Skills and Expertise
Research Items (61)
The field research is based on in-situ monitoring of the temperature-moisture regime of natural rock mass in volcanic tuffs localized in the Tekov Museum of rock dwellings in Brhlovce preserved as historical heritage. The temperature and moisture changes are the parameters that influence deterioration processes of rock massive. The moisture probe uses the increase of thermal conductivity of porous structure when pores are filled by air/vapour, water or ice. The correlation between thermophysical properties and water content in pore exists. For this kind of measurements we calibrate the moisture sensors and determine change of thermal conductivity of porous material for dry and water saturated states in the temperature range that is typical for the locality climate. The moisture monitoring in the field conditions at different depths in the rock massif when they are exposed to climate changes was studied by moisture probes. The experiment was carried out for the needs of correlations between laboratory and field research.
A new model for the sample of square cross section with cuboid geometry including the effect of heat loss from the surface of the sample was tested using the theory of sensitivity coefficients. Theoretical calculation of model uncertainty and derived analytical formulas are presented. Results of the uncertainty analysis set out the range of experimental conditions under which the model is valid and the uncertainty of estimated parameters is low. Propagation of error for non-stochastic dynamic measurements based on the sensitivity coefficients shows limitations related to a range of model validity. The analysis improves the accuracy of measurements. The model was used for data evaluation of thermophysical parameters measured on the sandstone from the locality Pravcicka brana. Evaluation procedure was tested on experimental data measured under different experimental conditions. In conclusion, the discussion of the experiment optimization is presented.
The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly(methylmethacrylate) and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory. http://dx.doi.org/10.1063/1.1150635 http://scitation.aip.org/content/aip/journal/rsi/71/6/10.1063/1.1150635
This paper studies three contact transient methods for the measurements of the thermophysical properties of porous building materials - autoclaved aerated concrete and calcium silicate boards reinforced by cellulose fibers. The methods used were the pulse transient, transient plane source and the hot strip method. These methods measure three thermophysical parameters - thermal conductivity, thermal diffusivity and specific heat - in one single measurement. Data from these methods are analyzed and compared with results obtained by classical methods. Paper download: http://www.tpl.fpv.ukf.sk/engl_vers/thermophys/proceedings/03/bohac.pdf
Recently the physical model for the temperature field generated by thermophysical single-probe sensor in a shape of planar disc has been derived. The model accounts cylindrical sample having final radius and infinite length. The prototype of measuring electronics RTA was build that operates with auto balancing bridge. For the measurements the single-transition method is used. While the measurement error of the temperature response measured by thermocouple was 1% at the height of temperature response 1°C, the sensitivity of the measurement with the automatically balanced bridge is better and the signal to noise ratio is improved about 10 times. The measuring electronics was tested for measuring the temperature response using a single-sensor. This sensor generates the heat pulse and sense the temperature response in the same time. The next advantage is that the temperature response to the generated step-wise pulse is much smaller and it can be reduced to the level of 1-8° C compared to stationary method like guarded hot plate method. The effect of the temperature field generated by the probe is much smaller, which in the case of measurement of porous materials at the presence of moisture is beneficial, as the resulting redistribution of moisture under the created temperature gradient is negligible. There were derived basic models for the evaluation of this type of experiment. The probe should be in form of full cylinder or an annulus. The derived temperature function counts the outer and inner diameter of annulus. Putting the inner radius to zero we get the solution for full circle probe, so the model is universal. The model counts also the heat losses from the outer surface of the sample, when the time of measurement exceed the time when the penetration depth of generated heat pulse rich the outer radius of sample. The estimated output parameters from single measurement are the thermal conductivity, thermal diffusivity and specific heat. The heat transfer coefficient is additional parameter fitted as free parameter of the model.
- Jul 2018
- THERMOPHYSICS 2018: 23rd International Meeting of Thermophysics 2018
The In the frame of extending the renewable energy systems, the use of the shallow geological bedrock below the houses is used for the seasonal heat storage purposes. Thus, the knowledge of the thermophysical properties of the soft clay loam materials present in the bedrock is important. On the basis of the known thermal diffusivity, thermal conductivity and specific heat of the materials around the energetic needle, one can calculate the time dependency of the heat dissipated and transferred into the surrounding. This allows calculating the temperature maps that can specify in more detail the heat penetration depth during the seasonal storage and pumping out of the heat accumulated during the year seasons. The aim is to optimize the efficiency of the system. The clay loams in the free nature contain high level of the moisture and thus have high values of specific heat. The pulse transient method was used to get the thermophysical parameters of these materials. Specimens were drilled out from the bedrock at depths 50, 150 and 250cm from the surface. The measured values of equilibrium sorption moisture show that obtained materials are very different. In the paper we show the possible influence of the redistribution of water content during the shooting of the heat pulse. The water redistribution deforms the temperature response. This effect was avoided by lowering the heat pulse power to minimal values that still allows the evaluation of the measurement.
Cement-based composites change their properties in dependence on added materials. Scientific papers display results on changes in various mechanical and thermophysical properties. In this paper, the effect of different amount of plastic in two shapes (granules and fibers) and horse manure on thermophysical and mechanical properties of cement-based composites are tested. To understand the structural changes 1-D process of water uptake and porosity measurements were done. The economic growth brings new possibilities for industry development but also increasing problem with waste disposal. Our tests were aimed at finding the optimal balance between plastic disposal in cement based materials and changes in some important properties. The best results of thermophysical properties were for plastic and natural fibers, where horse manure samples had even better mechanical properties than plastic ones.
