Amaresh Dalal | Indian Institute of Technology Guwahati (original) (raw)
Papers by Amaresh Dalal
Journal of heat transfer, Mar 7, 2014
The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circul... more The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov-Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr) = 6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, a, is varied between 0 and 2. The range of nanoparticle volume fractions (<j)) considered isO<(¡)< 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration-deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in a and (p.
Journal of Heat Transfer
The present work demonstrates entropy generation due to laminar mixed convection of water-based n... more The present work demonstrates entropy generation due to laminar mixed convection of water-based nanofluid past a square cylinder in vertically upward flow. Streamline upwind Petrov–Galerkin (SUPG) based finite element method is used for numerical simu-lation. Nanosized copper (Cu) and alumina (Al 2 O 3) particles suspended in water are used with Prandtl number (Pr) ¼ 6.2. The range of nanoparticle volume fractions consid-ered is 0–20%. Computations are carried out at a representative Reynolds number (Re) of 100 with Richardson number (Ri) range À0.5 < Ri < 0.5, both values inclusive. For both the nanofluids (Al 2 O 3 –water and Cu–water nanofluids), total entropy generation decreases with increasing nanoparticle volume fractions. It is found that for the present case of mixed convection flows with nanofluids, thermal irreversibility is much higher than that of frictional irreversibility. The Bejan number decreases with increasing nano-particle volume fractions. [
Journal of Heat Transfer, 2015
The present work investigates the mixed convective flow and heat transfer characteristics past a ... more The present work investigates the mixed convective flow and heat transfer characteristics past a triangular cylinder placed symmetrically in a vertical channel. At a representative Reynolds number, Re = 100, simulations are carried out for the blockage ratios β=1/3,1/4, and 1/6. Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range -1.0≤Ri≤1.0. At a blockage ratio of 1/3, suppression of vortex shedding is found at Ri = 1, whereas von Kármán vortex street is seen both at β=1/4 and 1/6, respectively. This is the first time that such behavior of blockage ratio past a triangular cylinder in the present flow configuration is reported. Drag coefficient increases progressively with increasing Ri and a slightly higher value is noticed at β=1/3. For all β, heat transfer increases with increasing Ri. Flattening of Nuavg –Ri curve beyond Ri>0.75 is observed at β=1/3.
Computers & Fluids, 2014
Fundamental understanding of droplet dynamics and the concomitant implications of wall wettabilit... more Fundamental understanding of droplet dynamics and the concomitant implications of wall wettability and viscosity are critical in the areas like enhanced oil recovery and clean energy conversion. In this work, mesoscopic illustration of droplet dynamics in a channel, based on the two-phase lattice Boltzmann model is presented in order to reveal the role of viscosity-wettability interaction. The impact of critical physicochemical determinants, including capillary number, viscosity ratio and droplet size is explored. Temporal evolution of wetted length and wetted area for a combination of viscosity ratios and wettability scenarios is furnished in detail in order to elucidate the droplet displacement dynamics. Droplet behavioral patterns stemming from uniform and mixed-wet wall characteristics in conjunction with capillary number and viscosity ratio have been investigated.
Fundamentals of Convective Heat Transfer, 2019
Fundamentals of Convective Heat Transfer, 2019
Fundamentals of Convective Heat Transfer, 2019
Physics of Fluids, 2019
The dynamics of a droplet in shear flow under the influence of an external electric field are inv... more The dynamics of a droplet in shear flow under the influence of an external electric field are investigated by performing extensive numerical simulations. The study is carried out by solving two-dimensional electrohydrodynamic equations, and the interface is captured using a volume-of-fluid approach. It is observed that with an increase in the drop size, a confined drop exhibits enhanced deformation and preferred orientation with the flow direction. For the case of dielectric fluids, the deformation of the drops can be either enhanced or reduced by varying the permittivity ratio and electric field strength. The nature of the polarisation forces acting at the interface can be either compressive or tensile depending on the magnitude of the permittivity ratio. The local electric field intensity inside the drop is significantly altered due to the permittivity contrast between the fluids. The computations for leaky dielectric fluids reveal that the deformation of the drop can be effective...
