Computational fluid dynamics simulation of a nanofluid-based annular solar collector with different metallic nano-particles

A numerical study of convective heat transfer in an annular pipe solar collector system is conducted. The inner tube contains pure water and the annular region contains nanofluid. Three-dimensional steady-state incompressible laminar flow comprising water-based nanofluid containing a variety of metallic nano-particles (copper oxide, aluminium oxide and titanium oxide nano-particles)is examined. The Tiwari-Das model is deployed for whichthermal conductivity, specific heat capacity and viscosity of the nanofluid suspensions is evaluated as a function of solid nano-particle volume fraction. Radiative heat transfer is also incorporated using the ANSYS solar flux and Rosseland radiative models. The ANSYS FLUENTfinite volume code (version 18.1) is employed to simulate the thermo-fluid characteristics. Mesh-independence tests are conducted. The influence of volume fraction on temperature, velocity, pressure contours is computed and visualized.Copper oxide nanofluid is observed to achieve the best temperature enhancement. Temperature contours at cross-sections of the annulus are also computed

Numerical study of nanofluid-based direct absorber solar collector systems with metallic/carbon nanoparticles, multiple geometries and multi-mode heat transfer

Nanofluids are complex colloidal suspensions comprising nanoparticles (metallic or carbon based or both) suspended in a base fluid (e.g. water). The resulting suspension provides demonstrably greater thermal performance than base fluids on their own without the agglomeration or sedimentation effects associated with larger (micron-sized) particles. The substantial elevation in thermal conductivity achieved with nanoparticles has made nanofluids very attractive for numerous energy applications including solar collectors. Solar energy is a clean, renewable source available and is essential for all life to exist on earth. Current technology which harvests solar energy with heat transfer fluids (HTFs) e.g., Direct Absorber Solar Collectors (DASCs), Flat Plat Solar Collector (FPCs), Parabolic Trough Solar Collector (PTSCs) etc, still requires continuous improvement in achieving higher efficiencies and greater sustainability. Nanotechnology has emerged as a significant area in recent years and features the use of sophisticated “green” nanomaterials embedded in conventional engineering materials. In this PhD a range of different DASC geometries are explored (annular, trapezoidal, prismatic, quadrilateral, biomimetic channel etc) with a variety of real nanofluids (water-based with metallic nanoparticles such as silver, copper, gold, zinc, titanium etc or carbon based e.g. diamond, graphite etc). Viscous incompressible laminar flows using Newtonian fluid models (Navier-Stokes equations) with thermal convection and radiative heat transfer are considered both with and without thermal buoyancy. Several thermal radiative flux models are deployed to mimic solar radiation effects such as the Rosseland model, P1 Traugott model, Chandrasekhar discrete ordinates model (DOM). ANSYS FLUENT and MAPLE symbolic software are used as the numerical tools to solve the relevant boundary value problems. Generally, the Tiwari-Das nanoscale model is used although the Buongiorno two-component nanofluid model (with thermophoresis and Brownian motion) has also been deployed. Extensive visualizations of streamline and isotherms are computed. Validation with alternative numerical methods and experimental studies is also included. Comprehensive appraisal of the relative performance of different nanofluids is evaluated. Generally, non-magnetic nanoparticles are studied although for the biomimetic channel (solar pump) case magnetic nanoparticles are addressed. The simulations show the significant improvement in thermal conductivities (and thermal efficiency) achieved with different types of geometry and nanoparticle type. Aspect ratio and inclination effects are also considered for some DASC cases. Extensive physical interpretation of thermofluid characteristics is provided. Where possible key dimensionless scaling parameters (Rayleigh number, Nusselt number, Prandtl number, Rosseland number etc) are utilized. The analyses reported herein constitute significant novel developments in solar collector nanofluid dynamics and many chapters have been published in leading international journals and conferences. The results have furnished good guidance for solar designers to assist in the selection of different geometries, nanoparticle types and volume fraction (percentage doping) for larger scale deployment in the future. Furthermore, some pathways for extending the current simulations to e.g. non-Newtonian nanofluid physics, turbulence etc are also outlined

