Papers by Dr. Virendra Kumar
9 September, 2022
Natural fibres have recently emerged as a pool of organic compounds that for different applicatio... more Natural fibres have recently emerged as a pool of organic compounds that for different applications. Among
several natural products, the fibres of Bombax ceiba contain several naphthalene‐based compounds. Hence,
Bombax ceiba may exhibit the potential of adsorbing a variety of pollutants. In this study, the adsorption of
arsenite (As(III)) and arsenate (As(V)), from the aqueous stream was investigated using density functional theory (DFT) calculations. 1,4‐Naphthaquinone, 1‐Naphthyl ether, Hemigossypol, and Naphthol were chosen as
adsorbent molecules for As(III) and As(V) ions as they form the major portion of the Bombax ceiba fibres.
CAM‐B3LYP/6‐311G level of DFT theory was used to calculate electrostatic potential maps, HOMO‐LUMO distributions, chemical potential, and hardness to gain quantitative information on the interactions. The adsorption energies and recovery time were calculated based on the thermodynamic feasibility of the interactions of
As(III) and As(V) ions with Bombax ceiba fibres. The results showed that As(III) and As(V) ions adsorbed physically on the Bombax ceiba fibres. The results can be used to further modify naturally occurring Bombax ceiba
fibres to develop sustainable solutions.
In this investigation, the extensive wear behaviour of materials was studied using SiC reinforced... more In this investigation, the extensive wear behaviour of materials was studied using SiC reinforced magnesium alloy composites fabricated through the stir casting process. The wear properties of AZ91 alloy composites with a small variation (i.e., 3%, 6%, 9% and 12%) of SiC particulates were evaluated by varying the normal load with sliding velocity and sliding distance. The worn surfaces were examined by scanning electron microscope to predict the different wear mechanisms on the pin while sliding on the hard disk in the dry sliding wear test condition. The microhardness of the SiC reinforced AZ91 composites was found to be more than the un-reinforced AZ91 alloy. Pins tested at load 19.62 N, and 2.6 m/s exhibited a series of short cracks nearly perpendicular to the sliding direction. At higher speed and load, the oxidation and delamination were observed to be fully converted into adhesion wear. Abrasion, oxidation, and delamination wear mechanisms were generally dominant in lower sliding velocity and lower load region, while adhesion and thermal softening/melting were dominant in higher sliding velocity and loads. The wear rate and coefficient of friction of the SiC reinforced composites were lower than that of the unreinforced alloy. This is due to the fact of higher hardness exhibited by the composites. The wear behaviour at the velocity of 1.39 m/s was dominated by oxidation and delamination wear, whereas at the velocity of 2.6 m/s the wear behaviour was dominated by abrasion and adhesion wear. It was also found that the plastic deformation and smearing occurred at higher load and sliding velocity.
In this work, aluminium alloy ADC12 reinforced with various amounts of ZrB 2 (0 wt.%, 3 wt.%, 6 w... more In this work, aluminium alloy ADC12 reinforced with various amounts of ZrB 2 (0 wt.%, 3 wt.%, 6 wt.%, 9 wt.%) were synthesized by an in-situ reaction of molten aluminium with inorganic salts K 2 ZrF 6 & KBF 4. XRD, EDAX, and SEM techniques are used for the characterization of the fabricated composite. XRD analysis revealed the successful in situ formation of ZrB 2 in the composite. From the SEM images, it was concluded that the distribution of reinforcement was homogeneous in the composites. A study of mechanical and tribological properties under the dry sliding condition of ZrB 2 -reinforced ADC12 alloy has also been carried out. It is seen that there is an increase in tensile strength by 18.8%, hardness by 64.2%, and an increase in wear resistance of the material after reinforcement. The ductility of the material decreased considerably with an increase in the amount of reinforcement. The composite's impact strength decreased by 27.7% because of the addition of hard ZrB 2 particulates.
