Transient analysis of third-grade viscoelastic nanofluid flow external to a heated cylinder with buoyancy effects

Nanotechnology is rapidly embracing numerous areas of manufacturing and process engineering. New types of nanomaterials are being exploited to improve, for example, coating integrity, anti-corrosion characteristics and other features of fabricated components. Motivated by these developments, in the current study a mathematical model is developed for unsteady free-convective laminar flow of third-grade viscoelastic fluid (doped with nano-particles) from a semi-infinite vertical isothermal cylinder, as a model of thermal coating flow of a pipe geometry. Non-Newtonian behavior is simulated with the thermodynamically robust third grade Reiner-Rivlin model which accurately represents polymer fluids. Nanoscale effects are analyzed with the Buongiorno two-component nanofluid model. The governing equations comprise a set of highly coupled, nonlinear, multi-degree partial differential equations featuring viscoelastic and nanofluid parameters. An implicit Crank-Nicolson numerical scheme is implemented to solve the emerging nonlinear problem with appropriate initial and boundary conditions. Detailed graphical plots for velocity, temperature and nano-particle volume fraction are presented for a range of different parameters (i.e., third-grade fluid parameter, Brownian motion parameter, thermophoretic parameter, buoyancy ratio parameter, Lewis number). Additionally, distributions of the heat transfer coefficient, skin friction and Sherwood number at the cylinder surface are visualized. Furthermore, streamlines, isotherms and nano-particle volume fraction contour plots are included for variation of the third-grade parameter. Contour plots for the third-grade nanofluid flow are found to deviate significantly from those corresponding to Newtonian nanofluids. Validation of the numerical solutions with earlier studies is also included. KEYWORDS: Third-grade viscoelastic nanofluid, Thermal convection, Cylinder, Thermophoresis, Brownian motion, Implicit numerical method, Contour plots, Industrial coating

Bejan flow visualization of free convection in a Jeffrey fluid from a semi-infinite vertical cylinder : influence of Deborah and Prandtl numbers

This article studies the pattern of heat lines in free convection non-Newtonian flow from a semi-infinite vertical cylinder via Bejan’s heat function concept. The viscoelastic Jeffrey fluid model is employed. The time-dependent, coupled, non-linear conservation equations for momentum and energy (heat) are solved computationally with the unconditionally stable finite difference Crank-Nicolson method. Extensive graphical results are presented for the influence of Deborah number (viscoelastic parameter) and Prandtl number (with ranges 0 - 0.8 and 0.68 - 7.2, respectively) on thermal and flow characteristics including time histories of overall skin friction and heat transfer rate. Lower values of Deborah number indicate that the material acts in a more fluid-like manner whereas the higher values of Deborah number correspond to the material showing characteristics more associated with a solid. The solutions indicate that the time taken for the flow-field variables to achieve the steady-state is increased with higher values of Deborah number. Boundary flow visualization is presented using heat lines, isotherms and streamlines. It is observed that as Deborah number increases the intensity of heat lines increases and they tend to deviate from the hot cylindrical wall. Furthermore, the flow field variables for the Newtonian fluid case exhibit a significantly different pattern from that of Jeffrey fluid

Supercritical heat transfer characteristics of couple stress convection flow from a vertical cylinder using an equation of state approach

The present work describes numerical simulations of the supercritical heat transfer characteristics of couple stress fluid flow from a vertical cylinder using the equation of state approach. Redlich-Kwong (RK-EOS) and Van der Waals (VW-EOS) equations of state (EOS) are deployed to derive the equation for the thermal expansion coefficient (β). The β values calculated based on RK-EOS are sufficiently close to the experimental values when compared with those based on VW-EOS. Due to the presence of couple stresses in the fluid, highly nonlinear coupled partial differential equations are generated. These primitive equations are reduced to dimensionless form by using suitable non-dimensional quantities. An unconditionally stable finite difference technique is used to solve the normalized conservation equations under physically viable boundary conditions, in order to describe the natural convection heat transfer characteristics of couple stress fluid external to a vertical cylinder in the supercritical region. For different values of the emerging physical parameters, numerical data for couple stress fluid for the case of Nitrogen is generated and presented in the form of graphs and tables. The present computations indicate that the velocity field is suppressed close to the cylinder whereas it is enhanced away from the cylinder with increasing values of reduced temperature in the supercritical fluid region. The reverse behavior is observed for reduced pressure. The present results are compared with the previous results and found to be in good agreement. Applications of the model include super-critical coating dynamics in the aerospace and medical industries

