ENERGY INPUT OF A CENTRIFUGAL STAGE INTO THE ATTACHED PIPING SYSTEM DURING MILD SURGE 111111111111, L11111111111

ABSTRACT NOMENCLATURE . Subjected to an oscillating flow rate a compressor may feed ad-A area ditional (excitational) energy into the attached piping system. The Ard relative distance from the stability line relation between this additional energy input and the instantaneous a velocity of sound behavior of a centrifugal compressor stage is dealt in a first part. B stability parameter as defined by Tperiod P In a second part for the same centrifugal compressor the energy To time constant contribution of several stage segments during mild surge oscillat time tions was determined from detailed instantaneous measurements. As V volume a result the contribution of each stage segment to the conservation V volumetric flow rate of the mild surge pulsation emerges. Although at the investigated r radius mild surge frequencies the stage segments no longer behave strictly U2 impeller tip speed quasi-steadily their contribution to the additional energy input is Greek symbols found to be mainly determined by the slope of their quasi-steady characteristic. am perturbation quantit

High Rates of Hepatitis C Virus Reinfection and Spontaneous Clearance of Reinfection in People Who Inject Drugs: A Prospective Cohort Study

Hepatitis C virus reinfection and spontaneous clearance of reinfection were examined in a highly characterisedcohort of 188 people who inject drugs over a five-year period. Nine confirmed reinfections and 17 possiblereinfections were identified (confirmed reinfections were those genetically distinct from the previous infection andpossible reinfections were used to define instances where genetic differences between infections could not beassessed due to lack of availability of hepatitis C virus sequence data). The incidence of confirmed reinfection was28.8 per 100 person-years (PY), 95%CI: 15.0-55.4; the combined incidence of confirmed and possible reinfectionwas 24.6 per 100 PY (95%CI: 16.8-36.1). The hazard of hepatitis C reinfection was approximately double that ofprimary hepatitis C infection; it did not reach statistical significance in confirmed reinfections alone (hazard ratio [HR]:2.45, 95%CI: 0.87-6.86, p=0.089), but did in confirmed and possible hepatitis C reinfections combined (HR: 1.93,95%CI: 1.01-3.69, p=0.047) and after adjustment for the number of recent injecting partners and duration of injecting.In multivariable analysis, shorter duration of injection (HR: 0.91; 95%CI: 0.83-0.98; p=0.019) and multiple recentinjecting partners (HR: 3.12; 95%CI: 1.08-9.00, p=0.035) were independent predictors of possible and confirmedreinfection. Time to spontaneous clearance was shorter in confirmed reinfection (HR: 5.34, 95%CI: 1.67-17.03,p=0.005) and confirmed and possible reinfection (HR: 3.10, 95%CI: 1.10-8.76, p-value=0.033) than primary infection.Nonetheless, 50% of confirmed reinfections and 41% of confirmed or possible reinfections did not spontaneouslyclear.Conclusions: Hepatitis C reinfection and spontaneous clearance of hepatitis C reinfection were observed at highrates, suggesting partial acquired natural immunity to hepatitis C virus. Public health campaigns about the risks ofhepatitis C reinfection are required

Visualization of rotating stall in a full size water model of a single-stage centrifugal compressor

Un banc d'essais en eau d'un étage de compresseur centrifuge à diffuseur aubé a été construit en vue de l'étude des instationnarités d'écoulement telles que le décollement tournant. Ce modèle permet de ralentir les phénomènes dans un rapport allant de 15 à 50 et offre ainsi des possibilités de visualisation dans une machine à l'échelle 1. Des mesures temporelles de pression en divers emplacements de la machine ont démontré l'aptitude du modèle à reproduire les principales caractéristiques du décollement tournant observé dans les essais en air. L'analyse en eau a ainsi permis des études d'instationnarités sur une large plage de fonctionnement. A débit partiel, l'instabilité de l'écoulement se traduit par une seule cellule de décollement tournant s'étendant de la conduite d'entrée où un vortex avec mouvement de précession apparaît, jusqu'à la sortie du diffuseur, avec une vitesse angulaire égale à 0,28 fois la vitesse de rotation de la machine. Les instationnarités au début de ce décollement et leurs évolutions ont été visualisées (vidéo). Les images montrent bien le rôle prépondérant des échanges de quantité de mouvement entre la roue et le diffuseur et ont conduit à la mise en place d'un modèle permenant l'évaluation de la vitesse de propagation à l'aide de données géométriques