By introducing constant rate of momentum change approach for real fluid ejector design, the cruci... more By introducing constant rate of momentum change approach for real fluid ejector design, the crucial geometrical parameters such as nozzle exit position, mixing, and diffuser section lengths are optimized. With the numerical validation of the proposed model, the effect of geometrical parameters on the entrainment ratio is independently studied for water vapor at on-design conditions. It is observed that the geometrical parameters strongly affect the performance of the ejector. Adjusting the nozzle exit positions (NXP) in the upstream direction (upto − 4 mm) from its on-design (NXP = 0) helps in higher secondary flow entrainment. The optimum nozzle exit position is − 4 mm, with a maximum entrainment ratio of 0.593 compared to on-design 0.354. The optimal mixing and diffuser section lengths of the ejector are 95 mm and 250 mm, respectively. The optimal mixing and diffuser lengths are the on-design lengths, which have an entrainment ratio of 0.354. Keywords Nozzle exit position • Ejector geometry • CRMC • Jet pump • Entrainment ratio List of symbols Symbols Ω Area (m 2) L Length (m) α CRMC constanṫ M Momentum of stream (kg m/s) M Mach number (−) m Mass flow rate (kg/s) φ Entrainment ratio C Velocity (m/s) w Molecular weight a, b Constant (Redlich Kwong) γ Specific heat ratio (-) R Individual gas constant (J/kg K) C p Specific heat at constant pressure (J/kg k) G k Generation of turbulent kinetic energy μ t Turbulent viscosity G ω Generation of dissipation D Cross diffusion term ω Dissipation rate ∝ 1, ∝ 2 Sutherland constant Subscripts n Nozzle m Mixing d Diffuser p Primary flow s Secondary flow o Stagnation condition e Exit i, j, k Space component * S. K. Yadav
The present study proposes variety ofnovel composites fabricated from Rambans (Agave) fibers and ... more The present study proposes variety ofnovel composites fabricated from Rambans (Agave) fibers and recognizes its physical and mechanical behavior by varying its proportion in the fiber-reinforced polyester resin composite. The physical and mechanical properties of composites are determined . The mechanical properties (hardness, tensile, flexural and impact-resistant) and the scanning electron microscopy for fractured surfaces were analyzed to further characterize the composite surfaces. The maximum tensile strength of the composite is found to be 95.27 MPa with 4.7 Jm -2 impact strength. It is concluded that the above composite composition leads to better mechanical properties, which can be used in many applications in place of conventional natural fibers.
In recent times, demand for light weight and high strength materials fabricated from natural fibr... more In recent times, demand for light weight and high strength materials fabricated from natural fibres has increased tremendously. The use of natural fibres has rapidly increased due to their high availability, low density, and renewable capability over synthetic fibre. Natural leaf fibres are easy to extract from the plant (retting process is easy), which offers high stiffness, less energy consumption, less health risk, environment friendly, and better insulation property than the synthetic fibre-based composite. Natural leaf fibre composites have low machining wear with low cost and excellent performance in engineering applications, and hence established as superior reinforcing materials compared to other plant fibres. In this review, the physical and mechanical properties of different natural leaf fibre-based composites are addressed. The influences of fibre loading and fibre length on mechanical properties are discussed for different matrices-based composite materials. The surface modifications of natural fibre also play a crucial role in improving physical and mechanical properties regarding composite materials due to improved fibre/matrix adhesion. Additionally, the present review also deals with the effect of silane-treated leaf fibre-reinforced thermoset composite, which play an important role in enhancing the mechanical and physical properties of the composites.
