Effect of a DC corona electrical discharge on the airflow along a flat plate

Ability of a DC electrical discharge to control low-velocity airflow along a flat plate is analyzed. Specifically, the electrodes are flush mounted on the insulating surface of the plate creating a tangential corona discharge at close vicinity of the wall. In this paper, visualizations of the low-velocity airflow (up to 1.4 m/s corresponding to Re=16 000) along the flat plate are presented. They show that the ionic wind induced by the corona discharge modifies the original airflow considerably, resulting in the airflow reattachment to the wall and reduction of the wake size. Velocity measurements by particle imaging velocimetry and by Pitot tube are conducted in a wind-tunnel loop for higher airflow velocities (up to 11 m/s corresponding to Re=117 800). Results show that the corona discharge at such high airflow velocities does affect significantly the velocity profile within the viscous boundary layer.     

Flow electrification in transformers: relevance of ECT and leakage current measurements

The accumulated charge Q on a well insulated pressboard part being probably the most relevant parameter for flow electrification evolution inside transformers but clearly not measurable in situ, we compare in this paper this parameter with others possible to measure. The two most commonly used are oil parameters: ECT (electrostatic charging tendency) and, to a smaller extent, the continuous aging test for tan /spl delta/. Another is not so often used because of measurements difficulties, but was considered to be one of the most relevant: the leakage current. Thus in this paper we compare on two facilities (specially made for that) the accumulated charge Q to the ECT and leakage current. We find that, even if sometimes a correct correlation exists between these parameters, several cases show a bad correlation. Thus monitoring transformers by analyzing only ECT or leakage current seems to be hazardous.     

Static electrification by laminar flows through artificiallyroughed pipes

The mechanism of static electrification of hydrocarbon liquids flowing through artificially roughed metallic pipes is analyzed. Only the case of a laminar flow is considered. The equations of motion of the liquid are computed in the case of circular pipes with periodic roughness of rectangular cross section in the axial direction. The results reveal the formation of eddies, which depend on the size and the period of the roughness and on the Reynolds number. After determining the charge convected in a smooth pipe and the velocity profile in a rough one, it is possible to predict the convected space charge in terms of the roughness characteristics. The experimental results obtained with different rough pipes and several Reynolds numbers are in good agreement with the predictions, making it possible to explain the observations made during previous experiments on static electrification in rough pipes     

A critical approach to measure streaming current: case of fuels flowing through conductive and insulating polymer pipes

Electrostatic charge generation phenomenon in the case of hydrocarbons flowing through pipes has been studied for a long time. The charge generation depends on the nature of both the liquid and the solid. Because of the introduction of new plastic materials and due to fuel composition evolution, it became necessary to perform a comprehensive study of the subject in the particular case of an automotive environment. The streaming current measurement permits one to characterize charge generation when a fuel flows through a plastic pipe. However, this measurement must be carefully managed. In this paper, we are working on the validity and the accuracy of such measurements. The case of conductive and insulating pipes, and the double-layer development influence, are analyzed and discussed. In particular, we give a detailed methodology in order to measure reliable streaming currents and to wisely derive the space-charge density at the wall (/spl rho//sub w/). Experimental results are presented for some solid/liquid couples.     

Experimental study of the detachment and the reattachment of an airflow along an inclined wall controlled by a surface corona discharge-application to a plane turbulent mixing layer

This paper analyzes experimentally the ability of an electrohydrodynamic actuator to modify the properties of a plane turbulent mixing layer in the wake region of an inclined flat plate (expansion corner). The experiments consists of applying a surface corona discharge established between two electrodes flush mounted on the surface of the test profile. Two cases are investigated. First, one considers the application of the corona to an airflow which is naturally detached at the trailing edge of the test profile and the experiments is repeated with an airflow naturally attached. In this paper, the behavior of the discharge with free air stream up to 35 m/s and measurements by particle image velocimetry for a velocity range from 6 to 16 m/s are presented. The results show that: 1) the discharge regime depends on the free air stream velocity; 2) when the airflow is naturally detached, the corona discharge allows increasing the velocity and the thickness of the mixing layer; 3) when the airflow is naturally attached, it is possible to reduce the velocity and to increase the thickness of the mixing layer; and 4) using a pulse discharge, one observes that the effect of the actuator on the mixing layer is different according to the discharge frequency.     