Question - Which instrument is required for measurement of Thermal Conductivity, Specific Heat and Thermal Diffusivity?
Steffen Feja is partially right about the difficulties at the measurements. However, the problem is already connected with a chamber for the measurement and specimen geometry. We are using several chambers for different temparature ranges from -40°C up to 1400°C. All chambers were build for transient techniques, but in some of them the stationsary technique is available. This allow the use any transient technique for any kind of solid material and with a special container also the liquid and gass. The list of some transient techniques used in our laboratory withthe chamber for the measurement from -40 up to 250°C is available at the page http://www.fu.sav.sk/index.php?id=167&L=2 and on the page http://thermophys.savba.sk/Methods.htm. The methods are based on the models, so no calibration is necessary. Transient methods are based on the models with combination of usually two thermophysical parameters included. The third one is calulated form the formula ThermlaConductivity=TheramDiffusivity*Density*SpecificHeat . Otherwise you have to use three diffrent apparatusses like it is described in a acontributions above.
The measurement of thermal properties of materials that do not keep the form is problematic, because usually, the basic condition of the most models predicts constant dimensions. The plastic materials like clay or loam in natural condition always contain some water and thus are viscous and squeeze out of specimen holder when clamped even at weak force produced by specimen holder. Thus, the specimen dimensions are changing in during the measurement when it is not placed in a solid container. Even at this arrangement the shrinkage of material at the measurements causes the lowering the specimen thickness when using two probe method like pulse transient technique. This effect problem could be lowered or neglected at single probe techniques like the planar hot disk or this newly derived hot tube method. Hot tube method is derived for the probe made as the rectangular plane bended around the solid cylinder or tube made of thermally low conducting material. The probe generates the heat and the rate of temperature rise in it is driven by heat transfer ability of the measured surrounding material. Such a probe should be used in laboratory as well as in the field conditions. . . a)Corresponding author: email@example.com b)firstname.lastname@example.org c) email@example.com
The problems of the measurement of thermophysical properties of materials are recently focused in many research and industrial branches. The problems of the last period are rising from the needs of increasing consumption of the energy. To solve the problems of how to get available of the renewable sources on one side and measures preventing energy losses on the other side are highly demanded. Thus the industry of new highly efficient and smart materials was established for a new production. This state invokes the need of development of the testing measurements and underlying physical methods and apparatuses. The other side of the problem is to understand of the thermophysical backgrounds. The question is how the materials structure is connected with the changes in measured thermophysical parameters. The paper gives the review of basic physical phenomena presented at the investigation of thermal properties of materials. One of the basic problems is to define the phenomena as we are observing them. Theoretically all the observations in the literature that corresponds to the phenomena described in school books of the basic courses in physics and the underlying sciences. The book of Mr. Moore “Physical Chemistry” seems to be good source for the explanation of the basic problems in thermodynamics. The measure of internal energy of materials is the temperature and thus the thermal behavior reflects well any kind for the structure changes. Some illustrations are presented when the similar materials having nearly the same stoichiometry should possess different values of the specific heat, thermal diffusivity and thermal conductivity, commonly marked as the thermophysical parameters. The next problems in this research are the measurement methods. By single division, we can define some classes based on the type of generated temperature filed that is necessary for the material characterization. The classical methods are stationary techniques, steady state techniques and methods based on steady or balanced heat flow generation. In the last decades the methods based on transient regime were developed and used. The basic problem when comparing the accuracy of the listed methods rises from so called data consistency condition. This condition set the value of the thermal conductivity to be equal to the value of material volume density multiplied by thermal diffusivity and specific heat. Classical methods are measuring just one parameter. Usually when we have measured one of these parameters, and we will use the next one from literature, and put it into the data consistency equation to calculate the third one. Moreover the calculated results obtained by variation of the couples of input parameters do not fit the data consistency condition at all. The problem is usually counted on different origin of methods used for the measurements of particular parameters. In the comparison with the stationary methods, the transient methods are able to determine all three parameters from the single measurements and thus are able to fulfill this condition. The list of some transient methods developed and used at the Institute of Physics, SAS is given. In principle there are two classes of techniques based on single probe sensors and double probe sensors. The most developed method is the pulse transient method that uses two probes for the measurement, the heat source and thermocouple. For this technique more than ten models accounting different experimental arrangements and different types of disturbance effects is counted. The Hot Ball technique has been used also as the secondary type of humidity sensor. In this case the sensor inserted into the porous media is calibrated on the water content in pores. The principle of dependency of the thermal conductivity on moisture content is used. The next class of the transient techniques uses single-probe sensors where the heat source and thermometer are unified. The new sensors for the hot circle and planar hot disc techniques were developed recently. The older single probe techniques are the hot wire, hot strip and hot disc, The mathematical background for the development of physical models uses solution of the basic heat equation for the initial and boundary conditions stated according the real experiment when possible. Some of the models developed are solving the particular problems with the disturbance effects that are increasing uncertainty of the parameters estimation. In between the characteristic effects belong the heat capacity of the heat source-sensor itself, the heat contact resistance, the heat losses from the free sample surface and the temperature of the thermally stabilized heat exchangers in between which he experiment is usually realized. 1. Moore Walter J., Fyzikální chemie (Physical Chemistry in orig.), Praha, SNTL - nakladatelství technické literatury, 1979, Ev. No: 171504-21958, p.98
Question - How can we measure thermal conductivity of a material?
