Computational Thermal Sciences: An International Journal, 2021
The present work deals with the fluid flow and heat-transfer from a flat heated surface owing to ... more The present work deals with the fluid flow and heat-transfer from a flat heated surface owing to impingement of a turbulent annular jet. A parametric study has been conducted for a fixed non-dimensional jet exit-to-target surface distance (H = 2) at different Reynolds number (Re = 10,000–50,000). After the validation of present model with published results, a comprehensive study has been carried out solving Reynolds-averaged Navier-Stokes equation as well as energy equation. The transition shear stress transport model is used for turbulent closure. It has been observed that, the strength, shape, and size of recirculation zones in the flow domain, are strongly dependent of Reynolds number. Increasing Reynolds number magnifies the size of this zone. At high Reynolds number, turbulence contributes to local enhancement of heat-transfer at the impingement zone. Finally, Nusselt number (Nu) is found to scale with Reynolds number in the form Nu = 0.026 × Re0.7896.
Present trend of semi-solid processing is directed towards rheocasting route which allows manufac... more Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of Al-Si-Mg (A356) alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. ...
PURPOSE Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supporte... more PURPOSE Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here. METHOD In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%. RESULTS Transient form o...
Abstract This work presents a case study of thermodynamic performance of a condenser used in a 21... more Abstract This work presents a case study of thermodynamic performance of a condenser used in a 210 MW thermal power station at Mejia in West Bengal, India. The analysis involves an improvement of actual overall heat transfer coefficient by varying tube materials and fouling resistance. Exergy Destruction Factor (EDF) is introduced to quantify the percentage of exergy loss from the condenser wall. From this study, it is revealed that the second law performance of the condenser increases with the increase in thermal conductivity of the tube materials, decreases with the increase in fouling resistance and decreases with the increase in condenser pressure at the turbine outlet. The actual overall heat transfer coefficient can be increased up to 6% by selecting better conducting tube materials. While the EDF decreases with the increase in cooling water temperature rise and increases with the increase in cooling water inlet temperature, EDF is found to decrease with the increased cooling water mass flow rate.
IOP Conference Series: Materials Science and Engineering, 2021
Present paper deals with the numerical study of fluid flow and heat transfer due to an annular tu... more Present paper deals with the numerical study of fluid flow and heat transfer due to an annular turbulent jet impingement on a flat heated plate. The geometrical configurations of annular jet was selected such a way that the mass and momentums efflux at the annular jet exit will be same as a circular jet having same inner diameter at a particular Reynolds number. Three dimensional turbulent flow field was resolved using Transition SST Model by solving the mass, momentum and energy equation with SIMPLE algorithm. A highly refined mesh was used for numerical computation after validation of present model with established results of same geometrical configuration. The flow structure and heat transfer characteristic of the annular jet was compared with the conventional circular jet and also with an established two dimensional study of same configurations and reported in this paper. It was observed that that two dimensional studies on annular jet under predicts heat transfer characteristics.
Abstract The present work reports fabrication of graphene nanoplatelets (0.1, 0.3 and 0.5 wt%) re... more Abstract The present work reports fabrication of graphene nanoplatelets (0.1, 0.3 and 0.5 wt%) reinforced aluminium matrix naocomposites through non-contact ultrasonic vibrations assisted stir casting process. Microstructure, tensile strength, microhardness and tribological properties of fabricated samples have been examined. The influence of T6 heat treatment on mechanical properties of developed samples was also investigated. Incorporation of graphene in base matrix resulted in grain refinement and an increase of about 37% in ultimate tensile strength and 27% in micro hardness of cast composites. Strength and grain refining action of graphene was attributed as the reason for increment in mechanical properties. Heat treatment causes further improvement of about 83% and 34% in ultimate tensile strength and microhardness of fabricated composites as compared to heat treated base matrix. The enhancement in properties of heat-treated samples was attributed to age hardening. Addition of self-lubricating graphene in aluminium matrix resulted in improved wear behavior of prepared composites. Reduction of about 24% in coefficient of friction of graphene-aluminium composites as compared to base matrix is reported.
