Browse Items (11808 total)
Sort by:
-
Study of the structural, optical, electrical and electrochemical properties of copper oxide thin films synthesized by spray pyrolysis
In our present study we focus on characterizing copper oxide (CuO) thin films synthesized at various substrate temperatures and to assess the electrochemical performance of the optimized sample. The spray pyrolysis method was used to fabricate CuO thin film samples, with the substrate temperatures ranging from 250 to 400C. The coatings underwent characterization through different analytical techniques, including X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman spectroscopy, and Hall effect measurements. All the thin film samples were confirmed to have a monoclinic phase. The presence of Cu=O was confirmed by Raman spectroscopy. All the samples exhibited P type conductivity except the one synthesized at 400C. Galvanostatic chargedischarge studies revealed a pseudocapacitive nature for the optimized sample synthesized at 350C. The symmetrical charging and discharging curves imply excellent material reversibility, indicating long-term cyclic stability. The Nyquist plot exhibited a semicircle at high frequencies, representing the materials intrinsic resistance and a linear behavior at low frequencies, depicting the ion transfer resistance. The electrode demonstrated favorable electrochemical properties and potential use of the material in supercapacitor applications. 2024, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature. -
Study of the personal factors influencing voluntary turnover amongst women
In a country where the economic and social independence of a woman is dependent on the way households are structured and organised, the rise in their education and decline in their workforce participation rate is an indication of their paradoxical situation. In this study we evaluate the direct effect of the factors in the personal domain of women on her career break decision. The data from 402 Indian women was analysed using Exploratory Factor Analysis and Confirmatory Factor Analysis, which was then followed by Structural Equation Modelling to check the conceptual model developed through literature review. In present study support personal predictors to turnover intention outcome model, confirming the influence of role conflict, role expectation, role perception, stress, financial soundness, role overload and guilt. Role perception and expectation of women were most significant factors influencing turnover intention of women, implying that the most important change needed is for a change in their own mindset and those around them to arrest their exit from the workforce. 2021 Ecological Society of India. All rights reserved. -
Study of the diffuse ultraviolet background radiation at high galactic latitudes
The diffuse background radiation is observed throughout the whole sky and across every wavelength of the electromagnetic spectrum. The study of this background is of great importance as it contains photons coming from a va- riety of astrophysical environments, traveling over the time scales of a few hundred light years to the age of the universe itself. After the discovery of the cosmic microwave background, the diffuse sky in all the other wave- lengths was studied with great interest as they could provide useful insights into the formation history of the universe. In the work outlined in this the- sis, I will be describing this diffuse background radiation observed in the ultraviolet (UV) region. Over more than three decades of observations of the diffuse sky in the UV has revealed our lack of understanding of all the components that con- tribute to the observed background sky in this wavelength region. Initial studies arrived at controversial conclusions with one group suggesting that most of the observed diffuse surface brightness is due to the dust scat- tered starlight while another group suggested contribution from an exotic component along with the dust scattered component. We will explore this background sky in detail by trying to identify individual components and quantify its contribution at various regions in the sky. We have started our analysis at the Galactic pole regions with |b| > 80 using the data from Galaxy Evolution Explorer (GALEX) in the ultravio- let band. A major Galactic component of the diffuse sky in the UV is the starlight scattered by interstellar dust (also called Diffuse Galactic Light: DGL). We chose to study the Galactic poles due to the low dust environ- ment in these regions and easier modeling of the DGL component. We found consistent offsets in the UV data at a level of 230 290 photons s?1 cm?2 sr?1 1 (hereafter photon units) in the far-UV (FUV: 1539 and 480 580 photon units in the near-UV (NUV: 2316 when the UV surface brightness was compared with Galactic tracers like E(B-V) and the infrared surface brightness. These offsets represent the UV brightness at zero column densities. Part of this offset comes from the