Dynamic Plane Source Research Articles

A New Numerically Improved Transient Technique for Measuring Thermal Properties of Anisotropic Materials

A new transient technique of the thermal conductivity and diffusivity measurement for anisotropic materials is presented and validated. It is based on measuring the through-plane properties using the extended dynamic plane source (EDPS) method and in-plane conductivity employing the transient plane source (TPS) and modified dynamic plane source (MDPS) methods. The key advantage of this technique is that only one pair of specimens is required for measurements. While the EDPS method is implemented on real measurements, the TPS and MDPS are applied to the finite elements method (FEM) simulation of the experiment. The accuracy of the results is enhanced by the application of the FEM and is better than 1% for materials with through-plane conductivity of less than 2 W m−1 K−1 and a specimen thickness of 9 mm.

The Application of the Finite Elements Method in the Transient Measurements of Thermophysical Parameters

The finite elements method (FEM) is used to improve the extended dynamic plane source (EDPS) method to obtain more accurate values of the thermal conductivity and diffusivity of the specimen. A method of transformation of the FEM-calculated response into an analytical form, which can be used in fitting the measured temperature response, has been described and verified. Furthermore, a modification of the EDPS method designated as EDPS1 is designed, where only one piece of specimen is used. Since there is no analytical formula for the new method, the analytical formula for EDPS is used. Hence, the initial estimates of the specimen parameters for the EDPS1 method are very rough and the FEM numerical evaluations must be repeated several times until the estimates reach relative errors of around 1%.

Comparison of the new plane source method to the step wise transient method for thermal conductivity and diffusivity measurement

This paper describes a new method for measuring both the thermal conductivity and thermal diffusivity for solid materials, referred to as the new plane source (NPS) method. This method is quite similar to the Extended dynamic plane source (EDPS) method; however, the essential difference is the location of the temperature measurement. The NPS measures the temperature of the specimen at both the heat source and also at the heat sink using a thermocouple. The accuracy of the NPS method was verified by comparing the measurement results with the step-wise transient (SWT) method for two solid materials: silica glass and polymethylmethacrylate (PMMA). The difference in results between the NPS method and the SWT method was found to be 0.6%. The results of conductivity measurements by the NPS method of glass and PMMA were 1.019 and 0.1904 W·K−1 m−1, respectively. As for the measured thermal diffusivities, they were 0.504 and 0.1136 mm2 s−1, respectively. The standard uncertainties of the estimates were less than 0.9%.

Applying the EDPS Method to the Research into Thermophysical Properties of Solid Wood of Coniferous Trees

The results of using the EDPS (extended dynamic plane source) method to determine thermophysical properties of solid wood of coniferous trees growing in Slovakia with 0% and 12% equilibrium moisture content are presented in the paper. Solid wood of two different tree species: Norway spruce (Picea abiesL.) and Scots pine (Pinus sylvestrisL.) was used in the research. The research was carried out independently in three anatomical planes. Coefficients of thermal conductivity, thermal diffusivity, and specific heat capacity were determined following the research. Comparing the research results to the values determined by other authors and already published models to calculate individual parameters, the fact that the data gathered using the EDPS method can be accepted in case of all studied thermophysical properties can be stated.

Thermal properties of selected bee products

Knowledge of bee products’ physical properties has a decisive importance for the monitoring of their quality. Thermophysical parameters are very important properties. Thermal conductivity and thermal diffusivity of selected bee products (honey, bee pollen and perga) were measured by two different methods. For identification of thermal conductivity and thermal diffusivity transient methods were used: Hot Wire (HW) and Dynamic Plane Source (DPS) method with an instrument Isomet 2104. The principle of measuring process is based on the analysis of timetemperature relation. In the first series of measurements thermal conductivity and diffusivity at constant laboratory temperature of 20 °C were measured. The second series was focused on identification of the changes in the thermophysical parameters during temperature stabilisation in the temperature range of 5–25 °C. For samples with constant temperature standard deviations and probable errors in % were calculated. For relations of thermal parameters to temperature graphical dependencies were obtained. Two different thermophysical methods were used for improvement of data reliability and data statistics.

