Guillermo Ovando | Intituto Tecnologico de Veracruz (original) (raw)

Papers by Guillermo Ovando

Physics of Fluids, Feb 1, 2009

The vortex formation in a two-dimensional Cartesian cavity, which their vertical walls move simul... more The vortex formation in a two-dimensional Cartesian cavity, which their vertical walls move simultaneously with an oscillatory velocity and the horizontal walls are fixed pistons, is studied numerically. The governing equations were solved with a finite element method combined with an operator splitting scheme. We analyzed the behavior of vortical structures occurring inside a cavity with an aspect ratio of height-to-width of 1.5 for three different displacement amplitudes of the vertical oscillatory walls ͑amplitude/ width= Y = 0.2, 0.4, and 0.8͒ and Reynolds numbers based on the cavity width of 50, 500, and 1000. Two vortex formation mechanisms are identified: ͑a͒ the shear, oscillatory motion of the moving boundaries coupled with the fixed walls that provide a translational symmetry-breaking effect and ͑b͒ the sharp changes in the flow motion when the flow meets the corners of the cavity. The vortex cores were identified using the Jeong-Hussain criterion and it is found that the area occupied by the cores decreases as the Reynolds number increases and increases as Y increases. All flows studied are cyclic symmetric and for low Y and Re values they are also symmetric with respect to the vertical axis dividing the cavity in two sides. In asymmetric flows, the unbalance between the vortices on each side of the midvertical line generates a vortex that occupies the central part of the cavity. The breakdown of the axial symmetry was studied for a fixed value of the oscillation amplitude, Y = 0.8, taking Re as the bifurcation parameter. The results indicate that the symmetry is broken through a supercritical pitchfork bifurcation.

Fluid dynamics for a Newtonian fluid in the absence of body forces in a two-dimensional cavity wi... more Fluid dynamics for a Newtonian fluid in the absence of body forces in a two-dimensional cavity with top and bottom curved walls was studied numerically. The vertical walls are fixed and the curved walls are in motion. The Navier-Stokes equations were solved using the finite element method combined with the operator splitting scheme. We analyzed the behaviour of the velocity fields, the vorticity fields and the velocity profiles of the fluid inside the cavity. The analysis was carried out for two different Reynolds numbers of 50 and 500 with two ratios (R = 1, −1) of the top to the bottom curved lid speed. For these values of parameters the flow is characterized by vortex formation inside the cavity. The spatial symmetry on the flow patterns are also investigated. We found that when the velocities of the top and bottom walls have opposite direction only one cell is formed in the central part of the cavity; however when the velocities of the top and bottom walls have the same direction the vortex formation inside the cavity is more complex.

Journal of Non-Equilibrium Thermodynamics, 2005

The e¤ect of a constant magnetic field on the stability of a compressible, electrically conductin... more The e¤ect of a constant magnetic field on the stability of a compressible, electrically conducting fluid contained in a duct with an axial temperature gradient is studied. A plausible physical model of the phenomenon is presented and its linear stability is analyzed. The study includes the consideration of a general state equation for the working fluid and the variation of its physical properties with temperature. An expression for the critical thermal gradient required to generate thermoacoustic standing waves is found as a function of the external magnetic field. The potential application of this work is in the context of thermoacoustic prime movers with magnetohydrodynamic transducers.

Brazilian Journal of Chemical Engineering, 2014

A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled... more A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.

The flow in a rectangular cavity driven by the oscillatory motion of the vertical walls has been ... more The flow in a rectangular cavity driven by the oscillatory motion of the vertical walls has been numerically studied for three different Reynolds numbers (Re) based on the cavity width: 50, 500 and 1000 and three different displacement amplitudes of the vertical oscillatory walls ...