Thermally conductive polymer nanocomposites have increasing interest due to their potential advantages in many appplication areas such as electronic devices, photovoltaic cells, electromagnetic interference shielding devices, super capacitors, low-power rechargeable batteries and light-emitting diodes. Among thermally conductive filler materials, the graphene nanoplatelet (GNP) has been used commonly in the recent years because of the excellent thermal conductivity, mechanical properties and electrical properties. The defect free single layer graphene has thermal conductivity of 4840 - 5300 W/mK, electrical conductivity of 600 000 S/m, excellent gas impermeability and the Young´s modulus value of 1.0 TPa. The high-density polyethylene (HDPE) is the most widely used thermoplastic polymer in polymer nanocomposites application., because of its properties including good processability, chemical resistance, nontoxicity, ease of recycling, , biocompatibility and low cost. In this study the effect od GNP concentration on the thermophysical properties of HDPE nanocomposites was investigated. HDPE/GNP nanocomposites were fabricated by melt mixing method up to volume fraction (vol.) of 10 % of GNP content, followed by compresion molding. The thermophysical properties of samples were determined by Pulse Transient method. The results show that the thermal conductivityb and thermal diffusivity of HDPE/GNP nanocomposites increase with increasing of GNP content. An increase of 76.3 % and 86.3% in thermal diffusivity of the HDPE/GNP nanocomposites with 10 vol. % of GNP content was observed. Keywords: Polymer composites, Thermophysical properties, Planar disk transient method
The problem of the measurement of clay loam materials in plastic consistency is more or less difficult as they can change the shape during the long time measurements. The specimen thickness is expected as the constant during all the experiment measured by transient pulse method. In a case of plastic clay loam, it can change the form during the measurement because of the squeeze of the material even under the gravity condition. Thus the specimen surface wall should be reinforced by special dimensionally well-defined thin wall container. In this paper the special container in a form of thin tube rings bounded by central annular ring was constructed and used for the measurements. The heat source was inserted into the tube rings through the nozzle in the middle part and the thermocouple was inserted through the drilled openings at defined distance from the heat source. System clamped the heat source together with the rings at desired distance from the thermocouple. This distance represents the thickness of tested specimen. The soft plastic material fill the inner space of tube rings in such a way to fulfill the geometry conditions for this method. The need of soft clay loam material measurement is to test its thermal properties because of the interest to use it as the heat storage material below the buildings. The measured clay loam containing some moisture has quite high values of specific heat and thus the use of it as the heat storage material is promising.
In general, among the most significant exogenous factors causing the rock mass deterioration the temperature oscillations and water content have been considered. Monitoring and the interpretation of the water content inside the rock mass especially using non-destructive methods is relatively difficult. The aim of the paper is to evaluate the partial monitoring results of temperature and water content in the different depths of the tuff rock mass based on transient hot-ball method. In the rock mass three hot-ball sensors were inserted in different depths (10 cm, 37 cm and 53.5 cm). The hot-ball sensors were laboratory calibrated before final embedding into rock mass. The results obtained from the real in situ monitoring were compared with the laboratory obtained data and the correlation was set up. For the data presentation 8 month period of in situ monitoring was used (from April to December 2013). In the processing of real in situ data integrated precipitation data records from the weather station were implemented at the site under study. Partial results of in situ monitoring indicate the difference in water content and the temperature with the depth. The gradual decrease of water content with depth inside the rock mass has been recorded. Along with the temperature and coefficient of thermal conductivity measuring, the surface temperature and moisture at the rock face have been measured and the correlation was confirmed.
Question - What is the physical difference between Specific Heat and thermal conductivity?
In the discussion before, there are only answers about the definition of specific heat according which we can measure this parameter. Viorel Sandu is not so true when think that it doesn't tell you anything about the structure. There are several consequences of second thermodynamical law. One of them define the specific heat as a measure of ordering of the structure. So the value of specific heat measured for perfect crystal is the lowest one because the material is in the minimum of thermodynamical state. With the increasing the number of defects the structure is disordered and the result is the higher value of specific heat. This is the reason for different values of specific heat for the same material but in different thermodynamical state.
The building industry is using modern materials that are usually extremely porous to improve the thermal insulation properties. The performance of these materials depends on their thermophysical properties. This paper discusses the heat transport properties in Calcium-Silicate boards reinforced by cellulose fibers measured by pulse transient method. Thermophysical data were measured at various thickness of the specimen. Analysis of influence of the effects of contact area for little thickness and heat losses from the sample surface for large thickness is shown. Data stability interval was found for a MIDDLE range of specimen thickness. Correction procedure is used for heat loss effects from the specimen surface. Thermophysical properties of mentioned material was measured in air and vacuum atmosphere. Influence of the environmental atmosphere on heat transport in porous systems is observed and discussed.
