In the present thesis a study on the thermal state of steelmaking ladles was undertaken. The transient hot wire method was verified for thermal conductivity measurements on metallurgical slags and applied to ladle slag measurements. Temperature measurements on ladles in an industrial environment were carried out. The emissivities of the outer and inner shells of steelmaking ladles were investigated. Two dynamic models were developed to predict the heat transfer and fluid flow in a preheating and teeming ladle. The gathered thermal conductivity values for ladle slag were used to study the effect of the slag layer on the top surface of the melt on heat transfer and fluid flow in a teeming ladle. In the first stage, the transient hot-wire method was verified to measure the thermal conductivity of metallurgical slags at steelmaking temperatures. A numerical model was developed, cold model experiments were conducted and test measurements using a high temperature experimental setup were carried out. To minimize natural convection and to obtain more reliable measurements, the crucible diameter, the hot-wire diameter, the applied current, the position of the wire in the crucible and the cooling on the upper surface of the crucible were studied. Investigations into the choice of sheathing material of the circuit exposed to the slag were also made. It was found that only certain materials were suitable for slag measurements depending on slag composition and temperature. The electrical resistivity of the hot wire was measured to make the thermal conductivity calculation more reliable. The wire diameter also played a major role due to the heat generation per surface area. The thermal conductivity should be derived from the values measured during the first seconds. In this initial stage, the effect of the natural convection as a function of the wire position in the crucible, the cooling on the top surface and the diameter of the crucible are negligible. A compromise has to be made in choosing the electrical current, since higher current results in higher sensitivity but at the same time in more natural convection. In the second stage, the thermal conductivities of four different ladle slags were measured at 1773 K, 1823 K, 1873 K and 1923 K using the transient hot wire method. Very good reproducibility was obtained. The thermal conductivity did not vary substantially with the variation of slag composition at 1873 K and 1923 K, at which the slag samples were all entirely liquid. The thermal conductivities were low. It was found that the precipitation of solid phase resulted in a considerable increase of thermal conductivity. In the third stage, a two dimensional model was developed in order to predict the temperature distribution in the ladle wall during the preheating process. The model calculated the heat transfer and the velocity field in the gas phase inside the ladle as well as the heat transfer in the solid walls during the preheating process. Measurements of the temperature profiles in an industrial ladle were carried out using an infrared thermography. The measurements were made both inside and outside the ladle. The model predictions were found to be in reasonably good agreement with the measured temperatures. It was found that the preheating time could be minimized when the working lining became thinner. The effect ofthe distance between the lid and the ladle was also studied by the model. The results indicated that there was no significant temperature change on the upper side wall of the ladle. On the lower side wall and bottom the temperature changed slightly. The temperature difference in the lower part of the ladle could be explained by the larger flame distance from the bottom layer. In the fourth stage, a two dimensional axisymmetric model was developed to predict the heat flux in a steelmaking ladle during the teeming process. The model predicts dynamically the flow fields in both the liquid phase and the gas phase along with the movement of the liquid upper surface. The model also predicts the temperature distributions in the liquid metal, gas phase and all layers in the ladle wall. Again, industrial measurements were performed using an infrared thermography, both inside the ladle after teeming and at the wall outside the ladle during the whole process sequence. The model predictions were found to be in agreement with the measured data. It was found that the heat transfer to the surrounding atmosphere and the conductivity of the highly insulating layer were the most important factors for the heat loss. The decrease of the thickness of the working lining was found to have limited effect on the total heat flux. In the fifth and final stage, the effect of the slag layer on the top surface of the melt, on fluid flow and on heat transfer in a teeming ladle was investigated theoretically. The two dimensional axisymmetric model developed in the fourth stage was used. To predict the effect of the slag layer a stationary heat conduction boundary condition including thermal conductivity and slag layer thickness was employed. Different calculations with differing thermal conductivity values for the slag layer were carried out. The calculations showed that the effect of the slag layer was insignificant. This could be explained by the similarity of the thermal conductivity of slag and gas phase. / <p>QC 20121010</p>

