An experimental study is performed to determine mixing performance in gas-ladles with throughflow having tap-addition of particles. Behavior of ascending gas bubbles in the plume and recirculating liquid-particle two-phase flow is visualized by means of direct photography aided by white light-sheet illumination. The path line profile and the history of ascending velocity of gas bubbles from the gas-injection nozzle installed at the ladle bottom are measured with the aid of the image processing method. It is disclosed that a rhythm is discovered in bubble detachment from the nozzle tip. This rhythm repeats by cycle and is characterized by two distinct patterns, forming the discrete bubbles regime and continuous jet regime for lower and higher air injection rates, respectively. Inspective of air injection rate, the growth of each bubble can be divided into the initial, intermediate, and final stages. Each stage has its own distinct bubble growth velocity, path line profile, and ascending velocity. The theoretical equation is derived to correlate experimental data on bubble path line.
Pressure distribution and the effect of air injection in the separated flow over a spiked-hemisphere were investigated at a Mach number of 3·3, and Reynolds number around the transitional value. Pressure distribution along the spike as well as over the body was measured in the absence of injection. Air was injected into the separated flow at the spike tip and base and reattachment region through one or more orifices drilled normal to the surface, and the resulting flow patterns were observed using the schlieren technique. The results show that (i) the pressure variation along the spike is similar to a two-dimensional separated flow in the transition régime; and (ii) the mass injection at the spike tip has a strong destabilizing effect regardless of injection rate, while the injection from spike base and reattachment region can be either slightly stabilizing or destabilizing depending on the flow condition.
Axial turbomachines have a radial gap between the casing and the rotor blades. The static pressure difference between the suction and the pressure side of the impeller blades produces a secondary flow over the tip of the rotor blades. This tip clearance flow is important for the aerodynamic performance of the fan. Fan pressure and efficiency drop, and the usable range of the performance characteristics is diminished as the rotor flow is stalled at low flow rates. Previous investigations have shown that one method for increasing the aerodynamic performance is to control the flow in the tip clearance gap via air injection into the gap. The goal of this paper is to compare the different effects of steady and unsteady air injection on the aerodynamic performance curves and to implement various closed-loop extremum-seeking control algorithms. The main purpose of these active flow control methods is to stabilize the flow at operating points, where it is stalled otherwise. To compare the effect of steady and unsteady air injection, the aerodynamic performance curves (fan pressure rise and efficiency) were measured for different sets of frequencies with the air injection rate held constant. To control the air injection rate automatically and to find optimal actuation parameters, a SISO-extremum-seeking control algorithm was applied. For the improvement of the control performance, the controller was extended by a slope-seeker. Moreover, an extended Kalman filter was used to speed up the control via a faster slope detection to accelerate the estimation of the local gradient of the static input-output map of the process. This new approach led to an almost fivefold increase in closed-loop control speed.
A laboratory-scale experimental study of in-situ combustion for enhanced oil recovery is presented. The effects of oil saturation, preheating of the oil-sand bed, porosity of sand, and air-injection rate on both the time history of liquid yield and the total liquid yield have been determined. From the measured temperature profiles and charred length of oil-sand bed, the propagation rate of combustion front has been deduced. The volumetric concentrations of CO2 and O2 in the effluent gas have been measured. The rate of liquid yield is highest in the initial periods of insitu heating or combustion. Air-injection rate, although it has an indirect influence on the temperatures achieved in the bed, exerts only a weak effect on the liquid yield. The increase in porosity of sand increases the liquid yield rate. The relative effects of air injection rate, oil saturation, and the porosity of sand under combustion conditions are simulated well by preheating the bed.
Simulation study of fireflooding (Part 3) - On the influence of residual oil saturation, oil density and air injection rate.