The aim of the paper is to evaluate the weathering and the damage of rock dwellings in Brhlovce village (Slovakia) based on terrain research of the natural rock mass as well as on laboratory research. A new principle of a sensor for monitoring of moisture in the porous materials/volcanic tuffs/ is presented. The sensor principle is based on hot ball method. A hot ball method is used for measuring thermal conductivity. In fact, the thermal conductivity of porous structure is dependent on moisture content in pores e.g. when pores are filled by air/vapour, water or ice. Additionally it is dependent on thermodynamic conditions like temperature gradient and temperature history. Laboratory research of moisture regime was studied using moisture sensor that was finally embedded into rock mass directly. In situ monitoring of the temperature-moisture regime of volcanoclastic rocks where the dwellings were carved out has been running more than one year. The temperature/moisture regime is monitored from October 2011 up to nowadays. of peripheral parts of Štiavnica stratovolcano. Age of these neovolcanic formation products is dated about 15 milion years (Brestenská et al. 1982). All volcanoclastic complexes of strata are very heterogeneous from grain size aspect of view. The tuff in Brhlovce is lithologically described as the ash andesite tuff with variable proportion of volcanic glass matrix and crystalline sandy or fine grains. Sporadic rests of plants and wood were identified in tuffs. In studied locality volcanic sedimentary sequences is in horizontal positions. The collapses of the rock marquis on two dwellings in a museum neighbourhood randomly happened in March 2011 and in November 2012 (Figure 1a). A large block of rocks crashed down. The reason was the simultaneous impact of water influence as well as impact of vegetation in rock discontinuities and cracks. The goal of monitoring is to prevent similar events. Moisture in the rock walls has destructive impact that is caused by cycles of drying—wetting and freezing—thawing processes. The moisture regime is monitored by a new moisture sensor in connection with RTM electronic unit in order to understand the weathering processes of rock dwellings. A simple electronic device RTM is constructed that serve for long time monitoring of moisture in real conditions. The sensor has been placed in the wall of the rock
- Oct 2010
This article deals with the theory and performance of a sensor for measuring thermal conductivity. The sensor, in the form of a small ball, generates heat and simultaneously measures its temperature response. An ideal model of the hollow sphere in an infinite medium furnishes a working equation of the hot-ball method. A constant heat flux through the surface of the ball generates the temperature field. The thermal conductivity of the surrounding medium is to be determined by the stabilized value of the temperature response, i.e., when the steady-state regime is attained. Error components of the sensor are discussed due to analysis of the deviations of the real hot-ball construction from the ideal model. The functionality of a set of hot balls has been tested, and the calibration for a limited range of thermal conductivities was performed. A working range of thermal conductivities of tested materials has been estimated to be from 0.06 W· m−1 · K−1 up to 1 W· m−1 · K−1.
Rocks belong to porous materials where content of pore significantly influence its thermophysical properties. Porous structure plays an important role in heat and fluid transport. A set of effects can be found in such structures like freezing, thawing, evaporation, etc. Highly innovative testing technique based on transient methods has been used for thermophysical analysis in which the specific heat, thermal diffusivity and thermal conductivity is determined, anomalies of the thermophysical parameters connected with freezing and thawing of water in pores are measured, propagation of freezing and thawing fronts are detected and diffusion of moisture in pore structure is monitored on sandstone and Gioia marble. Pulse transient method is based on generation of a heat disturbance by plane heat source fixed in the sample. Specific heat, thermal diffusivity and thermal conductivity are determined from the parameters of the temperature response to this heat disturbance. A heat source in the step-wise heating regime was applied to the frozen sample to study basic characteristics of the propagation of thawing front. In both experiments a sample is used that consists of three parts of size 50x50x10 mm assembled in a rectangle 50x50x30 mm where in first contact of the specimen parts a plane of heat source and in the second one a thermometer is fixed. The sample has to be conditioned prior the measurement to obtain the required thermodynamic state, i.e. the initial temperature and moisture stage. An appropriate heating and cooling regime allows measuring the anomalies of specific heat, thermal conductivity and thermal diffusivity connected with freezing and thawing. The hot ball transient method for measuring thermal conductivity is used for monitoring the moisture diffusion. Principle of the hot ball method is based on generation of the heat in a step-wise regime by a sensor in a form of small ball in diameter of 2 mm that, in addition, it monitors its temperature. A calibration of the sensor in thermal conductivity versus moisture is performed. The sensor is fixed in a place where the information on thermal conductivity/moisture needs to be obtained. The sensor gives information on temperature and thermal conductivity/moisture. Thermophysical analysis has been performed on sandstone (porosity 17 %) and marble (porosity 0.3 %), where variations in thermophysical parameters in dry and water saturated stage were determined as well as effects corresponding to freezing and thawing were established. Propagation of thawing front was analyzed on sandstone (porosity 17 %). The sample was preconditioned to obtain a fully saturated and fully frozen stage. Diffusion of moisture was studied on marble plate of the Florence Duomo Cathedrale using hot ball sensor. Monitoring has been performed in dry and rainy seasons. Variation in moisture was detected in rainy season that correlate to day-night temperature changes.
The rock mass deterioration is caused by exogenous factors from which the main role play the temperature andmoisture content. A monitoring system of the rock moisture content based on the transient Hot-ball method of measuringof the thermal conductivity of materials was installed on the Perún`s rock at the Spiš Castle. So called, hot ball methodwas used for the estimation of the water content in various depths inside the rock mass in order to assess its eff ect on thetemperature penetration depth beneath the surface, which might control the volumetric change (dilation) of the rock cliffand its stability. The preliminary results showed relation between q/Tm index and the precipitation registered by the nearbymeteorological station. This dependence was manifested in the near subsurface parts of the rock face while the deeper sensorswere not infl uenced. This suggests that the surface parts of the travertine rock body are more prone to the temperaturedilation eff ects and therefore the thermal fl ux through the upper 40 cm of rock is faster than through the deeper parts.