Water

This study reports for the first time the isolation, identification and characterization of lipas... more This study reports for the first time the isolation, identification and characterization of lipase-producing thermophilic strain from the geothermal water of the El Chichón volcano crater lake. Two strains were identified by 16S rRNA sequencing as Geobacillus jurassicus CHI2 and Geobacillus stearothermophilus CHI1. Results showed that G. jurassicus CHI2 is Gram-positive, able to ferment maltose, fructose and sucrose and to hydrolyze starch and casein; while G. stearothermophilus CHI1 showed to be Gram-variable, able to ferment maltose and fructose and to hydrolyze starch. Colonies of both strains presented irregular shape, umbilicated elevation of gummy texture and cells presented flagellar movement to survive in fluids with high temperature and mass gradients due to complex phenomena of heat and mass transfer present in the geothermal fluids. Lipase production for G. stearothermophilus CHI1 was also evaluated. It was found that this strain possesses a growth associated with extrace...

Applied Sciences

This paper presents an educational mobile assistant application for type 1 diabetes patients. The... more This paper presents an educational mobile assistant application for type 1 diabetes patients. The proposed application is based on four mathematical models that describe the glucose-insulin-glucagon dynamics using a compartmental model, with additional equations to reproduce aerobic exercise, gastric glucose absorption by the gut, and subcutaneous insulin absorption. The medical assistant was implemented in Java and deployed and validated on several smartphones with Android OS. Multiple daily doses can be simulated to perform intensive insulin therapy. As a result, the proposed application shows the influence of exercise periods, food intakes, and insulin treatments on the glucose concentrations. Four parameter variations are studied, and their corresponding glucose concentration plots are obtained, which show agreement with simulators of the state of the art. The developed application is focused on type-1 diabetes, but this can be extended to consider type-2 diabetes by modifying t...

Brazilian Journal of Chemical Engineering

Heat Transfer Research

In the present paper, we systematically study the effects of the heater length (Wp), as well as o... more In the present paper, we systematically study the effects of the heater length (Wp), as well as of the Richardson (Ri), Lewis (Le), and Reynolds (Re) numbers on the irreversibility production of double-diffusive mixed convection in an open enclosure with a reactant fluid. The fluid with temperature-dependent viscosity and thermal conductivity enters and leaves the enclosure through the inlet and outlet located at the left and right, respectively. Moreover, a heat source located at the bottom wall transfers energy to the fluid, and thermochemical conversion takes place inside the enclosure. At the inlet the fluid is considered to have a high concentration, while a low concentration is imposed over the heater. The studied cases cover Ri = 0.75–5, Le = 0.1–5, Wp = 0.2–0.4, and Re = 100–1000. The results include the temperature and concentration contours, average concentration profiles, average Nusselt number, global total entropy generation, and the average Bejan number. Simulations indicate that the thermochemical conversion is practically independent of the length of the heater, and its highest value or lowest concentration of the flow occurs at Le = 5, Ri = 1.25, and Re = 100. Furthermore, the entropy production is minimized at Wp = 0.3, Re = 100, Ri = 0.75, and Le = 2.5. Therefore, the optimal condition of the thermochemical conversion device is attained at Le = 2.5, Wp = 0.3, Re = 100, and 0.75 ≤ Ri ≤ 1.25.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2012

In electric power plants, the boiler drum has the function of generating steam for its later use ... more In electric power plants, the boiler drum has the function of generating steam for its later use in the turbines. Because of the steam inside the drum, this component is subjected to high temperatures and pressure during the startup of the boiler, causing temperature gradients through the wall of the drum generating thermal stresses coupled with the mechanical stresses induced by the steam pressure. The thermomechanical analysis of the drum presented here was carried out by means of the finite element method and using actual measurements of the starting-up process of a power plant boiler up to the drum temperature is stabilized. The simulation includes the temperature distribution through the wall of the drum and the effect of temperature gradients in the thick walls up to the temperature steady state is reached. In addition the drum stresses caused by the vapor pressure coupled with those generated by the temperature distribution in the wall of the drum were also analyzed. Finally,...