Osnovne toplotne i geometrijske karakteristike drvnih i orijentiranih ravnih ploča (OSB) korišćenih u zgradama niske energetske potrošnje

This paper deals with the thermal properties and densities of selected wood types and oriented strand boards used in low-energy buildings. Basic thermophysical parameters such as thermal conductivity, as well as the density of each sample, were measured in the study. The thermal conductivity of the samples was measured by the transient method, i.e. the extended dynamic plane source (EDPS) method. The EDPS method is a modification of the dynamic plane source method for low thermally conductive materials. A total of two identical disc-shaped samples of the material tested and two metal blocks of sufficient geometrical size were enrolled in the study. In the first measurement series, the thermal conductivity of the samples was measured at a constant laboratory temperature of 20 °C, and the measurement was performed 100 times for each sample. The second measurement series was focused on the density determination of the material tested. The densities of the wood and oriented strand board samples were calculated from the geometric dimensions and mass of the samples measured. The results obtained were statistically processed. Furthermore, the experimental results pertinent to the thermal conductivity of the wood types tested were within the range of 0.103 - 0.275 W.(m.K)-1, whereas the thermal conductivity values of the oriented strand board samples ranged from 0.109 to 0.129 W.m-1.K-1. The present results are characteristic of the wood obtained from Slovak timber harvesting localities, as well as of wood products made from wood waste.

Selected physical properties of various diesel blends

AbstractThe quality determination of biofuels requires identifying the chemical and physical parameters. The key physical parameters are rheological, thermal and electrical properties. In our study, we investigated samples of diesel blends with rape-seed methyl esters content in the range from 3 to 100%. In these, we measured basic thermophysical properties, including thermal conductivity and thermal diffusivity, using two different transient methods – the hot-wire method and the dynamic plane source. Every thermophysical parameter was measured 100 times using both methods for all samples. Dynamic viscosity was measured during the heating process under the temperature range 20-80°C. A digital rotational viscometer (Brookfield DV 2T) was used for dynamic viscosity detection. Electrical conductivity was measured using digital conductivity meter (Model 1152) in a temperature range from −5 to 30°C. The highest values of thermal parameters were reached in the diesel sample with the highest biofuel content. The dynamic viscosity of samples increased with higher concentration of bio-component rapeseed methyl esters. The electrical conductivity of blends also increased with rapeseed methyl esters content.

Thermophysical properties of OSB boards versus equilibrium moisture content

The basic thermophysical properties of oriented strand boards were determined experimentally for use in humid conditions (OSB3) depending on the moisture content. The dependency between the thermal conductivity, thermal diffusivity, specific heat capacity, and the moisture content in the range of 0% to 10%, was examined. The non-stationary extended dynamic plane source (EDPS) experimental method was used. EDPS method was modified for anisotropic materials, i.e. with special considerations of heat-loss effect occurring at the edge of measuring samples, finite geometry of the sample and orthotropic thermal conductivity, for use with anisotropic materials. The validity of the experimental method was verified on polymethylmethacrylate (PMMA) samples. The error rate of measurements conducted on PMMA samples was less than 3%, and for OSB3 boards it was less than 5.5%. Based on the experimental results, regression equations of the dependency between the monitored properties and the moisture content were determined. In the case of thermal conductivity and thermal capacity, the determined dependencies showed a high correlation rate.

Transient Methods and their Usage for Flour Thermophysical Parameters Measurement

This article focuses on temperature relations of selected thermophysical parameters for three different types of wheat flour. The main objective of experiment was to determine the thermal conductivity, thermal diffusivity and volume specific heat of wheat flour produced in Slovakia. Measurements were performed in laboratory settings. Thermal parameters were measured by the thermal analyser Isomet 2104 with two types of probes – a linear probe and plane probe. Measurement by the linear probe is based on the hot wire method, and measurement by the plane probe is based on the extended dynamic plane source method. Both methods are described in the text. Two types of measurement methods were used because of the non-homogenous structure of measured material. All thermophysical parameters were measured during the temperature stabilisation in the temperature interval 5–24 °C. Obtained graphical relations had linear increasing progresses with high values of determination coefficients in all cases.