extragalactic background light (EBL) originating in background galaxies, Quasi-Stellar Objects (QSOs), etc. After careful estimation of this EBL component, we found a residual UV surface brightness of about 120 180 photon units in the FUV and 300 400 photon units in the NUV. The DGL component came to be about 120 photon units in these regions. We also found evidence for contribution from molecular hydrogen fluorescence at a column density of log NH > 20.2 (NH is in cm?2). We conclude that this contribution from H2 is from the cirrus features present at high Galactic latitudes. We further confirmed our findings at the north and south Galactic poles by studying the region between latitudes 70< b < 80 where we found similar offsets and the fluorescence contribution from H2 at the same levels as in the NGP. We proposed a possible contribution to the observed residual surface brightness coming from Hawking evaporation of Primordial Black Holes. But the level of this radiation was not sufficient to account for the entirety of the observed excess. The failure of this explanation only further deepens the mystery of the source of the excess surface brightness of the UV sky. -
Study of the diffuse ultraviolet background radiation at high galactic latitudes
The diffuse background radiation is observed throughout the whole sky and across every wavelength of the electromagnetic spectrum. The study of this background is of great importance as it contains photons coming from a variety of astrophysical environments, traveling over the time scales of a few hundred light years to the age of the universe itself. After the discover of the cosmic microwave background, the diffuse sky in all the other wavelengths was studied with great interest as the could provide useful insights into the formation history of the universe. -
Study of the Balmer Decrements for Galactic Classical Be Stars Using the Himalayan Chandra Telescope of India
In a recent study, Banerjee et al. (2021) produced an atlas of all major emission lines found in a large sample of 115 Galactic field Be stars using the 2-m Himalayan Chandra Telescope (HCT) facility located at Ladakh, India. This paper presents our further exploration of these stars to estimate the electron density in their discs. Our study using Balmer decrement values indicate that their discs are generally optically thick in nature with electron density (ne) in their circumstellar envelopes (CEs) being in excess of 1013 cm-3 for around 65% of the stars. For another 19% stars, the average ne in their discs probably range between 1012 cm-3 and 1013 cm-3. We noticed that the nature of the H? and H? line profiles might not influence the observed Balmer decrement values (i.e. D34 and D54) of the sample of stars. Interestingly, we also found that around 50% of the Be stars displaying D34 greater than 2.7 are of earlier spectral types, i.e. within B0B3. 2024 Societe Royale des Sciences de Liege. All rights reserved. -
Study of Surface Waves Transmission in Orthotropic Bilateral Structure
This research work depicts the study of transmission of surface Rayleigh elastic waves in orthotropic layer having corrugated boundary resting over a pre-stressed orthotropic substrate. As a result, this study is made to spot the Rayleigh elastic wave transference under the consequence of initial stress in orthotropic material medium. Consequence of corrugation parameter, layer width parameter, initial stress parameter and density parameter on Rayleigh elastic wave propagation are marked separately. Distinguished parametric graphs are drawn following numerically the analytical study to exhibit the influence of distinct considered parameters on Rayleigh wave phase velocity of propagation. Frequency equations are obtained in closed determinant form under certain boundary conditions. Some particular cases have been deduced. Parametric results on the phase velocities yield a significant conclusion of which some are: (a) The corrugation parameter affects the more on phase velocity in comparison to initial stress (b) The orthotropic height stiffening can monotonically decrease the speed of phase. The present models may be applicable in engineering composites and for seismologist. 2023, The Author(s), under exclusive licence to Springer Nature India Private Limited. -
Study of surface wave velocity in distinct rheological models with flexoelectric effect in piezoelectric aluminium nitride structure