European Journal of Mechanics - B/Fluids, 2013

ABSTRACT The steady vortex formation and thermal behavior in a two-dimensional square ventilated ... more ABSTRACT The steady vortex formation and thermal behavior in a two-dimensional square ventilated cavity is numerically studied. The governing equations of mass, momentum and energy are solved with a finite element method combined with an operator splitting scheme. We analyze the flow occurring inside the enclosure with a centered circular obstruction and a heater plate located at the center of the lower wall of the cavity. The size of the heater is varied for five different lengths. The simulations are obtained for Richardson and Prandtl numbers of 0.01 to 10.0 with a Reynolds number of 400. Results are reported in the form of streamlines, isotherms, average Nusselt number, average bulk fluid and obstruction temperatures. The effects of the heater length, Richardson number and Prandtl number on the hydrodynamics and thermal behavior have been investigated. Four vortex formation mechanisms are identified: (a) the inertial effect of the inlet jet which moves from the lower left sidewall to the upper right sidewall, (b) the detachment of the boundary layer from the wall located above of the entrance of the cavity and from the obstruction, (c) the rolling up of the fluid when this meets with the corners of the cavity and (d) the thermal boundary layer formed on the heater which originates a thermal plume with instabilities traveling upward. It is observed that for low Prandtl numbers with large heater sizes and high Richardson numbers the temperature of the obstruction is increased.

Brazilian Journal of Chemical Engineering, 2010

A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a ... more A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a short channel with a backward-facing step is carried out in this work for the Reynolds number range of 0.00054 ≤ Re ≤ 54. We studied the steady state fluid dynamics, phase change and heat transfer of the flow. We analyzed the flow behavior occurring for different outflow velocities and three different configuration of the step. The incompressible working fluid was glass. The temperature, streamline, phase change and pressure fields are obtained and analyzed as a function of position. In order to obtain a better understanding of the step angle influence on the fluid dynamics, we obtained the heat transfer flux rates and the axial velocity profiles.

Entropy

Heat exchangers play an important role in different industrial processes; therefore, it is import... more Heat exchangers play an important role in different industrial processes; therefore, it is important to characterize these devices to improve their efficiency by guaranteeing the efficient use of energy. In this study, we carry out a numerical analysis of flow dynamics, heat transfer, and entropy generation inside a heat exchanger; an aqueous medium used for oil extraction flows through the exchanger. Hot water flows on the shell side; nanoparticles have been added to the water in order to improve heat transfer toward the cold aqueous medium flowing on the tube side. The aqueous medium must reach a certain temperature in order to obtain its oil extraction properties. The analysis is performed for different Richardson numbers (Ri = 0.1–10), nanofluid volume fractions (φ = 0.00–0.06), and heat exchanger heights (H = 0.6–1.0). Results are presented in terms of Nusselt number, total entropy generation, Bejan number, and performance evaluation criterion. Results showed that heat exchange...

Paper published in Brazilian Journal of Chemical Engineering, 2010

A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a ... more A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a short channel with a backward-facing step is carried out in this work for the Reynolds number range of 0.00054 ≤ Re ≤ 54. We studied the steady state fluid dynamics, phase change and heat transfer of the flow. We analyzed the flow behavior occurring for different outflow velocities and three different configuration of the step. The incompressible working fluid was glass. The temperature, streamline, phase change and pressure fields are obtained and analyzed as a function of position. In order to obtain a better understanding of the step angle influence on the fluid dynamics, we obtained the heat transfer flux rates and the axial velocity profiles.

Paper published in Brazilian Journal of Chemical Engineering, 2014

A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled... more A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.

Paper published in Heat Transfer Research , 2017

In the present paper, we systematically study the effects of the heater length (Wp), as well as o... more In the present paper, we systematically study the effects of the heater length (Wp), as well as of the Richardson (Ri), Lewis
(Le), and Reynolds (Re) numbers on the irreversibility production of double-diffusive mixed convection in an open enclosure with a reactant fluid. The fluid with temperature-dependent viscosity and thermal conductivity enters and leaves
the enclosure through the inlet and outlet located at the left and right, respectively. Moreover, a heat source located at the
bottom wall transfers energy to the fluid, and thermochemical conversion takes place inside the enclosure. At the inlet the
fluid is considered to have a high concentration, while a low concentration is imposed over the heater. The studied cases
cover Ri = 0.75–5, Le = 0.1–5, Wp = 0.2–0.4, and Re = 100–1000. The results include the temperature and concentration
contours, average concentration profiles, average Nusselt number, global total entropy generation, and the average Bejan
number. Simulations indicate that the thermochemical conversion is practically independent of the length of the heater, and
its highest value or lowest concentration of the flow occurs at Le = 5, Ri = 1.25, and Re = 100. Furthermore, the entropy
production is minimized at Wp = 0.3, Re = 100, Ri = 0.75, and Le = 2.5. Therefore, the optimal condition of the thermochemical conversion device is attained at Le = 2.5, Wp = 0.3, Re = 100, and 0.75 ≤ Ri ≤ 1.25.

