Investigation of the flow patterns and power requirements in agitated systems: effects of the design of baffles and vessel base
INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING
Authors: Foukrach, Mohammed; Ameur, Houari
Abstract
The flow patterns and power consumption of a six-blade Rushton turbine (RT) in a cylindrical vessel are characterized in this paper. We focus on the effects of the shape of the vessel base by studying two cases: a conical and a dished shape. In addition, the effects of the height of the vessel base (h(2)) are explored and four cases are considered, namely: h(2)/D = 1/10, 1/6, 1/5 and 1/3 (D: vessel diameter). In the second part of our investigation, a new design of baffles (a triangular-shaped baffle) is suggested and a comparison is made between the performance of the standard and the triangular baffles. The main findings revealed that the conical shape of the vessel base provides a slight enhancement in the axial circulation at almost the same power input for the dished bottomed vessel. For Re < 2 x 10(4), the power required by both types of baffles is the same; however, above this value of Re, a reduction by about 4% in power consumption is given by the standard baffles. Also, and for all shapes of baffles and vessel bases, a reduction in power consumption may be obtained by increasing the height of the vessel base.
Effects of Flame Behaviors on Combustion Noise from Lean-Premixed Hydrogen Low-Swirl Flames
AIAA JOURNAL
Authors: Shoji, Takeshi; Iwasaki, Yuki; Kodai, Kato; Yoshida, Seiji; Tachibana, Shigeru; Yokomori, Takeshi
Abstract
This experimental study explored the influence of global/local flame behaviors on direct combustion noise produced by a lean-premixed gaseous H-2/air low-swirl turbulent jet flame, with a focus on the mechanism resulting in characteristic peaks in combustion noise spectra. Ten kilohertz OH* chemiluminescence and OH planar laser-induced fluorescence (OH-PLIF) imaging were used to study the spatiotemporal evolution of heat release and flame structure fluctuations, respectively, whereas 2-D particle image velocimetry (2-D PIV) measurements at 4 Hz were applied to study the mean-based relation between the velocity/vorticity fields and flame structures. Pressure and global heat release fluctuation measurements carried out alongside these optical diagnostics revealed pronounced double peaks in both combustion noise and global heat release fluctuation spectra at global equivalence ratios of phi >= 0.45. Spectral proper orthogonal decomposition of the OH* chemiluminescence and OH-PLIF images revealed that the first peak in the noise spectra to be caused by flame oscillations over nearly the entire flame region, whereas the secondary peak was attributed to periodically generated vortical flame structures near the downstream side of the flame boundary. The 2-D PIV results suggest that vortical flame structures are likely generated by the interaction between the flame and the inner/outer shear layers.