IOP Conference Series: Earth and Environmental Science, 2020
Microbial Fuel Cell (MFC) has various application potential as in generation of bioelectricity, b... more Microbial Fuel Cell (MFC) has various application potential as in generation of bioelectricity, bio-hydrogen production, waste water treatment and it is also used as biosensors. It would not be possible to headway without mentioning that MFCs have quite a many similarities with Chemical Fuel Cells (CFC). It is seen that a lot of research is carried out for CFCs as compared to MFCs. Most of the research works on MFCs include experimental approach while very few computational studies have been carried out for MFCs. So an endeavour is made to create a model which mimics the working by simulating the key physical and biochemical processes occurring. Results imply that variation of current density occurs with change in Reynolds number (Re) and kinetic rate of reaction (k) which lead to the study of effects of variation of flow rates, turbulence and the action of different bacteria in the efficiency of MFCs. The current density achieved computationally is around 512 mA/m2 for Re=5 and k=1...
Journal of Clinical Medicine, 2019
Epithelial to mesenchymal transition (EMT) induces cell migration, invasion, and drug resistance,... more Epithelial to mesenchymal transition (EMT) induces cell migration, invasion, and drug resistance, and consequently, contributes to cancer metastasis and disease aggressiveness. This study attempted to address crucial biological parameters to correlate EMT and drug-treated cancer cells traversing through microcapillaries, reminiscent of metastatic conditions. MDA-MB-468 breast cancer cells induced to undergo EMT by treatment with 20 ng/mL of epidermal growth factor (EGF) were initially passed through several blockages and then through a constricted microchannel, mimicking the flow of invasive metastatic cells through constricted blood microcapillaries. EMT cells acquired enhanced migratory properties and retained 50% viability, even after migration through wells 10–15 μm in size and a constricted passage of 7 μm and 150 μm in length at a constant flow rate of 50 μL/h. The hydrodynamic properties revealed cellular deformation with a deformation index, average transit velocity, and ent...
Advanced Powder Technology, 2018
Specularity coefficient (/) and particle-particle restitution coefficient (e) are two important p... more Specularity coefficient (/) and particle-particle restitution coefficient (e) are two important parameters governing the flow physics of dispersed gas-particle flows. In this work, a detailed numerical analysis is carried out to get an insight into the effects of these two parameters in the flow hydrodynamics of dispersed gas-particle flows through horizontal channels. Investigations have also been carried out to find the /-e pair for which the phase velocities become an extremum. It has been found that at a particular value of e, both gas and particle velocities at the centerline of the channel increase with increase in the value of /, whereas near the wall, they tend to decrease. At a fixed non-zero value of /, both gas and particle velocities tend to increase with increase in the value of e. For / equal to zero, which corresponds to free-slip boundary condition for particle velocity, there is no significant variations in gas and particle velocities with changes in e. Out of all combinations of values of / and e investigated herein, it is found that both gas and particle velocities attain a maximum value when both the values of / and e are maximum.
Journal of Computational Physics, 2018
Abstract In [1] , the authors proposed a charge-conservative numerical framework for simulating e... more Abstract In [1] , the authors proposed a charge-conservative numerical framework for simulating electrohydrodynamic two-phase flows where the electric force was discretely treated as the divergence of Maxwell stress tensor because the use of volume-averaged electric force was found to be inaccurate. In this letter, we show that this framework still suffers from inaccuracies, particularly at high permittivity ratios and propose a simple solution that involves reconstruction of electric displacement rather than the electric field. We demonstrate the efficacy of the new remedial approach through simple numerical experiments for different electrical behaviour of the fluids over a range of permittivity ratios.
Physics of Fluids, 2018
Tongue shaped cavities are seen during the hydrophobic sphere impact, jet impact, and impact of a... more Tongue shaped cavities are seen during the hydrophobic sphere impact, jet impact, and impact of a train of microdrops on a deep liquid pool. For the multiple microdrops’ impact, the mechanisms, which lead to deep cavity formation and later bubble entrapment inside the liquid pool, are presented here. The investigations are performed in an air–water system at large values of Froude numbers, thus having a negligible effect of gravity. Depending on the train length, the capillary wave generating from each drop impact affects the necking. The temporal variation of the neck radius shows power law behavior. We delineate the distinctive feature of pinch-off of the cavity in terms of the critical length of the train. Pinch-off is observed when the penetration depth of the cavity is more than three times the diameter of the cavity.
