Diffusion Foundations and Materials Applications Vol. 30

Abstract: The most widely used materials in building construction are porous materials and the combined effect of rising dampness with soluble salts is one major problem. This phenomenon is caused by the migration of the salt ions dissolved in water into the porous network of the construction materials in the building walls, which causes fractures in the materials after several cycles of crystallization/dissolution. This work presents an extensive experimental campaign with different cycles of water absorption (capillarity absorption tests) and drying (drying tests). The samples of building material used are red brick, and the samples were, previously, submitted to capillarity absorption tests with two different saturated solutions (sodium sulphate and potassium chloride). The results showed that the two salts studied influence the porous materials and their capillary coefficient in clearly different ways and the samples immersed in sodium chloride present higher drying rates than those immersed in a saturated sodium sulphate solution.

Abstract: In order to contribute for a better understanding of the moisture diffusion in infrared (IR) drying of residual seeds from passion fruit processing, the effective moisture diffusivity (D_eff) in the particles was determined from experimental drying kinetics using two different approaches, in which it is considered either as a constant parameter during the process or as dependent on moisture ratio (XR). Experiments were conducted with the seeds arranged in a single layer and exposed to three IR source temperature levels (50, 65 and 80°C). The IR source was set at a distance of 15 cm from the samples. The average effective moisture diffusivity was in the range from 2.76 x 10^-11 to 11.03 x 10^-11 m² s^-1. The activation energy for IR drying was 53.3 kJ/mol. Results of D_eff as a function of XR, obtained using the slope method, indicated that at higher IR source temperatures the vapor diffusion is the main mechanism of moisture transport, while at lowest drying temperature, the process is controlled by both liquid and vapor diffusion.

Abstract: The growing concern with the environment has driven the development of new technologies for the treatment of produced water. In this context, the filtering hydrocyclone appears as an interesting alternative for the treatment of these waters contaminated with oil from the petroleum industry. This research addresses the flow of fluids inside a hydrocyclone equipped with a porous wall (membrane) containing two tangential inlets and two concentric outlets, with the aim of study the impact of the formation of the polarization layer by concentration on the oily water separation process using CFD. Concentration fields and transmembrane pressure, concentration, and permeate flux profiles are presented and analyzed. The results show that the proposed filtering cyclonic separator concentrates the oil in the central region of the equipment, however, for high oil concentrations; the core expands and approaches the porous wall. Furthermore, the increase in the oil volume fraction causes a decline in the permeate flux, and an increase in feed velocity causes a decrease in the polarization layer.

Abstract: In this paper, we cope with the problem of presents a numerical analysis for heat transfer in a duct with geometry circular annular elliptical using the Galerkin-based integral method. The analysis is performed for different geometries of the duct (circular annular circular and circular annular elliptical), and the method is validated for circular cylindrical geometry. Parameters such as mean temperature and mean and location Nusselt numbers for two boundary conditions: constant wall temperature and axial constant heat flux in the wall with constant wall temperature are presented and analyzed.

Abstract: The manufacture of ceramic brick goes through the stages of raw material extraction, clay homogenization, material conformation, drying and firing. Drying is the phase that needs greater care, as it involves removing part of the moisture from the brick, in order to preserve its quality after process. This work aims to predict heat and mass transfer in the drying of ceramic bricks in oven using computational fluid dynamics. Considering the constant thermophysical properties, a transient three-dimensional mathematical model was used to predict mass and energy transfer between the material and air during the process. Drying simulations at temperature of 100°C were performed with the air flow in the frontal direction to the ceramic brick holes and the results were compared with those obtained for the air flow in the perpendicular direction to the brick holes reported in the literature. It was found that the position of the brick in relation to the direction of air flow inside the oven affected directly the drying and heating kinetics, and the distribution of temperature and moisture content inside the brick. The positioning of the holes in the brick parallel to the direction of the air flow resulted in reduction at the drying time and, consequently, in energy savings in the process, more uniform drying, and improvement in the product quality.

Abstract: Heavy oils, due to their high viscosity, have greater viscous resistance to flow, requiring high pumping power for transport and increasing operating cost. As an alternative to minimize this problem, the core-flow technique emerged, which consists of injecting water simultaneously with the oil flow, causing the heavy oil to be surrounded by a layer of water and flowing in the center of the duct without touching the pipe wall, consequently reducing the friction pressure gradient. Thus, this work aims to numerically study the core-annular flow of oil, water and gas in a cylindrical duct with an elliptical cross-section, considering a three-dimensional, isothermal and incompressible flow. For the numerical solution of the governing equations, the software Ansys FLUENT 15.0 was used. It was found that the lubrication provided by the water on the duct wall reduced the pressure variation by 7.20 times compared to the heavy oil single-phase flow, proving the good efficiency of the core-flow technique.

Abstract: Climate change is one of the most debated issues today around the world, given its global impact. The construction industry in the European Union (EU) accounts for 40% of energy consumption and 36% of greenhouse gas emissions. Thus, the continuous improvement of energy efficiency in buildings plays a key role in achieving the carbon neutrality goal by 2050. At a time when the irreversible point of global warming may have already been reached, change becomes urgent, with one of the solutions being the use of renewable energies. Among renewable energies, solar is considered not only one of the most promising ones but also one of the energies with the greatest potential growth. The accelerated use of solar PV allows a reduction of carbon dioxide of approximately 4.9 gigatonnes. In the last decades, solar panels presented a great improvement in their efficiency and power output over and, in addition to the production of electricity, their heat can also be harnessed. Therefore, the objective of this work is to study a photovoltaic panel solution in which the heat produced indirectly by it contribution to the heating of a house and, consequently, to thermal comfort. In this work, it was analysed the feasibility of a PV solution that intends to take advantage of the hot air, indirectly produced by it, for subsequent heating of a house. Numerical simulations were performed using Ansys^® Fluent, Release 18.1, software and considering a 3D model of a house with PV panels installed in the roof. The results showed the solution under study is not feasible in winter, since solar radiation is not enough for heating using this contribution. However, this solution, although not avoiding the use of other heating means, can help in heating, contributing to the reduction of some needs.

Abstract: In addition, the majority of electricity consumed in buildings (58%) should come from renewable sources. Together with solar thermal, modern biomass, and district heating, overall renewables could ramp up to 81%, from 36% today’s contribution for the sector. Nonetheless, to materialize these predictions, a global investment of around USD 32 trillion (28 trillion euros) is expected between now and 2050. In the European Union, the nearly zero-energy building standard (nZEB) will be obligatory for all new buildings by 2021. Although the increase in energy demand will be reduced with this measure, it does not really affect the energy consumption at present. It is imperative to design energy efficiency retrofit and renovation financing schemes. For many years to come, only measures taken in existing buildings will have a significant effect on the total energy demand in the building stock. Firstly, this work presents a brief analysis of active and passive solutions for an energy-efficient building. Secondly, in this work it identified a set of active and passive solutions, which, in a combined way, develop the thermal performance of a residential building, allowing it to become energetically autonomous. The program EnergyPlus was used to execute the thermo-energetic simulations for the diverse scenarios considered, in the study case. The numerical results showed that the implementation of passive solutions improves the energy performance of the buildings, and the use simultaneously of an active solution, a renewable energy source, allows the reach of the energy-autonomous of the building.