MPa using a transient hot-wire instrument. A total of 447 thermal conductivity data points were measured along six isotherms. Each isotherm includes data at nine pressures, which were chosen to be at equal density increments starting at a pressure of 0.1 MPa (or slightly above the saturation pressure of R-1130(E) at temperatures above its normal boiling point) to a maximum pressure of 25 MPa. The combined expanded uncertainty of the presented experimental data is 1.4% at a 95% confidence level. The experimental data were used to evaluate the performance of an extended corresponding states (ECS) model and a residual entropy scaling (RES) model. Both models were applied in a totally predictive mode, and in a mode where the experimental data were used to tune the model parameters. A volume-translated Peng–Robinson equation of state was used to provide thermodynamic properties needed to apply both models. In a totally predictive mode, the ECS model had an average absolute relative deviation (ΔAARD) of 6.89% relative to the experimental data with the largest deviation being − 8.33%. The RES model in a totally predictive mode showed an ΔAARD of 2.55% with the largest deviation being − 5.81%. When model parameters were fitted to the experimental data, both the ECS and the RES model represented the experimental data to within its uncertainty of 1.4%.

Thermal conductivity measurements using the transient hot-wire method: a review

The accurate determination of the thermal conductivity of any material is a key element in understanding its actual thermal performance, thus assigning its suitability for a particular application. This, of course, includes its efficiency while being used, lifetime, probability of failure or breakdown, and most importantly, user safety. Several methods are used to measure the thermal conductivity of materials. However, the transient hot-wire method has many practical advantages over other methods due to its relative simplicity and suitability for different materials. The hot-wire method can deliver accurate measurements of gases, liquids, and some solids over a relatively-wide thermal conductivity range. Furthermore, with careful design of the hot-wire instrument, it can be used to measure the thermal conductivity at elevated temperature and under high pressure, which is essential for many industrial applications. In turn, this has made the method one of the most frequently used. This review paper explains the theory of the hot-wire method and demonstrates the technical developments of hot-wire instruments. The paper also presents the advances of electric circuits used to measure the resistance of the hot wire, thus its temperature, during the transient experiment. In addition, it shows the calibration of the hot wire together with the calculation of thermal conductivity.

Thermal Conductivity of Binary Mixtures of 1,1,1,2-Tetrafluoroethane(R-134a), 2,3,3,3-Tetrafluoropropene (R-1234yf), and trans-1,3,3,3-Tetrafluoropropene (R-1234ze(E)) Refrigerants.

A total of 2160 thermal conductivity data points, measured using a transient hot-wire instrument, are reported for binary mixtures of R-134a, R-1234yf, and R-1234ze(E) refrigerants from 200 to 340 K to pressures of 12 MPa for mixtures containing R-1234yf and to 50 MPa for R-134a/1234ze(E) mixtures. Data are reported at compositions of approximately (0.33/0.67) mole fraction and (0.67/0.33) mole fraction for each binary mixture investigated. The estimated relative expanded uncertainty of the thermal conductivity measurements is less than 2%. The data are used to refit binary interaction parameters for the Extended Corresponding States (ECS) model implemented in REFPROP (version 10.0). Additionally, the data in this study are used to assess the performance of a generalized entropy scaling model for refrigerants. Finally, the strengths and weaknesses of the ECS and entropy scaling models are compared.

Low-Speed DSMC Simulations of Hotwire Anemometers at High-Altitude Conditions

Numerical simulations of hotwire anemometers in low-speed, high-altitude conditions have been carried out using the direct simulation Monte Carlo (DSMC) method. Hotwire instruments are commonly used for in-situ turbulence measurements because of their ability to obtain high spatial and temporal resolution data. Fast time responses are achieved by the wires having small diameters (1–5 μm). Hotwire instruments are currently being used to make in-situ measurements of high-altitude turbulence (20–40 km). At these altitudes, hotwires experience Knudsen number values that lie in the transition-regime between slip-flow and free-molecular flow. This article expands the current knowledge of hotwire anemometers by investigating their behavior in the transition-regime. Challenges involved with simulating hotwires at high Knudsen number and low Reynolds number conditions are discussed. The ability of the DSMC method to simulate hotwires from the free-molecular to slip-flow regimes is demonstrated. Dependence of heat transfer on surface accommodation coefficient is explored and discussed. Simulation results of Nusselt number dependence on Reynolds number show good agreement with experimental data. Magnitude discrepancies are attributed to differences between simulation and experimental conditions, while discrepancies in trend are attributed to finite simulation domain size.