Paper published in European Journal of Mechanics B/Fluid, 2013

highlights: • We studied the heating of a circular solid obstruction inside an open cavity. • Mi... more highlights:
• We studied the heating of a circular solid obstruction inside an open cavity. • Mixed convection in presence of an obstruction was investigated.
• Four vortex formation mechanisms were identified.

paper Published in Brazilian Journal of Chemical Engineering, 2019

This paper presents a numerical analysis of entropy generation in a two-dimensional rectangular c... more This paper presents a numerical analysis of entropy generation in a two-dimensional rectangular channel where the inlet flow undergoes thermal decomposition resulting from a chemical reaction. The model considered viscosity and thermal conductivity to be dependent of temperature. Irreversibility due to mass transport was included in the entropy generation analysis. Relevant applications of this study are possible for the design of power generation systems and reactors. The effects of the Reynolds number, Schmidt number, and length of the heat source on thermal fluid dynamics, mass transfer, and irreversibility were also investigated. It was found that thermal decomposition increases at: a) low Reynolds numbers, b) low Schmidt numbers, and c) increased length of heat source. Additionally, overall entropy generation increased when Reynolds number and length of heat source were increased, although in all cases, overall irreversibility attains a minimum value at a specific Schmidt number.

Paper published in Applied Sciences, 2020

This paper presents an educational mobile assistant application for type 1 diabetes patients. The... more This paper presents an educational mobile assistant application for type 1 diabetes patients. The proposed application is based on four mathematical models that describe the glucose-insulin-glucagon dynamics using a compartmental model, with additional equations to reproduce aerobic exercise, gastric glucose absorption by the gut, and subcutaneous insulin absorption. The medical assistant was implemented in Java and deployed and validated on several smartphones with Android OS. Multiple daily doses can be simulated to perform intensive insulin therapy. As a result, the proposed application shows the influence of exercise periods, food intakes, and insulin treatments on the glucose concentrations. Four parameter variations are studied, and their corresponding glucose concentration plots are obtained, which show agreement with simulators of the state of the art. The developed application is focused on type-1 diabetes, but this can be extended to consider type-2 diabetes by modifying the current mathematical models.

Paper published in Water, 2020

This study reports for the first time the isolation, identification and characterization of lipas... more This study reports for the first time the isolation, identification and characterization of lipase-producing thermophilic strain from the geothermal water of the El Chichón volcano crater lake. Two strains were identified by 16S rRNA sequencing as Geobacillus jurassicus CHI 2 and Geobacillus stearothermophilus CHI 1. Results showed that G. jurassicus CHI 2 is Gram-positive, able to ferment maltose, fructose and sucrose and to hydrolyze starch and casein; while G. stearothermophilus CHI 1 showed to be Gram-variable, able to ferment maltose and fructose and to hydrolyze starch. Colonies of both strains presented irregular shape, umbilicated elevation of gummy texture and cells presented flagellar movement to survive in fluids with high temperature and mass gradients due to complex phenomena of heat and mass transfer present in the geothermal fluids. Lipase production for G. stearothermophilus CHI 1 was also evaluated. It was found that this strain possesses a growth associated with extracellular lipase production with a high activity of 143 U/mL at 8.3 h of incubation time, superior to the activities reported for other microorganisms of genus Geobacillus; for this reason, it can be said that the thermal flow of the El Chichón volcano crater lake can be a useful source of lipase-producing thermophilic bacteria.