The European Physical Journal Applied Physics, 2020
Heat transfer performance of microchannel are becoming an important area of research with the cur... more Heat transfer performance of microchannel are becoming an important area of research with the current fast growing scenario of high speed computing and miniaturized electronic devices. These devices pile up large amount of heat accompanied by smaller surface area to release it. The current work examines unsteady, laminar flow heat transfer inside a novel twisted sinusoidal wavy microchannel. The channel with square cross section is wavy in nature as well as twisted. The first half portion of the channel is twisted clockwise, whereas the twist in the remaining part is having counterclockwise twist. The novel geometry promotes mixing of fluid layers leading to transport augmentation. The inlet pulsation follows sinusoidal pattern in time. The thermal performance parameter of the proposed novel geometry was assessed within a Reynolds number range of 1–100. Both the pulsation amplitude and Strouhal number are varied during the course of this study. To solve the governing equations, a fi...
International Communications in Heat and Mass Transfer, 2020
Abstract In the present study, a numerical simulation is carried out to analyze the effect of tur... more Abstract In the present study, a numerical simulation is carried out to analyze the effect of turbulent intensity on the flow behavior of flow past two dimensional bluff bodies. Triangular prism, diamond and trapezoidal shaped bodies with the same hydraulic diameter D, a dimensionless length scale are taken into consideration as bluff bodies. The objective of the numerical analysis is to cover cross flow at both turbulent and laminar regime with varying Reynolds number upto 200,000 and inlet intensities ranging between 5% and 40%. The flow medium used is air at a constant Prandtl number. The energy, momentum and continuity equations are dealt with transition SST Model for closure of turbulence. The results obtained through numerical simulation are validated with other published results by researchers and show good agreements. This present study reveals that transition SST Model can be efficiently used to cover both laminar and turbulent flow regimes to estimate the heat transfer. The impact of inlet turbulent intensity on augmentation of heat transfer using bluff bodies has been evaluated. It is observed from the study that the turbulent intensity significantly affects drag coefficient.
The transport phenomena in microchannel are significant in designing MEMS devices. The current st... more The transport phenomena in microchannel are significant in designing MEMS devices. The current study investigates numerically the simultaneously developing unsteady laminar flow and heat transfer inside a twisted sinusoidal wavy microchannel. At the inlet sinusoidal varying velocity component is applied. Varying pulsating amplitude and frequency represented by the Strouhal number was studied for Reynolds numbers ranging from 1 to 100. The governing equations are solved with a finite volume based numerical method. In comparison with steady flow, it was found that imposed sinusoidal velocity at the inlet can provide improved heat transfer performance at different amplitudes and frequencies while keeping the pressure drop within acceptable limits.
Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
In this work, two parameters Weibull distribution method and Rayleigh distribution method have be... more In this work, two parameters Weibull distribution method and Rayleigh distribution method have been used to estimate the wind energy potential at Imphal, Manipur located in northeast India with the...
In the present paper, along with experimental study, CFD analysis of forced convection in a twist... more In the present paper, along with experimental study, CFD analysis of forced convection in a twisted tube is performed, using the transition SST model which can predict the change of flow regime from laminar through transition to turbulent. The differential governing equations are discretized by the finite volume method. The investigations are conducted for Reynolds numbers ranging from 100 to 50000 covering laminar, transitional and turbulent regimes, and for three length and three pitch ratios. The predictions are observed to show a good agreement with the measurements and published correlations of other authors. The analysis indicates that the large length ratio and small pitch ratio yields a higher heat transfer rate with relatively low performance penalty. The transition from laminar to turbulent regime is observed between Reynolds numbers of 2500 to 3500 for all cases. For almost all investigated cases the performance factors are greater than unity.
Computer Methods and Programs in Biomedicine, 2019
BACKGROUND AND OBJECTIVE Entropy generation is associated with the irreversibility of any thermod... more BACKGROUND AND OBJECTIVE Entropy generation is associated with the irreversibility of any thermodynamic system. It provides an indication of lost energy and hence the efficiency of a system. In this paper, an attempt has been made to study the effects of specific humidity, relative humidity, ambient temperature change, breathing air friction with the respiratory tract on the entropy generation during the respiration process at different physiological conditions. METHODS To address the above issues, a human respiratory tract model with realistic length to diameter ratio at different branches has been considered. The analysis examines air flow rates of 6 lpm and 60 lpm during rest and exercise condition respectively; corresponding to breathing rates of 30 and 60 per minute, respectively. The body temperature has been considered at 36°C, and ambient condition of air has been taken at 25°C DBT and 50% RH. The respiratory tract geometry has been modelled on the basis of Weibel's experimental results. RESULTS It has been noticed that, at a particular Lewis number entropy generation per day decreases with the increase in specific humidity, again at a particular specific humidity entropy generation increases with the decrease in Lewis number. For a particular physical condition and Lewis number entropy generation decreases with the increase in relative humidity. In this work, it has been observed that negentropy increases with the increase in ambient temperature for a constant relative humidity, however the net entropy generation is always positive. This study reports that, maximum resistance of flow occurs where duct aspect ratio (i.e. tract diameter to length) is minimal. For a typical geometry of air passage, velocity of flow increases up to 3rd generation then it is decreases gradually till 23rd generation. Amount of entropy generation goes on reducing as the duct goes on bifurcating except for the third generation where a local peak in entropy generation is observed. This is a consequence of typical geometry of human respiratory duct. This work reveals that, at rest entropy generation due to conditioning of breathing air is higher than its frictional component and during heavy physical activity, entropy generation due to breathing air friction with the respiratory tract is higher than its air conditioning component. CONCLUSIONS Entropy generation is significantly higher due to conditioning of breathing air than that of frictional effect with the tract. This is a preliminary attempt in quantifying this aspect and the authors believe that, these two components of entropy generation have a probable connection with the bronchial thermoplasty, which helps to treat the asthma.
