The Influence of geometrical and operational parameters on internal flow characteristics of Internally Mixing Twin-Fluid Y-Jet Atomizers

Internally mixing twin-fluid Y-jet atomizers are widely used in coal fired thermal power plants for start-up, oil-fired thermal power plants and industrial boilers. The flow through internally mixing Y-jet atomizers is numerically modeled using the compressible Navier-Stokes equations; Wall Modeled Large Eddy Simulations (WMLES) is used to resolve the turbulence with Large Eddy Simulations whereas the Prandtl Mixing Length Model is used for modeling the subgrid scale structures, which are affected by geometric and operational parameters. Moreover, the Volume-of-Fluid (VOF) method is used to capture the development and fragmentation of the liquid-gas interface within the Y-jet atomizer. The numerical results are compared with correlations available in open literature for the pressure drop; further results are presented for the multiphase flow regime maps available for vertical pipes. The results show that the mixing point pressure is strongly dependent on the mixing port diameter to airport diameter ratio, specifically for gas to liquid mass flowrate ratio (GLR) in the range 0.1 < GLR < 0.4; the mixing port length moderately affects the mixing point pressure while the angle between mixing and liquid ports is found not to have an appreciable effect. Moreover, it is found that the vertical pipe multiphase flow regime maps in the literature could be applied to the flow through the mixing port of the twin-fluid Y-jet atomizer. The main flow regimes found under the studied operational conditions are annular and wispy annular flow

Using Computational Fluid Dynamics To Accurately Model Agricultural Spray Nozzles

Computational fluid dynamics (CFD) is a tool used by engineers in many industries to study fluid flow. A relatively new industry to adopt the use of CFD is the agricultural industry. The present work seeks to understand whether CFD can be used to accurately model spray nozzles. A spray nozzle commonly used in agricultural spraying was simulated. First, the impact of factors such as mesh size, mesh type, and physics models have on the solution were investigated. Next, a method to pulse the spray was determined. This was required to compare simulation results with experimental data. A user-defined function was used to define a pulsed velocity inlet in order to pulse the spray. The domain was then extended to allow the examination of a slice 20 inches below the nozzle. The results were compared to experimental data collected from the Raven Sprayer Testbed. Results from these studies suggested that CFD could be used to model spray nozzles but the validity of the results is strongly related to the available computational resources. These simulations were carried out using Star-CCM+. Lastly, Large Eddy simulations were conducted to capture the liquid jet breakup within the spray plume. The results suggested that the liquid jet breakup could be modeled using CFD, but again sufficient computational resources are required. These simulations were performed in OpenFOAM

Development and validation of a two-phase computational model for an alternative fire suppression agent

[ES] Halon1301 se ha utilizado como agente de extinción de incendios en sistemas activos de extinción de incendios en motores de aviones, APU (Unidad de potencia auxiliar) y protección contra incendios de carga durante más de 50 años. En 1987, una investigación realizada por el Protocolo de Montreal muestra que Halon está dañando el medio ambiente debido a sus propiedades que agotan el ozono. Por lo tanto, el uso de gases de halón ha sido prohibido en la industria por el protocolo de Montreal (1994) y Kyoto (1998). Por lo tanto, es el reemplazo de gases de halón lo que es más ecológico. Entre estas alternativas, Novec-1230 es una alternativa sostenible que funciona de manera rápida, limpia y eficiente. El sistema de extinción de incendios requiere que se diluya una concentración específica del agente de extinción de incendios (4-6% para Novec-1230 y 5% para Halon) en el aire para extinguir el fuego. El problema de cambiar la fase de la niebla rápidamente despresurizada de un sistema de extinción de incendios es un tema de gran interés debido al efecto del modelado de estos fenómenos en una simulación exitosa para diseñar estas modificaciones. Debido a la gran diferencia de presiones entre el recipiente y el ambiente, se espera que la descarga a través de la boquilla sea crítica. En este informe, se utilizan dos agentes de supresión de incendios alternativos diferentes y dos boquillas: agua y Novec1230. El objetivo principal de este proyecto es desarrollar un nuevo modelo de subcuadrícula para un U-RANS CFD Euleriano-Euleriano de dos fases que pueda usarse para reducir el costo computacional y aumentar la precisión de los enfoques tradicionales basados en Eulerian-Lagrangian. Estos dos enfoques se realizan con el software comercial CFD (ANSYS Fluent). Como validación, los rendimientos de pulverización como la forma de pulverización, el ángulo del cono de pulverización se comparan con los resultados experimentales.[EN] Halon1301 has been used as a fire suppression agent in active fire extinction systems in aircraft engines, APU (Auxiliary Power Unit) and cargo fire protection for more than 50 years. In 1987, a research carried out by the Montreal Protocol shows that Halon is damaging the environment because of its ozone-depleting properties. Therefore, the use of Halon gases has been banned in the industry by the Montreal (1994) and Kyoto (1998) protocol. So, it is indeed to find replacement of halon gases which is more eco friendly. Among these alternatives, Novec-1230 is a sustainable alternative that works quickly, cleanly and efficiently. The fire suppression system requires a specific concentration of the fire suppression agent (4-6 % for Novec-1230 and 5% for Halon) to be diluted in the air to extinguish the fire. The problem of changing the phase of the rapidly depressurized mist of a fire suppression system is a topic of high interest due to the effect of the modelling of these phenomena in a successful simulation to design these modifications. Due to the high difference of pressures between the container and the ambient, the discharge through the nozzle is expected to be critical. In this report, two di&#64256;erent alternative &#64257;re suppression agents and two nozzles are used - Water and Novec1230. The main goal of this project is to develop a new sub-grid model for a two-phase Eulerian-Eulerian CFD U-RANS that can be used to reduce the computational cost and increase the accuracy of traditional approaches based on Eulerian-Lagrangian. These two approaches are performed with CFD commercial software (ANSYS Fluent). As validation, spray performances such as spray shape, spray cone angle are compared with experimental results.Shaparia, NR. (2020). Development and validation of a two-phase computational model for an alternative fire suppression agent. Universitat Politècnia de València. http://hdl.handle.net/10251/157474TFG