This study investigates the propagation of surface seismic waves at the loosely bonded interface of a visco-piezoelectric composite structure, incorporating the flexoelectric effect. The structure consists of a viscoelastic layer placed over a piezoelectric substrate, with the upper layer's shear stiffness modelled using the KelvinVoigt approach. An analytical method based on the separation of variables is employed to derive the complex dispersion relations for both electrically open- and short-circuit boundary conditions. Numerical simulations reveal the significant influence of various parameters on the wave's phase velocity and attenuation coefficient. Furthermore, a graphical comparison of three rheological modelsMaxwell, Newton, and KelvinVoigtis presented. The results show that the attenuation is lower in the Maxwell and Newton models compared to the KelvinVoigt model. Key findings include the bonding parameter's direct proportionality with phase velocity and inverse relationship with attenuation, and the pronounced impact of flexoelectricity on both phase velocity and attenuation. This theoretical framework offers insights into the piezo-flexoelectric coupling, with potential applications in designing sensors, actuators, energy harvesters, and nano-electronic devices. The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024. -
Study of suction and injection combination on the onset of double-diffusive convection in a micropolar fluid
The effect of suction and injection combination (SIC) on the onset of double-diffusive convection in a micropolar fluid is studied us- ing linear stability theory. The eigenvalue is obtained for free-free, rigid-free, rigid-rigid velocity boundary combinations with isother- mal or adiabatic on the spin-vanishing boundaries numerically using Galerkin Technique. The influence of various micropolar fluid param- eters on the onset of convection has been analyzed. It is found that by adjusting SIC it is possible to control the double-diffusive convection in a micropolar fluid. It is also observed that the effect of Prandtl number on the stability of the system is dependent on the SIC being pro-gravity or anti-gravity. -
Study of substitution effects on structure and properties of high temperature superconductors and isostructure compounds
The branch of physics which deals with the properties of solid materials and their constituent particles such as protons, neutrons and electrons is known as solid state physics. There are wide ranges of physical properties of solids. Some of the materials are very good conductors of heat and electricity whereas others are bad conductors. -
Study of substituion effectson structure and properties of high temperature superconductors and isostructure compounds
The thesis mainly describes the investigation of the structural formation of higher order members of bismuth system of superconductors Bi1.6sPb0.35Sr2CazCu4Oy (n = 4, 2234 phase), Bi1.6sPb0.35Sr2Ca4CusOy (n = 5, 2245 phase) and Bi1.65Pb0.35Sr2CasCu,Oy (n = 9, 2289 phase). The samples were synthesized by solid state reaction technique. Micro-structural and morphological features of the synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). The XRD pattern of all the samples revealed the presence of Bismuth 2212 and 2223 phases of which 2223 phase was found to be the predominant. Superconducting transition temperature (Tc) of the samples measured by self-inductance method and dc four probe method showed Tc value around 110 K. There was no signature of the formation of 2234, 2245 or 2289 phases in this investigation. newlineFormation of Bi-2245 compound was further investigated by preparing the sample in a new matrix route. The Tc on set of this sample was found to be 127 K which was the highest reported ever in bismuth system superconductors. The complete replacement of copper by nickel in bismuth system superconductor Bi2SraCu06 (2201) was ttempted by preparing the sample in air by solid state reaction method under open and closed environment. Morphological and microstructural features of the synthesized sample Bi2Sr2Ni0g was investigated by X-ray diffraction, SEM and EDAX. The analysis of X-ray diffraction pattern revealed that nickel can replace copper completely and form a single phase Bi2Sr2Ni06 only when prepared in a closed environment in air. This phase formation of BizSr2NiOo was reported first time. -
Study of stacking structure of amorphous carbon by X-ray diffraction technique
Random layered (graphene) structural parameters of the coals such as aromaticity fa, coal rank, number of carbon atoms per aromatic lamellae (n), lateral size La and stacking height Lc are determined using X-ray diffraction technique (XRD). It is found that the structural parameters like fa & Lc increases, where as interlayer spacing d002 decreases with increase in carbon content, aromaticity and coal rank. The number of layers and average number of carbon atoms per aromatic graphene are found to be varying from 7 to 8 and 16-21 for the coal samples with carbon content of 72- 77.4%. A good linear relationship exists between number of layers and stacking height of the aromatic lamellae in coal. 2012 by ESG. -
-
Study of single and two component convection in micropolar liquid /
In this thesis, we study linear and non-linear analysis of RayleighBénard and double diffusive convection in a micropolar liquid. The effect of non-uniform basic temperature gradient, non-uniform basic concentration gradient, temperature modulation at the boundary and gravity modulation are studied.