Gravity effects on upper airway area and lung volumes during parabolic flight

We measured upper airway caliber and lung volumes in six normal subjects in the sitting and supine positions during 20-s periods in normogravity, hypergravity [1.8 + head-to-foot acceleration (Gz)], and microgravity ( approximately 0 Gz) induced by parabolic flights. Airway caliber and lung volumes were inferred by the acoustic reflection method and inductance plethysmography, respectively. In subjects in the sitting position, an increase in gravity from 0 to 1. 8 +Gz was associated with increases in the calibers of the retrobasitongue and palatopharyngeal regions (+20 and +30%, respectively) and with a concomitant 0.5-liter increase in end-expiratory lung volume (functional residual capacity, FRC). In subjects in the supine position, no changes in the areas of these regions were observed, despite significant decreases in FRC from microgravity to normogravity (-0.6 liter) and from microgravity to hypergravity (-0.5 liter). Laryngeal narrowing also occurred in both positions (about -15%) when gravity increased from 0 to 1.8 +Gz. We concluded that variation in lung volume is insufficient to explain all upper airway caliber variation but that direct gravity effects on tissues surrounding the upper airway should be taken into account.     

High prevalence and usual persistence of serum monoclonal immunoglobulins evidenced by sensitive methods in renal transplant recipients

BACKGROUND: The occurrence of serum monoclonal immunoglobulins in kidney transplant recipients is well known but their significance and predictive value for the occurrence of lymphoma are a matter of debate. We therefore conducted a study of monoclonal immunoglobulins by a sensitive method during the long-term follow up of grafted patients. METHODS: Monoclonal immunoglobulins were characterized by high-resolution electrophoresis, conventional immunoelectrophoretic analysis, and a sensitive Western blotting procedure in the serum from 84 renal transplant recipients prior to grafting and subsequently, with a 1-8-year follow-up and excluding the patients who developed posttransplant lymphoma. RESULTS: Low abundance monoclonal immunoglobulins were detectable prior to transplantation in 56 cases (66.6%) and after graft in 72 cases (85.5%) (and in 1 case (1.2%) and 18 cases (21.4%) of cases respectively, by immunoelectrophoresis). These abnormalities were often multiple in individual sera. Monoclonal components detected by immunoblotting were transient in 23.8% of patients only (whereas those evidenced by immunoelectrophoresis usually became undetectable by this method) and their pattern was remarkably stable in the majority of cases. The frequency of post-transplant monoclonal immunoglobulins was higher in patients of more than 50 years of age than in younger patients. The appearance of monoclonal components after grafting and their transient character correlated with CMV infections. No correlation was found with various other parameters. The isotypic distribution of monoclonal immunoglobulins with an IgM, IgG3, and IgG1 predominance and an abnormally low kappa/lambda ratio was the same as that observed in various immunodeficiency states. The monoclonal immunoglobulin pattern in three further patients who developed post-transplant lymphoma was unremarkable. CONCLUSION: Monoclonal immunoglobulins hence are not discriminant for lymphoma and their characterization does not appear to be necessary in the evaluation of followed up grafted patients, at least for a prediction of post-transplant lymphoma.     

Ancient Science, Current Problems: Insight into the Vitality of Electrostatics Research Today

Electrostatics, though one of the oldest sciences, is also nowadays a dynamical and very wide research area. Static charge, well known for its destructive power when accumulating in storms and causing lightning, is now used in many systems as a mastered force to produce acoustic waves, to control aerodynamics, to filter pollution. Its control still remains a very important challenge in many systems, from spacecrafts, high voltage cables, to petro chemistry, and agriculture. We intend here only to highlight some aspects of this very rich and multiform science, without forgetting the great pioneers, Gilbert and Faraday.     

Experimental study of the stacking sequence effect on polymer/composite multi-layers submitted to thermomechanical cyclic loadings

Fast filling of hydrogen pressure tank leads to thermomechanical stresses in vessel structure. In this paper, the aim is to study the thermomechanical behaviour of the material used in the vessel structure. Flat coupons made of the same constituents as the hydrogen tank materials and with different stacking sequences have been tested under quasi-static tensile tests and fatigue. Three types of fatigue tests have been performed in order to understand damage mechanisms due to interactions between thermal and mechanical stresses: thermomechanical fatigue, 1 Hz mechanical fatigue and mechanical fatigue with a constant stress level stage. Damage development has been followed by acoustic emission and microscopic observations. Results show that, whatever the applied loading, there is a significant influence of the stacking sequence of the composite part. Moreover, the comparison of the material response to the different types of fatigue has revealed the harmful role of coupled temperature/mechanical cyclic stresses.