Physics of Fluids, Feb 1, 2009

The vortex formation in a two-dimensional Cartesian cavity, which their vertical walls move simul... more The vortex formation in a two-dimensional Cartesian cavity, which their vertical walls move simultaneously with an oscillatory velocity and the horizontal walls are fixed pistons, is studied numerically. The governing equations were solved with a finite element method combined with an operator splitting scheme. We analyzed the behavior of vortical structures occurring inside a cavity with an aspect ratio of height-to-width of 1.5 for three different displacement amplitudes of the vertical oscillatory walls ͑amplitude/ width= Y = 0.2, 0.4, and 0.8͒ and Reynolds numbers based on the cavity width of 50, 500, and 1000. Two vortex formation mechanisms are identified: ͑a͒ the shear, oscillatory motion of the moving boundaries coupled with the fixed walls that provide a translational symmetry-breaking effect and ͑b͒ the sharp changes in the flow motion when the flow meets the corners of the cavity. The vortex cores were identified using the Jeong-Hussain criterion and it is found that the area occupied by the cores decreases as the Reynolds number increases and increases as Y increases. All flows studied are cyclic symmetric and for low Y and Re values they are also symmetric with respect to the vertical axis dividing the cavity in two sides. In asymmetric flows, the unbalance between the vortices on each side of the midvertical line generates a vortex that occupies the central part of the cavity. The breakdown of the axial symmetry was studied for a fixed value of the oscillation amplitude, Y = 0.8, taking Re as the bifurcation parameter. The results indicate that the symmetry is broken through a supercritical pitchfork bifurcation.

Fluid dynamics for a Newtonian fluid in the absence of body forces in a two-dimensional cavity wi... more Fluid dynamics for a Newtonian fluid in the absence of body forces in a two-dimensional cavity with top and bottom curved walls was studied numerically. The vertical walls are fixed and the curved walls are in motion. The Navier-Stokes equations were solved using the finite element method combined with the operator splitting scheme. We analyzed the behaviour of the velocity fields, the vorticity fields and the velocity profiles of the fluid inside the cavity. The analysis was carried out for two different Reynolds numbers of 50 and 500 with two ratios (R = 1, −1) of the top to the bottom curved lid speed. For these values of parameters the flow is characterized by vortex formation inside the cavity. The spatial symmetry on the flow patterns are also investigated. We found that when the velocities of the top and bottom walls have opposite direction only one cell is formed in the central part of the cavity; however when the velocities of the top and bottom walls have the same direction the vortex formation inside the cavity is more complex.

Journal of Non-Equilibrium Thermodynamics, 2005

The e¤ect of a constant magnetic field on the stability of a compressible, electrically conductin... more The e¤ect of a constant magnetic field on the stability of a compressible, electrically conducting fluid contained in a duct with an axial temperature gradient is studied. A plausible physical model of the phenomenon is presented and its linear stability is analyzed. The study includes the consideration of a general state equation for the working fluid and the variation of its physical properties with temperature. An expression for the critical thermal gradient required to generate thermoacoustic standing waves is found as a function of the external magnetic field. The potential application of this work is in the context of thermoacoustic prime movers with magnetohydrodynamic transducers.

Brazilian Journal of Chemical Engineering, 2014

A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled... more A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.

The flow in a rectangular cavity driven by the oscillatory motion of the vertical walls has been ... more The flow in a rectangular cavity driven by the oscillatory motion of the vertical walls has been numerically studied for three different Reynolds numbers (Re) based on the cavity width: 50, 500 and 1000 and three different displacement amplitudes of the vertical oscillatory walls ...

