Anoop K. Gupta

Cd(II) coordination polymers constructed with a flexible carboxylate linker and pyridyl co-linkers: variation in the network topologies and photoluminescence properties

Six new coordination polymers (CPs) of Cd(II), {[Cd3(L)2(H2O)5(μ-H2O)]·6H2O}n (1), {[Cd3(L)2(4,4′-bpy)3(H2O)2]·4(H2O)·(DEF)}n (2), {[Cd(HL)(dpe)0.5(H2O)]2·(H2O)}n (3), {[Cd(HL)(dpd)0.5(H2O)]}n (4), {[Cd(HL)(1,2-dpe)0.5]}n (5), and {[Cd3(L)2(1,3-dpp)2]·3H2O}n (6) (where H3L = 5-(2-carboxybenzyloxy)isophthalic acid, 1,3-dpp = 1,3-di(4-pyridyl)propane, 1,2-dpe = 1,2-di(4-pyridyl)ethane, dpd = 1,2-di(pyridin-4-yl)diazene, dpe = 1,2-di(4 pyridyl)ethylene, and 4,4′-bpy = 4,4′-bipyridyl), were synthesized under solvothermal/hydrothermal conditions and structurally characterized via elemental analysis, IR spectroscopy, and single-crystal and powder X-ray diffraction. Compound 1 displays infinite 2D sheets, which stack upon each other to form a supramolecular 3D network. Topologically, the network can be viewed as a 3,3,3,5-connected four nodal net, which was assigned to a novel topological type, pkb9. Compound 2 shows a 3D assembly with the 3,4,6-connected topology sqc130. Compound 3 and 4 form interdigitated 3D supramolecular networks with a 4-connected sql/Shubnikov topology. Compound 5 shows an unusual 2D → 3D framework with a 3,8-connected tfz-d; UO3 topology. In compound 6, 2D → 3D packing was observed due to weak C–H⋯O interactions that aided in the formation of a 3D network with a 4-connected sql/Shubnikov topology. The luminescence properties of all the compounds in their solid state and as emulsions in various solvents were investigated using nitroaromatic compounds.

Mixed convection from a spheroid in Bingham plastic fluids: Effect of buoyancy-assisted flow

ABSTRACT In this work, laminar mixed convection from an isothermal spheroidal particle immersed in a Bingham plastic fluid is studied numerically in the buoyancy-assisted regime. The results reported herein encompass the following ranges of conditions: Reynolds number, 0.1 ≤ Re ≤ 100; Prandtl number, 10 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 100; Richardson number, 0 ≤ Ri ≤ 8; and aspect ratio of the spheroid, 0.2 ≤ e ≤ 5. In particular, consideration is given to the effect of shape and orientation of the particle on the detailed flow and temperature fields (in terms of streamlines, iso-vorticity, and isotherm contours), morphology of the yielded–unyielded regions, and the local and surface-averaged Nusselt number. All else being equal, the propensity for flow separation is seen to be greater for oblates (e < 1) than that for prolates (e > 1). In both cases, this reduces with the increasing Bingham number and/or the Richardson number. Both drag coefficient and the Nusselt number show a positive dependence on the Bingham number as well as on the Richardson number. Overall, the drag coefficient increases as the particle shape changes from an oblate to prolate, whereas the reverse trend is obtained for the average Nusselt number, which is in line with the general inference that more drag corresponds to more heat transfer. Finally, the average Nusselt number is correlated with the pertinent dimensionless parameters (Re, Pr, Bn, Ri, e) via a simple correlation, thereby enabling its prediction for intermediate values of the parameters and/or in a new application.

Effect of confinement on forced convection from a heated sphere in Bingham plastic fluids

