Buoyant convective flow of different hybrid nanoliquids in a non-uniformly heated annulus

A sealed annular geometry containing nanoliquids with differently heated boundaries aptly describes the geometrical structure of many important cooling applications. The present study reports the numerical investigation on the effect of axially varying temperature in the form of sinusoidal thermal profiles along the side walls of an annular enclosure containing different hybrid nanoliquids with insulated horizontal boundaries. An implicit FDM based approach is adopted to solve the transient and steady-state model equations and numerical simulations are presented to describe the qualitative flow behavior as well as the quantitative thermal transport rates. The prime objective of the analysis is to enhance the buoyant flow circulation strength as well as the associated thermal dissipation rates and is achieved by identifying a suitable combination of nanoparticle along with a proper choice of geometrical parameters. Numerical predictions revealed the buoyant motion and thermal dissipation rate could be effectively controlled by a proper selection of phase deviation. Further, the appropriate combination of nanoparticles is another crucial parameter in enhancing the thermal transport in the geometry

MHD convective flow of Ag-TiO2 hybrid nanofluid in an inclined porous annulus with internal heat generation

The current article deals with the computational study of buoyant convection and heat dissipation processes of hybrid nanoliquid saturated in an inclined porous annulus. The fluid flow movement in the porous annular region is modeled using Darcy???Brinkman???Forchheimer model. The vertical boundaries of the cylinder are subjected to uniform but different heating profiles and horizontal surfaces are maintained adiabatic. In the current investigation, for the conservation laws which govern the considered physical process, numerical simulations have been performed using the time-splitting ADI (Alternating Direction Implicit) and line over-relaxation methods. Computations have been performed for broad range of physical and geometric parameters, such as Hartmann number (), geometric inclination angle (), Darcy number (), aspect ratio () and internal heat generation () to address their impacts on hybrid nanofluid movement and associated heat dissipation rate in the annulus. In addition, heat transfer rate has also been estimated by considering the impact of concentration of each nanoparticle present in the hybrid nanofluid pair. The outcome of numerical computations reveal that an increment in Darcy number enhances the average Nusselt number. Additionally, it has been noticed that the geometric tilt angle of 30?? results in dissipating maximum amount of thermal energy in the system. Through this investigation, it is also noticed that shallow annular enclosure exhibits greater amount of heat transport compared to other aspect ratios. Also, significant impact of magnetic field on fluid flow and thermal transport rate has been noticed from the detailed numerical simulations. Further, an enhancement in internal heat generation deteriorates the heat transfer rate and this reduction becomes more steep as the internal heat generation increases

Reactivity of allenylphosphonates toward salicylaldehydes and activated phenols: facile synthesis of chromenes and substituted butadienes

The reaction of salicylaldehydes with allenylphosphonates in the presence of a base leads to a variety of phosphono-chromenes and allylic phosphonates. Optimization of reaction conditions reveals that DBU (base) in DMSO (solvent) is the best combination in most cases, with DBU acting as an organocatalyst. PEG-400 also gave good results, but the yields were slightly lower than that in DMSO. Several of the key products have been characterized by single-crystal X-ray crystallography. Interconversion of E and Z isomers of phosphono-chromenes is demonstrated by 31P NMR spectroscopy. A novel P-C bond cleavage reaction of some of these chromenes leading to substituted enones is also reported. In a few cases, phenol addition products are also isolated. In order to probe the pathways in the latter reaction, allenylphosphonates have also been treated with activated phenols in the presence of base to selectively afford either allylic phosphonyl ethers or vinylic phosphonyl ethers depending on the substituents on the allenylphosphonate. Theoretical calculations were consistent with experimental results. Finally, utilization of allylic phosphonyl ether in the Horner-Wadsworth-Emmons reaction to afford substituted trans-1,3-butadiene in good yields is demonstrated

Optimization of entropy generation and thermal mechanism of MHD hybrid nanoliquid flow in a sinusoidally heated porous cylindrical chamber