This work studied the hot wire method in measuring thermal conductivity at room temperature. The purpose is to find the optimized experimental conditions to minimize natural convection in liquid for this method, which will be taken as reference for high temperature thermal conductivity measurement of slag. Combining room temperature experiments and simulation with COMSOL Multiphysics 4.2a, the study on different experimental parameters which may influence the accuracy of the measured thermal conductivity was conducted. The parameters studied were the diameter of crucible, the position of wire in the liquid, including z direction and x-y plane position, diameter of the hot wire, and current used in the measurement. In COMSOL simulations, the maximum natural convection velocity value was used to evaluate the natural convection in the liquid. The experiment results showed after 4~5 seconds of the measuring process, the natural convection already happened. Also when current was fixed, the thinner the hot wire, the larger convection it would cause. This is because thinner wire generates more heat per unit surface area. Using higher current in measuring, more heat generation improved accuracy of result but also had earlier and larger effect on convection. Both simulation and experiments showed that with the height of the liquid fixed, the smaller diameter of the crucible (not small to the level which is comparable with hot wire diameter), the higher the position in z direction (still covered by liquid), the less natural convection effect existed. But the difference was not significant. The radius-direction position change didn’t influence the result much as long as the wire was not too close to the wall.

The hot wire method, with pH and temperature sensors, was evaluated to determine its usefulness and application for cheese production automation. Coagulation of milk substrate was measured with the hot wire instrument and by four other methods: Formagraph, Brookfield®, vixcometer, Omnispec™ bioactivity monitor, and Sommer and Matsen rolling bottle method. The hot wire, using the time at maximum slope, detected coagulation before methods that measure resistance to shear, and after methods that measure light reflectance. Coagulation time was not significantly different from the industry standard rolling bottle method used by Sommer and Matsen. the hot wire instrument was also used to distinguish samples that formed curd at different rates. This was accomplished by measuring the rate of temperature change of the hot wire probe during curd formation. Milk samples of varying protein, fat, and calcium concentrations were prepared to determine if the instrument could be used to predict a consistent curd cut-point. The pH level was also adjusted, and rennet additions were varied. Coagulation was monitored simultaneously with the hot wire system and a Formagraph. All five factors (pH, calcium, fat, protein, and rennet) had significant effects on cut time estimations (CT20) on the Formagraph. Linear correlations (R2) ranging from .74 to .94 were obtained using stepwise regressions when comparing hot wire and compositional data with the Formagraph. A Formagraph was used to measure effects of calcium, pH, and rennet changes on the coagulation properties of late lactation milk. Calcium, pH, and rennet treatments significantly affected the coagulation parameters measured by the Formagraph. However, response among the poor coagulating samples to treatments to improve coagulation was sample dependent. General composition and SDS-PAGE fractionation data could not be used as an indicator of poor or good coagulability of samples. The hot wire method worked well for monitoring coagulation time and curd firming rate, but did not measure maximum curd firmness well. Curd firming rates determined from the hot wire data are acceptable for estimation of a curd cut time. Added benefits of the hot wire method for monitoring cheese manufacture are that stirring, coagulation, and healing of curd can also be measured. Therefore, the rates of change of important parameters, such as pH, temperature, and coagulation during critical processing steps, can easily be determined by a computer and displayed, printed out, or saved for future evaluation.

The study demonstrates the systematic investigation of thermophysical properties of synthetic slags and commercial mold fluxes in a wide temperature range. Focal points of the work are (i) the development and the construction of the transient hot-wire method for the thermal conductivity measurement of solid and molten slags and (ii) the investigation of the thermal conductivity of all layers of casting powders being in the mold. The work includes viscosity, density and surface tension measurements as well as the investigation of characteristic temperatures. The crystallization behavior of mold fluxes was characterized using a SHTT/DHTT (single hot and double hot thermocouple technique). The study discusses the temperature dependence, the influence of the basicity and the non-bridging oxygen per tetrahedra (NBO/T) on the slag properties. The novelty of the work is the systematic characterization of properties of two commercial mold fluxes and the thermal conductivity measurement in the glass transition temperature range.