Numerical Modelling of Diesel Spray Using the Eulerian Multiphase Approach

This research investigates high pressure diesel fuel injection into the combustion chamber by performing computational simulations using the Euler-Eulerian multiphase approach. Six diesel-like conditions were simulated for which the liquid fuel jet was injected into a pressurised inert environment (100 % N2) through a 205 µm nozzle hole. The analysis was focused on the liquid jet and vapour penetration, describing spatial and temporal spray evolution. For this purpose, an Eulerian multiphase model was implemented, variations of the sub-model coefficients were performed, and their impact on the spray formation was investigated. The final set of sub-model coefficients was applied to all operating points. Several simulations of high pressure diesel injections (50, 80, and 120 MPa) combined with different chamber pressures (5.4 and 7.2 MPa) were carried out and results were compared to the experimental data. The predicted results share a similar spray cloud shape for all conditions with the different vapour and liquid penetration length. The liquid penetration is shortened with the increase in chamber pressure, whilst the vapour penetration is more pronounced by elevating the injection pressure. Finally, the results showed good agreement when compared to the measured data, and yielded the correct trends for both the liquid and vapour penetrations under different operating conditions

CFD Simulation of Pressure Drop and Liquid Holdup in a Trickle Bed Reactor

Trickle Bed Reactors have etched a ubiquitous presence in chemical processing sector. From petroleum and petrochemical products, fine chemicals to biochemical, wastewater treatment, they are almost everywhere. Products worth of 300 billion US $ are processed by these reactors on an annual average. A complete understanding of hydrodynamics, fluid phase mixing, interphase and interparticle heat and mass transfer and reaction kinetics of TBR can help us to extract the full potential of TBR. Studying the variation of pressure drop and liquid holdup is crucial for evaluation of performance of trickle bed reactors and can help in further optimizing their performance. This project focuses on the effect of gas and liquid velocities on the pressure drop and liquid holdup in a trickle-Bed reactor operating at ambient temperature and atmospheric pressure. Pressure drop and liquid holdup are two critical hydrodynamics parameters that influence other parameters directly and indirectly and hence, these two parameters are preferred for hydrodynamic study of TBR. Their variation along longitudinal and transverse direction is the focus of this project. A comparison of results from different simulation scenarios (using different pressure values as patching values) made in this project helps in understanding how different initial guess can affect the final solution in simulating real-life TBR operation. It is found that pressure ranging up to 10000 Pa as patching pressure value can lead to a converging solution. Afterwards, solution instability creeps in leading to impractically higher values of pressure and liquid holdup and sometimes ending up with divergence. Even the effect of gas and liquid velocity is studied on the two parameters. The variation of the two hydrodynamic parameters with changing liquid velocities and gas velocities are also studied

Mixing and Demixing Processes in Multiphase Flows With Application to Propulsion Systems

A workshop on transport processes in multiphase flow was held at the Marshall Space Flight Center on February 25 and 26, 1988. The program, abstracts and text of the presentations at this workshop are presented. The objective of the workshop was to enhance our understanding of mass, momentum, and energy transport processes in laminar and turbulent multiphase shear flows in combustion and propulsion environments