Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
24
1
2012
TWO-FLUID-1D-AVERAGED MODEL EQUATIONS FOR A PIPE UNDERGOING ARBITRARY MOTIONS
1-45
10.1615/MultScienTechn.v24.i1.10
Herve
Lemonnier
DTN/SE2T/LIEX/ CEA/Grenoble, 38054 Grenoble Cedex 9, France
N.
Coutris
Department of Mechanical Engineering, Clemson University, Clemson South Carolina 29634-0921, USA
fluid structure interaction
two-phase flow model
mechanical loads
water hammer
WAHALoads
The WAHA code aims at describing two-phase water hammers in piping systems with emphasis on the calculation of the mechanical loads induced on the pipes. A new two-fluid model is derived which is appropriate for studying the interaction of a deformable pipe with the flow it contains. The equations are provided in two different sets of variables: Eulerian and Lagrangian with respect to the pipe. The new equations are compared to those of the plain two-fluid model for a rectilinear pipe and obviously they do not seem to be of a different nature, though many new terms appear, the significance of which is shortly outlined. The theoretical derivation of these equations is aimed primarily at calculating reaction forces applied on a piping system from the results of one-dimensional thermal-hydraulic code for future inclusion in full form in the WAHA code.
HYDRODYNAMIC STUDY OF A HOLLOW FIBER MEMBRANE SYSTEM USING EXPERIMENTALLY AND NUMERICALLY DERIVED SURFACE SHEAR STRESSES
47-66
10.1615/MultScienTechn.v24.i1.20
Nicolas
Ratkovich
University of Los Andes
M.
Hunze
FlowConcept GmbH, Vahrenwalder Strasse 7, 30165 Hannover, Germany
I.
Nopens
BIOMATH, Department of Mathematical Modelling, Statistics and Bioinformatics. Ghent University, Coupure Links 653, B-9000, Ghent, Belgium
submerged membrane system
gas-liquid flow
shear stress
CFD
Computational fluid dynamics (CFD) models can be used to gain insight into the shear stresses induced by air sparging on submerged hollow fiber membrane bioreactor (MBR) systems. It was found that the average range of shear stresses obtained by the CFD model (0.30-0.60 Pa) and experimentally (0.39-0.69 Pa) were in good agreement, with an error less that 15%. Based on comparison of the cumulative frequency distribution of shear stresses from experiments and simulation, (i) moderate shear stresses (i.e., 50th percentile) were found to be accurately predicted (model: 0.24-0.45 Pa; experimental: 0.25-0.49 Pa) with an error of less than 5%; (ii) high shear stress (i.e., 90th percentile) predictions were much less accurate (model: 0.60-1.23 Pa; experimental: 1.04-1.90 Pa) with an error up to 38%. This was attributed to the fact that the CFD model only considers the two-phase flow (50th percentile) and not the movement of fibers. The latter is likely due to shielding effects or fiber sway, significantly affecting shear stresses at the high end of the distribution. However, this was not accounted for in the model in this study. Despite these deviations, the CFD model in its current state can be used to gain insight into the order of magnitude and shear stress distribution. Inclusion of fiber movement is recommended.
OSCILLATING MENISCUS AND SLUGS IN A SQUARE CAPILLARY: A HYDRODYNAMIC STUDY
67-87
10.1615/MultScienTechn.v24.i1.30
Ajay
Tripathi
Department of Mechanical Engineering, Jaypee University of Engineering & Technology , A-B Road, Raghogarh, Guna (M.P.), India
S. K.
Agrawal
Mechanical Engineering Department, Motilal Nehru National Institute of Technology, Allahabad (U.P.), India
contact angle
curvature
oscillating meniscus
square capillary
Improvements in fabrication capability have given rise to mini/micro systems for heat and mass transfer operations. These systems may involve single- as well as multiple-phase flow. Understanding the local hydrodynamics of uniform/oscillating menisci or air plug/liquid slug/Taylor bubble flow inside such systems (i.e., capillaries/channels) will help us in manipulating the performance parameters, which will further improve the efficiency of multiphase microsystems. The present work aims not only to study the interfacial contact line behavior of an oscillating single meniscus and liquid slug formed between different fluids, but also various hydrodynamic properties. An eccentric cam follower system has been fabricated to provide sinusoidal oscillations of the fluid in a square glass capillary having hydraulic diameter of 2.0 mm. Experiments are done with two different fluids, namely, deionized water and silicone oil. A high-speed CCD camera is used to take images of the oscillating meniscus. Contact angle measurements are carried out for water along the length of the capillary at different oscillating frequencies, ranging from 0.25 Hz to 0.75 Hz. Besides dynamic contact angle information, curvature values of the oscillating Taylor front, film thickness, and pinning effect were observed for these fluids.