Vanes

This feature has the same function as the quasi-axial How. In this design, longitudinal radial vanes are welded to the conveyor hub. say 6 to 12 in number, and a ribbon flight is welded on the outer edge of the vanes. The vanes extend from the feed zone to the front hub. 

In this design axial flow of liquor is assured without any circumferential surface slip. The liquor cannot rotate around the helix due to the build-up of cake in front of the flight sealing under the vanes. 

One problem with this dcxdce is the possible uneven distribution of flow between the vanes. To overcome this, a small number of holes in the vanes will allow some flow between the channels. It is important to make the number of channels match the number of feed ports in the conveyor. 

In design this is similar to the fully axial conveyor, except that the vanes arc angled to the radii and there are many tiiore of them. In present designs the number of vanes are 48 to 9h or more depending upon the siKe of decanter. They extend from just forward of the feed zone to the front hub. 

The principle of these vanes is that they act like discs in a disc centrifuge separator. By virtue of the vane angle the effective settling distance for the solids is much reduced. 

---

Impingement demister systems are designed to intercept liquid particles before the gas outlet. They are usually constructed from wire mesh or metal plates and liquid droplets impinge on the internal surfaces of the mist mats or plate labyrinth as the gas weaves through the system. The intercepted droplets coalesce and move downward under gravity into the liquid phase. The plate type devices or vane packs are used where the inlet stream is dirty as they are much less vulnerable to clogging than the mist mat. 

Ship-shaped FPSOs must be designed to weather vane i.e. must have the ability to rotate in the direction of wind or current. This requires complex mooring systems and the connections with the well heads must be able to accommodate the movement. The mooring systems can be via a single buoy or, in newer vessels designed for the harsh environments of the North Sea, via an internal or external turret. Figure 10.33 shows a schematic of the Shell-BP Foinaven FPSO. 

Cracks detection in welds, mounting hardwares, rivets, on blades and vanes, turbine disks, rotors blades, etc. 

Before testing, the blades have to be painted black to ensure a symmetrical thermal radiation. Painting is done in an additional cabin. After the measurement the blades or vanes are cleaned in an ultrasonic bath. 

For qualitative examinations of the inner cooling structures (blades and vanes) the transmission-thermography is used. The procedure is principly depicted in illustration 3. 

The air is streaming through the supply pipes directly into the blade which is mounted on a turntable. The blade is measured in different positions, so that all important surface areas can be examined. The time for a complete blade examination is approximatly 5 minutes. The blades or vanes are mounted manuell, otherwise the process is running fully automatically. 

The efficiency of gas turbines is limited by the maximum allowable turbine inlet temperature (TIT). The TIT may be increased by cooling of the blades and vanes of the high pressure turbine. Cooling channels can be casted into the components or may be drilled afterwards. Non-conventional processes like EDM, ECD or Laser are used for drilling. Radiographic examination of the drilled components is part of the inspection procedure. Traditional X-Ray film technique has been used. The consumable costs, the waste disposal and the limited capacity of the two film units lead to the decision to investigate the alternative of Real-Time X-Ray. 

Much of the fundamental work on prostaglandins and related compounds was car ried out by Sune Bergstrom and Bengt Samuelsson of the Karohnska Institute (Sweden) and by Sir John Vane of the Wellcome Foundation (Great Britain) These three shared the Nobel Prize for physiology or medicine m 1982... 

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

Fig. 7. Control of fan performance with inlet vane control. SoHd lines marked A and N show normal performance without vanes (vanes wide open). As vanes are progressively closed, static and power curves are modified as indicated by dashed lines. Intersection ( - ) of the system resistance curve with these reduced pressure curves at points B, C, D, and E shows how imparting more spin to the inlet air reduces flow. Projecting points A to E vertically downward to the corresponding power curve locates fan power points A through E7 Power savings achieved over throttling control can be estimated by projecting points B through E vertically downward to the A power curve and comparing the value with that from the proper reduced power curve. To...

Axial fans are classified as propeller, tube-axial, and vane-axial (Fig. 9). The choice of fan requited is determined by the resistance (static pressure) the fan must work against as well as the volume flow requited. PtopeUet fans usually discharge iato a plenum or directly iato the atmosphere. Tube-axial fans are usually mounted ia ducts as ia an air conditioning system. Vane-axial fans are also mounted ia ducts but feature a stationary guide vane on the discharge side that straightens the air flow to improve efficiency. Tube-axial fans can work at static pressures up to 623 Pa (2.5 ia. H2O) vane-axial fans can work up to 2000 Pa (8 ia. H2O). 

Fig. 9. Types of axial-flow fans where the dashed arrows denote the direction of air flow (a) propeller fans (b) tube-axial fans (c) vane-axial fans (17).

Fig. 5. Operating sequence for a rotating-vane positive-displacement meter.

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Cup anemometers have shaped cups mounted on the spokes of a wheel. The cups, under the action of the fluid forces, spin in a horizontal plane about a vertical shaft mounted in bearings. Vane or propeller types use a multibladed rotor, the axis of which is parallel to the flow direction as the rotating member. Both designs are commonly used for wind speed measurement or similar appHcations such as the velocity in ventilation ducts. Because of inertia, anemometers are most accurate under steady conditions. Velocity fluctuations cause readings that are too high. 

Current Meters. Various vane designs have been adapted for open-channel flow measurement. The rotating element is partially immersed and rotates rather like a water wheel. Operation is similar to that of vane anemometers. 

Although the above description has concentrated on separation from a smooth surface, separation also occurs at sharp edges. Where separation is undesirable for a process reason, it can often be eliminated by redirecting the flow using turning vanes, ie, forcing it to hug the surface. 

---