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Biocomposite development, as a sustainable alternative to fossil-derived materials with diverse industrial applications, requires expediting the design process and reducing production costs. Simulation methods offer a solution to these challenges. The main aspects to consider in simulating composite materials successfully include accurately representing microstructure geometry, carefully selecting mesh elements, establishing appropriate boundary conditions representing system forces, utilizing an efficient numerical method to accelerate simulations, and incorporating statistical tools like experimental designs and re-regression models. This study proposes a comprehensive methodology encompassing these aspects. We present the simulation using a numerical homogenization technique based on FEM to analyze the mechanical behavior of a composite material of a polyhydroxybutyrate (PHB) biodegradable matrix reinforced with cylindrical inclusions of flax and kenab. Here, the representative volume element (RVE) considered the geometry, and the numerical homogenization method (NHM) calculated the macro-mechanical behavior of composites. The results were validated using the asymptotic homogenization method (AHM) and experimental data, with error estimations of 0.0019% and 7%, respectively. This model is valuable for predicting longitudinal and transverse elastic moduli, shear modulus, and Poisson's coefficient, emphasizing its significance in composite materials research.
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The Stefan problem regarding the formation of several liquid-solid interfaces produced by the oscillations of the ambient temperature around the melting point of a phase change material has been addressed by several authors. Numerical and semi-analytical methods have been used to find the thermal response of a phase change material under these type of boundary conditions. However, volume changes produced by the moving fronts and their effects on the thermal performance of phase change materials have not been addressed. In this work, volume changes are incorporated through an additional equation of motion for the thickness of the system. The thickness of the phase change material becomes a dynamic variable of motion by imposing total mass conservation. The modified equation of motion for each interface is obtained by coupling mass conservation with a local energy-mass balance at each front. The dynamics of liquid-solid interface configurations is analyzed in the transient and steady periodic regimes. Finite element and heat balance integral methods are used to verify the consistency of the solutions to the proposed model. The heat balance integral method is modified and adapted to find approximate solutions when two fronts collide, and the temperature profiles are not smooth. Volumetric corrections to the sensible and latent heat released (absorbed) are introduced during front formation, annihilation, and in the presence of two fronts. Finally, the thermal energy released by the interior surface is estimated through the proposed model and compared with the solutions obtained through models proposed by other authors.
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Two mass-accommodation methods are proposed to describe the melting of paraffin wax used as a phase-change material in a centrally heated annular region. The two methods are presented as models where volume changes produced during the phase transition are incorporated through total mass conservation. The mass of the phase-change material is imposed as a constant, which brings an additional equation of motion. Volume changes in a cylindrical unit are pictured in two different ways. On the one hand, volume changes in the radial direction are proposed through an equation of motion where the outer radius of the cylindrical unit is promoted as a dynamical variable of motion. On the other hand, volume changes along the axial symmetry axis of the cylindrical unit are proposed through an equation of motion, where the excess volume of liquid constitutes the dynamical variable. The energy-mass balance at the liquid-solid interface is obtained according to each method of conceiving volume changes. The resulting energy-mass balance at the interface constitutes an equation of motion for the radius of the region delimited by the liquid-solid interface. Subtle differences are found between the equations of motion for the interface. The differences are consistent with mass conservation and local mass balance at the interface. Stationary states for volume changes and the radius of the region delimited by the liquid-solid interface are obtained for each mass-accommodation method. We show that the relationship between these steady states is proportional to the relationship between liquid and solid densities when the system is close to the high melting regime. Experimental tests are performed in a vertical annular region occupied by a paraffin wax. The boundary conditions used in the experimental tests produce a thin liquid layer during a melting process. The experimental results are used to characterize the phase-change material through the proposed models in this work. Finally, the thermodynamic properties of the paraffin wax are estimated by minimizing the quadratic error between the temperature readings within the phase-change material and the temperature field predicted by the proposed model.
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Front tracking and enthalpy methods used to study phase change processes are based on a local thermal energy balance at the liquid-solid interface where mass accommodation methods are also used to account for the density change during the phase transition. Recently, it has been shown that a local thermal balance at the interface does not reproduce the thermodynamic equilibrium in adiabatic systems. Total thermal balance through the entire liquid-solid system can predict the correct thermodynamic equilibrium values of melted (solidified) mass, system size, and interface position. In this work, total thermal balance is applied to systems with isothermal-adiabatic boundary conditions to estimate the sensible and latent heat stored (released) by KNO3 and KNO3/NaNO3 salts which are used as high-temperature phase change materials. Relative percent differences between the solutions obtained with a local thermal balance at the interface and a total thermal balance for the thermal energy absorbed or released by high-temperature phase change materials are obtained. According to the total thermal balance proposed, a correction to the liquid-solid interface dynamics is introduced, which accounts for an extra amount of energy absorbed or released during the phase transition. It is shown that melting or solidification rates are modified by using a total thermal balance through the entire system. Finally, the numerical and semi-analytical methods illustrate that volume changes and the fraction of melted (solidified) solid (liquid) estimated through a local thermal balance at the interface are not invariant in adiabatic systems. The invariance of numerical and semi-analytical solutions in adiabatic systems is significantly improved through the proposed model.
Assuntos
Transição de Fase , Temperatura , Análise de Elementos Finitos , Nitratos/química , Compostos de Potássio/química , SoluçõesRESUMO
Seis pacientes portadores de tumores parietales del tórax resecados, fueron reparados mediante prótesis cubiertas por epiplón mayor traspuesto. El empleo de este tejido fue de elección para casos en que debieron ser ser extirpados músculos contiguos invadidos y por consiguiente hubiera sido necesario colgajos musculares o miocutáneos distantes para una adecuada reconstrucción. En lugar de ellos, hemos elegido el epiplón, el cual además, produjo mejor resultado estético. No hemos observado complicaciones atribuibles al procedimiento
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Humanos , Masculino , Feminino , Adulto , Pessoa de Meia-Idade , Cirurgia Plástica/métodos , Cirurgia Torácica/métodos , Omento/cirurgia , Neoplasias Torácicas/cirurgia , Retalhos Cirúrgicos/normas , Telas Cirúrgicas , Omento/irrigação sanguínea , Radioterapia/efeitos adversos , Neoplasias Torácicas/complicaçõesRESUMO
Seis pacientes portadores de tumores parietales del tórax resecados, fueron reparados mediante prótesis cubiertas por epiplón mayor traspuesto. El empleo de este tejido fue de elección para casos en que debieron ser ser extirpados músculos contiguos invadidos y por consiguiente hubiera sido necesario colgajos musculares o miocutáneos distantes para una adecuada reconstrucción. En lugar de ellos, hemos elegido el epiplón, el cual además, produjo mejor resultado estético. No hemos observado complicaciones atribuibles al procedimiento (AU)