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

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

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

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

Screening for Uncorrected Refractive Error Among Primary School Children In South-South Nigeria

A study on screening for uncorrected refractive error in primary school children has not been done in Bayelsa State, South-South Nigeria. This study aims to screen for uncorrected refractive error among primary school children in Bayelsa State and use the data to plan for an effective school Eye Health Program. A cross sectional study on screening for uncorrected refractive error in school children was carried out in Yenagoa Local Government Area of Bayelsa State, South-South Nigeria in June 2009. A multistage sampling technique was used to select the study population (pupils aged between 5-15 years). Visual acuity for each eye was assessed by an optometrist and a community ophthalmic nurseoutside the classroom, at a distance of 6 meters. Unaided distant visual acuity of 6/12 or less which improved with pin hole,in a child not currently using corrective glasses, was considered an uncorrected refractive error. Funduscopy was done inside a poorly lit classroom. Data was analyzed with EPI INFO version 6 and scientific calculator. A total of 1,242 school children consisting of 658 females and 584 males were examined.About 97.7% of pupils had normal vision of 6/6 while 26 eyes (1%) had visual acuity of 6/12 or less. Of the 26 eyes with visual acuityof 6/12 or less, 22improved when presented with pin-hole. A total of 12 pupils had uncorrected refractive error, giving a population prevalence of 0.97%.The 8-10 yearage-range had the highest proportion (41.7%) of cases of uncorrected refractive error. The prevalence of uncorrected refractive error in primary school children in Bayelsa State, South-South Nigeria was 0.97% and most eyes (97.7%) had normal vision.Keywords: Uncorrected refractive error, Screening, School children

Dynamic testing and modelling of solar collectors

Solar-thermal collectors operating under real conditions rarely reach steady-state operation due to temporal fluctuations in the climate/environmental conditions and thermal loads. Figure 1 shows typical UK weather map. The incident irradiance, the ambient temperature and the wind speed can vary during the day as shown in Figures 2-4. These figures show the data collected in London at a temporal resolution of 1-minute. As a consequence of the time-varying inputs, collector models that describe dynamic behaviour are required for the accurate prediction of the thermal output and for optimising the control strategy of such systems. We develop detailed 3-D thermal sub-models that can be adapted to various geometries or collector configurations, including vacuum-tube thermal collectors, sheet-and-tube thermal and PV/T collectors

Solar heat and power with thermal energy storage in the UK

Solar energy has the potential to cover a high fraction of the demand for heat and electricity in residential buildings. Fig. 1 shows the variation in incident solar irradiation received across Europe. In London the annual solar irradiation is ~1100 kWh/m2 per year, while the typical domestic energy consumption per household is ~12000 kWh/year for heating and ~4000 kWh/year for electricity. Thus the solar energy received on a rooftop of ~15 m2 is enough potentially enough to provide the entire annual demand for domestic energy. Our research focuses on various aspects of two solar technologies for the combined provision of heating and power (CHP): solar organic Rankine cycle systems with low-to-medium temperature solar-thermal collectors (Figs. 2-3) and hybrid photovoltaic/thermal (PVT) systems. (Fig.4)

Knowledge, Attitude And Practice Of Screening For Cervical Cancer Among Female Students Of A Tertiary Institution In South Eastern Nigeria.

Background: Cervical cancer is the second commonest cancer of females worldwide and the commonest cancer of the female genital tract in our environment. It can be prevented through early detection by cervical screening (Pap smear). Objective: The objective of this study is to determine the knowledge, attitude and practice of cervical cancer screening among female undergraduates. Method: A pre tested questionnaire was administered to third and fourth year female students of the Faculty of Natural Sciences, Nnamdi Azikiwe University Awka, Nigeria. Result: Out of the 220 students involved in the study, 134 (60.9) had knowledge of cervical cancer and 118 (53.6%) were sexually active with the average age at sexual debut being 21.2 years. The mean age of the students was 23.8 years and the age range was 17 to 39 years with 175 (80%) in the age range of 20- 29 years. About 2/3 of the students did not know about Pap smear and worse still, none of them had undergone a Pap screening test before. This low participation in screening for cervical cancer was attributed to several reasons including ignorance of the existence of such a test, lack of awareness of centers where such services are obtainable, ignorance of the importance of screening and the risk factors to the development of cervical cancer. Conclusion: There is good level of awareness of cervical cancer among the female undergraduates but poor knowledge and participation in cervical cancer screening. The development of a comprehensive cervical cancer screening strategy is being recommended to improve participation with a view to prevent cervical cancer by early detection and treatment of the pre-malignant stages. Keywords: Cervical cancer, screening, female undergraduates. Nigerian Journal of Clinical Practice Vol. 11 (3) 2008: pp. 216-21