Physics of Fluids, 2018
This study presents droplet dynamics due to capillarity-wettability interaction through a partial... more This study presents droplet dynamics due to capillarity-wettability interaction through a partially obstructed channel confinement based on a mesoscopic, two-phase lattice Boltzmann model. To explore the dynamic behavior of droplet motion past an obstruction, the effects of the modified capillary number and surface wettability, including the obstruction size and architecture, are elucidated. In this work, a single spherical obstruction and different spherical agglomerate structures have been considered. The mesoscale simulations exhibit interesting two-phase flow physics and pattern formations due to droplet pinching, break up, and surface adherence owing to the underlying wettability-capillarity characteristics. This study further reveals a trade-off, between the time required for the bulk droplet fluid to pass by and/or through the obstruction and the fraction of the droplet fluid volume adhering to the surface, depending on the combination of the capillary number and surface wett...
Chemical Engineering and Processing - Process Intensification, 2018
The present study considers the mixing characteristics of gaseous species in a channel with wavy ... more The present study considers the mixing characteristics of gaseous species in a channel with wavy walls. Waviness imparted along the walls are uniquely defined by the wavelength (λ), amplitude (a) and phase difference (PD). A quasi-incompressible formulation in a three-dimensional collocated finite volume framework is employed for the numerical simulations. Results show that wavy channels lead to enhanced mixing, quantified by the mixing efficiency (M), compared to that of a plane channel. Moreover, the use of asymmetric channels (with 0 • PD) shows better mixing capability than their symmetric counterparts (with 180 • PD) for same wavelength and amplitude. We argue, based on numerical results that the enhanced mixing in the asymmetric channels is due to the generation of alternate recirculation patterns, leading to higher transverse velocities. These transverse convective currents combined with diffusion are observed to aid the mixing process. A complete set of parametric studies is subsequently carried out to investigate the effect of the geometric parameters of waves along with Reynolds number, Peclet number for the 0 • PD wavy channel. It is observed that for a given length, there exists a critical wave number that maximizes the mixing efficiency.
International Journal of Heat and Mass Transfer, 2018
The development of a non-Boussinesq flow solver for simulating combined radiative-convective heat... more The development of a non-Boussinesq flow solver for simulating combined radiative-convective heat transfer is presented on arbitrary polygonal meshes using the ideas of low-Mach number asymptotics. A segregated approach for solving the governing equations using a fractional step methodology on finite-volume method is adapted to handle the low-Mach number formulation. Simulations are carried out for two-and three-dimensional problems involving combined convective-radiative heat transfer both in the small and large temperature difference regimes. It is shown through investigations over a range of Gay-Lussac's and Planck numbers that non-Boussinesq effects could become significant due to the sole influence of large temperature difference and radiative heat transfer. Furthermore, the influence of non-Boussinesq effect on overall heat transfer is larger for the three-dimensional simulation of a given radiation-convection heat transfer problem relative to the two-dimensional assumption for the same problem. Interestingly, even at the low-temperature difference with the presence of significant radiation the Boussinesq approximation fails. This study clearly identifies the limits of validity of the Boussinesq approximation and conclusively prove that solutions to radiation-convection heat transfer problems are best acquired using a quasi-incompressible approach as described in this work.
Numerical Heat Transfer, Part A: Applications, 2018
The phenomena of liquid-solid contact during film boiling due to the effect of surface-wettabilit... more The phenomena of liquid-solid contact during film boiling due to the effect of surface-wettability have been focused in the present study. The numerical simulations during film boiling exhibit the collapse of vapor layer when the surface-wettability is sufficiently high, that is, for the hydrophilic surface. Vapor film collapse results in contact of liquid with the heated surface, which transforms the boiling mode more toward the nucleate regime. The contact area of liquid increases with time. However, such transition is not observed in the case of hydrophobic surface or the surface with higher contact angles. When a sufficiently strong electric field is applied across the liquid-vapor interface, the vapor film collapses and results in similar transition from film boiling to nucleate boiling. The required intensity of electric field at which the vapor film collapses increases with the increase in surface-superheat.