Water

This study reports for the first time the isolation, identification and characterization of lipas... more This study reports for the first time the isolation, identification and characterization of lipase-producing thermophilic strain from the geothermal water of the El Chichón volcano crater lake. Two strains were identified by 16S rRNA sequencing as Geobacillus jurassicus CHI2 and Geobacillus stearothermophilus CHI1. Results showed that G. jurassicus CHI2 is Gram-positive, able to ferment maltose, fructose and sucrose and to hydrolyze starch and casein; while G. stearothermophilus CHI1 showed to be Gram-variable, able to ferment maltose and fructose and to hydrolyze starch. Colonies of both strains presented irregular shape, umbilicated elevation of gummy texture and cells presented flagellar movement to survive in fluids with high temperature and mass gradients due to complex phenomena of heat and mass transfer present in the geothermal fluids. Lipase production for G. stearothermophilus CHI1 was also evaluated. It was found that this strain possesses a growth associated with extrace...

Applied Sciences

This paper presents an educational mobile assistant application for type 1 diabetes patients. The... more This paper presents an educational mobile assistant application for type 1 diabetes patients. The proposed application is based on four mathematical models that describe the glucose-insulin-glucagon dynamics using a compartmental model, with additional equations to reproduce aerobic exercise, gastric glucose absorption by the gut, and subcutaneous insulin absorption. The medical assistant was implemented in Java and deployed and validated on several smartphones with Android OS. Multiple daily doses can be simulated to perform intensive insulin therapy. As a result, the proposed application shows the influence of exercise periods, food intakes, and insulin treatments on the glucose concentrations. Four parameter variations are studied, and their corresponding glucose concentration plots are obtained, which show agreement with simulators of the state of the art. The developed application is focused on type-1 diabetes, but this can be extended to consider type-2 diabetes by modifying t...

Brazilian Journal of Chemical Engineering

Heat Transfer Research

In the present paper, we systematically study the effects of the heater length (Wp), as well as o... more In the present paper, we systematically study the effects of the heater length (Wp), as well as of the Richardson (Ri), Lewis (Le), and Reynolds (Re) numbers on the irreversibility production of double-diffusive mixed convection in an open enclosure with a reactant fluid. The fluid with temperature-dependent viscosity and thermal conductivity enters and leaves the enclosure through the inlet and outlet located at the left and right, respectively. Moreover, a heat source located at the bottom wall transfers energy to the fluid, and thermochemical conversion takes place inside the enclosure. At the inlet the fluid is considered to have a high concentration, while a low concentration is imposed over the heater. The studied cases cover Ri = 0.75–5, Le = 0.1–5, Wp = 0.2–0.4, and Re = 100–1000. The results include the temperature and concentration contours, average concentration profiles, average Nusselt number, global total entropy generation, and the average Bejan number. Simulations indicate that the thermochemical conversion is practically independent of the length of the heater, and its highest value or lowest concentration of the flow occurs at Le = 5, Ri = 1.25, and Re = 100. Furthermore, the entropy production is minimized at Wp = 0.3, Re = 100, Ri = 0.75, and Le = 2.5. Therefore, the optimal condition of the thermochemical conversion device is attained at Le = 2.5, Wp = 0.3, Re = 100, and 0.75 ≤ Ri ≤ 1.25.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, 2012

In electric power plants, the boiler drum has the function of generating steam for its later use ... more In electric power plants, the boiler drum has the function of generating steam for its later use in the turbines. Because of the steam inside the drum, this component is subjected to high temperatures and pressure during the startup of the boiler, causing temperature gradients through the wall of the drum generating thermal stresses coupled with the mechanical stresses induced by the steam pressure. The thermomechanical analysis of the drum presented here was carried out by means of the finite element method and using actual measurements of the starting-up process of a power plant boiler up to the drum temperature is stabilized. The simulation includes the temperature distribution through the wall of the drum and the effect of temperature gradients in the thick walls up to the temperature steady state is reached. In addition the drum stresses caused by the vapor pressure coupled with those generated by the temperature distribution in the wall of the drum were also analyzed. Finally,...