The problem investigated in this thesis through a light on externally controlled internal convection in a micropolar liquid. The problems investigated in this thesis have possible application in geophysics, astrophysics, oceanography engineering and in space situations with gjitter connected with gravity stimulation study. With this motivation, we investigate in this thesis four problems and their summary is given below one by one.
(i) EFFECT OF GRAVITY MODULATION ON HEAT
TRANSFER BY RAYLEIGH-BÉNARD CONVECTION IN A
MICROPOLAR LIQUID The vertical oscillation, or g-jitter or gravity modulation, is known to appear in the situation of the satellite. In the laboratory, Rayleigh-Bénard system subjected to time-periodic vertical oscillations may be useful in regulating the onset of convection and heat transfer. This aspect is also in
focus in the thesis. In this problem the effect of time-periodic body force or grtavity modulation on the onset of Rayleigh-Bénard convection in a micropolar liquid is investigated. The linear and non-linear analyses are performed. The linear theory is based on normal mode analysis and perturbation method. The expression for correction Rayleigh number is obtained as a function of frequency of modulation and other micropolar
liquid parameters. The non-linear analysis is based on the truncated Fourier series representation. The resulting non-autonomous Lorenzvii model is solved numerically to quantify the heat transport. It is observed that the gravity modulation leads to delayed convection and reduced heat transfer.
(ii) LINEAR AND WEAKLY NON- LINEAR STABILITY
ANALYSIS OF DOUBLE-DIFFUSIVE CONVECTION IN A
MICROPOLAR LIQUID The linear and non-linear stability analysis of double diffusive convection in a micropolar liquid layer heated and saluted below and cooled from above is studied. The linear and non-linear analyses are respectively based on normal mode technique and truncated
representation of Fourier series. The influence of various parameters on the onset of convection has been analyzed in the linear case. The resulting autonomous Lorenz model obtained in non-linear analysis is solved numerically to quantify the heat and mass transforms through Nusselt and Sherwood number. It is observed that the increase in coupling parameter, micropolar heat conduction parameter and solutal Rayleigh number
increases the heat and mass transfer. (iii) THE EFFECT OF NON - UNIFORM TEMPERATURE / CONCENTRTION DISTRIBUTION ON THE ONSET OF DOUBLE-DIFFUSIVE CONVECTION IN A MICROPOLAR LIQUID The effect of non-uniform temperature/concentration distribution on the onset of double diffusive convection in a micropolar liquid layer heated and soluted below and cooled from above between two parallel
plates of infinite extend separated by a thin layer is studied using linear stability analysis based on normal mode technique. The eigen value is obtained for free-free, rigid-free, rigid-rigid, velocity boundary conditions with isothermal temperature boundary conditions using Galerkian method. It is observed that by choosing the appropriate non-uniformviii temperature or concentration gradient it is possible to advance or delay
the onset of double diffusive convection. (iv) EFFECT OF TEMPERATURE MODULATION ON THE ONSET OF DOUBLE – DIFFUSIVE CONVECTION IN A MICROPOLAR LIQUID
The effect of temperature modulation on the onset of double-diffusive convection in a micropolar liquid is investigated by making a linear stability analysis. The stability of a horizontal layer of fluid heated from below is examined when, in addition to a steady temperature difference between the walls of the layer, a time-periodic sinusoidal perturbation is applied to the wall temperatures. The Venezian approach is adopted in arriving at the critical Rayleigh and wave numbers for small amplitude
temperature. -
Study of single and two component convection in micropolar liquid
In this thesis, we study linear and non-linear analysis of RayleighBard and double diffusive convection in a micropolar liquid. The effect of non-uniform basic temperature gradient, non-uniform basic concentration gradient, temperature modulation at the boundary and gravity modulation are studied. newlineThe problem investigated in this thesis through a light on externally controlled internal convection in a micropolar liquid. The problems investigated in this thesis have possible application in geophysics, newlineastrophysics, oceanography engineering and in space situations with gjitter connected with gravity stimulation study. With this motivation, we investigate in this thesis four problems and their summary is given below one by one. (i) EFFECT OF GRAVITY MODULATION ON HEAT TRANSFER BY RAYLEIGH-BARD CONVECTION IN A MICROPOLAR LIQUID newlineThe vertical oscillation, or g-jitter or gravity modulation, is