Using Selected Transient Methods for Measurements of Thermophysical Parameters of Building Materials

Abstract This article deals with thermophysical properties of red and white bricks. If we want to protect the high standard of quality building materials, we need to know the physical parameters which can evaluate the quality. The most important for building materials are mainly thermophysical, mechanical parameters and parameters which can determine the structure of materials. The article presents results of thermophysical parameters measurements of red and white bricks during the temperature stabilization for different values of moisture content. For our measurements, we have chosen a hot wire method and a dynamic plane source method. Both methods are classified as transient methods and they are very convenient for measurements of thermophysical parameters of materials with a compact structure. The results of measurements show that temperature and moisture content have a significant effect on thermophysical parameters of bricks.

Modified Dynamic Plane Source Method for Measuring Thermophysical Parameters of Solids

The authors proposed and experimentally verified a new method of measurements of thermal conductivity and thermal diffusivity of homogeneous and isotropic materials with thermal conductivities of <\({2\,{\rm W} \cdot{\rm m}^{-1} \cdot{\rm K}^{-1}}\) . The theoretical model and the experimental arrangement of the method, referred to as the modified dynamic plane source method, are described. The influence of the floating temperature of the heat sink was analyzed and included into the evaluation. The method was both theoretically and experimentally compared with other transient methods, namely, transient plane source and extended dynamic plane source methods. Two different polymethylmethacrylate materials were measured at laboratory temperature using all three methods, obtaining results with coefficients of variation of <2 % and 5 % for the thermal conductivity and thermal diffusivity, respectively. In addition, the sensor calibration and the sources of measurement uncertainty are outlined.

Alternative fitting procedures to enhance the performance of resistive sensors for thermal transient measurements

The main concern in most of transient techniques is to obtain a controlled heat flow in a prescribed direction, so that the actual boundary conditions in the experiment agree with those assumed in the theory. Enhancements of the fitting procedures in transient dynamic techniques have been established. One of these dynamic techniques known as the extended dynamic plane source is discussed in details. This technique has been used for simultaneous measurements of thermal conductivity, diffusivity and the specific heat from a single transient recording of the temperature increase. The technique uses a resistive sensor as both, a plane heat source and temperature sensor, i.e. in similar manner as the wire in the transient hot-wire method. The sensor consists of a resistive heater pattern cut from a thin sheet of metal (Ni) covered on both sides with thin layers of an insulating material. The conducting pattern of the sensor, known as the hot-disk configuration, has the shape of spiral strips. Infrared camera images of the sensor were taken, at the beginning of the transient recording, to illustrate the deviations from the ideal conditions due to design defects within the sensor. Alternative fitting procedures have been introduced in order to meet the design criteria of heat and temperature sensor and to fulfil the isothermal boundary conditions required by experimental setup. Within the total time of transient recording, and using a sequence of computational steps, it is possible to find a correct “optimal” time interval to enhance the fitting procedures. These computational steps are based on fitting procedures that provides the selection of the optimal time interval within the total measuring time and thus to obtain more accurate and reliable results. These procedures have been tested using measurements on acrylic “Plexiglas” sample; the corresponding deviations from published data did not exceed 1.5% and 2% in thermal conductivity and diffusivity, respectively. It is another alternative to the standard fitting procedures which mainly based on linear regression and least square fitting. It is anticipated that these fitting procedures have the potential to be used in similar transient techniques.

Dynamic Measurements of the Temperature Coefficient of Resistance in the Transient Plane Source Sensor

The extended dynamic plane source (EDPS) method is one of the transient methods for measurements of the thermal conductivity and thermal diffusivity in solids. This technique uses a transient plane source (TPS) sensor, which serves as the heat source and thermometer. Its calibration consists of measuring the temperature dependence of the TPS sensor resistance and computing the temperature coefficient of resistance (TCR) using least-squares (LS) estimation. The goal of this study is to calibrate the TPS sensor directly in the apparatus for the EDPS method. The article presents an uncertainty assessment of the TCR measurement. The main sources of uncertainty stem from resistance measurements of the constant resistor and platinum thermometer calibration. The LS estimate of the TCR in a nickel TPS sensor is 4.83 × 10−3 K−1 at 20 °C and 4.57 × 10−3 K−1 at 45 °C with a combined standard uncertainty better than 0.04 × 10−3 K−1, which is 0.7 %.