Transient analysis of Casson fluid thermo-convection from a vertical cylinder embedded in a porous medium : entropy generation and thermal energy transfer visualization

Thermal transport in porous media has stimulated substantial interest in engineering sciences due to increasing applications in filtration systems, porous bearings, porous layer insulation, biomechanics, geomechanics etc. Motivated by such applications, in this article a numerical investigation of entropy generation effects on the heat and momentum transfer in unsteady laminar incompressible boundary layer flow of a Casson viscoplastic fluid over a uniformly heated vertical cylinder embedded in a porous medium is presented. Darcy’s law is employed to simulate bulk drag effects at low Reynolds number for an isotropic, homogenous porous medium. Heat line visualization is also included. The mathematical model is derived and normalized using appropriate transformation variables. The resulting time-dependent non-linear coupled partial differential conservation equations with associated boundary conditions are solved with an efficient unconditionally stable implicit finite difference Crank Nicolson scheme. The time histories of average values of momentum and heat transport coefficients, entropy generation and Bejan number, as well as the steady-state flow variables are computed for several values of non-dimensional parameters arising in the flow equations. The results indicate that entropy generation parameter and Bejan number are both elevated with increasing values of Casson fluid parameter, Darcy number, group parameter and Grashof number. To analyze the heat transfer process in a two-dimensional domain, plotting heat lines provides an excellent approach in addition to streamlines and isotherms. The dimensionless heat function values are shown to correlate closely with the overall rate of heat transfer. Bejan’s heat flow visualization implies that the heat function contours are compact in the neighbourhood of the leading edge of the boundary layer on the hot cylindrical wall. It is observed that as the Darcy number increases, the deviations of heat lines from the hot wall are reduced. Furthermore the deviations of flow variables from the hot wall for a Casson fluid are significant compared with those computed for a Newtonian fluid and this has important implications in industrial thermal materials processing operations

Unsteady free convective heat transfer in third-grade fluid flow from an isothermal vertical plate : a thermodynamic analysis

The current study investigates theoretically and numerically the entropy generation in time-dependent free-convective third-grade viscoelastic fluid convection flow from a vertical plate. The non-dimensional conservation equations for mass, momentum, and energy are solved using a Crank-Nicolson finite difference method with suitable boundary conditions. Expressions for known values of flow-variables coefficients are also derived for the wall heat transfer and skin friction and numerically evaluated. The effect of Grashof number, Prandtl number, group parameter (product of dimensionless temperature difference and Brinkman number) and third-grade parameter on entropy heat generation is analyzed and shown graphically. Bejan line distributions are also presented for the influence of several control parameters. The computations reveal that with increasing third-grade parameter the entropy generation decreases and Bejan number increases. Also, the comparison graph shows that contour lines for third-grade fluid vary considerably from the Newtonian fluid. The study is relevant to non-Newtonian thermal materials processing systems

Seedless Pattern Growth of Quasi-Aligned ZnO Nanorod Arrays on Cover Glass Substrates in Solution

A hybrid technique for the selective growth of ZnO nanorod arrays on wanted areas of thin cover glass substrates was developed without the use of seed layer of ZnO. This method utilizes electron-beam lithography for pattern transfer on seedless substrate, followed by solution method for the bottom-up growth of ZnO nanorod arrays on the patterned substrates. The arrays of highly crystalline ZnO nanorods having diameter of 60 ± 10 nm and length of 750 ± 50 nm were selectively grown on different shape patterns and exhibited a remarkable uniformity in terms of diameter, length, and density. The room temperature cathodluminescence measurements showed a strong ultraviolet emission at 381 nm and broad visible emission at 585–610 nm were observed in the spectrum