known to appear in the situation of the satellite. In the laboratory, Rayleigh-Bard system subjected to time-periodic vertical oscillations may be useful in regulating the onset of convection and heat transfer. This aspect is also in newlinefocus in the thesis. In this problem the effect of time-periodic body force or grtavity modulation on the onset of Rayleigh-Bard convection in a micropolar liquid is investigated. The linear and non-linear analyses are performed. The linear theory is based on normal mode analysis and perturbation method. The expression for correction Rayleigh number is obtained as a function of frequency of modulation and other micropolar liquid parameters. The non-linear analysis is based on the truncated Fourier series representation. The resulting non-autonomous Lorenzvii model is solved numerically to quantify the heat transport. It is observed that the gravity modulation leads to delayed convection and reduced heat newlinetransfer. (ii) LINEAR AND WEAKLY NON- LINEAR STABILITY ANALYSIS OF DOUBLE-DIFFUSIVE CONVECTION IN A MICROPOLAR LIQUID. -
Study of rotating Bard-Brinkman convection of Newtonian liquids and nanoliquids in enclosures
Taylor-Bard convection of water and water-based nanoliquids confined in three different types of high porosity rectangular enclosures, viz., shallow, square and tall, is studied analytically using both infinitesimal and finite amplitude stability analyses. We make use of the modified-Buongiorno-Brinkman model(MBBM) for the governing equations concerning nanoliquid-saturated porous enclosures bounded by rigid-rigid boundaries and obtain analytical results. Among three types of enclosures, maximum and minimum heat transfers are observed in tall and shallow enclosures respectively. Water well dispersed with a dilute concentration of single-walled carbon nanotubes(SWCNTs) is considered as a working medium. The water-SWCNTs is able to flow in the porous medium because the medium is loosely-packed with porosity in the range 0.5 ? ? ? 1. In addition to this, the maximum volume fraction of nanoparticles considered in the system is 6% and thus this does not alter the fluidity of the system. We found from the study that the presence of low concentration(volume fraction-0.06) of SWCNTs in a water-saturated porous medium effectively improves the heat transport of the system due to its high thermal conductivity and large surface area. Due to the presence of a porous medium, however, the onset of convection gets delayed and heat transport in nanoliquids gets substantially reduced in a Bard-Brinkman configuration resulting from the weak thermal conductivity of the porous medium. Thus the porous medium acts as the heat storage system. Also, in a rotating frame of reference the heat transport gets reduced and rotation serves as an external mechanism of regulating heat transport in the system. The nonlinear dynamics of the system is studied using the 6-mode Lorenz model. Chaotic motion in the system is studied using the maximum Lyapunov exponent(MLE). The Hofp-bifurcation point of the system along with the MLE is used to investigate periodic, nearly periodic and mildly chaotic behaviors of the system. 2020 -
Study of Rayleigh-Benard Dynamical System Involving Newtonian and Nanofluids in Rectangular and Cylindrical Enclosures
Analyzing and#64258;uid and#64258;ow behavior in the presence of temperature gradients subjected to internal and external forces in diand#64256;erent geometries is essential for optimization newlineprocesses for various engineering applications, guiding the design of more efcient thermal systems. This thesis focuses on investigating the Rayleigh-Bard convection problems occupying rectangular and cylindrical enclosures. The linear and newlineweakly nonlinear analyses are carried out that reveal the results on regular convection, heat transport and chaotic motion for each of the problems. Steady and newlineunsteady states of the Rayleigh-Bard system are studied using the Lorenz model. The dynamical system is investigated to look for possible chaotic motion. Fluid systems can exhibit chaotic behavior, and understanding the chaotic nature of these and#64258;ows is essential for accurate predictions of their evolution over time. In view of this, the regular, chaotic, and periodic natures of the dynamical system is thoroughly analyzed. Further, the inand#64258;uence of various parameters on the indicators of chaos is explored. Additionally, the thermal performance of the system is looked into by introducing nanoparticles/nanotubes into the base and#64258;uid. newlineWith the aformentioned motivation, we now present the abstract of each of the problems considered in this thesis one-by-one. 1. Impact of boundary conditions on Rayleigh-Bard convection: stability, heat transfer and chaos In the frst problem of the thesis, discussed in Chapter 3, a comparison is made newlinebetween the results of Rayleigh-Bard convection problem for diand#64256;erent boundary combinations, namely, rigid-rigid-isothermal, rigid-free-isothermal and free-free isothermal boundaries for a Newtonian and#64258;uid. The linear and weakly-nonlinear analyses reveal that the onset of regular and chaotic motions in the case of rigid-freeisothermal boundaries happens later than that of free-free isothermal boundaries but earlier than rigid-rigid-isothermal boundaries.+ -