Thermal slip in oblique radiative nano-polymer gel transport with temperature-dependent viscosity : solar collector nanomaterial coating manufacturing simulation

Nano-polymeric solar paints and sol-gels have emerged as a major new development in solar cell/collector coatings offering significant improvements in durability, anti-corrosion and thermal efficiency. They also exhibit substantial viscosity variation with temperature which can be exploited in solar collector designs. Modern manufacturing processes for such nano-rheological materials frequently employ stagnation flow dynamics under high temperature which invokes radiative heat transfer. Motivated by elaborating in further detail the nanoscale heat, mass and momentum characteristics, the present article presents a mathematical and computational study of the steady, two-dimensional, non-aligned thermo-fluid boundary layer transport of copper metal-doped water-based nano-polymeric sol gels under radiative heat flux. To simulate real nano-polymer boundary interface dynamics, thermal slip is analysed at the wall. A temperature-dependent viscosity is also considered. The conservation equations for mass, normal and tangential momentum and energy are normalized via appropriate transformations to generate a multi-degree, ordinary differential, non-linear, coupled boundary value problem. Numerical solutions are obtained via the stable, efficient Runge-Kutta-Fehlberg scheme with shooting quadrature in MATLAB symbolic software. Validation of solutions is achieved with a Variational Iterative Method (VIM) utilizing Langrangian multipliers. The impact of key emerging dimensionless parameters i.e. obliqueness parameter, radiation-conduction Rosseland number (Rd), thermal slip parameter (ALPHA), viscosity parameter (m), nanoparticles volume fraction (PHI) on non-dimensional normal and tangential velocity components, temperature, wall shear stress, local heat flux and streamline distributions is visualized graphically. Shear stress and temperature are boosted with increasing radiative effect whereas local heat flux is reduced. Increasing wall thermal slip parameter depletes temperatures

Peristaltic pumping of magnetic nanofluids with thermal radiation and temperature-dependent viscosity effects : modelling a solar magneto-biomimetic nanopump

Nanofluids have shown significant promise in the thermal enhancement of many industrial systems. They have been developed extensively in energy applications in recent years. Solar energy systems are one of the most promising renewables available to humanity and these are increasingly being re-designed to benefit from nanofluids. Most designs of solar collectors involve fixed (rigid) geometries which may be cylindrical, parabolic, tubular or flat-plate types. Modern developments in biomimetics have identified that deformable conduit structures may be beneficial for sustainable energy systems. Motivated by these aspects, in the current work we present a novel model for simulating a biomimetic peristaltic solar magnetohydrodynamic nanofluid-based pump. The working fluid is a magnetized nanofluid which comprises a base fluid containing suspended magnetic nano-particles. The novelty of the present work is the amalgamation of biomimetics (peristaltic propulsion), magnetohydrodynamics and nanofluid dynamics to produce a hybrid solar pump system model. Heat is transferred via distensibility of the conduit in the form of peristaltic thermal waves and buoyancy effects. An externally applied magnetic field achieves the necessary circuit design for generating Lorentzian magnetic body force in the fluid. A variable viscosity modification of the Buongiorno nanofluid model is employed which features thermophoretic body force and Brownian dynamic effects. To simulate solar loading conditions a thermal radiative flux model is also deployed. An asymmetric porous channel is investigated with multiple amplitudes and phases for the wall wavy motion. The channel also contains a homogenous, isotropic porous medium which is simulated with a modified Darcy model. Heat generation/absorption effects are also examined. The electrically-conducting nature of the nanofluid invokes magnetohydrodynamic effects. The moving boundary value problem is normalized and linearized using the lubrication approach. Analytical solutions are derived for axial velocity, temperature and nanoparticle volume fraction. Validation is conducted with Maple numerical quadrature. Furthermore, the salient features of pumping and trapping phenomena discourse briefly. The observations demonstrate promising features of the solar magnetohydrodynamic peristaltic nanofluid pump which may also be exploited in spacecraft applications, biological smart drug delivery etc