Progress in Computational Fluid Dynamics, An International Journal, 2017
This paper encapsulates results of a numerical investigation on flow and heat transfer of an inco... more This paper encapsulates results of a numerical investigation on flow and heat transfer of an incompressible medium with constant properties through an isothermal circular tube with alternating inclined ribs. Simulations are conducted for laminar, transitional, and turbulent flow regimes. As turbulence model, the transitional shear stress transport model is employed. The problem is investigated for four rib angle of attack values, as well as for a plain tube without any ribs. All configurations are observed to lead to a thermal performance factor close to or greater than unity. Within the investigated range, the larger thermal performance factors are observed to occur for the intermediate Reynolds numbers. Maximum values in the range 2.0-2.5 are predicted for the Reynolds number of 2,000, where a subsequent drop to values within the range 1.0-1.5 are found to occur for Reynolds numbers around 3,000-4,000, which may be attributed to the transitional effects.
Computational Thermal Sciences: An International Journal, 2021
The present work deals with the fluid flow and heat-transfer from a flat heated surface owing to ... more The present work deals with the fluid flow and heat-transfer from a flat heated surface owing to impingement of a turbulent annular jet. A parametric study has been conducted for a fixed non-dimensional jet exit-to-target surface distance (H = 2) at different Reynolds number (Re = 10,000–50,000). After the validation of present model with published results, a comprehensive study has been carried out solving Reynolds-averaged Navier-Stokes equation as well as energy equation. The transition shear stress transport model is used for turbulent closure. It has been observed that, the strength, shape, and size of recirculation zones in the flow domain, are strongly dependent of Reynolds number. Increasing Reynolds number magnifies the size of this zone. At high Reynolds number, turbulence contributes to local enhancement of heat-transfer at the impingement zone. Finally, Nusselt number (Nu) is found to scale with Reynolds number in the form Nu = 0.026 × Re0.7896.
Present trend of semi-solid processing is directed towards rheocasting route which allows manufac... more Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of Al-Si-Mg (A356) alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. ...
PURPOSE Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supporte... more PURPOSE Abnormalities in blood vessels by virtue of complex blood flow dynamics is being supported by non-Newtonian behavior of blood. Thus it becomes a focus of research to most of the researchers. Additionally, consideration of real life patient specific model of vessel as well as patient specific inlet flow boundary condition implementation was limited in literature. Thus a thorough implementation of these considerations was done here. METHOD In this work, a numerical investigation of hemodynamic flow in stenosed artery has been carried out with realistic pulsating profile at the inlet. Flow has been considered to be laminar due to arresting condition of cardiovascular state of the subject. Two non- Newtonian rheological models namely, Power Law viscosity model and Quemada viscosity model have been used. Two different patient- specific pulsatile profiles are considered at the inlet of a long stenosed artery with varying degree of stenoses from 25% to 80%. RESULTS Transient form o...
Abstract This work presents a case study of thermodynamic performance of a condenser used in a 21... more Abstract This work presents a case study of thermodynamic performance of a condenser used in a 210 MW thermal power station at Mejia in West Bengal, India. The analysis involves an improvement of actual overall heat transfer coefficient by varying tube materials and fouling resistance. Exergy Destruction Factor (EDF) is introduced to quantify the percentage of exergy loss from the condenser wall. From this study, it is revealed that the second law performance of the condenser increases with the increase in thermal conductivity of the tube materials, decreases with the increase in fouling resistance and decreases with the increase in condenser pressure at the turbine outlet. The actual overall heat transfer coefficient can be increased up to 6% by selecting better conducting tube materials. While the EDF decreases with the increase in cooling water temperature rise and increases with the increase in cooling water inlet temperature, EDF is found to decrease with the increased cooling water mass flow rate.