The present paper deals with the application of the transient techniques for thermophysical analysis of the structural changes in materials. The technique has been applied for study of equilibrium transitions as well as for kinetic transitions. A special methodology has been developed to study kinetic transitions like crystallization, melting, etc. in a "pseudo-equilibrium states" by the help of porous structures. The paper includes three different issues: the transient methods for measuring thermodynamic and transport parameters, data analysis and application of the pulse transient method for measurements of materials in thermodynamic equilibrium, pseudoequilibrium and in non-equilibrium (quasi-equilibrium) states. Equilibrium transitions in CsPbCl3 and CsPbBr3 single crystals, kinetic transitions of freezing and thawing water in porous stones and non-equilibriums states in E-glass and Al2O3 ceramics during sintering have been studied.
Measurements of the thermophysical properties of Gioia marble in the temperature range from −20 to 60°C are presented. Thermophysical properties, namely, thermal diffusivity, thermal conductivity, and specific heat, were measured by the pulse transient technique. The data were compared for dry and water-saturated states. Despite the very low porosity of marble of about 0.6 vol%, an increase of the transport property parameters (thermal diffusivity and thermal conductivity) up to 20% after water saturation was found. To verify the differences in the transport parameters, the ultrasonic pulse velocity method was employed. A detailed analysis of thermophysical property data during the freeze/thaw process for dry and water-saturated marble was carried out in the temperature range from −8 to 1°C, where an anomaly in the water freezing process was observed. In order to study artificial aging of Gioia marble, up to 60 freeze/thaw cycles were performed. No significant changes in the thermophysical properties of Gioia marble were observed during the artificial aging process.
In this paper we bring the new physical approach to a solution of deficiency in a large amount of testing material. It is a real problem of finite geometry of the specimen that additional effects harm the efficiency of standard way of the measurement evaluation. Three different models used for data evaluation are discussed in this paper. As a model material a PMMA specimen was used. There are discussed two approaches how to avoid the problem of heat loss effect in real experiment. The ideal one that assumes infinite geometry in a model and the limited time of recorded data used for parameters evaluation as the temperatures recorded at short times are not influenced by heat loss effect. The new model introduces next parameter -a heat transfer coefficient that represents heat loss effect from the free sample surface. Thermophysical data are given also numerically and agree with recommended data within 6% for all discussed models.
The paper introduces novel equipment RT-Lab for measuring thermophysical properties of various materials by means of the transient methods we have developed in our laboratories. The entire measuring process can be realized by the RT-Lab. The equipment can operate in several measuring regimes and different transient methods. Functionality of the RT-Lab was verified by measurement of the thermophysical properties of the standard material BK7 using pulse transient method. The RT-Lab replaced the electronic unit RT 1.02 that for its operation required two additional expensive equipments, the programmable power source (KEPCO ABC 15-7 DM) and the precise multimeter (KEITHLEY-2010). full text: http://www.measurement.sk/2007/S3/Stofanik.pdf
Stones belong to porous materials where water in pores plays an important role during the freeze–thaw process. A thermophysical analysis based on the pulse transient method has been used to study an ageing cycle, namely the freeze–thaw cycle. Thermophysical analysis is based on measuring the thermophysical properties under specific thermodynamic conditions. The transient method determines the specific heat, thermal diffusivity, and thermal conductivity by a single measurement. A specimen of Sander sandstone was analyzed in both dry and water-saturated states. Typical anomalies of all thermophysical parameters at the freeze–thaw point as well as differences for the dry and saturated states were found. The changes of thermophysical parameters measured when using freeze–thaw cycles correspond to stone ageing. The freeze–thaw cycle can often be encountered in building physics, concrete construction, etc
- Oct 2005
This paper discusses differences in thermophysical parameters (thermal conductivity λ, thermal diffusivity a, and specific heat c) that can be found when experimental methods with different measuring regimes are used. Two classes of methods are compared, namely, classical methods using steady-state, equilibrium, and dynamic measuring regimes and transient methods. The data consistency formula λ = acρ gives a picture on data reliability when single-parameter methods are used. Results of analysis are verified on published, recommended, and measured data by transient methods considering homogenous materials (stainless steel A 310, BK 7, Perspex) and heterogeneous materials (composite C/C–SiC, aerated autoclaved concrete). Satisfactory agreement on data for the thermophysical parameters was found on homogenous materials only.
The paper describes a novel approach of the system clock frequency versus temperature dependency compensation. Realized digital signal processing system reduces the systematic error due to sampling frequency versus temperature dependency below ± 0.15 ppm over a temperature range between -45°C and +95°C. The system clock signal is derived from a dual-mode crystal oscillator. Since all the necessary temperature information are obtained directly from a crystal itself rather than from an external sensor, temperature offset and lag effects are eliminated.
The presented contribution discusses a class of the transient methods using the heat source and the sensor inserted into the medium. Six variants of the transient methods exist, namely methods using the line heat source, plane heat source or the heat source in the form of the disc inserted into the medium. Methods can use a heat pulse or a heat flux in the form of a step wise function for the generation of the temperature field. The accuracy analysis was performed for methods where technical details are known. The conditions for the intercomparison measurements are discussed. Technical details of three methods are known, only namely the Hot Wire, Pulse Transient and the Gustafsson Probe. Parameters estimation was performed for these methods to reach agreement in experimental data to be better than 1% during intercomparison.