The two-stage ejector has been suggested to replace the single-stage ejector geometrical configur... more The two-stage ejector has been suggested to replace the single-stage ejector geometrical configuration better to utilize the discharge flow's redundant momentum to induce secondary flow. In this study, the one-dimensional gas dynamic constant rate of momentum change theory has been utilized to model a two-stage ejector along with a single-stage ejector. The proposed theory has been utilized in the computation of geometry and flow parameters of both the ejectors. The commercial computational fluid dynamics tool ANSYS-Fluent 14.0 has been utilized to predict performance and visualize the flow. The performance in terms of entrainment ratio has been compared under on-design and off-design conditions. The result shows that the two-stage ejector configuration has improved (≈57%) entrainment capacity than the singlestage ejector under the on-design condition. Computational fluid dynamics, constant rate of momentum change, ejector, entrainment ratio, two stage Date
Acta Metallurgica et Materialia, 1995
ABSTRACT
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Optical Engineering, 1990
Energy, 2018
Ejectors invariably convert momentum and kinetic energy of incoming fluids into enthalpy and henc... more Ejectors invariably convert momentum and kinetic energy of incoming fluids into enthalpy and hence pressure. Since ejectors are primarily viewed as energy exchange devices, it would be appropriate to design an ejector with its geometry being a function of the rate of energy change. This would shift ejector design approach from conventional geometry based one to that of flow physics-based approach. Hence, the paper presents a unique approach to evolving ejector design considering it primarily to be a function energy change within the system, specifically being constant rate of kinetic energy change (CRKEC). This approach has benefits in terms of mitigating the occurrence of thermodynamic shock, which is a major irreversibility that besets conventional ejector systems. A 1-D gas dynamic model including frictional effects for a more realistic design has been developed for estimating supersonic ejector geometry based on CRKEC approach. The model has been used to predict the geometry of a supersonic air ejector for typical input parameters viz., entrainment ratio (u) ~0.53, recovery ratio(z) ~1.4, primary stagnation pressure(P op) ~5.7 bar, secondary stagnation pressure(P os) ~0.7 bar. The results have been verified through detailed numerical analysis using Navier-Stokes system of equations with turbulence in a 2-D axi-symmetric formulation. Also, the experimental results on the developed prototype, which have also been discussed, are observed to be in close agreement with predictions of 1-D gas dynamic model and the numerical studies.
Springer Nature, 2018
The development of the welding process has provided an alternative improved way of satisfactorily... more The development of the welding process has provided an alternative improved way of satisfactorily producing aluminium joints, in a faster and reliable manner. The aim of the present work is focused on the comparative study on the mechanical and dry sliding wear (tribological property) behaviour of welding joint fabricated by friction stir welding (FSW), tungsten inert gas (TIG) and metal inert gas (MIG) on 6 mm thick aluminium alloy 7075 T6. The samples were fabricated, and their testing was carried out as per the ASTM standards. The maximum tensile strength (242.3 MPa) and impact strength (12 J) and join efficiency (44%) were obtained for FSW joints, whereas these properties for TIG and MIG welded joints were on the lower side. The elongation at the break was found to be higher for FSW joint as compared to that of TIG and MIG joints. The minimum specific wear rate was obtained for FSW joint as compared to that of TIG and MIG joints. Microstructure results show that the smaller grain sizes were obtained in the weld centre of FSW, whereas grain growth was observed in TIG and MIG welds. FSW joints were better than TIG and MIG joints.
Elsevier, 2018
Ejectors invariably convert momentum and kinetic energy of incoming fluids into enthalpy and henc... more Ejectors invariably convert momentum and kinetic energy of incoming fluids into enthalpy and hence pressure. Since ejectors are primarily viewed as energy exchange devices, it would be appropriate to design an ejector with its geometry being a function of the rate of energy change. This would shift ejector design approach from conventional geometry based one to that of flow physics-based approach. Hence, the paper presents a unique approach to evolving ejector design considering it primarily to be a function energy change within the system, specifically being constant rate of kinetic energy change (CRKEC). This approach has benefits in terms of mitigating the occurrence of thermodynamic shock, which is a major irreversibility that besets conventional ejector systems. A 1-D gas dynamic model including frictional effects for a more realistic design has been developed for estimating supersonic ejector geometry based on CRKEC approach. The model has been used to predict the geometry of a supersonic air ejector for typical input parameters viz., entrainment ratio (ω) ∼0.53, recovery ratio(ζ) ∼1.4, primary stagnation pressure(Pop) ∼5.7 bar, secondary stagnation pressure(Pos) ∼0.7 bar. The results have been verified through detailed numerical analysis using Navier-Stokes system of equations with turbulence in a 2-D axi-symmetric formulation. Also, the experimental results on the developed prototype, which have also been discussed, are observed to be in close agreement with predictions of 1-D gas dynamic model and the numerical studies.