IOP Conference Series: Materials Science and Engineering, 2021
Present paper deals with the numerical study of fluid flow and heat transfer due to an annular tu... more Present paper deals with the numerical study of fluid flow and heat transfer due to an annular turbulent jet impingement on a flat heated plate. The geometrical configurations of annular jet was selected such a way that the mass and momentums efflux at the annular jet exit will be same as a circular jet having same inner diameter at a particular Reynolds number. Three dimensional turbulent flow field was resolved using Transition SST Model by solving the mass, momentum and energy equation with SIMPLE algorithm. A highly refined mesh was used for numerical computation after validation of present model with established results of same geometrical configuration. The flow structure and heat transfer characteristic of the annular jet was compared with the conventional circular jet and also with an established two dimensional study of same configurations and reported in this paper. It was observed that that two dimensional studies on annular jet under predicts heat transfer characteristics.
Abstract The present work reports fabrication of graphene nanoplatelets (0.1, 0.3 and 0.5 wt%) re... more Abstract The present work reports fabrication of graphene nanoplatelets (0.1, 0.3 and 0.5 wt%) reinforced aluminium matrix naocomposites through non-contact ultrasonic vibrations assisted stir casting process. Microstructure, tensile strength, microhardness and tribological properties of fabricated samples have been examined. The influence of T6 heat treatment on mechanical properties of developed samples was also investigated. Incorporation of graphene in base matrix resulted in grain refinement and an increase of about 37% in ultimate tensile strength and 27% in micro hardness of cast composites. Strength and grain refining action of graphene was attributed as the reason for increment in mechanical properties. Heat treatment causes further improvement of about 83% and 34% in ultimate tensile strength and microhardness of fabricated composites as compared to heat treated base matrix. The enhancement in properties of heat-treated samples was attributed to age hardening. Addition of self-lubricating graphene in aluminium matrix resulted in improved wear behavior of prepared composites. Reduction of about 24% in coefficient of friction of graphene-aluminium composites as compared to base matrix is reported.
The European Physical Journal Applied Physics, 2020
Heat transfer performance of microchannel are becoming an important area of research with the cur... more Heat transfer performance of microchannel are becoming an important area of research with the current fast growing scenario of high speed computing and miniaturized electronic devices. These devices pile up large amount of heat accompanied by smaller surface area to release it. The current work examines unsteady, laminar flow heat transfer inside a novel twisted sinusoidal wavy microchannel. The channel with square cross section is wavy in nature as well as twisted. The first half portion of the channel is twisted clockwise, whereas the twist in the remaining part is having counterclockwise twist. The novel geometry promotes mixing of fluid layers leading to transport augmentation. The inlet pulsation follows sinusoidal pattern in time. The thermal performance parameter of the proposed novel geometry was assessed within a Reynolds number range of 1–100. Both the pulsation amplitude and Strouhal number are varied during the course of this study. To solve the governing equations, a fi...
International Communications in Heat and Mass Transfer, 2020
Abstract In the present study, a numerical simulation is carried out to analyze the effect of tur... more Abstract In the present study, a numerical simulation is carried out to analyze the effect of turbulent intensity on the flow behavior of flow past two dimensional bluff bodies. Triangular prism, diamond and trapezoidal shaped bodies with the same hydraulic diameter D, a dimensionless length scale are taken into consideration as bluff bodies. The objective of the numerical analysis is to cover cross flow at both turbulent and laminar regime with varying Reynolds number upto 200,000 and inlet intensities ranging between 5% and 40%. The flow medium used is air at a constant Prandtl number. The energy, momentum and continuity equations are dealt with transition SST Model for closure of turbulence. The results obtained through numerical simulation are validated with other published results by researchers and show good agreements. This present study reveals that transition SST Model can be efficiently used to cover both laminar and turbulent flow regimes to estimate the heat transfer. The impact of inlet turbulent intensity on augmentation of heat transfer using bluff bodies has been evaluated. It is observed from the study that the turbulent intensity significantly affects drag coefficient.