Enterocutaneous fistula due to mesh fixation in the repair of lateral incisional hernia: a case report

Enterocutaneous fistula following mesh repair of incisional hernia is usually due to mesh erosion of the underlying viscus and presents late. We describe an early enterocutaneous fistula due to an unusual but a potential mode of bowel injury during mesh fixation. This case is reported to emphasize the need for greater attention to the technique of mesh fixation. We suggest laparoscopic guidance to prevent this serious complication in lateral Incisional hernias with ill defined edges of the defect

The very lithium rich post-AGB SB2 binary HD172481

Double lined spectroscopic binaries in an evolved stage of evolution are expected to be extremely rare since they must consist of equally luminous and thus almost equally evolved objects, which requires an extremely similar initial mass. In this contribution we discuss such rare double evolved SB2 system: HD172481. This binary includes an F-type post-AGB object and an M-type AGB companion. The spectrum shows a surprisingly strong LiI 670.8nm line with an equivalent width of 54mA yielding a lithium abundance of log(Li)=3.6. Several explanations for this huge lithium content are explored.Comment: 7 pages, 5 figures, to appear in the proceedings of: "Post-AGB Objects (Proto-Planetary Nebulae) as a Phase of Stellar Evolution", held in Torun, Poland, July 5-7, 2000; eds. R. Szczerba, R. Tylenda, and S.K. Gorny. See also the accepted A&A paper at http://xxx.lanl.gov/abs/astro-ph/001048

Rapamycin-loaded nanoparticles for inhibition of neointimal hyperplasia in experimental vein grafts

<p>Abstract</p> <p>Background</p> <p>Nanoparticles possess several advantages as a carrier system for intracellular delivery of therapeutic agents. Rapamycin is an immunosuppressive agent which also exhibits marked antiproliferative properties. We investigated whether rapamycin-loaded nanoparticles(NPs) can reduce neointima formation in a rat model of vein graft disease.</p> <p>Methods</p> <p>Poly(lactic-co-glycolic acid) (PLGA) NPs containing rapamycin was prepared using an oil/water solvent evaporation technique. Nanoparticle size and morphology were determined by dynamic light scattering methodology and electron microscopy. In vitro cytotoxicity of blank, rapamycin-loaded PLGA (RPLGA) NPs was studied using MTT Assay. Excised rat jugular vein was treated ex vivo with blank-NPs, or rapamycin-loaded NPs, then interposed back into the carotid artery position using a cuff technique. Grafts were harvested at 21 days and underwent morphometric analysis as well as immunohistochemical analysis.</p> <p>Results</p> <p>Rapamycin was efficiently loaded in PLGA nanoparticles with an encapsulation efficiency was 87.6%. The average diameter of NPs was 180.3 nm. The NPs-containing rapamycin at 1 ng/ml significantly inhibited vascular smooth muscular cells proliferation. Measurement of rapamycin levels in vein grafts shown that the concentration of rapamycin in vein grafts at 3 weeks after grafting were 0.9 ± 0.1 μg/g. In grafted veins without treatment intima-media thickness was 300.4 ±181.5 μm after grafting 21 days. Whereas, Veins treated with rapamycin-loaded NPs showed a reduction of intimal-media thickness of 150.2 ± 62.5 μm (p = 0.001). CD-31 staining was used to measure luminal endothelial coverage in grafts and indicated a high level of endothelialization in 21 days vein grafts with no significant effect of blank or rapamycin-loaded NPs group.</p> <p>Conclusions</p> <p>We conclude that sustained-release rapamycin from rapymycin loaded NPs inhibits vein graft thickening without affecting the reendothelialization in rat carotid vein-to-artery interposition grafts and this may be a promising therapy for the treatment of vein graft disease.</p