In this work, the performance study of an automobile radiator using nanofluid in comparison with ... more In this work, the performance study of an automobile radiator using nanofluid in comparison with distilled water as coolant in the heat exchanger-based radiator is evaluated. The distilled water and nanofluid are flown through the radiator consisting of upright tubes with an elliptical-shaped cross section. Forced air is passed through the radiator perpendicular to the direction of fluid flow in tubes. The experiments are performed with three different volumetric concentrations of nanofluid (Al 2 O 3 -water), with different flow rates, air flow velocities, and fluid inlet temperatures. The results obtained from this study demonstrate that an increase in fluid flow rate and air flow rate improves the heat transfer performance. It was found that an enhancement in heat transfer rate was found to be the maximum up to 44.29% at 0.2% volume fraction of alumina-distilled water-based nanofluid in comparison with distilled water. The effectiveness of radiator was found maximum up to 40.3% at 0.2% volume fraction of alumina-distilled water based nanofluid at 40 LPH.
Tung (Aleurites Fordii) is cultivated in China, Argentina, Paraguay, Africa, India, and United St... more Tung (Aleurites Fordii) is cultivated in China, Argentina, Paraguay, Africa, India, and United States. Tung oil has various applications like as a drying agent for paints and varnishes, termite control as well as cleaning and polishing compounds. The Tung shell and de-oiled cake are residues after decortications of the Tung seeds. This paper has been aimed for thermal degradation and gasification of Tung shells. Thermal degradation of the Tung shell was carried out at heating rates of 10, 15, and 20°C/min from room temperature to 750°C under nonisothermal conditions, and N 2 was used as a carrier gas. Based on the thermogravimetric analysis and differential thermogravimetric analysis results, it was found that Tung shells have low thermal stability. These shells were gasified in the downdraft wood gasifier. The calorific value of producer gas was calculated to be 4.75 MJ/Nm 3 . The conversion efficiency of the gasifier for Tung shells was higher (93 %) as compared to the wood (84 %). The producer gas generated from shells could be used for heat and or power generation for rural areas. Also a solution to reduce the disposal problem of toxic Tung shells generated from oil expellers.
IJESD, 2010
The variations in mean velocity profiles of the x component along x-axis of the four jets at the ... more The variations in mean velocity profiles of the x component along x-axis of the four jets at the designed Mach number is discussed in this research paper. It is found that the velocity profiles are fairly symmetrical about y=0. The velocities and its gradients decay along x-axis. Due to the effect of entrainment in the shear layer, the velocity between four jets increases with x-axis. It observed that the dynamic pressure inside the nozzle, just before the exit of the jet is maximum where the velocity of flow is maximum while in space between two nozzles is less and near the nozzle wall the static pressure is maximum. The static pressure inside the nozzle is minimum. It decreases with velocity increase, while static pressure is more in the space between the two jets in compression to flow domain. The jet is designed for streamline flow and hence the intensity of turbulence is less inside nozzle as compared to atmosphere. The turbulence intensity has value of 3.43x10 3 (%) at nozzle exit. This is because of the eddy creation and reversal of flow at the base region of circular duct. Further downstream, as flow gets agitated and the turbulence intensity increases. A maximum of 6.78x10 3 (%) is attained and beyond which the turbulent intensity goes on decreasing steadily.
IJCEA, 2010
The variations in mean velocity profiles of the x component along x-axis of the twin jets at the ... more The variations in mean velocity profiles of the x component along x-axis of the twin jets at the designed Mach number is discussed in this research paper. The variations in mean velocity profiles of the x component along x-axis of the twin jets at B=9 and M e 1.74 are discussed, where maximum velocity 5.97x10 2 at the exit of the jet. It is found that the velocity profiles are fairly symmetrical about y=0. The velocities and its gradients decay along x-axis. Due to the effect of entrainment in the shear layer, the velocity between two jets increases with x-axis. At the same time, the width of twin jets was found to increase. It observed that the static pressure inside the nozzle is minimum where the velocity of flow is maximum while in gap between two nozzles and near the nozzle wall the static pressure is maximum. The dynamic pressure increases with increase of velocity, the dynamic pressure is maximum just before the exit of jet i.e., 2.30x10 5 Pa. The jet is designed for streamline flow and hence the intensity of turbulence is less inside nozzle as compared to flow regime. The turbulence intensity has high value of 2.37x10 3 (%) at nozzle exit. This is because of the eddy creation and reversal of flow at the base region of circular duct. Further downstream, as flow gets agitated and the turbulence intensity increases. A maximum of 7.7x10 3 (%) is attained and beyond which the turbulent intensity steadily decreases. While the turbulence of kinetic energy range 1 to 8.9x10 3 m²/s². Index Terms-four jet, Mach number, De Laval nozzle, turbulence intensity, flow reversal.