Journal of heat transfer, Mar 7, 2014
The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circul... more The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov-Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr) = 6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, a, is varied between 0 and 2. The range of nanoparticle volume fractions (<j)) considered isO<(¡)< 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration-deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in a and (p.
Journal of Heat Transfer
The present work demonstrates entropy generation due to laminar mixed convection of water-based n... more The present work demonstrates entropy generation due to laminar mixed convection of water-based nanofluid past a square cylinder in vertically upward flow. Streamline upwind Petrov–Galerkin (SUPG) based finite element method is used for numerical simu-lation. Nanosized copper (Cu) and alumina (Al 2 O 3) particles suspended in water are used with Prandtl number (Pr) ¼ 6.2. The range of nanoparticle volume fractions consid-ered is 0–20%. Computations are carried out at a representative Reynolds number (Re) of 100 with Richardson number (Ri) range À0.5 < Ri < 0.5, both values inclusive. For both the nanofluids (Al 2 O 3 –water and Cu–water nanofluids), total entropy generation decreases with increasing nanoparticle volume fractions. It is found that for the present case of mixed convection flows with nanofluids, thermal irreversibility is much higher than that of frictional irreversibility. The Bejan number decreases with increasing nano-particle volume fractions. [
Journal of Heat Transfer, 2015
The present work investigates the mixed convective flow and heat transfer characteristics past a ... more The present work investigates the mixed convective flow and heat transfer characteristics past a triangular cylinder placed symmetrically in a vertical channel. At a representative Reynolds number, Re = 100, simulations are carried out for the blockage ratios β=1/3,1/4, and 1/6. Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range -1.0≤Ri≤1.0. At a blockage ratio of 1/3, suppression of vortex shedding is found at Ri = 1, whereas von Kármán vortex street is seen both at β=1/4 and 1/6, respectively. This is the first time that such behavior of blockage ratio past a triangular cylinder in the present flow configuration is reported. Drag coefficient increases progressively with increasing Ri and a slightly higher value is noticed at β=1/3. For all β, heat transfer increases with increasing Ri. Flattening of Nuavg –Ri curve beyond Ri>0.75 is observed at β=1/3.
Computers & Fluids, 2014
Fundamental understanding of droplet dynamics and the concomitant implications of wall wettabilit... more Fundamental understanding of droplet dynamics and the concomitant implications of wall wettability and viscosity are critical in the areas like enhanced oil recovery and clean energy conversion. In this work, mesoscopic illustration of droplet dynamics in a channel, based on the two-phase lattice Boltzmann model is presented in order to reveal the role of viscosity-wettability interaction. The impact of critical physicochemical determinants, including capillary number, viscosity ratio and droplet size is explored. Temporal evolution of wetted length and wetted area for a combination of viscosity ratios and wettability scenarios is furnished in detail in order to elucidate the droplet displacement dynamics. Droplet behavioral patterns stemming from uniform and mixed-wet wall characteristics in conjunction with capillary number and viscosity ratio have been investigated.
Fundamentals of Convective Heat Transfer, 2019
Fundamentals of Convective Heat Transfer, 2019
Fundamentals of Convective Heat Transfer, 2019
Physics of Fluids, 2019
The dynamics of a droplet in shear flow under the influence of an external electric field are inv... more The dynamics of a droplet in shear flow under the influence of an external electric field are investigated by performing extensive numerical simulations. The study is carried out by solving two-dimensional electrohydrodynamic equations, and the interface is captured using a volume-of-fluid approach. It is observed that with an increase in the drop size, a confined drop exhibits enhanced deformation and preferred orientation with the flow direction. For the case of dielectric fluids, the deformation of the drops can be either enhanced or reduced by varying the permittivity ratio and electric field strength. The nature of the polarisation forces acting at the interface can be either compressive or tensile depending on the magnitude of the permittivity ratio. The local electric field intensity inside the drop is significantly altered due to the permittivity contrast between the fluids. The computations for leaky dielectric fluids reveal that the deformation of the drop can be effective...
