Analysis of Thermal Plume Dispersion into the Sea by Remote Sensing and Numerical Modeling

The aim of this work was to study, by remote sensing and numerical modeling, the thermal dispersion of a plume discharged into the sea by a nuclear power plant. The case study is the thermal discharge of the Laguna Verde nuclear power plant, located on the coast of the Gulf of Mexico. First, the thermal plume dispersion was characterized by applying remote sensing for different scenarios. Afterwards, Delft3D-FLOW numerical simulations were performed to expand the analysis of the thermal processes for a case in which the thermal plume tends towards the intake of the power plant. This thermal analysis was carried out by comparing the behavior of different dimensionless parameters. Moreover, the results of the numerical simulations were used to investigate the performance of the AEM and the k-L and k-ε turbulence models, available in the Delft3D-FLOW model. An LES turbulence model contribution was also analyzed. The results show that forced convection is predominant near the plume discharge area and at the vicinity of the intake structure. According to the metrics calculated, all turbulence models produced good agreement with the remote sensing data, except when the LES scheme was considered. Finally, the use of remote sensing and numerical simulations is helpful to better understand thermal plume dispersion.

Development of Nusselt number correlation in natural convection over the walls of a blast furnace: A CFD approach

Blast furnaces are large and costly devices, and contribute enormous wealth to world economy. A tiny improvement of furnace performance can translate to huge saving not only in cost of operation but also in air pollution. It presents a numerical solution of the continuity, momentum, and energy equations for a fluid domain surrounding the outer cylindrical surface of a vertical cylinder with the specific longitudinal section using ANSYS FLUENT 18. The main parameters of this study are the dimensionless ratio of cylinder length to the maximum diameter varying between 3.24 and 5.4, the Rayleigh number ranging between 104 and 107, and the cylinder surface temperature ([Formula: see text]) varying between 375 K and 600 K, the ambient temperature being taken as 300 K. These parameters have been varied during the simulation to determine their influence on the free convection characteristics. The study clearly shows that the computed Nusselt number increases with increase of Rayleigh number and surface temperature, the increment being minimal for high values of length to the maximum diameter. It is also observed from the simulation that the rate of heat transfer goes down with increase of length to the maximum diameter. The results present local heat transfer and skin friction coefficients over the outer cylindrical surface of the blast furnace of chosen dimensions. The thermal plume and the velocity vector field around the furnace are displayed. An empirical Nusselt number to Rayleigh number relationship has been proposed for the blast furnace of any size within range of Rayleigh numbers covered in this study. This formula derived is correct within ±5%, and is expected to be very useful to field engineers.

An Analysis of a Laminar-Turbulent Transition and Thermal Plumes Behavior in a Paramagnetic Fluid Subjected to an External Magnetic Field

Transition to turbulence and changes in the fluid flow structure are subjects of continuous analysis and research, especially for unique fields of research such as the thermo-magnetic convection of weakly magnetic fluids. Therefore, an experimental and numerical research of the influence of an external magnetic field on a natural convection’s fluid flow was conducted in the presented research. The experimental part was performed for an enclosure with a 0.5 aspect ratio, which was filled with a paramagnetic fluid and placed in a superconducting magnet in a position granting the enhancement of the flow. The process was recorded as temperature signals from the thermocouples placed in the analyzed fluid. The numerical research enabled an investigation based not only on temperature, but velocities as well. Experimental and numerical data were analyzed with the application of extended fast Fourier transform and wavelet analysis. The obtained results allowed the determination of changes in the nature of the flow and visualization of the influence of an imposed strong magnetic field on a magnetic fluid. It is proved that an applied magnetic field actuates the flow in Rayleigh-Benard convection and causes the change from laminar to turbulent flow for fairly low magnetic field inductions (2T and 3T for ΔT = 5 and 11 °C respectively). Fast Fourier transform allowed the definition of characteristic frequencies for oscillatory states in the flow, as well as an observation that the high values of magnetic field elongate the inertial range of the flow on the power spectrum density. Temperature maps obtained during numerical simulations granted visualizations of thermal plume formation and behavior with increasing magnetic field.