Study of Natural Convection with Local Thermal Non Equilibrium Effects in Nanoliquid-Saturated Low Porosity Enclosures
Natural convection of nanoliquid in densely packed vertical porous enclosure is studied by subjecting the vertical walls to constant heat flux under local thermal non-equilibrium (LTNE) assumptions. Water, copper nanoparticles and porous material made of aluminum foam, glass balls and sand are considered for the study. The governing equations are modelled using single-phase model. Thermophysical properties of nanoliquid and nanoliquid-saturated porous medium are calculated using phenomenological laws and mixture theory. An analytical expression for velocity and temperature profiles of nanoliquid (base liquid+nanoparticles) and solid (porous medium) phases has been obtained. Weighted average Nusselt number is expressed as a function of aspect ratio, volume fraction, and properties concerning LTNE effects. LTNE effect is shown to be a heat transfer enhancing mechanism. The presence of nanoparticles is to enhance the heat transfer in water. Local thermal equilibrium results are obtained as a limiting case of the present study and so obtained results are compared with previously published paper in the literature. 2022, The Author(s), under exclusive licence to Springer Nature India Private Limited. -
Study of Nanolayered Structure of Commercially Available Carbon Materials and Soot
Developments in the modern world periodically call for the discovery or invention of new and exotic materials. In the present situation, to develop unique and novel materials, which move beyond the barriers of the physical limits of the amount of micro- miniaturization possible as well as the current technology and take advantage of the opportunities not yet imagined, is not at all a need but a necessity. The advent of Nano technology of carbon allotropes is a giant leap towards this goal. The starting of the era of carbon nanomaterials traces back to 1985 when the fullerenes with a foot ball structure were accidently discovered. From then on, the field of carbon nanotechnology was in the constant limelight on account of the amazing properties displayed by the various allotropes of carbon. These properties are dependent mainly on the type of hybridization present in the nanostructures, which categorizes them to amorphous or crystalline. Also, there exist some structures which are the combination of these two and are termed as nanocrystalline or turbostratic structures. The discovery of graphene, which has a turbostratic structure and is the thinnest material known and the strongest ever measured, with outstanding properties such as highest room temperature electrical conductivity; high mechanical robustness etc was a ground breaking one. These remarkable properties open up a wide range of potential applications ranging from clean energy to nano-electronics to bio-medical devices. Thus, it is a necessity to explore and characterize various effective sources of these nanomaterials. The present study is an attempt to investigate such efficient, easily available and cost-effective precursors. Soot, also known as black carbon, is a fine-grained solid residue that results from incomplete combustion of hydrocarbons and is a widely used precursor for the production of carbon nanomaterials. Carbon soot is a major component of smoke from the combustion of carbon-rich organic fuels and hydrocarbons and hence has a vast number of sources. In the study presented here soot obtained from the thermal decomposition of commercially available kerosene, diesel oil, paraffin wax and lubricant oil is investigated. Nanostructure of the commercially available carbon black is also studied. Various techniques such as Micro Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), High Resolution Scanning Electron Microscopy (HR-SEM), Electron dispersive spectroscopy (EDS) and elemental analysis are employed for the structural and morphological characterization of the samples. Raman scattering is used as a probe to study the disorder in the carbon skeleton materials. The intensity ratio of the D and G modes occurring in the spectra is proportional to the number of rings at the edge of the grain and also indicates the quality of