Sandro Metrevelle Marcondes de LIma e Silva

Identification of temperature-dependent thermal properties of solid materials

This work proposes an experimental technique for the simultaneous estimation of temperature-dependent thermal diffusivity, α, and thermal conductivity, λ, of insulation materials. The thermal model used considers a transient one-dimensional heat transfer problem. The determination of these properties is done by using the principle of the Mixed technique. In this technique two objective functions are defined, one in the frequency domain and the other in the time domain. The objective function in the frequency domain is based on the square difference between experimental and calculated values of the phase angle, while the other objective function is the least square error function of experimental and calculated signals of temperature. The properties α and λ are obtained by using an experimental apparatus that basically consists of a Polyvinyl Chloride (PVC) sample exposed to different temperatures inside an oven. The temperature inside the oven is controlled by a PID temperature controller. The properties α and λ were estimated for 7 (seven) points of average temperature in a range from 20 oC to 66 oC. The properties were determined with an additional heating of approximately 4.5 K on the frontal surface. Analyses of sensitivity, sensors location and sample dimensions were also made. Keywords : thermal properties estimation, heat conduction, optimization, experimental methods

Analyses of Effects of Cutting Parameters on Cutting Edge Temperature Using Inverse Heat Conduction Technique

During machining energy is transformed into heat due to plastic deformation of the workpiece surface and friction between tool and workpiece. High temperatures are generated in the region of the cutting edge, which have a very important influence on wear rate of the cutting tool and on tool life. This work proposes the estimation of heat flux at the chip-tool interface using inverse techniques. Factors which influence the temperature distribution at the AISI M32C high speed steel tool rake face during machining of a ABNT 12L14 steel workpiece were also investigated. The temperature distribution was predicted using finite volume elements. A transient 3D numerical code using irregular and nonstaggered mesh was developed to solve the nonlinear heat diffusion equation. To validate the software, experimental tests were made. The inverse problem was solved using the function specification method. Heat fluxes at the tool-workpiece interface were estimated using inverse problems techniques and experimental temperatures. Tests were performed to study the effect of cutting parameters on cutting edge temperature. The results were compared with those of the tool-work thermocouple technique and a fair agreement was obtained.

A dynamic thermal identification method applied to conductor and nonconductor materials

A method for determining simultaneously the thermal diffusivity, α, and the thermal conductivity, λ, of conductor and nonconductor materials is presented. The precise knowledge of these properties is especially important in heat transfer problems such as heat generation, cooling behavior in machining processes, or in developing of new materials. Additional difficulties can appear in the determination of α and λ of conductor materials. Problems of low sensitivity due to the small temperature gradient, heat loss in one-dimensional (1D) experiments, and thermal contact resistance can be cited. In this sense, a transient three-dimensional (3D) thermal model is developed. A minimization of an objective function based on the square difference between experimental and numerical phase angle in the frequency domain is used to determine α. Another objective function, a least square error function of measured and calculated temperatures, is used to obtain λ. One novelty of this technique is the use of a 3D thermal model that allows the optimizing of the experimental apparatus choosing optimal sensor locations. Three different materials are investigated in this work: a AISI304 stainless steel sample and two samples of polymers (polythene and polyvinyl chloride (PVC)). The estimation results for both conductor and nonconductor sample have shown good agreement with literature.

Thermal effusivity estimation of polymers in time domain

An accurate knowledge of thermophysical properties is very important, for example, to optimize the engineering design and the development of new materials for many applications. Thermal effusivity is a thermal property which presents an increasing importance in heat conduction problems. This property indicates the amount of thermal energy that a material is able to absorb. The estimation can be done by simulating a transient heat transfer model. In this case a one-dimensional semi-infinite thermal model is used. A resistance heater in contact with the sample generates a heat pulse. Variations of temperature and heat flux are measured simultaneously on the top surface of the sample. In this work, thermal effusivity is estimated in time domain through the minimization of the objective function, defined as the square difference between experimental and theoretical temperatures. The golden section technique is used for minimizing this objective function. A sensitivity analysis and a comparison between the semi-infinite and the finite models were also done to define the number of points to be used in the estimation. Measurements were carried out with three different polymers: polymethyl methacrylate, polyvinyl chloride and polyethylene. In all cases studied the results are in good agreement with literature. In addition, an uncertainty analysis is also presented.

An alternative approach to thermal analysis using inverse problems in aluminum alloy welding

Purpose The purpose of this article is the determination of the temperature fields in a weld region has always been an obstacle to the improvement of welding processes. As an alternative, the use of inverse problems to determine the heat flux during the welding process allows an analysis of these processes. Design/methodology/approach This paper studies an alternative for the thermal analysis of the tungsten inert gas welding process on a 6,060 T5 aluminum alloy. For this purpose, a C++ code was developed, based on a transient three-dimensional heat transfer model. To estimate the amount of heat delivered to the plate, the specification function technique was used. Lab experiments were carried out to validate the methodology. A different experimental methodology is proposed to estimate the emissivity (radiation coefficient). Findings The maximum difference between experimental and numerical temperatures is lower than 5 per cent. The determined emissivity value for the aluminum 6,060 T5 presented a good agreement with literature values. The thermal fields were analyzed as function of the positive polarity. The specification function method proved to be an adequate tool for heat input estimation in welding analysis. Originality/value The proposed methodology proves to be a cheaper way to estimate the heat flux on the sample. The estimated power curves for the welding process are presented. The methodology to calculate the emissivity (radiation coefficient) was validated.

EXPERIMENTAL ANALYSIS OF THE INFLUENCE OF HEAT SINK GEOMETRIC PARAMETERS ON NATURAL CONVECTION

In this work, the steady state heat transfer by natural convection in heat sinks with rectangular fins positioned vertically and horizontally was studied. The heat transfer by radiation was also considered. Several analyses were performed to determine the optimal number and position of the sensors used to measure the temperature on the heat sinks horizontally and vertically positioned. These analyses confirmed an almost uniform temperature distribution in the heat sink. This uniformity allowed the use of thermocouples only in the center of the heat sink. Twelve heat sinks were designed to study how their geometric parameters such as height, spacing and thickness of the fins, influence the heat transfer by free convection. In addition, in this work, two correlations using the dimensionless parameters Nusselt and Rayleigh are proposed. These correlations were obtained by using the results from the 12 heat sinks vertically and horizontally positioned considering a temperature range between 20 °C and 100 °C. Furthermore, studies were done to identify which of the 12 analyzed heat sinks managed to remove the greatest amount of heat in a given temperature range. The results were compared with those obtained from empirical correlations found in literature.