Este trabalho apresenta o estudo, a implementação e a caracterização de transdutores compostos por uma estrutura formada por grades de Bragg (FBG, Fiber Bragg Gratings) e grades de período longo (LPG, Long Period Gratings) em fibra óptica com cobertura metálica autoaquecida para medição da condutividade térmica e da difusividade térmica de materiais baseado no método do fio quente (HWM, Hot-Wire Method) convencional. O autoaquecimento da fibra óptica do dispositivo desenvolvido neste trabalho é provocado pela luz de espectro infravermelho injetada por um laser de bombeamento, que é espalhada por uma LPG e absorvida por um filme fino metálico depositado na superfície da fibra. Os transdutores apresentados são compactos, simples, robustos e imunes a interferências eletromagnéticas. O arranjo experimental utilizando o dispositivo híbrido LPG-FBG foi capaz de medir as condutividades térmicas do ar atmosférico e da água comum com precisões de 27% e 14%, respectivamente. Foram identificados vários fatores que afetam a precisão e a exatidão das medidas realizadas, sendo propostas diversas formas de correções de modo a melhorar o desempenho do arranjo. Foi demonstrada com sucesso a viabilidade da aplicação original do arranjo experimental utilizando o dispositivo híbrido LPG-FBG em fibra óptica autoaquecida para a medição de propriedades térmicas de fluidos (ar e água). / This work presents the study, implementation, and characterization of transducers composed of a structure formed by Fiber Bragg Gratings (FBG) and Long Period Gratings (LPG) in optical fiber with self-heating coverage for measurement of thermal conductivity and thermal diffusivity of materials based on the Hot-Wire Method (HWM). The self-heating fiber optic device developed in this work is caused by the light of infrared spectrum injected by a pumping laser, which is spread by an LPG and absorbed by a thin metallic film deposited on the surface of the fiber. The transducers are compact, simple, robust and immune to electromagnetic interference. The experimental arrangement using the optical fiber sensor based on LPG-FBG hybrid structure was able to measure the thermal conductivity of atmospheric air and water with accuracies of 27% and 14%, respectively. Several factors were identified that affect the precision and the accuracy of the measures carried out, whereby various forms of corrections are being proposed to improve overall performance. The viability of the original application of the experimental arrangement using the LPG-FBG hybrid device in self-heating optical fiber for the measurement of thermal properties of fluids (air and water) has been successfully demonstrated.

Este trabalho apresenta o estudo, a implementação e a caracterização de transdutores compostos por uma estrutura formada por grades de Bragg (FBG, Fiber Bragg Gratings) e grades de período longo (LPG, Long Period Gratings) em fibra óptica com cobertura metálica autoaquecida para medição da condutividade térmica e da difusividade térmica de materiais baseado no método do fio quente (HWM, Hot-Wire Method) convencional. O autoaquecimento da fibra óptica do dispositivo desenvolvido neste trabalho é provocado pela luz de espectro infravermelho injetada por um laser de bombeamento, que é espalhada por uma LPG e absorvida por um filme fino metálico depositado na superfície da fibra. Os transdutores apresentados são compactos, simples, robustos e imunes a interferências eletromagnéticas. O arranjo experimental utilizando o dispositivo híbrido LPG-FBG foi capaz de medir as condutividades térmicas do ar atmosférico e da água comum com precisões de 27% e 14%, respectivamente. Foram identificados vários fatores que afetam a precisão e a exatidão das medidas realizadas, sendo propostas diversas formas de correções de modo a melhorar o desempenho do arranjo. Foi demonstrada com sucesso a viabilidade da aplicação original do arranjo experimental utilizando o dispositivo híbrido LPG-FBG em fibra óptica autoaquecida para a medição de propriedades térmicas de fluidos (ar e água). / This work presents the study, implementation, and characterization of transducers composed of a structure formed by Fiber Bragg Gratings (FBG) and Long Period Gratings (LPG) in optical fiber with self-heating coverage for measurement of thermal conductivity and thermal diffusivity of materials based on the Hot-Wire Method (HWM). The self-heating fiber optic device developed in this work is caused by the light of infrared spectrum injected by a pumping laser, which is spread by an LPG and absorbed by a thin metallic film deposited on the surface of the fiber. The transducers are compact, simple, robust and immune to electromagnetic interference. The experimental arrangement using the optical fiber sensor based on LPG-FBG hybrid structure was able to measure the thermal conductivity of atmospheric air and water with accuracies of 27% and 14%, respectively. Several factors were identified that affect the precision and the accuracy of the measures carried out, whereby various forms of corrections are being proposed to improve overall performance. The viability of the original application of the experimental arrangement using the LPG-FBG hybrid device in self-heating optical fiber for the measurement of thermal properties of fluids (air and water) has been successfully demonstrated.