IOP Conference Series: Earth and Environmental Science, 2020
Microbial Fuel Cell (MFC) has various application potential as in generation of bioelectricity, b... more Microbial Fuel Cell (MFC) has various application potential as in generation of bioelectricity, bio-hydrogen production, waste water treatment and it is also used as biosensors. It would not be possible to headway without mentioning that MFCs have quite a many similarities with Chemical Fuel Cells (CFC). It is seen that a lot of research is carried out for CFCs as compared to MFCs. Most of the research works on MFCs include experimental approach while very few computational studies have been carried out for MFCs. So an endeavour is made to create a model which mimics the working by simulating the key physical and biochemical processes occurring. Results imply that variation of current density occurs with change in Reynolds number (Re) and kinetic rate of reaction (k) which lead to the study of effects of variation of flow rates, turbulence and the action of different bacteria in the efficiency of MFCs. The current density achieved computationally is around 512 mA/m2 for Re=5 and k=1...
Journal of Clinical Medicine, 2019
Epithelial to mesenchymal transition (EMT) induces cell migration, invasion, and drug resistance,... more Epithelial to mesenchymal transition (EMT) induces cell migration, invasion, and drug resistance, and consequently, contributes to cancer metastasis and disease aggressiveness. This study attempted to address crucial biological parameters to correlate EMT and drug-treated cancer cells traversing through microcapillaries, reminiscent of metastatic conditions. MDA-MB-468 breast cancer cells induced to undergo EMT by treatment with 20 ng/mL of epidermal growth factor (EGF) were initially passed through several blockages and then through a constricted microchannel, mimicking the flow of invasive metastatic cells through constricted blood microcapillaries. EMT cells acquired enhanced migratory properties and retained 50% viability, even after migration through wells 10–15 μm in size and a constricted passage of 7 μm and 150 μm in length at a constant flow rate of 50 μL/h. The hydrodynamic properties revealed cellular deformation with a deformation index, average transit velocity, and ent...
Advanced Powder Technology, 2018
Specularity coefficient (/) and particle-particle restitution coefficient (e) are two important p... more Specularity coefficient (/) and particle-particle restitution coefficient (e) are two important parameters governing the flow physics of dispersed gas-particle flows. In this work, a detailed numerical analysis is carried out to get an insight into the effects of these two parameters in the flow hydrodynamics of dispersed gas-particle flows through horizontal channels. Investigations have also been carried out to find the /-e pair for which the phase velocities become an extremum. It has been found that at a particular value of e, both gas and particle velocities at the centerline of the channel increase with increase in the value of /, whereas near the wall, they tend to decrease. At a fixed non-zero value of /, both gas and particle velocities tend to increase with increase in the value of e. For / equal to zero, which corresponds to free-slip boundary condition for particle velocity, there is no significant variations in gas and particle velocities with changes in e. Out of all combinations of values of / and e investigated herein, it is found that both gas and particle velocities attain a maximum value when both the values of / and e are maximum.
Journal of Computational Physics, 2018
Abstract In [1] , the authors proposed a charge-conservative numerical framework for simulating e... more Abstract In [1] , the authors proposed a charge-conservative numerical framework for simulating electrohydrodynamic two-phase flows where the electric force was discretely treated as the divergence of Maxwell stress tensor because the use of volume-averaged electric force was found to be inaccurate. In this letter, we show that this framework still suffers from inaccuracies, particularly at high permittivity ratios and propose a simple solution that involves reconstruction of electric displacement rather than the electric field. We demonstrate the efficacy of the new remedial approach through simple numerical experiments for different electrical behaviour of the fluids over a range of permittivity ratios.
Physics of Fluids, 2018
Tongue shaped cavities are seen during the hydrophobic sphere impact, jet impact, and impact of a... more Tongue shaped cavities are seen during the hydrophobic sphere impact, jet impact, and impact of a train of microdrops on a deep liquid pool. For the multiple microdrops’ impact, the mechanisms, which lead to deep cavity formation and later bubble entrapment inside the liquid pool, are presented here. The investigations are performed in an air–water system at large values of Froude numbers, thus having a negligible effect of gravity. Depending on the train length, the capillary wave generating from each drop impact affects the necking. The temporal variation of the neck radius shows power law behavior. We delineate the distinctive feature of pinch-off of the cavity in terms of the critical length of the train. Pinch-off is observed when the penetration depth of the cavity is more than three times the diameter of the cavity.