the sample. FT-IR spectroscopy is used to characterize qualitatively the functional groups of carbon materials. XRD is the most common analytical technique used for determining the structure of ordered and disordered carbons from the positions of the diffraction peaks at 2?? angle. The structural parameters like the size of the ordered grains along c and a axis (Lc and La), the average spacing of the crystallographic (002) planes (d002) can be determined through Scherrer equations. SEM micrographs give the surface morphology of the nanomaterials present and the EDS analysis gives the abundance of the microscopic constituents. Elemental composition of the samples can be derived from the elemental analysis using CHNS (Carbon Hydrogen Nitrogen Sulphur) analyser. The present study shows that all the samples investigated obeys the Tuinstra-Koening relation and posses a nanocrystalline structure. The ratio of the defect and graphite bands is found to be very low, especially in the case of diesel soot which has a value very much lower than those reported in the earlier studies, indicating high quality and a low amount of disorder in the samples. HR-SEM micrographs clearly indicate that the carbon nanostructured present in the samples are in the form of non-uniform nanospheres with diameter varying between 26-100 nm. The characteristic diffraction peak of graphene corresponding to (100) diffraction is observed in the x-ray diffraction profiles of all the samples. The interlayer spacing determined in all the samples lies very close to that of graphite. The H/C atomic ratio from the CHNS analysis is found to be very low and confirms the nanocrystalline structure of the materials. The graphite band position in the IR spectra indicates that the nanospheres formed are to be composed more of crystalline graphitic carbon. From the EDS analysis it is evident that all the samples have very high carbon content and are free from impurities and thus concludes that the materials and methods used in the present study for the synthesis of carbon nanospheres possessing a nanocrystalline structure are efficient and cost effective and are good precursors for graphene. -
Study of nanofluid flow in a stationary cone-disk system with temperature-dependent viscosity and thermal conductivity
The substantial temperature gradient experienced by systems operating at relatively high temperatures significantly impacts the transport characteristics of fluids. Hence, considering temperature-dependent fluid properties is critical for obtaining realistic prediction of fluid behavior and optimizing system performance. The current study focuses on the flow of nanofluids in a stationary cone-disk system (SCDS), taking into account temperature-dependent thermal conductivity and viscosity. The influence of Brownian motion, thermophoresis, and Rosseland radiative flux on the heat transport features are also examined. The Reynolds model for viscosity and Chiam's model for thermal conductivity are employed. The Navier-Stokes equation, the energy equation, the incompressibility condition, and the continuity equation for nanoparticles constitute the governing system. The Lie-group transformations lead the self-similar ordinary differential equations, which are then solved numerically. Multi-variate non-linear regression models for the rate of heat and mass transfers on the disk surface were developed. Our study reveals a notable decrease in the rate of heat and mass transfer when pre-swirl exists in the flow. The significant influence of nanofluid slip mechanisms on the effective temperature and nanofluid volume fraction (NVF) within the system is highlighted. Furthermore, the variable viscosity property enhances the temperature and NVF of the SCDS. 2024 Author(s). -
Study of nanofluid flow and heat transfer in a stationary cone-disk system
Rheometric, viscosimetric, bio-medical, and several other pharmaceutical machineries utilize the structural advantages provided by the geometry of a stationary conical diffuser. The problem of the Buongiorno nanofluid flow in the conical gap of a stationary cone-disk system for isothermal boundaries is studied. The governing system, comprising the incompressibility condition, NavierStokes equation, energy conservation equation, and conservation of Nanoparticle Volume Fraction (NVF) equation, is analyzed. The Lie-group theory has been used to derive a self-similar model. Solutions of the self-similar equations were computed numerically, and the expressions for the Nusselt number and Sherwood number are obtained. The parametric investigation reveals that the heat and mass transfer rate subside significantly when pre-swirl is introduced to the flow. Furthermore, the nanofluid slip mechanisms enhance the effective temperature of the system. 2023 Elsevier Ltd