The present computational investigation explores the fluid and thermal characteristics along with entropy generation due to buoyancy-driven magnetohydrodynamic (MHD) convective flow of aqueous hybrid nanoliquid filled in a nonuniformly heated porous cylindrical chamber. The fluid motion in the enclosure is modeled by Brinkman - extended Darcy model. The modeled equations are resolved by finite difference approach. The computations are conducted for Rayleigh number (103-105), Hartmann number (0-50), Darcy number (10-5-10-1), different nanoparticle shapes and nanoparticle volume fraction (Ag/MgO: 0-0.05) to understand the characteristic of flow, thermal and irreversibility distribution. With vast numerical simulations, the outcomes reveal that though the buoyancy force is greater, the fluidity cannot be enhanced unless the permeability and magnetic field strength are optimally maintained. As Ra, Ha and Da is varied respectively from 103 to 105, 50 to 0 and 10-5 to 10-1, the fluidity has been enhanced by 99.39%, 83.26% and 99.79%. Among all considered parametric combinations, it has been noticed that the choice of Ha = 0, Ra = 105, Da = 10-1 with proper ratio of nanoparticles enhance the system efficiency. However, minimal entropy generation can be achieved with greater Hartmann and lower Darcy numbers. Furthermore, it has been found that blade shaped nanoparticles lead to increase the performance of thermal system

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

A range of phosphinoylindoles was prepared in one-pot from functionalized propargyl alcohols and a suitable P(III) precursor via a base-mediated reaction. The reaction proceeds via the intermediacy of allenylphosphine oxides. Similarly, phosphinoylisocoumarins were prepared from allenylphosphine oxides in a trifluoroacetic acid-mediated reaction; the latter also acts as a solvent. Interestingly, in the presence of wet trifluoroacetic acid, in addition to phosphinoylisocoumarins, phosphorus-free isocoumarins were also obtained. Key products were characterized by single crystal X-ray crystallography

Double diffusive convective transport and entropy generation in an annular space filled with alumina-water nanoliquid

Many of the engineering/industrial applications involving the energy transport undergoes entropy generation which is unavoidable and this leads to degradation of system efficiency. Several researchers working in this field are exploring new ways to minimize the entropy generation so that the efficiency of the system could be enhanced. Motivated by these applications, the current article scrutinizes the rate of entropy generation along with thermal and solutal transport resulting from double-diffusive convective phenomenon in a nanoliquid-filled annular enclosure. Along vertical surfaces of the annulus, the uniform temperature and concentration conditions are specified, while the upper and lower boundaries are maintained as insulated and impermeable. The set of non-linear coupled governing equations in vorticity-stream function form supported by related initial and boundary conditions are computed numerically using time-splitting technique. The influence of various controlling parameters namely the buoyancy ratio (-5 <= N <= 5), Lewis number (0.5 <= Le <= 2), aspect ratio (0.5 <= Ar <= 2) and nanoparticle volume fraction (0 <= phi <= 0.05) on fluid movement, temperature, concentration and entropy production are scrutinized and variation in thermal and solutal dissipation rates, entropy production and Bejan number are graphically illustrated and are discussed with physical interpretation. Through the vast range of computational experiments, it has been found that the quantity of generated entropy in an enclosure is greater during aided flow compared tot hat of opposing case. Further, it has also been found that higher thermal and solutal performance rates with minimal loss of system energy (entropy generation) could be achieved with a shallow annulus

Double diffusive convective transport and entropy generation in an annular space filled with alumina-water nanoliquid

Many of the engineering/industrial applications involving the energy transport undergoes entropy generation which is unavoidable and this leads to degradation of system efficiency. Several researchers working in this field are exploring new ways to minimize the entropy generation so that the efficiency of the system could be enhanced. Motivated by these applications, the current article scrutinizes the rate of entropy generation along with thermal and solutal transport resulting from double-diffusive convective phenomenon in a nanoliquid-filled annular enclosure. Along vertical surfaces of the annulus, the uniform temperature and concentration conditions are specified, while the upper and lower boundaries are maintained as insulated and impermeable. The set of non-linear coupled governing equations in vorticity-stream function form supported by related initial and boundary conditions are computed numerically using time-splitting technique. The influence of various controlling parameters namely the buoyancy ratio ($$-5 \le N \le 5$$), Lewis number ($$0.5\le {Le} \le 2$$), aspect ratio ($$0.5\le {Ar} \le 2$$) and nanoparticle volume fraction ($$0\le \phi \le 0.05$$) on fluid movement, temperature, concentration and entropy production are scrutinized and variation in thermal and solutal dissipation rates, entropy production and Bejan number are graphically illustrated and are discussed with physical interpretation. Through the vast range of computational experiments, it has been found that the quantity of generated entropy in an enclosure is greater during aided flow compared to that of opposing case. Further, it has also been found that higher thermal and solutal performance rates with minimal loss of system energy (entropy generation) could be achieved with a shallow annulus