Measurement regime analysis and the analysis of experimental geometry of the specimen for the pulse transient technique are presented. Optimization of the measurement of thermal diffusivity, thermal conductivity and specific heat is analyzed for building materials like autoclaved aerated concrete (AAC), calcium silicate, glass BK7 and polymer PMMA. The disturbance effects connected with specimen geometry and the heat source are discussed. Source:http://www.tpl.fpv.ukf.sk/engl_vers/thermophys/2005/papers/Bohac_Vretanar_Kubicar.pdf
The transient methods for the testing of thermophysical properties of materials are suitable for the material characterization, regarding the stability of the structure or structure changes invoked by treatment after production within technology process. Contact pulse transient technique is sensitive enough to be able to record the change in material structure during any kind of material treatment that influences overall material property. The reliability of any method in practice depends on fact how much does fit the model with experimental conditions. A detailed study has to be performed to find experimental circumstances when disturbing effects influence experimental data. In this paper we discuss the methodology of mathematical tests of physical model for pulse transient method. Additional tests were found for the case of real experiment when disturbance effects like heat loss from the specimen surface and non-ideality of the heat source influence the ideal model.
A batch of specimens based on a system of a rubber matrix mixed with various concentration of fine pine tree particles, were investigated by studying the variation in thermophysical properties. The pine tree particles were added into a styrene-butadiene rubber matrix in different quantities (0, 10, 20, 40 and 60 wt. %). The thermophysical properties behaviour with increasing pine tree particles concentration was found to be different from the originally expected behaviour. Thermophysical properties of materials are very sensitive to any kind of the change of the material structure and thus we can distinguish relatively small changes in material structure. The particle-rubber interface surfaces as well as the inter-contacting particle-particle interface surfaces should be important parameters when modelling the thermal conductivity behaviour. The results of the thermophysical measurements of styrene butadiene rubber filled with pine tree particles will be used for construction and analysis of a new model of thermal transport in similar materials. Introduction New materials bring new problems into science. Anomalous behaviour of thermophysical properties have previously been observed for composite materials consisting of a matrix blended with powder particles, which have been processed in various ways during manufacturing. The purpose of this work is to investigate the thermophysical properties behaviour of a well-defined composite material consisting of a matrix filled with particulate powder filler. The Hot Disk Thermal Constants Analyser – sometimes referred to as the Transient Plane Source (TPS) or Gustafsson Probe  – was used for measurements of thermal conductivity, thermal diffusivity and specific heat capacity. The experimental arrangement of this method is based on the assumption that a heat source in the shape of a double spiral is placed inside an infinite and initially isothermal sample. By passing a step-wise electrical current through the spiral, heat is generated in the source and immediately dissipates into the sample. Simultaneously, the transient temperature response of the double spiral is recorded by following the resistance increase as a function of time. The relation between temperature and resistance increase is governed by the temperature coefficient of resistivity of the double spiral material. A typical temperature increase versus time is depicted in Figure 2 (left). Typically, the total temperature increase during an experiment is between 0.2 K and 5 K – depending on the particular sample and sensor configuration used. A basic experimental setup is illustrated in Figure 1.
- Mar 2004
- 10th International Symposium on Experimental Mineralogy, Petrology and
Stones belong to porous materials where water in pores plays an important role on durability during the freeze/thaw process. Highly innovative thermophysical analysis based on the pulse transient method has been used to study the ageing cycle namely the freeze/thaw cycle. Thermophysical analysis is based on measuring the thermophysical properties at specific thermodynamic condition. Experimental Work The method determines specific heat, thermal diffusivity and thermal conductivity within a single measurement . The specimen of sandstone was conditioned to obtain dry or saturated stage. A nonisothermal measuring regime during the freeze and thaw experiments using the cooling and heating rate of 0.02 K/min. Typical anomalies of the all thermophysical parameters as well as differences for dry, and saturated stage. were found. The hysteresis of the anomalies was found. Field Work A class of the transient methods will be presented. Differences in the individual methods will be shown. Evaluation procedure and details on experimental technique of the pulse transient method will be discussed. Methods are suitable for measurement of the nonhomogenous materials especially for minerals and rocks at The specific thermodynamic condition.  L. Kubičár, Pulse Method for Measuring Basic Thermophysical Parameters, in Wilson and Wilson’s Comprehensive Analysital Chemistry, Vol XII, Thermal analysis, Part E, G. Svehla, ed. (Elsevier Amsterdam 1990) 1 – 350
The measurements of thermophysical parameters of Single Wall Carbon Nanotubes (SWNT) HiPCO in the temperature range from -20 up to 70 °C are presented. In order to inter-compare and to validate the measured data, three different experimental techniques were used. DSC as an equilibrium method for measuring specific heat, Flash transient method for measuring the thermal diffusivity and Pulse transient method for measuring all thermophysical parameters the thermal diffusivity, the specific heat and the thermal conductivity. Good agreement of values measured by these different methods was found.
Thermophysical properties of aerated concrete and phenolic foam were investigated by the pulse transient method. Effects of contact area and heat losses from the free specimen surface were noted. Optimisation of specimen geometry to ensure data stability is discussed. A procedure is described for correcting heat loss effects from the specimen surface. Thermophysical properties of the two porous materials were measured in various surrounding atmospheres.
Intercomparison measurements have been made on Perspex (polymethylmethacrylate) and stainless steel A310 by pulse transient and stepwise transient methods. Both methods belong to the transient techniques that give specific heat, thermal diffusivity, and thermal conductivity within a single measurement. Measuring times and time windows for data evaluation are given for both measuring techniques. Criteria for characteristic parameters of the ideal model by pulse transient are given. Experimental results are compared with recommended and published data for thermal conductivity, specific heat, and thermal diffusivity. Deviations from published and recommended data were found. Data uncertainties in thermal conductivity caused by these deviations are up to 6% for Perspex and up to 10% for stainless steel A310.