The transport phenomena in microchannel are significant in designing MEMS devices. The current st... more The transport phenomena in microchannel are significant in designing MEMS devices. The current study investigates numerically the simultaneously developing unsteady laminar flow and heat transfer inside a twisted sinusoidal wavy microchannel. At the inlet sinusoidal varying velocity component is applied. Varying pulsating amplitude and frequency represented by the Strouhal number was studied for Reynolds numbers ranging from 1 to 100. The governing equations are solved with a finite volume based numerical method. In comparison with steady flow, it was found that imposed sinusoidal velocity at the inlet can provide improved heat transfer performance at different amplitudes and frequencies while keeping the pressure drop within acceptable limits.
Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
In this work, two parameters Weibull distribution method and Rayleigh distribution method have be... more In this work, two parameters Weibull distribution method and Rayleigh distribution method have been used to estimate the wind energy potential at Imphal, Manipur located in northeast India with the...
In the present paper, along with experimental study, CFD analysis of forced convection in a twist... more In the present paper, along with experimental study, CFD analysis of forced convection in a twisted tube is performed, using the transition SST model which can predict the change of flow regime from laminar through transition to turbulent. The differential governing equations are discretized by the finite volume method. The investigations are conducted for Reynolds numbers ranging from 100 to 50000 covering laminar, transitional and turbulent regimes, and for three length and three pitch ratios. The predictions are observed to show a good agreement with the measurements and published correlations of other authors. The analysis indicates that the large length ratio and small pitch ratio yields a higher heat transfer rate with relatively low performance penalty. The transition from laminar to turbulent regime is observed between Reynolds numbers of 2500 to 3500 for all cases. For almost all investigated cases the performance factors are greater than unity.
Computer Methods and Programs in Biomedicine, 2019
BACKGROUND AND OBJECTIVE Entropy generation is associated with the irreversibility of any thermod... more BACKGROUND AND OBJECTIVE Entropy generation is associated with the irreversibility of any thermodynamic system. It provides an indication of lost energy and hence the efficiency of a system. In this paper, an attempt has been made to study the effects of specific humidity, relative humidity, ambient temperature change, breathing air friction with the respiratory tract on the entropy generation during the respiration process at different physiological conditions. METHODS To address the above issues, a human respiratory tract model with realistic length to diameter ratio at different branches has been considered. The analysis examines air flow rates of 6 lpm and 60 lpm during rest and exercise condition respectively; corresponding to breathing rates of 30 and 60 per minute, respectively. The body temperature has been considered at 36°C, and ambient condition of air has been taken at 25°C DBT and 50% RH. The respiratory tract geometry has been modelled on the basis of Weibel's experimental results. RESULTS It has been noticed that, at a particular Lewis number entropy generation per day decreases with the increase in specific humidity, again at a particular specific humidity entropy generation increases with the decrease in Lewis number. For a particular physical condition and Lewis number entropy generation decreases with the increase in relative humidity. In this work, it has been observed that negentropy increases with the increase in ambient temperature for a constant relative humidity, however the net entropy generation is always positive. This study reports that, maximum resistance of flow occurs where duct aspect ratio (i.e. tract diameter to length) is minimal. For a typical geometry of air passage, velocity of flow increases up to 3rd generation then it is decreases gradually till 23rd generation. Amount of entropy generation goes on reducing as the duct goes on bifurcating except for the third generation where a local peak in entropy generation is observed. This is a consequence of typical geometry of human respiratory duct. This work reveals that, at rest entropy generation due to conditioning of breathing air is higher than its frictional component and during heavy physical activity, entropy generation due to breathing air friction with the respiratory tract is higher than its air conditioning component. CONCLUSIONS Entropy generation is significantly higher due to conditioning of breathing air than that of frictional effect with the tract. This is a preliminary attempt in quantifying this aspect and the authors believe that, these two components of entropy generation have a probable connection with the bronchial thermoplasty, which helps to treat the asthma.
Progress in Computational Fluid Dynamics, An International Journal, 2017
This paper encapsulates results of a numerical investigation on flow and heat transfer of an inco... more This paper encapsulates results of a numerical investigation on flow and heat transfer of an incompressible medium with constant properties through an isothermal circular tube with alternating inclined ribs. Simulations are conducted for laminar, transitional, and turbulent flow regimes. As turbulence model, the transitional shear stress transport model is employed. The problem is investigated for four rib angle of attack values, as well as for a plain tube without any ribs. All configurations are observed to lead to a thermal performance factor close to or greater than unity. Within the investigated range, the larger thermal performance factors are observed to occur for the intermediate Reynolds numbers. Maximum values in the range 2.0-2.5 are predicted for the Reynolds number of 2,000, where a subsequent drop to values within the range 1.0-1.5 are found to occur for Reynolds numbers around 3,000-4,000, which may be attributed to the transitional effects.
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