In this work, the momentum and heat transfer characteristics of a heated sphere in tubes filled with Bingham plastic fluids have been studied. The governing differential equations (continuity, momentum and thermal energy) have been solved numerically over wide ranges of conditions as: Reynolds number, 1 ≤ Re ≤ 100; Prandtl number, 1 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 100 and blockage ratio,0 ≤ λ ≤ 0.5 where λ is defined as the ratio of the sphere to tube diameter. Over this range of conditions, the flow is expected to be axisymmetric and steady. The detailed flow and temperature fields in the vicinity of the surface of the sphere are examined in terms of the streamline and isotherm contours respectively. Further insights are developed in terms of the distribution of the local Nusselt number along the surface of the sphere together with their average values in terms of mean Nusselt number. Finally, the wall effects on drag are present only when the fluid-like region intersects with the boundary wall. However, heat transfer is always influenced by the wall effects. Also, the flow domain is mapped in terms of the yielded- (fluid-like) and unyielded (solid-like) sub-regions. The fluid inertia tends to promote yielding whereas the yield stress counters it. Furthermore, the introduction of even a small degree of yield stress imparts stability to the flow and therefore, the flow remains attached to the surface of the sphere up to much higher values of the Reynolds number than that in Newtonian fluids. The paper is concluded by developing predictive correlations for drag and Nusselt number.

Change in synthetic strategy for MOF fabrication: from 2D non-porous to 3D porous architecture and its sorption and emission property studies

A 3D cadmium metal organic framework, {[Cd(BDC)(BPz)]·2DMF·H2O}n (1) (BPz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole, BDC = benzene-1,3-dicarboxylic acid), has been synthesized using a solvent diffusion method. Compound 1 is a porous framework with the total solvent accessible void volume of 41.5% and exhibits a 6-c uninodal net with pcu topology. It shows selective CO2 gas uptake (46.2 cc g−1 at 195 K) over N2 and CH4 and selective water vapor uptake (130 cc g−1) over methanol and ethanol solvent vapors at room temperature. Photoluminescence study of 1 dispersed in different solvents was also performed.

Structural diversity of Zn(II) based coordination polymers constructed from a flexible carboxylate linker and pyridyl co-linkers: fluorescence sensing of nitroaromatics

The flexible carboxylate linker, H3L = 5-(2-carboxybenzyloxy)isophthalic acid, and a group of N-donor co-linkers such as 1,2-di(4-pyridyl)ethylene (dpe), 1,2-di(4-pyridyl)ethane (1,2-dpe), 1,2-di(pyridin-4-yl)diazene (dpd), and 1,3-di(4-pyridyl)propane (1,3-dpp), give rise to five new coordination polymers (CPs) with Zn(II) ions. These are {[Zn2(L)(μ-OH)(dpe)(H2O)]}n (1), {[Zn(L)(1,2-dpe)1.5]·H2O}n (2), {[Zn(HL)(dpd)1.5]2·2(H2O)}n (3), {[Zn(HL)(1,3-dpp)]}n (4), and {[Zn5(L)4(H2O)2]·8(H2O) (1,2-dpe)}n (5). CP 1 forms a densely packed 3D framework with a rare topological type, ose; 7/3/o5; sqc59. Both CP 2 and 3 form [2+2] metallacyclic units which form a 1D chain that links other chains by strong O–H⋯N type H-bonding to result in a 3D supramolecular network. CP 4 forms a 2D sheet structure stacking over each other by C–H⋯π and π⋯π interactions, to give rise to a 3D H-bonded supramolecular structure with topological type, sql/Shubnikov. CP 5 has two types of SBUs with a 3D anionic network where channels are filled up with the cationic 1,2-dpe ligands and water molecules which shows rare topological type, 6,10T9. The photoluminescence sensing of nitroaromatic compounds, especially 2,4,6-trinitrophenol (TNP), by 1–5 indicates that these CPs could be potential candidates for developing luminescent sensors for selective sensing of these species.

Effect of buoyancy-assisted flow on convection from an isothermal spheroid in power-law fluids