European Journal of Mechanics - B/Fluids, 2013

ABSTRACT The steady vortex formation and thermal behavior in a two-dimensional square ventilated ... more ABSTRACT The steady vortex formation and thermal behavior in a two-dimensional square ventilated cavity is numerically studied. The governing equations of mass, momentum and energy are solved with a finite element method combined with an operator splitting scheme. We analyze the flow occurring inside the enclosure with a centered circular obstruction and a heater plate located at the center of the lower wall of the cavity. The size of the heater is varied for five different lengths. The simulations are obtained for Richardson and Prandtl numbers of 0.01 to 10.0 with a Reynolds number of 400. Results are reported in the form of streamlines, isotherms, average Nusselt number, average bulk fluid and obstruction temperatures. The effects of the heater length, Richardson number and Prandtl number on the hydrodynamics and thermal behavior have been investigated. Four vortex formation mechanisms are identified: (a) the inertial effect of the inlet jet which moves from the lower left sidewall to the upper right sidewall, (b) the detachment of the boundary layer from the wall located above of the entrance of the cavity and from the obstruction, (c) the rolling up of the fluid when this meets with the corners of the cavity and (d) the thermal boundary layer formed on the heater which originates a thermal plume with instabilities traveling upward. It is observed that for low Prandtl numbers with large heater sizes and high Richardson numbers the temperature of the obstruction is increased.

Brazilian Journal of Chemical Engineering, 2010

A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a ... more A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a short channel with a backward-facing step is carried out in this work for the Reynolds number range of 0.00054 ≤ Re ≤ 54. We studied the steady state fluid dynamics, phase change and heat transfer of the flow. We analyzed the flow behavior occurring for different outflow velocities and three different configuration of the step. The incompressible working fluid was glass. The temperature, streamline, phase change and pressure fields are obtained and analyzed as a function of position. In order to obtain a better understanding of the step angle influence on the fluid dynamics, we obtained the heat transfer flux rates and the axial velocity profiles.

Entropy

Heat exchangers play an important role in different industrial processes; therefore, it is import... more Heat exchangers play an important role in different industrial processes; therefore, it is important to characterize these devices to improve their efficiency by guaranteeing the efficient use of energy. In this study, we carry out a numerical analysis of flow dynamics, heat transfer, and entropy generation inside a heat exchanger; an aqueous medium used for oil extraction flows through the exchanger. Hot water flows on the shell side; nanoparticles have been added to the water in order to improve heat transfer toward the cold aqueous medium flowing on the tube side. The aqueous medium must reach a certain temperature in order to obtain its oil extraction properties. The analysis is performed for different Richardson numbers (Ri = 0.1–10), nanofluid volume fractions (φ = 0.00–0.06), and heat exchanger heights (H = 0.6–1.0). Results are presented in terms of Nusselt number, total entropy generation, Bejan number, and performance evaluation criterion. Results showed that heat exchange...

Paper published in Brazilian Journal of Chemical Engineering, 2010

A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a ... more A numerical investigation of laminar flow in a two-dimensional, Cartesian flow that exits from a short channel with a backward-facing step is carried out in this work for the Reynolds number range of 0.00054 ≤ Re ≤ 54. We studied the steady state fluid dynamics, phase change and heat transfer of the flow. We analyzed the flow behavior occurring for different outflow velocities and three different configuration of the step. The incompressible working fluid was glass. The temperature, streamline, phase change and pressure fields are obtained and analyzed as a function of position. In order to obtain a better understanding of the step angle influence on the fluid dynamics, we obtained the heat transfer flux rates and the axial velocity profiles.

Paper published in Brazilian Journal of Chemical Engineering, 2014

A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled... more A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.

Paper published in Heat Transfer Research , 2017

In the present paper, we systematically study the effects of the heater length (Wp), as well as o... more In the present paper, we systematically study the effects of the heater length (Wp), as well as of the Richardson (Ri), Lewis
(Le), and Reynolds (Re) numbers on the irreversibility production of double-diffusive mixed convection in an open enclosure with a reactant fluid. The fluid with temperature-dependent viscosity and thermal conductivity enters and leaves
the enclosure through the inlet and outlet located at the left and right, respectively. Moreover, a heat source located at the
bottom wall transfers energy to the fluid, and thermochemical conversion takes place inside the enclosure. At the inlet the
fluid is considered to have a high concentration, while a low concentration is imposed over the heater. The studied cases
cover Ri = 0.75–5, Le = 0.1–5, Wp = 0.2–0.4, and Re = 100–1000. The results include the temperature and concentration
contours, average concentration profiles, average Nusselt number, global total entropy generation, and the average Bejan
number. Simulations indicate that the thermochemical conversion is practically independent of the length of the heater, and
its highest value or lowest concentration of the flow occurs at Le = 5, Ri = 1.25, and Re = 100. Furthermore, the entropy
production is minimized at Wp = 0.3, Re = 100, Ri = 0.75, and Le = 2.5. Therefore, the optimal condition of the thermochemical conversion device is attained at Le = 2.5, Wp = 0.3, Re = 100, and 0.75 ≤ Ri ≤ 1.25.