Improvements in the Dynamic Plane Source Method

Three sources of errors in the extended dynamic plane source (EDPS) method caused by the discrepancy between experiment and model are analyzed. The source effect is eliminated by introducing the nuisance parameter R0 and the surface effect by a surrounding vacuum. The original model assumes a constant heating power but a constant current is used in the experiment. Suppression of this effect leads to a new solution of the heat equation designated as the constant-current model. The measurements on polymethylmetacrylate (PMMA) in vacuum, evaluated by the constant-current model, provided results of λ = 0.191 W.m−1.K−1 and a = 0.118 ×10−6m2.s− 1, which are in good agreement with published values. The total standard uncertainty was estimated as 1.5 % for both thermophysical properties.

Uncertainty Analysis of Thermophysical Property Measurements of Solids Using Dynamic Methods

This work reports on an analysis of thermophysical properties (thermal conductivity, thermal diffusivity, and specific heat capacity) measurements of solids using dynamic methods. The influence of temperature measurement uncertainty on the parameter estimation uncertainty is studied using a least-squares procedure. The standard and difference analyses are used for optimizing the experiment with respect to the data window or time interval of measurements. The analysis is applied to the extended dynamic plane source method, and the results of numerical computations are illustrated in the form of contour plots.

Contribution to the Sensitivity Coefficients Analysis in the Extended Dynamic Plane Source (EDPS) Method

This work reports on a method for measuring thermophysical properties (thermal conductivity and diffusivity) of materials. The theory of the dynamic plane source method and experimental apparatus is described. The contribution of this work is the determination of the time interval within which the fitting procedure should be applied. A new algorithm for sensitivity coefficient analysis is presented, and the results are compared with those of a difference analysis of experiment modelling.

Thermal properties of multiphase polymeric materials and dynamic methods for their characterization

The thermal conductivity, diffusivity and specific heat of multi phase polymeric materials such as polystyrene and polymethylmethacrylate are reported. With emphasis on the thermal properties of such materials, a variety of implementation and classification regarding heat conduction will be highlighted. These properties were measured using dynamic methods namely; the transient plane source named also Gustafsson probe (TPS), the dynamic plane source (DPS) and the pulse transient technique (PTT), for measurements of thermal effusivity, thermal conductivity, thermal diffusivity and specific heat of solids One of the advantages considering these techniques is the possibility to extract all thermophysical parameters, the thermal conductivity, thermal diffusivity and specific heat from one single transient recording. Dynamic methods use a probe that is technically a resistive element, as the heat source. The first two TPS and DPS employ this probe as both heat source and temperature sensor. The later method PTT, for temperature sensing, uses a thermocouple placed apart of the heat source. A description of the main features and the principles on which these methods are based will be highlighted.

An extension to the dynamic plane source technique for measuring thermal conductivity, thermal diffusivity, and specific heat of dielectric solids

The recently developed dynamic plane source (DPS) technique for simultaneous determination of the thermal properties of fast thermally conducting materials with thermal conductivities between 200 and 2 W/mK has now been extended for studying relatively slow conducting materials with thermal conductivities equal or below 2 W/mK. The method is self-checking since the thermal conductivity, thermal diffusivity specific heat, and effusivity of the material are obtained independently from each other. The theory of the technique and the experimental arrangement are given in detail. The data evaluation procedure is simple and makes it possible to reveal the distortions due to the nonideal experimental conditions. The extension to the DPS technique has been implemented at room temperature to study the samples of cordierite-based ceramic Cecorite 130P (thermal conductivity equal to 1.48 W/mK), rubber (0.403 W/mK), and polycarbonate (0.245 W/mK). The accuracy of the method is within ±5%.

Dynamic plane source technique for simultaneous determination of specific heat, thermal conductivity and thermal diffusivity of metallic samples

A technique is developed for the simultaneous determination of specific heat, thermal conductivity and thermal diffusivity of metals. The method is of a transient heat-flow type where the heating element serves both as a heat source and the temperature detector. The experiment is arranged in such a way that the temperature development in the sample is close to adiabatic. The method has been tested on samples of pure iron (99.95% of purity), cast iron (SIS 2140) and austenitic stainless steel (SIS 2343). The results obtained were in an excellent agreement with the literature data for these materials. The accuracy of determination of specific heat has been additionally tested on an Al sample.