A Mechanism of Polymer Induced Drag Reduction in Turbulent Pipe

Polymer induced drag reduction in turbulent pipe flow was investigated using a non-intrusive laser based diagnostic technique, namely Particle Image Velocimetry (PIV). The drag reduction was measured in a pressure-driven flow facility, in a horizontal pipe of inner diameter 25.3 mm at Reynolds numbers ranging from 35 000 to 210 000. Three high- molecular-weight polymers (polyethylene oxide 2x10^6 – 8x10^6 Da) at concentrations in the range of 5 – 250 wppm were used. The results, obtained from the PIV measurements, show that the drag reduction scales with the magnitude of the normalized streamwise and spanwise rms velocity fluctuations in the flow. This scaling seems to universal, and is independent of the Reynolds number and in some cases also independent of the distance from the wall where the velocity fluctuations are considered. Furthermore, the instantaneous PIV observations indicate that as the level of drag reduction increases, the flow in the pipe is separated into a low-momentum flow region near the pipe wall and a high-momentum flow region in the turbulent core. Based on these findings a new mechanism of polymeric drag reduction is proposed in this paper

Thermographic Particle Velocimetry (TPV) for Simultaneous Interfacial Temperature and Velocity Measurements

AbstractWe present an experimental technique, that we refer to as ‘thermographic particle velocimetry’ (TPV), which is capable of the simultaneous measurement of two-dimensional (2-D) surface temperature and velocity at the interface of multiphase flows. The development of the technique has been motivated by the need to study gravity-driven liquid-film flows over inclined heated substrates, however, the same measurement principle can be applied for the recovery of 2-D temperature- and velocity-field information at the interface of any flow with a sufficient density gradient between two fluid phases. The proposed technique relies on a single infrared (IR) imager and is based on the employment of highly reflective (here, silver-coated) particles which, when suspended near or at the interface, can be distinguished from the surrounding fluid domain due to their different emissivity. Image processing steps used to recover the temperature and velocity distributions include the decomposition of each original raw IR image into separate thermal and particle images, the application of perspective distortion corrections and spatial calibration, and finally the implementation of standard particle velocimetry algorithms. This procedure is demonstrated by application of the technique to a heated and stirred flow in an open container. In addition, two validation experiments are presented, one dedicated to the measurement of interfacial temperature and one to the measurement of interfacial velocity. The deviations between the results generated from TPV and those from accompanying conventional techniques do not exceed the errors associated with the latter

An investigation of film wavy structure in annular flow using two simultaneous LIF approaches

The paper is devoted to development and validation of film thickness measurement techniques in interfacial gas-liquid flows. The specific flow investigated here is that of downwards (co-flowing) annular flow in a vertical pipe, however, many of the observations and findings are transferable to similar flow geometries. Two advanced spatially resolved techniques, namely planar laser-induced fluorescence and brightness-based laser-induced fluorescence , are used simultaneously in the same area of interrogation. A single laser sheet is used to excite fluorescence along one longitudinal section of the pipe, and two cameras (one for each method) are placed at different angles to the plane of the laser sheet in order to independently recover the shape of the interface along this section. This allows us to perform a cross-validation of the two techniques and to analyse their respective characteristics, advantages and shortcomings

Wave Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flow

The downwards co-current gas-liquid annular flows inside a vertically oriented pipe have been experimentally investigated. The measurements and characterisation were performed using advanced optical non-intrusive laser-based techniques, namely Laser Induced Fluorescence, and Particle Image/Tracking Velocimetry. The investigated conditions were in the range of ReL = 306 – 1,532 and ReG = 0 – 84,600. Temporal film thickness time traces were constructed using the Laser Induced Fluorescence images. Based on these, the wave frequency was evaluated using direct wave counting approach and power spectral density analysis. Additionally, qualitative PIV observations revealed the presence of recirculation zones within a wave front of disturbance waves

An experimental study of oil-water flows in horizontal pipes

© BHR Group 2015 Multiphase 17.This paper reports an effort to investigate the effect of flow velocities and inlet configurations on horizontal oil-water flows in a 32 mm ID acrylic pipe using water and an aliphatic oil (Exxsol D140) as test fluids. The flows of interest were analysed using pressure drop measurements and high-speed photography in an effort to obtain a flow pattern map, pressure gradient profiles and measures of the in situ phase fractions. The experiments reveal a particular effect of the inlet configuration on the observed flow patterns. A horizontal plate, installed at the inlet, generates a transition to stratified flow when the plate height closely matched the in situ water height at low water cuts

Development of a Thermographic Imaging Technique for Simultaneous Interfacial Temperature and Velocity Measurements

An experimental technique, hereby referred to as ‘thermographic particle velocimetry’ (TPV) and capable of recovering twodimensional (2-D) surface temperature and velocity measurements at the interface of multiphase flows is presented. The proposed technique employs a single infrared (IR) imager and highly reflective, silver-coated particles, which when suspended near or at the interface, can be distinguished from the surrounding fluid due to their different emissivity. The development of TPV builds upon our previous IR imaging studies of heated liquid-film flows; yet, the same measurement principle can be applied for the recovery of 2-D temperature- and velocity-field information at the interface of any flow with a significant density gradient between two fluid phases. The image processing steps used to recover the temperature and velocity distributions from raw IR frames are demonstrated by application of TPV in a heated and stirred flow in an open container, and include the decomposition of each raw frame into separate thermal and particle frames, the application of perspective distortion corrections and spatial calibration, and the implementation of standard particle image velocimetry algorithms. Validation experiments dedicated to the measurement of interfacial temperature and velocity were also conducted, with deviations between the results generated from TPV and those from accompanying conventional techniques not exceeding the errors associated with the latter. Finally, the capabilities of the proposed technique are demonstrated by conducting temperature and velocity measurements at the gas-liquid interface of a wavy film flow downstream of a localised heater