14 research outputs found
Mass, heat and momentum transfer in natural draft wet cooling tower with flue gas discharge
The paper presents CFD simulation results of a natural draught wet-coolingtower (NDWCT) with flue gas discharge. The problem considered is mixing of the fluegases with the rising plume and possible corrosion of the tower shell due to acid condensate.A previously developed CFD model of a NDWCT has been used in the analysis. Nowind conditions have been assumed and the results have shown that under this conditionthe corrosion is unlikely to occu
Thermophoresis and its effect on particle impaction on a cylinder for low and moderate Reynolds numbers
The effect of thermophoresis on the impaction of particles on a cylinder is
investigated for different particle sizes, particle conductivities, temperature
gradients and for Reynolds numbers between 100 and 1600. Simulations are
performed using the Pencil Code, a high-order finite difference code. An
overset-grid method is used to precisely simulate the flow around the cylinder.
The ratio of particles impacting the cylinder and the number of particles
inserted upstream of the cylinder is used to calculate an impaction efficiency.
It is found that both the particle conductivity and the temperature gradient
have a close to linear influence on the particle impaction efficiency for small
particles. Higher Reynolds numbers result in higher impaction efficiency for
middle-sized particles, while the impaction efficiency is smaller for smaller
particles. In general, it is found that thermophoresis only has an effect on
the small particles, while for larger particles the impaction efficiency is
controlled by inertial impaction.
Finally, an algebraic model, developed based on fundamental principles, which
describes the effect of thermophoresis is presented. The model is found to
accurately predict the DNS results. As such, this model can be used to
understand the mechanisms behind particle deposition due to the thermophoretic
force, and, more importantly, to identify means by which the deposition rate
can be reduced
Experimental research and CFD analysis of flow parameters in a SCR system for the original part and WALKER’s replacement
The article presents the results of experimental research and their comparison with CFD simulations for the original selective catalytic reduction system and WALKER replacement. The research was performed to develop the WALKER universal mixer. The SCR prototype without mixer and with the proposed mixer were tested and compared with the original VW part. The next step was reverse engineering, which consisted in scanning the tested parts with a laser and processing their point cloud in Leios2 program. Reverse engineering has allowed the reconstruction of 3D geometry of the tested parts in the Catia v5 program and then preparation their models for computational fluid dynamics. Numerical simulations were carried out in the Ansys Fluent program, thanks to which several quantities were determined e.g. uniformity index of gas flow through the monolith and coefficient of variation as a measure of mixing degree, which have a significant impact on the design of the mixer and the SCR system
A numerical study on the combustion of a resolved carbon particle
Combustion of a single, resolved carbon particle is studied using a novel numerical approach that makes use of an overset grid. The model is implemented into the framework of a compressible Direct Numerical Simulation (DNS) code. A method to artificially reduce the speed of sound is presented. For Mach numbers lower than 0.1 this method may dramatically improve numerical efficiency without affecting any physical aspects except for the acoustics. The ability of the model to simulate solid fuel combustion is demonstrated and all parts of the model are validated against experimental and numerical data. A sensitivity of the carbon conversion rate to selected parameters (diffusion coefficients and homogeneous and heterogeneous kinetics) is investigated. A strong dependence on the oxygen diffusivity is observed and explained
A numerical study on the combustion of a resolved carbon particle
Combustion of a single, resolved carbon particle is studied using a novel numerical approach that makes use of an overset grid. The model is implemented into the framework of a compressible Direct Numerical Simulation (DNS) code. A method to artificially reduce the speed of sound is presented. For Mach numbers lower than 0.1 this method may dramatically improve numerical efficiency without affecting any physical aspects except for the acoustics. The ability of the model to simulate solid fuel combustion is demonstrated and all parts of the model are validated against experimental and numerical data. A sensitivity of the carbon conversion rate to selected parameters (diffusion coefficients and homogeneous and heterogeneous kinetics) is investigated. A strong dependence on the oxygen diffusivity is observed and explained
A numerical study on the combustion of a resolved carbon particle
Combustion of a single, resolved carbon particle is studied using a novel numerical approach that makes use of an overset grid. The model is implemented into the framework of a compressible Direct Numerical Simulation (DNS) code. A method to artificially reduce the speed of sound is presented. For Mach numbers lower than 0.1 this method may dramatically improve numerical efficiency without affecting any physical aspects except for the acoustics. The ability of the model to simulate solid fuel combustion is demonstrated and all parts of the model are validated against experimental and numerical data. A sensitivity of the carbon conversion rate to selected parameters (diffusion coefficients and homogeneous and heterogeneous kinetics) is investigated. A strong dependence on the oxygen diffusivity is observed and explained.publishedVersio
The effect of turbulence on mass transfer rates between inertial polydisperse particles and fluid
The current work investigates how turbulence affects the mass transfer rate between inertial particles and fluid in a dilute, polydisperse particle system. Direct numerical simulations are performed in which all scales of turbulence are fully resolved and particles are represented in a Lagrangian reference frame. The results show that, similarly to a monodisperse system, the mass transfer rate between particles and fluid decreases as a result of particle clustering. This occurs when the flow time scale (based on the turbulence integral scale) is long relative to the chemical time scale, and is strongest when the particle time scale is one order of magnitude smaller than the flow time scale (i.e. the Stokes number is around 0.1). It is also found that for larger solid mass fractions, the clustering of the heavier particles is enhanced by the effect of drag force from the particles on the fluid (momentum back-reactions or two-way coupling). In particular, when two-way coupling is accounted for, locations of particles of different sizes are much more correlated, which leads to a stronger effect of clustering, and thus a greater reduction of the particle-fluid mass transfer rate. © 2019 Cambridge University Press
Preliminary design and modelling of a gas-fired thermoelectric generator
The paper discusses modelling of coupled heat transfer and electricity
generation in a thermoelectric generator designed for reliable island-mode
power supply. The considered generator is a new concept of a low power supply
(50 W) whose aim is to provide electricity for remote gas pressure reduction
stations with the purpose to maintain the control and automation equipment.
This equipment contributes to the system safety and minimizes the risk of
unintended methane emissions. The thermoelectric generator is designed for
reliable and maintenance-free operation and power supply. Natural gas is
burned in a partially premixed burner and the flue gas heats the hot side of
the thermoelectric generator. The combustion air cools the cold side of the
thermoelectric generator, providing the temperature difference required for
electricity generation occurring based on the Seebeck effect. The flow of air
and flue gas through the system is driven by chimney draft. The developed
model couples the heat transfer on the hot and the cold side, as well as the
generation of electrical energy inside the thermoelectric modules. The model
takes into account convection and conduction in the gas flow conduits and in
finned heat exchangers of the cold and hot sides. The analysis demonstrates
the relevance of design and operational parameters on the boundary
temperatures of the thermoelectric modules. The obtained results will be used
in further (ongoing) phase leading to the design and construction of a
prototype electricity generator dedicated for island-mode supply