Papers by Keyword: Thermal Diffusivity

Abstract: The need for reliable data on thermophysical properties of materials has increased continuously in the last period. The existing data, except for some pure elements or alloys and compounds, often unreliable, and in many cases the need for accurate and acceptable data, can only be achieved by measuring a given property. This paper focuses on elements of the used test methods associated with the description of the newly introduced parameter (effectiveness of dental coating). The selected method was the “pulse method” for determining thermal diffusivity (the method allows simultaneous determination of thermal diffusivity, specific heat capacity and thermal conductivity) directly applicable in the study of the thermal compatibility of metal-ceramic systems in dental applications.

Abstract: Magnesium, as a kind of lightweight engineering material whose reserves is considerable abundant in the earth, is green environment-friendly materials for the 21st century. Magnesium alloys with its proportion of smaller than the advantages of high strength, good thermal conductivity and easy machining, is becoming a hot spot of attention and research. In this paper, the effects of magnesium alloys thermal conductivity and heat diffusivity were analyzed by consulting documents. Researches showed that all effects of the electron or phonon movement had affected thermal conductivity and thermal diffusivity of alloys. Furthermore, the thermal conductivity and thermal diffusivity of rare earth magnesium alloy were summarized by literature data, Researches showed that Add moderate amount of rare earth elements can improve the thermal conductivity and heat diffusivity of magnesium alloys.

Abstract: 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.

Abstract: A novel peak diffusing measurement method is reported. In this method, a pulsed Gaussian heat source is focused on the material’s surface, and a thermal camera is utilized for detecting the temperature evolution. Specially, the peak temperature time t_max at different distance from the heat source center is extracted using the Singular Spectrum Analysis (SSA). Thermal diffusivity is then calculated by fitting multiple sets of extracted t_max into the derived regression equation. The advantage of this method is that it does not require the high precision time synchronization between the excitation source and detector. Also, the calculation process is very simple, which achieves an efficient in situ measurement of the thermal diffusivity. The measured radial thermal diffusivity of samples prepared from Ti and Ni is in good agreement with the reference data with a 1.8% and a 3.9% error bound.

Abstract: Push rod method for determining linear thermal expansion using vertical differential dilatometer was used in the study of the thermal compatibility of metal-ceramic systems for dental applications. The purpose of this study consisted in evaluating the effectiveness of dental coating by determining the ceramic metal bonding strength of metal-ceramic couples (Ni-Cr and Co-Cr alloy coated with dental ceramic) and correlation with the difference of linear thermal expansion coefficients of metals and ceramics.

Abstract: This paper presents a new kind of light emitting diode(LED) secondary light distribution lens which adopts the type of Fresnel lens surface. The research purpose of this paper is to improve the LED heat dissipation efficiency of the secondary light distribution lens and the light efficiency, so as to prolong the service life of the LED. In this paper, we use the numerical method for solving the partial differential equation to establish a freeform surface lens which could produce uniform illumination, then the innovative method of combine the Fresnel lens structure with freeform surface lens was proposed. The design of freeform surface Fresnel lens allows dramatically cut the thickness of the lens (as well as the weight and volume) , it can solve the problem of difficulty in heat dissipation. By comparing the ray tracing simulation results of original freeform surface lens and freeform surface Fresnel lens in optical simulation software, experiments show that the latter not only shows the same degree of illumination uniformity, but also greatly reduced the thickness of the lens.

Abstract: AISI 316 steel samples have been investigated by infrared thermography (IRT) after introducing controlled degrees of plastic deformation by means of tensile tests. Microstructural examinations of the same samples showed that the progressive decrease of thermal diffusivity observed for successive steps of plastic deformation is due to the increase of dislocation density. Dislocations affect thermal diffusivity in two ways, by acting as centres of scattering and by inducing elastic stress fields. To evaluate the two contributions, IRT measurements have been also carried out in-situ, during tensile tests at progressively increasing strain. For relevant plastic deformation, the dislocations mainly affect the thermal diffusivity by scattering mechanism. On the basis of these results, it can be concluded that thermal diffusivity is significantly affected by the increase of dislocations density therefore locally resolved IRT measurements seem promising to detect states of local plasticization in mechanical components.

Abstract: Thermal conducting silicone rubber composites filled with aligned nickel (Ni) nanoparticles induced by magnetic field were prepared by the solution mixing process. The structure, thermal, dielectric and magnetic properties of the silicone rubber composites were investigated by optical microscopy, laser flash thermal diffusivity analyzer, LCR digital meter and vibrating sample magnetometer. The results show that with the induction of magnetic field, Ni nanoparticles aligned form thermal conducting networks resulting in increase of the thermal diffusivity and relative dielectric constant of the silicone rubber composites.

Abstract: A photoflash method of thermal diffusivity measurement was used to determine the value of thermal diffusivity of a sandwiched aluminum layer in a three-layer sample when the sample is simultaneously subjected to both thermal and electric field gradients. The value of the thermal diffusivity of the sample initially measured before electric field was applied agreed well with other reported results. The thermal diffusivity was also found to decrease or increase under the influence of the electric field strength or direction.

Abstract: The paper contains the description of a method, equipment and results for predicting the wear resistance of cemented carbide cutting inserts by measuring their thermal diffusivity. Strong correlation between wear resistance and thermal diffusivity was found. This presented method has been patented.