─ Supersonic flows associated with missiles, aircraft, missile engine intake and rocket nozzles a... more ─ Supersonic flows associated with missiles, aircraft, missile engine intake and rocket nozzles are often steady. The shape of the nozzle geometry is increasingly attractive in heating, ventilation and air conditioning applications. The objective of the present work is to simulate and understand Supersonic flows with twin free jet Flow at various Mach numbers. The purpose is to precisely understand the fluid dynamics and variation of flow properties such as velocity, pressure and turbulence in supersonic flow regime for various Mach numbers (1.74, 2, and 3), pressure ratio and dimensionless spacing (B) between two jets. Twin jets flow, generated by two identical parallel axisymmetric nozzles, has been numerically investigated by FLUENT software. The Mach number at the nozzle exit is observed to be less in comparison with designed value. This is due to the viscosity and turbulence in fluid near the wall of the duct. The Mach number decreases due to shock wave and reversible flow. The results show that the twin jets attract each other. The jet flow field and the merging process of two jets vary with dimension less spacing between two jets. The width of the twin jet's flow spreads linearly downstream and grows with dimension less spacing. The merging between two jets occurs at the location closer to the nozzle exit for the cases with smaller spacing between nozzles.
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Papers by Dr. Virendra Kumar
several natural products, the fibres of Bombax ceiba contain several naphthalene‐based compounds. Hence,
Bombax ceiba may exhibit the potential of adsorbing a variety of pollutants. In this study, the adsorption of
arsenite (As(III)) and arsenate (As(V)), from the aqueous stream was investigated using density functional theory (DFT) calculations. 1,4‐Naphthaquinone, 1‐Naphthyl ether, Hemigossypol, and Naphthol were chosen as
adsorbent molecules for As(III) and As(V) ions as they form the major portion of the Bombax ceiba fibres.
CAM‐B3LYP/6‐311G level of DFT theory was used to calculate electrostatic potential maps, HOMO‐LUMO distributions, chemical potential, and hardness to gain quantitative information on the interactions. The adsorption energies and recovery time were calculated based on the thermodynamic feasibility of the interactions of
As(III) and As(V) ions with Bombax ceiba fibres. The results showed that As(III) and As(V) ions adsorbed physically on the Bombax ceiba fibres. The results can be used to further modify naturally occurring Bombax ceiba
fibres to develop sustainable solutions.
several natural products, the fibres of Bombax ceiba contain several naphthalene‐based compounds. Hence,
Bombax ceiba may exhibit the potential of adsorbing a variety of pollutants. In this study, the adsorption of
arsenite (As(III)) and arsenate (As(V)), from the aqueous stream was investigated using density functional theory (DFT) calculations. 1,4‐Naphthaquinone, 1‐Naphthyl ether, Hemigossypol, and Naphthol were chosen as
adsorbent molecules for As(III) and As(V) ions as they form the major portion of the Bombax ceiba fibres.
CAM‐B3LYP/6‐311G level of DFT theory was used to calculate electrostatic potential maps, HOMO‐LUMO distributions, chemical potential, and hardness to gain quantitative information on the interactions. The adsorption energies and recovery time were calculated based on the thermodynamic feasibility of the interactions of
As(III) and As(V) ions with Bombax ceiba fibres. The results showed that As(III) and As(V) ions adsorbed physically on the Bombax ceiba fibres. The results can be used to further modify naturally occurring Bombax ceiba
fibres to develop sustainable solutions.