The theory and the measurement regime of the pulse transient method are discussed by considering an ideal model, sensitivity coefficients, and their dependence. Difference analysis is used to estimate the time window in which the fitting procedure should be applied to the experimental data. The results of the analysis are verified for Perspex and A310 stainless steel by intercomparison measurements. Differences in the data obtained for the thermophysical parameters are within the accuracy of the instrument used for the measurements.
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.
Present contribution deals with the transient methods and their application in technology. Briefly characterization of the transient methods will be presented. Application is shown in several areas namely: optimisation of the technological parameters (sintering and polymerisation), estimation of the thermophysical parameters at the working condition of materials (measurements on porous materials in various surrounding atmospheres, and at different temperatures), studies of superionic phase transitions and intercomparison measurement of the thermal conductivity of Pyrex.
The main features of the pulse transient method are presented. The method gives the specific heat c and thermal diffusivity a for a single measurement, while thermal conductivity ? is calculated according to ?=ca?, where ? is the density. The pulse transient method is a dynamic method based on the measurement of the temperature response to a heat pulse produced within a specimen. An apparatus operating in the temperature range from -40 to 100°C is described. Errors are discussed. The thermophysical properties of a CsPbCl3 single crystal are determined using the pulse transient method for a temperature range between 10 and 65°C in the controlled heating and cooling regimes. The data show anomalies in the thermophysical properties around the phase transition temperature at 47°C. Discrepancies in comparison with previously published data are discussed.
A version of a transient method for measuring specific heat, thermal diffusivity and thermal conductivity is presented. The dynamic temperature field is generated by the passage of the electrical current through a planar electrical resistance made of thin metallic foil. The heat is produced in the form of a step-wise function. A thermocouple placed apart from the heat source measures the temperature response. The theory of the method, its experimental arrangement and the measuring regime for considering sensitivity coefficients are presented. Experimental data obtained on Perspex are compared with recommended and published data. The data on thermal conductivity agree to within ±0.7% whereas the specific heat is lower on average by 5.2% and the thermal diffusivity is higher by 3.5% when measurements were realized in vacuum. A shift in data of up to 10% was found for measurements made in air.
- Jan 1998
Boháč V, Kubičár L, Hrabĕ Z, 1998, "A transient method study of nonequilibrium effects in a sintering process" High Temperatures - High Pressures 30(6) 651 – 654 Received 20 April 1998 Abstract. Borosilicate glass (E-glass) samples of various bulk densities were prepared by sintering from the glass powder. The samples were investigated at room temperature by the transient method that gives data on the specific heat, thermal diffusivity, and thermal conductivity. The sintering process changes arrangements in the particle contact-surface region. The local deformations influence the anharmonicity of the structure which is responsible for the anharmonic contribution to the specific heat. The anharmonicity promotes the phonon - phonon interaction due to which the thermal diffusivity falls. PDF currently unavailable for this article. http://www.hthpweb.com/abstract.cgi?id=htec86
Page 135-160 in: https://books.google.sk/books?id=90Zlt4_QjLEC&printsec=frontcover&hl=sk#v=onepage&q&f=false
Purpose. Thermophysical properties of three tableting excipients; microcrystalline cellulose, lactose and dicalcium phosphate dihydrate were observed to evaluate their ability to resist temperature induced changes in tablet form. Methods. Two thermophysical parameters, thermal diffusivity and specific heat, were measured by a pulse heating method. The materials were also evaluated by differential scanning calorimetry (DSC). Results. Microcrystalline cellulose in tablet form was found to be rather insensitive to heating and cooling treatments, even though the tablets seemed to remain in a stressed state four weeks after tableting. This stress, indicated by low temperature anomalies, was observed by the pulse method, but not by DSC. When magnesium stearate was incorporated as a lubricant within the microcrystalline cellulose powder, the thermophysical parameters indicated that the internal structure of the tablets changed with heating and cooling. Magnesium stearate eliminated the low temperature anomalies as well. The heat treatment changed the thermophysical properties of tablets made of the crystalline excipients lactose and dicalcium phosphate dihydrate, permanently causing irreversible structural changes. Conclusions. The melting of the lubricant together with enhanced stress relaxation in the structure of microcrystalline cellulose most probably caused the improved thermal diffusivity. The observed thermophysical changes with the crystalline excipients were due to changes in tablet's structure and material. The combination of methods used was found to be an accurate and reliable way to obtain useful information on the structural changes and material relaxations of intact tablets during temperature treatment and age-related changes in material properties.
- Sep 1995
The thermal stability, inter-diffusion and interface effects in multilayer systems are important parameters as they affect the durability of electromigration properties of integrated circuits. Thermal stability and mixing of MoCu interfaces for MoCu multilayered systems after annealing up to 700°C for 1 h in a nitrogen atmosphere was studied. The experimental data hint at the significant grain boundary diffusion of Cu in Mo polycrystalline layers under annealing at 400°C. During annealing at higher temperature the grain boundary diffusion is accompanied by new compounds formation. The X-ray diffraction (XRD) data revealed the presence of compounds of CuMoO and CuMoN type. The crash of the film has been observed after annealing at temperatures above 500°C and the areas of silicon on top of the sample has been found. The average size of silicon locations in diameter is depending on the annealing temperature and was estimated as 8 and 16 μm for 600°C and 700°C, respectively. The concentration ratio fluctuations of CMoCCu in some locations have been observed and determined too.
