3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Numerical investigation of selective withdrawal of brine from salt cavern with entrainment of the light phase oil(2024) Moropane, Isaac SekontsheThis paper presents a numerical simulation of selective withdrawal of brine from salt cavern with entrainment of crude oil. Selective withdrawal is the siphoning of one layer of fluid from two immiscible fluids and avoiding the entrainment of other fluid. A trial of three incline siphons (60o , 75o and 90o ) were utilized and each passing through 2.54 cm silicon oil layer and face down below the liquid-liquid interface drawing water upwards. The siphons had a submergence depth of 2.54 cm below the liquid-liquid interface. The simulation was done using the software Ansys Academic, Student 2021 R1. The flow was simulated using two dimensions CFD. The volume of Fluid model and Pressure-based solver were adopted for this simulation. The turbulence model used in the CFD was standard k-epsilon. Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm was adopted for pressure velocity coupling. The results showed that, for avoiding oil entrainment, 90o siphon is better followed by 60o inclined, whereas the 75o inclined was the worse. The results obtained from CFD simulation were validated using experimental data and found to agree. The paper's findings can be useful for Petroleum Engineers to reduce oil entrainment in selective withdrawal from salt caverns in the Strategic Petroleum Reserve (SPR). By predicting the transition from selective withdrawal to oil entrainment, an improved design can optimize the withdrawal process. The design can be enhanced by adjusting the withdrawal rate, pressure, and siphon orientation to minimize the transition from selective withdrawal to oil entrainment. The consequences of oil in the brine system necessitate the separation of oil from the brine, the transfer of oil entrainment back into the salt caverns, and clean-up to avoid environmental contamination. This process of separating and cleaning oil from brine in a brine pond is more time-consuming and expensive.Item Design and verification of a controlled induced mass flow system(2018) Saligram, AleshaThe Medium Speed Wind Tunnel (MSWT) of the Aeronautic Systems Competency (ASC) within the Council for Scientific and Industrial Research (CSIR) performs majority static stability wind tunnel testing. The facility does not have an active inlet simulation capability, or a pressure system to support such a capability. Airframes with air breathing engines are tested with inlets either covered with fairings or left open to operate in a passive mode. To expand the wind tunnel offerings to include an inlet test capability, an active inlet flow induction and metering system was required. An ejector driven duct was designed to provide simulated engine air flow at rates and conditions appropriate for the MSWT size and operating envelope. Integral to the design was a mass flow metering system featuring a translating conical plug. To reduce the risk and size footprint the ejector unit comprised 14 ejectors clustered around a hollow central core housing the mass flow plug support and drive system. The ESDU 92042 software was utilised as the design tool to develop the ejector geometry and Computational Fluid Dynamics (CFD) was employed as a verification and off-design performance prediction tool. The entrained mass flow rate predicted by the CFD model for the 14-ejector unit exceeded the predicted entrained mass flow rate determined by the ESDU 92042 software. Experimental tests were performed to determine the actual entrained mass flow rate of a single ejector in order to verify the design predictions of the CFD model. The maximum entrained mass flow rate determined from the experiment is greater than the maximum entrained mass flow rate predicted by the CFD model. The CFD model over-predicts the entrained mass flow rates of the ejector in the sub-critical mode and will envisage it to under-predict the entrained mass flow rates in the critical mode. The experimental results for the single ejector suggest that the designed operating envelope predicted for the parallel arrangement of 14 ejectors should be reached.Item Vortices shed by accelerating flat plates(2017) Matjoi, Morapeli MichaelFlow around flat plates that were uniformly accelerated from rest with acceleration of 13g is analysed with overset mesh from Star CCM+ commercial CFD software. The particular interest is more on the vortices shed from the plate edges. Three 8mm thick plates of the same cross-sectional areas (108mm length equilateral triangular, 71mm length square and 80mm diameter circular) were simulated. The validation of the numerical method was achieved by using laser vapor sheet method to visualize the flow profiles of accelerating circular plate and comparing the CFD and experimental results. The CFD and experimental results were consistent with each other. It was found that when a plate accelerated in air, it displaced air particles out of its way. The shear layers of air separated from the front edges of the plate and rolled around a vortex core forming a primary vortex ring in the plate wake. The size of the primary vortex increased with Reynolds number (Re) that was increasing with time. This was because as Re increased, more fluid particles were displaced from the front face of the plate at a time. More displacement of the fluid particles led to shear layers separating from the plate edges with stronger momentum resulting in larger vortex ring. The shape of the primary vortex depended on the shape of the accelerating plate. For the circular plate, all the points on the front edge being equidistant from the plate centroid, fluid particles were evenly displaced from that separation edge. The result was an axis-symmetric ring of primary vortex around a circular vortex core. The asymmetric plates (triangular and square) did not evenly displace air particles from their edges of separation. The result was an asymmetric vortex ring. More air particles separated from the plate at separation points closest to the plate centroid and led to the largest vortical structure there. That is; the primary vortex ring was largest at the midpoints of the plate edges because they were the closest points of separation from the plate centroid. The size of the primary vortex continuously reduced from the mid-points of the plate edges to the corners. The corners had the smallest primary vortical structure due to being furthest points of separation from the plate centroid. The parts of the vortex ring from the two edges of the plate interacted at the corner connecting those edges.Item Low NOx coal burner temperature profile evaluation(2016) Smit, DewanStringent worldwide emissions legislation, the drive to lower carbon emissions, together with the ever increasing demand to preserve the environment has led to a considerable demand for cleaner and more efficient coal combustion technologies. A primary technology for the reduction of emissions of oxides of nitrogen (NOx) is the installation of low NOx coal combustion burners. Extensive research into various burner characteristics and, in particular, the aerodynamic characteristics required to improve combustion performance of low NOx coal burners has been extensively undertaken and is ongoing. In this work the aerodynamic behaviour of a full-scale, aerodynamically staged, single low-NOx coal burner was numerically investigated. The objective of the study was to develop a single low NOx burner CFD model in Ansys Fluent, to better characterize and understand the flame shape in terms of the temperature profile achieved. CFD serve as an additional tool to assist with plant optimization, design proposals and occurrence investigations. To have confidence in the single burner coal combustion CFD model, the results of the model were compared to data obtained from an existing operational low NOx burner on site during a pre-defined load condition. To further improve on the theoretical CFD combustion model, drop tube furnace (DTF) experiments have been done to calculate the single rate Arrhenius kinetic parameters (pre-exponential factor and activation energy) for coal devolatilization and char combustion of the specific South African coal used. The combustion CFD simulations showed with a lower than design air flow through the burner, a reduced amount of swirl was achieved. This reduced amount of swirl produces a jet like flame and influences the way in which the combustion species are brought together. Under these operating conditions the flame distance from the burner mouth was predicted to be 1.2 (m). A very promising result was obtained through CFD and compared well with the in-flame temperature measurement obtained through the burner centre-line of approximately 1.4 (m). In an attempt to improve the aerodynamic profile of the burner under the same operating conditions the swirl angle on the tertiary air (TA) inlet was increased. The increased swirl on the TA inlet of the burner showed an improvement on the aerodynamic profile and had a significant impact on the temperature distribution within the flame. The increased swirl resulted in an improved flame distance of approximately 0.5 (m) from the burner mouth. The effect of increased swirl on the temperature profile of the flame displayed the aerodynamic dependence of the low NOx burner on combustion performance.