Physics of Fluids, 2018
This study presents droplet dynamics due to capillarity-wettability interaction through a partial... more This study presents droplet dynamics due to capillarity-wettability interaction through a partially obstructed channel confinement based on a mesoscopic, two-phase lattice Boltzmann model. To explore the dynamic behavior of droplet motion past an obstruction, the effects of the modified capillary number and surface wettability, including the obstruction size and architecture, are elucidated. In this work, a single spherical obstruction and different spherical agglomerate structures have been considered. The mesoscale simulations exhibit interesting two-phase flow physics and pattern formations due to droplet pinching, break up, and surface adherence owing to the underlying wettability-capillarity characteristics. This study further reveals a trade-off, between the time required for the bulk droplet fluid to pass by and/or through the obstruction and the fraction of the droplet fluid volume adhering to the surface, depending on the combination of the capillary number and surface wett...
Chemical Engineering and Processing - Process Intensification, 2018
The present study considers the mixing characteristics of gaseous species in a channel with wavy ... more The present study considers the mixing characteristics of gaseous species in a channel with wavy walls. Waviness imparted along the walls are uniquely defined by the wavelength (λ), amplitude (a) and phase difference (PD). A quasi-incompressible formulation in a three-dimensional collocated finite volume framework is employed for the numerical simulations. Results show that wavy channels lead to enhanced mixing, quantified by the mixing efficiency (M), compared to that of a plane channel. Moreover, the use of asymmetric channels (with 0 • PD) shows better mixing capability than their symmetric counterparts (with 180 • PD) for same wavelength and amplitude. We argue, based on numerical results that the enhanced mixing in the asymmetric channels is due to the generation of alternate recirculation patterns, leading to higher transverse velocities. These transverse convective currents combined with diffusion are observed to aid the mixing process. A complete set of parametric studies is subsequently carried out to investigate the effect of the geometric parameters of waves along with Reynolds number, Peclet number for the 0 • PD wavy channel. It is observed that for a given length, there exists a critical wave number that maximizes the mixing efficiency.
International Journal of Heat and Mass Transfer, 2018
The development of a non-Boussinesq flow solver for simulating combined radiative-convective heat... more The development of a non-Boussinesq flow solver for simulating combined radiative-convective heat transfer is presented on arbitrary polygonal meshes using the ideas of low-Mach number asymptotics. A segregated approach for solving the governing equations using a fractional step methodology on finite-volume method is adapted to handle the low-Mach number formulation. Simulations are carried out for two-and three-dimensional problems involving combined convective-radiative heat transfer both in the small and large temperature difference regimes. It is shown through investigations over a range of Gay-Lussac's and Planck numbers that non-Boussinesq effects could become significant due to the sole influence of large temperature difference and radiative heat transfer. Furthermore, the influence of non-Boussinesq effect on overall heat transfer is larger for the three-dimensional simulation of a given radiation-convection heat transfer problem relative to the two-dimensional assumption for the same problem. Interestingly, even at the low-temperature difference with the presence of significant radiation the Boussinesq approximation fails. This study clearly identifies the limits of validity of the Boussinesq approximation and conclusively prove that solutions to radiation-convection heat transfer problems are best acquired using a quasi-incompressible approach as described in this work.
Numerical Heat Transfer, Part A: Applications, 2018
The phenomena of liquid-solid contact during film boiling due to the effect of surface-wettabilit... more The phenomena of liquid-solid contact during film boiling due to the effect of surface-wettability have been focused in the present study. The numerical simulations during film boiling exhibit the collapse of vapor layer when the surface-wettability is sufficiently high, that is, for the hydrophilic surface. Vapor film collapse results in contact of liquid with the heated surface, which transforms the boiling mode more toward the nucleate regime. The contact area of liquid increases with time. However, such transition is not observed in the case of hydrophobic surface or the surface with higher contact angles. When a sufficiently strong electric field is applied across the liquid-vapor interface, the vapor film collapses and results in similar transition from film boiling to nucleate boiling. The required intensity of electric field at which the vapor film collapses increases with the increase in surface-superheat.