This work aims to study numerically the moisture absorption in polymer composite reinforced with vegetable fibers using the Langmuir model which considers the existence of free and entrapped water molecules inside the material. A three-dimensional and transient modeling for describing the water absorption process inside the composite and its numerical solution via finite volume method were presented and discussed. Application has been made for polymer composites reinforced with sisal fiber. Emphasis was given to the effect of the layer thickness of fluid close to the wall of the composite in the progress of water migration. Results of the free and entrapped solute (water) concentration, local moisture content and average moisture content, at different times of process, and inside the composite were presented and analyzed. It was verified that concentration gradients of the molecules (free and entrapped) are higher in the material surface, at any time of the process, and concentration of free solute is greater than the concentration of entrapped solute. It was verified that the water layer thickness surrounding the composite strongly affects the moisture absorption rate.
Freezing is one the most efficient methods for conservation, especially, fruits and vegetables. Cashew is a fruit with high nutritional value and great economic importance in the Northeast region of Brazil, however, due to high moisture content, it is highly perishable. The numerical study of the freezing process is of great importance for the optimization of the process. In this sense, the objective of this work was to study the cooling and freezing processes of cashew apple using computational fluid dynamics technique. Experiments of cooling and freezing of the fruit, with the aid of a refrigerator,data acquisition system and thermocouples, and simulation using Ansys CFX® software for obtain the cooling and freezing kinetics of the product were realized. Results of the cooling and freezing kinetics of the cashew apple and temperature distribution inside the cashew apple are presented, compared and analyzed. The model was able to predict temperaturetransient behavior with good accuracy, except in the post-freezing period.
Cashew is a fruit with high nutritional value and great economic importance in the Northeast region of Brazil, however, due to high moisture content, it is highly perishable. Freezing is one the most efficient methods for conservationof biological products, especially, fruits and vegetables. Then, the optimizationof the freezing process by numerical simulation is crucial. In this sense, the objective of this work was to investigate the influence of the moisture content on the cooling and freezing processes of cashew appleby using thecomputational fluid dynamics technique. Results of the cooling and freezing kinetics of the cashew apple and temperature distribution inside the fruitduring these processes are presented and analyzed. It was verified that the variation inthe initial moisture content had small effect in the total time of the process, however the samples with higher moisture content presented higher heat transfer rate during the cooling period and lesser during the freezing period.
Freezing is a physical treatment commonly used in operations such as drying, conservation and lyophilization of foods. In the processing and potato industries, parameters like dimension and initial moisture content of the product has a great effect on the cooling, freezing and post-freezing kinetics. Therefore, this work presents a transient three-dimensional mathematical modeling including phase change to describe the heat transfer during the process, of cooling and freezing parallelepiped foods. The governing equation was solved numerically using the finite-volume technique and a full implicit formulation. As an application, this methodology was used to describe the freezing process of potato (french-fry). Numerical results of the temperature in the center of the product were compared to the experimental data reported in the literature and a good agreement was obtained. Results of the temperature distribution inside the solid and cooling, freezing and post-freezing kinetics are presented and analyzed. It was verified that, the smaller the dimensions and lower the initial moisture content of the product, the solidification of water inside the solid occurs even faster. The largest temperature gradients were identified in the surface, close to the regions of the borders of the solid.
The shape memory alloys have been used in the most different sectors such as aerospace, automotive and biomedical due to their ability to return to their original shape when subjected to high temperatures.Modeling and numerical simulation have become great allies in engineering due to the possibility of solving complex problems, especially in cases where experimental research is limited. In the present study, a two-dimensional mathematical model was developed to describe the solidification process of a Ni-Ti alloy in a stainless-steel metal mold sand-confined. It was considered the flow of a refrigerant (air) in the top of the mold. The energy conservation equation, including the phase change term, was discretized using finite volume method (FVM) and a fully implicit formulation. Results of the Ni-Ti alloy and mold temperature distributions over time are presented and analyzed.
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