Paper published in European Journal of Mechanics B/Fluid, 2013

highlights: • We studied the heating of a circular solid obstruction inside an open cavity. • Mi... more highlights:
• We studied the heating of a circular solid obstruction inside an open cavity. • Mixed convection in presence of an obstruction was investigated.
• Four vortex formation mechanisms were identified.

paper Published in Brazilian Journal of Chemical Engineering, 2019

This paper presents a numerical analysis of entropy generation in a two-dimensional rectangular c... more This paper presents a numerical analysis of entropy generation in a two-dimensional rectangular channel where the inlet flow undergoes thermal decomposition resulting from a chemical reaction. The model considered viscosity and thermal conductivity to be dependent of temperature. Irreversibility due to mass transport was included in the entropy generation analysis. Relevant applications of this study are possible for the design of power generation systems and reactors. The effects of the Reynolds number, Schmidt number, and length of the heat source on thermal fluid dynamics, mass transfer, and irreversibility were also investigated. It was found that thermal decomposition increases at: a) low Reynolds numbers, b) low Schmidt numbers, and c) increased length of heat source. Additionally, overall entropy generation increased when Reynolds number and length of heat source were increased, although in all cases, overall irreversibility attains a minimum value at a specific Schmidt number.

Paper published in Applied Sciences, 2020

This paper presents an educational mobile assistant application for type 1 diabetes patients. The... more This paper presents an educational mobile assistant application for type 1 diabetes patients. The proposed application is based on four mathematical models that describe the glucose-insulin-glucagon dynamics using a compartmental model, with additional equations to reproduce aerobic exercise, gastric glucose absorption by the gut, and subcutaneous insulin absorption. The medical assistant was implemented in Java and deployed and validated on several smartphones with Android OS. Multiple daily doses can be simulated to perform intensive insulin therapy. As a result, the proposed application shows the influence of exercise periods, food intakes, and insulin treatments on the glucose concentrations. Four parameter variations are studied, and their corresponding glucose concentration plots are obtained, which show agreement with simulators of the state of the art. The developed application is focused on type-1 diabetes, but this can be extended to consider type-2 diabetes by modifying the current mathematical models.

Paper published in Water, 2020

This study reports for the first time the isolation, identification and characterization of lipas... more This study reports for the first time the isolation, identification and characterization of lipase-producing thermophilic strain from the geothermal water of the El Chichón volcano crater lake. Two strains were identified by 16S rRNA sequencing as Geobacillus jurassicus CHI 2 and Geobacillus stearothermophilus CHI 1. Results showed that G. jurassicus CHI 2 is Gram-positive, able to ferment maltose, fructose and sucrose and to hydrolyze starch and casein; while G. stearothermophilus CHI 1 showed to be Gram-variable, able to ferment maltose and fructose and to hydrolyze starch. Colonies of both strains presented irregular shape, umbilicated elevation of gummy texture and cells presented flagellar movement to survive in fluids with high temperature and mass gradients due to complex phenomena of heat and mass transfer present in the geothermal fluids. Lipase production for G. stearothermophilus CHI 1 was also evaluated. It was found that this strain possesses a growth associated with extracellular lipase production with a high activity of 143 U/mL at 8.3 h of incubation time, superior to the activities reported for other microorganisms of genus Geobacillus; for this reason, it can be said that the thermal flow of the El Chichón volcano crater lake can be a useful source of lipase-producing thermophilic bacteria.