Experimental measurements and XCT based simulation of effective thermal conductivity of stacked ceramsites in molten-salt tank foundation

Solar energy is a sort of potential renewable energy in the future. Ceramsite is a kind of porous material with resistance to pressure and high temperature to be applied in the molten salt storage foundation of concentrated solar power plant (CSP), whose thermal conductivity is influential to the size of foundation and safety of system. Under this prospect, a hot wire instrument was designed independently for researching the thermal properties of stacked ceramsites with different particle size, density and porosity. The thermal conductivity varied from 0.089 to 0.113 W/mK when porosity decreased from 67.9 to 56.7%. In addition, X-ray computed tomography was used to analyze the porous distribution of stacked sample. Finally, the effective thermal conductivity was estimated by simulation based on the XCT data. The CT-simulation value of effective thermal conductivity ranged from 0.087 to 0.104 W/mK decreasing with porosity of 67.8 to 59.6%. The difference between the effective thermal conductivity obtained by hot wire experiment and XCT simulation is less than or equal to 1.1%, which, to some extent, verifies the accuracy and reliability of the two methods.

Experimental investigations on the liquid thermal conductivity of five saturated fatty acid methyl esters components of biodiesel

Abstract The utilization of biodiesel is a promising way to replace fossil fuels, and thermal conductivity of biodiesel is a very important thermophysical property for its applications. In this work, the transient hot-wire instrument with one bare platinum wire was used to measure the thermal conductivity of five pure components of biodiesel in liquid phase at atmospheric pressure. The measured substances include methyl butyrate, methyl pentanoate, methyl caproate, methyl caprylate, and methyl pelargonate, and the temperature range was from (283 to 358) K, (285 to 362) K, (263 to 368) K, (273 to 393) K, (278 to 383) K, respectively. The total standard uncertainty of the experimental results was estimated to be less than 2% and the repeatability was better than ±0.5%. The thermal conductivity data of each substance were fitted as a function of temperature. The average absolute relative deviation and maximum absolute relative deviation between the experimental data and calculated results were 0.17% and 0.44% for methyl butyrate, 0.25% and 0.58% for methyl pentanoate, 0.16% and 0.44% for methyl caproate, 0.15% and 0.47% for methyl caprylate, 0.15% and 0.33% for methyl pelargonate, respectively.

New Measurements of the Apparent Thermal Conductivity of Nanofluids and Investigation of Their Heat Transfer Capabilities

The aim of this paper is to investigate in depth whether adding nanoparticles or nanotubes to a fluid enhances its heat transfer capabilities. For this reason, the thermal conductivities and viscosities of a selection of nanofluids were thoroughly examined. The systems studied were (a) ethylene glycol with added CuO, TiO2, or Al2O3 nanoparticles and (b) water with TiO2 or Al2O3 nanoparticles or multiwall carbon nanotubes (MWCNTs). All of the measurements were conducted at 298.15 K. In a very recent paper, it was shown that instruments employing the transient hot-wire technique can produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the geometry of the hot wire. Furthermore, it was shown that an approximate analytic solution can be employed with equal success over the time range from 0.1 to 1 s, provided that four specific criteria are satisfied. Subsequently a transient hot-wire instrument was designed, constructed, and employed for the measurement ...

Necessary Conditions for Accurate, Transient Hot-Wire Measurements of the Apparent Thermal Conductivity of Nanofluids are Seldom Satisfied

The paper considers the conditions that are necessary to secure accurate measurement of the apparent thermal conductivity of two-phase systems comprising nanoscale particles of one material suspended in a fluid phase of a different material. It is shown that instruments operating according to the transient hot-wire technique can, indeed, produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the exact geometry of the hot wire. Furthermore, it is shown that an approximate analytic solution can be employed with equal success, over the time range of 0.1 s to 1 s, provided that (a) two wires are employed, so that end effects are canceled, (b) each wire is very thin, less than 30 \(\upmu \)m diameter, so that the line source model and the corresponding corrections are valid, (c) low values of the temperature rise, less than 4 K, are employed in order to minimize the effect of convection on the heat transfer in the time of measurement of 1 s, and (d) insulated wires are employed for measurements in electrically conducting or polar liquids to avoid current leakage or other electrical distortions. According to these criteria, a transient hot-wire instrument has been designed, constructed, and employed for the measurement of the enhancement of the thermal conductivity of water when TiO\(_{2}\) or multi-wall carbon nanotubes (MWCNT) are added. These new results, together with a critical evaluation of other measurements, demonstrate the importance of proper implementation of the technique.