This aim of task deals with study of heat dissipation mechanisms and the description of physical phenomena, which is accompanied by non-stationary measurement of thermal characteristics by the method "hot-wire method". In particular, we observe the coefficient of thermal conductivity and its dependence on various variables such as the temperature of the measured sample, its moisture state, the volume of the sample and its porosity. The above mentioned findings are used for the invention of the measuring device of a nonstationary gauge, which is based on regular heating and is dedicated to measuring the thermal conductivity coefficient and the heat capacity by the "hot-wire method" method. In the last part of the thesis is verified functionality of the proposed measuring device, the suitability of the created algorithm for the processing of the measured data and the evaluation of the results was verified. The reproducibility of the measurements was verified and the measured results were compared with the measurement methods, which are commonly used. the influence of humidity on the coefficient of thermal conductivity.

Dans le cadre de la conservation et de la réhabilitation des bâtis anciens, les matériaux utilisés pour leur construction doivent être caractérisés vis-à-vis de leurs propriétés de transferts thermiques et hydriques. La première étape du travail de recherche a concerné la mise au point d'un capteur de conductivité thermique et de teneur en eau des matériaux inorganiques poreux (pierres, bétons, enduits) constitutifs des monuments. Les méthodes d’investigation doivent rester non intrusives. Dans cet objectif, la voie suivie a été d'adapter la mesure de conductivité thermique par une méthode simplifiée du fil chaud, précédemment développée pour les fluides corrosifs, aux pierres de taille utilisées dans le bâti ancien. Afin de transférer cette technologie des fluides vers les solides, plusieurs étapes ont été effectuées : (1) des mesures avec le fil intégré, (2) des mesures de surface, (3) estimation de l'influence de la rugosité de la surface et (4) utilisation de la méthode pour l'estimation de la teneur en eau des matériaux tests.La seconde étape de la recherche a consisté en deux suivis microclimatiques effectués sur deux sites historiques : l'Hypogée des Dunes et l'abbatiale de Saint-Savin-sur-Gartempe. Le travail de thèse a consisté à évaluer l'impact des travaux effectués sur les conditions climatiques dans l'hypogée, et à déterminer l’influence des variations climatiques sur la formation d'un voile biologique dans la crypte de Saint-Savin. Pour ce faire, l'analyse corrélatoire est appliquée au traitement des donnés climatiques. / In the framework of preservation and rehabilitation of ancient buildings, materials used for their construction must be characterized with regards to thermal and hydric transfer properties. The first stage of our research work focused on the development of a sensor of thermal conductivity and moisture content of the inorganic porous materials (stone, concrete, render) making up the monuments. The methods of investigation have to remain non-invasive. For this purpose, the path followed was to adapt the measure of thermal conductivity by a simplified transient hot-wire method, previously developed for corrosive fluids, to dressed stones used in built heritage. In order to transfer this technology from fluids to the solids, several stages were carried out : (1) measures with the integrated wire, (2) surface measures, (3) estimation of the influence of surface roughness and (4) use of this method to estimate the moisture content of several test materials.The second stage of the research consisted in the microclimatic monitoring of two historical sites: the Hypogeum of the Dunes in Poitiers and the crypt of the abbey church of Saint-Savin-sur-Gartempe. The thesis work sought to evaluate the impact of construction work performed in the Hypogeum on the internal climatic conditions, and to determine the influence of climatic variations on the formation of a biological veil in the crypt of Saint-Savin. To this aim, correlative analysis is applied to the treatment of climatic data.

Presented work deals with appropriate ways of storing thermal energy and selection of materials for a high capacity storage unit. The thesis describes technologies currently used for long-term storage of thermal energy, the structural arrangement of the thermal unit, physical properties of the materials usable for construction of high-temperature storage units and the utilization of these materials. The thesis also describes the measuring procedure of the material characteristics and the method of evaluation. Size of the solar collector and the required volume of the storage for heat supplying of the selected building in the climatic conditions of the Czech Republic were designed.

This aim of task deals with study of heat dissipation mechanisms and the description of physical phenomena, which is accompanied by non-stationary measurement of thermal characteristics by the method "hot-wire method". In particular, we observe the coefficient of thermal conductivity and its dependence on various variables such as the temperature of the measured sample, its moisture state, the volume of the sample and its porosity. The above mentioned findings are used for the invention of the measuring device of a nonstationary gauge, which is based on regular heating and is dedicated to measuring the thermal conductivity coefficient and the heat capacity by the "hot-wire method" method. In the last part of the thesis is verified functionality of the proposed measuring device, the suitability of the created algorithm for the processing of the measured data and the evaluation of the results was verified. The reproducibility of the measurements was verified and the measured results were compared with the measurement methods, which are commonly used. the influence of humidity on the coefficient of thermal conductivity.