The development of thermal lattice Boltzmann models in incompressible limit

In this paper, an incompressible two-dimensional (2-D) and three-dimensional (3-D) thermohydrodynamics for the lattice Boltzmann scheme are developed. The basic idea is to solve the velocity field and the temperature field using two different distribution functions. A derivation of the lattice Boltzmann scheme from the continuous Boltzmann equation for 2-D is discussed in detail. By using the same procedure as in the derivation of the discretised density distribution function, we found that new lattice of four-velocity (2-D) and eight-velocity(3-D) models for internal energy density distribution function can be developed where the viscous and compressive heating effects are negligible. These models are validated by the numerical simulation of the 2-D porous plate Couette flow problem where the analytical solution exists and the natural convection flows in a cubic cavity

Numerical prediction of mixed convection heat transfer in an enclosure

In this article the transport mechanism of laminar mixed convection in a shear and buoyancy driven cavity flow with locally heated lower wall and moving cooled sidewalls is numerically studied using cubic interpolation profile method. This study focused on the interaction of forced convection with natural convection. The heat is locally introduced into the cavity with the dimensionless value of ԑ=1/5 of the non dimensional length of the bottom wall. Studies were conducted on the effect of mixed convection parameter Gr/Re2 (known as Richardson Number) in the range of 0.1-10. The results were illustrated in the form of streamline and isotherms. Three different regions can be detected as the Richardson number is increased: forced convection, mixed convection and natural convection

Lattice Boltzmann simulation of plume behavior from an eccentric annulus cylinder

In this paper, a double-population thermal lattice Boltzmann was applied to solve two dimensional, incompressible, thermal fluid flow problems. The simplest lattice BGK D2Q4 model was applied to determine the temperature field while D2Q9 for the density and velocity fields. The simulation of natural convection from a concentrically and eccentrically placed inner heated cylinder inside cold outer cylinder with Prandtl number 0.71 and Rayleigh number 5 x was observed that the combination of D2Q4 and D2Q9 10 5 were carried out and discussed quantitatively. It was able to reproduce the effect of buoyancy force in the system. We also found that the flow pattern including the boundary layers and vortices with heat transfer mechanisms is significantly influenced by the position of heated cylinder in the enclosure and excellent comparisons with previous studies

Design and optimizing of geometric for solar updraft tower using computational fluid dynamics (CFD)

There are many experimental and analytical approaches that have been physically proven in the last few decades for the Solar Updraft Tower (SUT) concept to provide energy from solar radiation. Solar chimneys with their potential advantages have gained more attention by fully utilising solar radiation energy to generate air movement by stack pressure. This movement is driving the heated air through the chimney channel and then drawing colder air through the building in a continuous cycle. A parametric study on the geometry of the solar updraft tower is carried out with a different slope angle of collector, different inlet height of collector and different diameter of chimney collector inlet height with fixed solar radiation at 800 W/m2. A validated model is compared with the experimental prototype constructed by the University of Zanjan, Iran. The result shows an incredible improvement in the power generated by a collector with 0 degree and the best entrance gap of collector and chimney diameter at 0.05 m and 0.05 m respectively. The findings and results are discussed and suggested for future works

Influence of volatile fatty acid concentration on biogas production in synthropic anaerobic digestion

Biogas is one type of renewable energy that can be produced from substrates in the form of industrial waste. Biogas formation is a complex series of biochemical processes and involves many types of anaerobic micro-organisms. In an anaerobic digester, synthropic reactions are considered to be the process steps that limit the formation of this biogas. This study aims to study the effect of volatile fatty acid substrate concentration (VFA) on the biogas production rate in a digester tank equipped with Rushton Impeller 6 bladed type mixer, which is rotated at a constant speed of 100 rpm. The simulations were performed in 3 dimensions under transient conditions using computational fluid dynamic (CFD) methods that are tied to the equilibrium equations of the synthropic reaction population (acetogenesis and methanogenesis) in the stirred reactor. This simulation uses a 3-phase Eulerian model and a k-epsilon RNG turbulence model to solve the momentum equation, species transport and population balance equation. The preferred solution method is PC-SIMPLE with First Order Upwind discretization. In this study 8 variations of substrate concentration were simulated. The validation results of the previous research showed very close results, with the difference is less than 1%. Hence, the VFA degradation process occurs efficiently and the VFA concentration profile in the 3-phase system is a heterogeneous flow pattern, so it is concluded that the calculation model used can be used to predict the biogas production rate quite well. Based on the simulation results of 8 types of VFA substrate concentrations observed after 70 seconds, it was found that the production and concentration of methane in biogas varied between 17.62% (variation-6) to 22.96% (variation-5). The biogas production varies between 0.61 g/l (reference model) to 0.95 g/l (variation-3). With this investigation, it can be done by simulation to get optimal mixer design, according to the type of substrate used and operating conditions of the digeste

Convective Boundary Conditions Effect on Cylindrical Media with Transient Heat Transfer

Lattice Boltzmann method is used to solve inside a cylindrical cavity with convective boundary condition is highlighted in this paper. Because of its simple, stable, accurate, efficient and ease for parallelization, we use the thermal Single Relaxation Time Bhatnagar Gross Krook (SRT BGK) mesoscopic approach in order to solve the energy equation. Thermal fields are simulated using D2Q9 scheme. We introduce and demonstrate numerically some usual cases (Dirichlet, Newmann) of Boundary conditions (Bcs). After validation, we extend the present work to the convective case. At the wall of the cavity, the unknown Thermal Distribution Functions (TDF) are exposed to the bounce back concept which is determined consistently by one of the imposed BCs. An in-house Fortran 90 code is used to analyze a variety of BCs inside a two-dimensional cavity. In validation, obtained results highlight a good agreement with literature. The present study is extended to deal with convective boundary condition for conduction transfer problems inside an axisymmetric cylindrical media subjected to heat generation and Newman boundary conditions

Nanoparticles: A review on their synthesis, characterization and physicochemical properties for energy technology industry

In this paper, an overview about nanoparticles (NPs), their synthesis, characterizations, thermal properties and applications is discussed. Specific morphology, size and magnetic properties of NPs can be controlled by NP synthetic techniques. NPs have a size range of between 1-100 nm. This tiny structure will cause NPs to have a large surface area that correlates with their physical and chemical properties. They can be classified into different classes based on their properties, shapes or sizes. The different groups include fullerenes, metal NPs, ceramic NPs and polymeric NPs. The physicochemical properties of NPs are the main characteristics used in determining the specific functions among the various applications of NPs. Due to their characteristics; they are widely used in various applications including the energy technology industry, medical, imaging and environmental applications. However, some NPs have disadvantages such as environmental toxicities which will be taken into account for further improvements

Natural convection of aluminium oxide-water nanofluid

As suspending nanoparticles in fluid-based give tremendous promise in heat transfer application, an understanding on the mechanism of heat transfer is indispensable. The present study dealt with natural convection of nanofluid inside a square cavity heated at the bottom, while the upper part was exposed to the atmosphere. Experimental studies have been performed for various physical conditions, such as volume fractions of nanoparticles varying from 0% to 2.0%, different dispersion techniques of nanoparticles in fluid-based, and heating time from 0 to 35 minutes. In general, dynamic viscosity of nanofluid clearly increased with volume fraction, but decreased with the increasing temperature. It was found that improper dispersion technique resulted in viscous solution. On top of that, transport mechanism of thermophoresis and Brownian diffusion were considered in analysing heat transfer across the cavity