A Novel Portable Absolute Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids

A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2 $$\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$ to $$4\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$ is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to $$\times $$ 120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.

Critical Review of Industrial Techniques for Thermal-Conductivity Measurements of Thermal Insulation Materials

This paper presents a critical review of current industrial techniques and instruments to measure the thermal conductivity of thermal insulation materials, especially those insulations that can operate at temperatures above \(250\,^{\circ }\hbox {C}\) and up to \(800~^{\circ }\hbox {C}\). These materials generally are of a porous nature. The measuring instruments dealt with here are selected based on their maximum working temperature that should be higher than at least \(250\,^{\circ }\hbox {C}\). These instruments are special types of the guarded hot-plate apparatus, the guarded heat-flow meter, the transient hot-wire and hot-plane instruments as well as the laser/xenon flash devices. All technical characteristics listed are quoted from the generally accessible information of the relevant manufacturers. The paper includes rankings of the instruments according to their standard retail price, the maximum sample size, and maximum working temperature, as well as the minimum in their measurement range.

Density Scaling of the Thermal Conductivity of a Jet Oil

The application of the new quantitative elastohydrodynamics, which employs real properties of the liquid lubricant, to practical tribology problems obviously requires property measurements at high pressure to parameterize the correlations. The thermal conductivity under elevated pressure has been shown to be essential for nonisothermal situations. A new transient hot-wire instrument for pressure to 600 MPa is described and validated. New measurements are presented of the temperature- and pressure-dependent thermal conductivity of a synthetic oil for jet aircraft engines. The density scaling law, , with exponent approximately equal to the standard value of 3 gives an excellent accounting of the results. The temperature dependence of the conductivity may be ignored in elastohydrodynamic lubrication (EHL) simulations without great loss of accuracy and it may be sufficient to describe the pressure dependence with a general expression, .

An Innovative Genetic Algorithm Approach for Direct Calibration of X-Probe Hot Wires

A new genetic algorithm (GA) based method for direct calibration of 2-D hot-wire probe and other instruments that can measure 2-D flow properties is introduced. This new method is an alternative for the previous QR method that is commonly used for calibration of the X-probe hot wires. The proposed GA method resulted in a much smaller error in the velocity estimation while preserving the number of sentences in its calibration equation format. In addition, it preserves the magnitude of its error even when the number of sentences in the calibration equation is decreased while the error in the QR method increases substantially for the same situation. Furthermore, the results were much closer to the real or natural behavior of the hot-wire data when compared with the QR method. Additionally, the GA method was applied for a large range of velocities (10–100 m/s) and the results revealed that the range of error did not vary significantly. The turbulent properties of the flow that were calculated by each method were not the same; however, the results from the GA method were smooth and had reasonable behavior.

Absolute measurement of thermal conductivity of poly (acrylic acid) by transient hot wire technique

The transient hot-wire method is considered the most accurate technique to measure the thermal conductivity of fluids. In this study, a transient hot wire instrument which employs 25.4-μm-diameter tantalum wire with an insulating tantalum pentoxide coating has been used. This hot-wire cell with a thin insulating layer is suitable for measurement of the thermal conductivity of electrically conducting and polar liquids. Measurements of the thermal conductivity of 50 wt% solution of PAA [poly (acrylic acid)] in water and PAA–Na in 50 wt% water are reported here. These measurements were obtained in the temperature range of 299–368 K at 1 atmospheric pressure. The measurement of thermal conductivity is estimated to be accurate within ±4%.

다중벽 탄소나노튜브와 PVP가 첨가된 나노유체의 특성 비교 연구

In this study, the characteristics of multi-walled carbon nanotubes added nanofluid were investigated. Sodium Dodecyl Sulfate, SDS, and Polyvinylpyrrolidone, PVP, were employed as the dispersant. SDS or PVP was added in pure water. And then, 0.0005, 0.001, 0.002, 0.003. 0.004, 0.005,0.01, and 0.02 vol% of CM-95 and CM-100 were dispersed respectively. The thermal conductivity and the viscosity were measured with a transient hot-wire instrument built for this study and the DV II+ Pro viscometer. The results showed that PVP had good thermal conductivity at 300 wt% and the thermal conductivity of CM-100 was better than that of CM-95. However, the viscosity of CM 100 was higher than that of CM 95.