Optical transmittance and reflectance measurements have been carried out on semiconducting β-iron disilicide layers formed by annealing of iron films evaporated onto silicon substrates and capped with amorphous silicon or SiOx thin overlayers. The dependence of the absorption coefficient on the energy of photons favours direct allowed transitions with the forbidden energy gap of 0.87 ± 0.04 eV.
A new computer program DVBS for the backscattering (BS) analysis and simulation of the backscattered ions energy spectra was developed. The stimulus was the possibility to calculate the depth concentration profiles from the BS spectra at the specimen interfaces and surfaces to obtain the diffusion coefficients. The program was being developed and improved since December 1989 till 1992, when the last version was finished, and is currently used at IP SAS and LNP JINR. The effects of detector resolution, straggling and non-Rutherford or resonant scattering cross section are included in the program analysis. Using graphics possibilities of a PC computer the program offers a very easy way to handle the data which allows to treat complicated multielement BS spectra and reduce the treatment error down to the theoretical accuracy limit of the method. The great advantage of this program is the possibility to display directly on the screen which part of the spectra corresponds to a given layer of the concentration profile. The interfaces between the layers for a given element in displayed concentration model (or concentration histogram) are linked directly to the corresponding channels in the simultaneously overlapped plots of the theoretically generated and experimentally measured spectra. Thus it is possible to adjust the concentration model on the base of the spectra comparison in a channel region which corresponds to a given layer. With new improved BS techniques, the heavy ions become frequently used. The DVBS can use any type of projectiles from proton to uranium and accepts user's scattering cross section, and stopping powers tabulated in a very simple way. This paper offers the short overview and new aspects and methods of the spectra treatment.
- Apr 1993
We report a study of the formation of tungsten silicide at the W-Si interface, induced by multipulse (up to 300 shots) XeCl excimer-laser irradiation of W(150 nm)/Si and W(500 nm)/Si samples. Laser fluences ranging from 0.6 to 1.8 J/cm2 were used. After laser treatment the samples were examined by different diagnostic techniques: Rutherford backscattering spectrometry, X-ray scattering, resistometry, and surface profilometry. Numerical computations of the evolution and depth profiles of the temperature in the samples as a consequence of a single 30 ns laser pulse were performed as well. The results indicate that it is possible to obtain a tungsten silicide layer at the W-Si interface at quite low fluences. The layer thickness increases with the number of laser pulses. Complete reaction of the 150 nm thick W film with silicon was obtained at the fluence of 1.2 J/cm2 between 30 and 100 laser pulses and at 1.5 J/cm2 after 30 laser pulses. The sheet resistance of these silicides was 5–10 . At the used fluences for the 500 nm thick W film only the onset of silicide synthesis at the W-Si interface was observed.
- Mar 1991
Amorphous bilayers with layers of Fe-Ni-B and Co-Fe-Cr-Si-B have been prepared by planar flow casting from a single crucible with two nozzles close to each other and with a partition between them forming two separate vessels. Such an arrangement has allowed us to obtain ribbons with two homogeneous layers, one on top of the other, along the whole ribbon length with high quality surface and with contact interlayer having submicron thickness. The character of the interlayer has been investigated by SEM, EMA, CS-TEM, AES and resistometry in the as-quenched state and after annealing below and after crystallization. From the results it seems evident that the process of connection of the two layers takes place below the crystallization temperature by mutual interdiffusion of component atoms, thus giving rise to mechanically solid connection.
The diffusion of the Au atoms in Ni-Si-B and Fe-Co-B metallic glasses is studied by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). The temperature dependence of the Au diffusion coefficients obeys an Arrhenius relation for both compositions with parameters Do = (10-07.82±2.22) m2 S-1 ΔE = (1.37 ± 0.18) eV for the Ni-Si-B and Do = (10-8.06±2.64) m2 S-1 ΔE = (1.60 ± 0.22) eV for the Fe-Co-B metallic glass. The possible mechanisms of the atomic transport are discussed.
The diffusion of the Au atoms in NiSiB and FeCoB metallic glasses is studied by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). The temperature dependence of the Au diffusion coefficients obeys an Arrhenius relation for both compositions with parameters D0 = (10−7.82±2.22) m2 s−1 ΔE = (1.37 ± 0.18) eV for the NiSiB and D0 = (10−8.06±2.64) m2 s−1 ΔE = (1.60 ± 0.22) eV for the FeCoB metallic glass. The possible mechanisms of the atomic transport are discussed.Die Diffusion von Au-Atomen in den metallischen NiSiB- und FeCoB-Gläsern mit AES und RBS untersucht. Die Temperaturabhängigkeit des Diffusionskoeffizienten von Gold erfüllt eine Arrheniusgleichung für die beiden Zusammensetzungen mit den Parametern D0 = (10−7,82±2,22) m2 s−1, ΔE = (1,37 ± 0,18) eV für NiSiB und D0 = (10−8,06 ± 2,64) m2 s−1, ΔE = (1,60 ± 0,22) eV für FeCoB. Die möglichen Mechanismen des Atomtransports werden disdutiert.
- Sep 1989
The diffusion ot Ti atoms in the Ni77Si3B20 metallic glass was studied by the Auger electron spectroscopy. The temperature dependence of the diffusion coefficient obeys the Arrhenius relation with the activation energyE=1·7 eV and the pre-exponential factorD 0=0·86 × ×10−4 m2 s−1. Possible mechanisms of the atomic transport in metallic glasses are discussed