In this work, the coupled momentum and energy equations have been solved to elucidate the effect of aiding-buoyancy on the laminar mixed-convection from a spheroidal particle in power-law media over wide ranges of the pertinent parameters: Richardson number, 0≤Ri≤5; Reynolds number, 1≤Re≤100; Prandtl number, 1≤Pr≤100; power-law index, 0.3≤n≤1.8, and aspect ratio, 0.2≤e≤5 for the case of constant thermo-physical properties. New results for the velocity and temperature fields are discussed in terms of the streamline and isotherm contours, surface pressure and vorticity contours, drag coefficient, local and surface averaged Nusselt number. The effect of particle shape on the flow is seen to be more pronounced in the case of oblates (e < 1) than that for prolates (e > 1). The propensity for wake formation reduces with the rising values of power-law index, Richardson number and slenderness of the body shape (e > 1). Also, the drag coefficient is seen to increase with the Richardson number and power-law index. All else being equal, the Nusselt number shows a positive dependence on the Richardson number and Reynolds number and an inverse dependence on the power-law index and aspect ratio of the spheroid. Limited results were also obtained by considering the exponential temperature dependence of the power-law consistency index. This factor can increase the values of the average Nusselt number by up to ~10-12% with reference to the corresponding values for the case of the constant thermo-physical properties under otherwise identical conditions. Finally, the present values of the Nusselt number have been consolidated in the form of Colburn j-factor as a function of the modified Reynolds and Prandtl numbers for each value of the aspect ratio (e). The effect of the temperature dependent viscosity is included in this correlation in terms of a multiplication factor.

Momentum and heat transfer characteristics of a thin circular disk in Bingham plastic fluids

ABSTRACT The laminar forced convection momentum and heat transfer aspects of a circular disk oriented normal to the flow and maintained at a constant flux or a constant temperature condition in a stream of a Bingham plastic fluid are studied over wide ranges of parameters as follows: Reynolds number, Re ≤ 150; Prandtl number, 1 ≤Pr ≤ 100; Bingham number, Bn ≤ 100, and thickness-to-diameter ratio, 0.01 ≤ (t/d) ≤ 0.075. The new results on hydrodynamics are analyzed in terms of streamline plots, recirculation length, morphology of yielded/unyielded regions, and drag coefficient, and on heat transfer aspects in terms of isotherm contours, local and average Nusselt number. The flow domain is spanned by the simultaneous existence of the yielded and unyielded sub-regions, depending upon the relative strengths of the fluid inertia (Re) and yield stress (Bn). All else being equal, the rate of heat transfer is higher for an isothermal disk than that for the isoflux condition. Both the drag and average Nusselt number bear a positive dependence on the Bingham number. The drag is influenced only slightly (∼5%) by thickness (t/d); however, the heat transfer can increase on this count by up to 15% under appropriate conditions. Finally, the present numerical results on drag and Nusselt number (in terms of jH-factor) have been correlated via simple empirical equations using the modified definitions of the Reynolds (Re*) and Prandtl number (Pr*), thereby enabling a priori estimation of drag and heat transfer in a new application.

Natural convection in Bingham plastic fluids from an isothermal spheroid: Effects of fluid yield stress, viscous dissipation and temperature-dependent viscosity

In this work, the buoyancy-induced convection from an isothermal spheroid is studied in a Bingham plastic fluid. Extensive results on the morphology of approximate yield surfaces, temperature profiles, and the local and average Nusselt numbers are reported to elucidate the effects of the pertinent dimensionless parameters: Rayleigh number, 102 ≤ Ra ≤ 106; Prandtl number, 20 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 103, and aspect ratio, 0.2 ≤ e ≤ 5. Due to the fluid yield stress, fluid-like (yielded) and solid-like (unyielded) regions coexist in the flow domain depending upon the prevailing stress levels vis-a-vis the value of the fluid yield stress. The yielded parts progressively grow in size with the rising Rayleigh number while this tendency is countered by the increasing Bingham and Prandtl numbers. Due to these two competing effects, a limiting value of the Bingham number (Bnmax) is observed beyond which heat transfer occurs solely by conduction due to the solid-like behaviour of the fluid everywhere in the domain. Such limiting values bear a positive dependence on the Rayleigh number (Ra) and aspect ratio (e). In addition to this, oblate shapes (e < 1) foster heat transfer with respect to spheres (e = 1) while prolate shapes (e > 1) impede it. Finally, simple predictive expressions for the maximum Bingham number and the average Nusselt number are developed which can be used to predict a priori the overall heat transfer coefficient in a new application. Also, a criterion is developed in terms of the composite parameter Bn∙Gr-1/2 which predicts the onset of convection in such fluids. Similarly, another criterion is developed which delineates the conditions for the onset of settling due to buoyancy effects. The paper is concluded by presenting limited results to delineate the effects of viscous dissipation and the temperature-dependent viscosity on the Nusselt number. Both these effects are seen to be rather small in Bingham plastic fluids.