Numerical Investigation of Bioaerosol Transport in a Compact Lavatory

The lavatory is a fertile area for the transmission of infectious disease through bioaerosols between its users. In this study, we built a generic compact lavatory model with a vacuum toilet, and computational fluid dynamics (CFD) is used to evaluate the effects of ventilation and user behaviors on the airflow patterns, and the resulting fates of bioaerosols. Fecal aerosols are readily released into the lavatory during toilet flush. Their concentration rapidly decays in the first 20 s after flushing by deposition or dilution. It takes about 315 s to 348 s for fine bioaerosols (<10 µm in diameter) to decrease to 5% of the initial concentration, while it takes 50 and 100 µm bioaerosols approximately 11 and <1 s, respectively, to completely deposit. The most contaminated surfaces by aerosol deposition include the toilet seat, the bowl, and the nearby walls. The 10 µm aerosols tend to deposit on horizontal surfaces, while the 50 and 100 µm bioaerosols almost always deposit on the bowl. In the presence of a standing thermal manikin, the rising thermal plume alters the flow field and more bioaerosols are carried out from the toilet; a large fraction of aerosols deposit on the manikin’s legs. The respiratory droplets generated by a seated coughing manikin tend to deposit on the floor, legs, and feet of the manikin. In summary, this study reveals the bioaerosol dilution time and the easily contaminated surfaces in a compact lavatory, which will aid the development of control measures against infectious diseases.

Effect of obstacle height on the nanofluid convection patterns inside a hollow square enclosure

This paper contains natural convection of Ag–MgO/water micropolar hybrid nanofluid in a hollow hot square enclosure equipped by four cold obstacles on the walls. The simulations were performed by the lattice Boltzmann method (LBM). The influences of Rayleigh number and volume fraction of nanoparticle on the fluid flow and heat transfer performance were studied. Moreover, the effects of some geometric parameters, such as cold obstacle height and aspect ratio, were also considered in this study. The results showed that when the aspect ratio is not large ([Formula: see text] or 0.4), at low Rayleigh number (103), the two secondary vortices are established in each main vortex and this kind of secondary vortex does not form at high Rayleigh number (106). However, at [Formula: see text], these secondary vortices occur again in the middle two vortices at [Formula: see text], which is similar to that at [Formula: see text]. At [Formula: see text], the critical Rayleigh number, when the dominated mechanism of heat transfer changes from conduction to convection, is 104. However, the critical Rayleigh number becomes 105 at [Formula: see text] or 0.6. When the cold obstacle height increases, the shape of the vortices inside the enclosure changes due to the different spaces. Besides, at [Formula: see text], for different cold obstacle heights, the location of the thermal plume is different, owing to the different shapes of vortices. Accordingly, the average Nusselt number increases by increment of the Rayleigh number, nanoparticle volume fraction, cold obstacle height and aspect ratio.

Investigation of transportation of nanofluid within non-equilibrium porous media

In this investigation, numerical modeling for the behavior of nanomaterial inside a porous zone with imposing Lorentz force has been illustrated. The working fluid is a mixture of H2O and CuO and due to concentration of 0.04, it is reasonable to use the homogeneous model. Two-temperature model for porous zone was employed in which new scalar for calculating temperature of solid region was defined. CVFEM has been applied to model this complex physics. Radiation terms were considered and their influence on Nu has also been considered. Verification with benchmark proves greater accuracy. Dispersing nanopowders helps the fluid to increase velocity and reduce the temperature of inner wall. Rise of Ra results in three strong eddies inside the zone which creates two thermal plumes and it reduces the temperature of square surface about 68%. With rise of Nhs, the power of counter-clockwise vortex reduces about 61.6% and inner wall becomes warmer about 33.3%. Raising the Ha makes thermal plume to vanish and cooling rate decreases about 46.6%. Augment of Nhs makes Nu to reduce about 5.08% while augment of Ra makes it to augment about 35.64%. Also, augmenting Ha makes Nu to decline about 56.45%.