Thermal Conductivity of Aqueous Mixtures of 2-n-Butoxyethanol at Pressures up to 150 MPa

This paper contains the results of new measurements of the thermal conductivity of mixtures of water and 2-n-butoxyethanol in the liquid phase within the temperature range of (304 to 346) K at pressures up to 150 MPa. The measurements were carried out with a transient hot-wire instrument and have an accuracy of ± 0.3 %. The investigation is the first conducted at high pressures on partially miscible mixtures whose components are of greatly differing thermal conductivity. It therefore provides a severe test of the methods of representing the thermal conductivity of liquid mixtures that are based on the hard-sphere theory of transport in liquids. It is shown that all of the experimental data may be represented to within ± 6 % by a “predictive” procedure based on the hard-sphere theory of liquids. However, a more detailed analysis of the results reveals small but systematic deviations from the universal behavior of the thermal conductivity as a function of molar volume that the predictive procedure and the hard-sphere theory have as their basis.

Thermal Conductivity of Building Materials Employed in the Preservation of Traditional Structures

Historic structures are a part of our cultural heritage and nowadays, in the polluted environment, the need of their preservation is more intense than ever. One of the anticipated problems includes new materials that have to be compatible with those existing in older structures. In the case of mortars, traditional binders such as lime, natural pozzolanas, brick dust, and white cement have been combined successfully. In the present article a series of mixtures combining lime, two types of natural pozzolanas, brick dust, and different types of cement have been produced in order to measure their thermal conductivity for the first time. The parameters tested are: the binder type, the proportion of the binders, and the water/binder ratio. For the measurement of the thermal conductivity of the samples, a commercial instrument was used. To test its operability and extend its range, a transient hot-wire instrument was employed.

Thermal conductivity and thermal diffusivity of poly(acrylic acid) by transient hot wire technique

The paper describes a new transient hot wire instrument which employs 25.4 μm diameter tantalum wire with an insulating tantalum pentoxide coating. This hot-wire cell with a thin insulating layer is suitable for measurement of the thermal conductivity and the thermal diffusivity of electrically conducting and polar liquids. This instrument has been used for experimental measurement of the thermal conductivity and the thermal diffusivity of poly(acrylic acid) solution (50 mass%) in the temperature range of 299 to 368 K at atmospheric pressure. The thermal conductivity data is estimated to be accurate within ±4%. Thermal diffusivity measurements have a much higher uncertainty (±30%) and need further refinement.

Determining Thermal Conductivity and Thermal Diffusivity of Low-Density Gases Using the Transient Short-Hot-Wire Method

The transient short-hot-wire method for measuring thermal conductivity and thermal diffusivity makes use of only one thermal-conductivity cell, and end effects are taken into account by numerical simulation. A search algorithm based on the Gauss–Newton nonlinear least-squares method is proposed to make the method applicable to high-diffusivity (i.e., low-density) gases. The procedure is tested using computer-generated data for hydrogen at atmospheric pressure and published experimental data for low-density argon gas. Convergence is excellent even for cases where the temperature rise versus the logarithm of time is far from linear. The determined values for thermal conductivity from experimental data are in good agreement with published values for argon, while the thermal diffusivity is about 10 % lower than the reference data. For the computer-generated data, the search algorithm can return both thermal conductivity and thermal diffusivity to within 0.02 % of the exact values. A one-dimensional version of the method may be used for analysis of low-density gas data produced by conventional transient hot-wire instruments.

A New Transient Hot-Wire Instrument for Measuring the Thermal Conductivity of Electrically Conducting and Highly Corrosive Liquids using Small Samples

The transient hot-wire technique is widely used for measurements of the thermal conductivity of most fluids. However, for some particular liquids such as concentrated nitric acid solutions or similar nitric mixtures, for which the thermal properties are important for industrial or security applications, this technique can be difficult to use, which is essentially due to incompatibility between measurement probe materials and highly electrically conducting and corrosive liquids. Moreover, the possible highly energetic (explosive) character of these liquids requires minimum volume liquid samples, and safety measurement devices and processes. It is the purpose of this paper to report on a new patented instrument, based on tantalum short-hot-wire probe technology, which responds to the above requirements and allows safe automated thermal-conductivity measurements of concentrated acid nitric solutions and similar nitric mixtures for liquid samples less than 2 cm3, with uncertainties better than 5%.

Fluid radiation effects in the transient hot-wire technique

The transient hot-wire technique is widely used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with a determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. The present work investigates the effect of fluid radiation on the measurements of the thermal conductivity of propane. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. Measurements at 372 K with a hot-wire instrument demonstrate the presence of radiation effects in both the liquid and vapor phase. The influence is much more pronounced in liquid propane at 15.5 MPa than in the vapor phase at 881.5 kPa. The technique employed to obtain radiation-free thermal conductivity measurements is described.