Coanda effects

Two types of floater aozzles are curreafly ia use and they are based on two different principles. The Bernoulli principle is used ia the airfoil flotatioa aozzles, ia which the air flows from the aozzle parallel to the web and the high velocities create a reduced pressure, which attracts the web while keeping the web from touching the nozzles. The Coanda effect is used to create a flotation nozzle when the air is focused and thus a pressure pad is created to support the web as shown ia Figure 19. 

Smokeless Steam Inspirating Air Coanda effect nozzles are used to inspirate air into the mixing chamber. Claim high efficiency of steam use. Claim low steam noise. Complex nozzles are a high-cost component. Brochure shows much R D back-up of basic design, in marked contrast to those of other vendors. Coanda effect is well understood and widely used, therefore working principle is well established. 

Jets discharging dose to the plane of the ceiling or wall are common in ventilation practice. The presence of an adjacent surface restricts air entrainment from the side of this surface. This results in a pressure difference across the jet, which therefore curves toward the surface. The curvature of the jet increases until it attaches to the surface. This phenomenon is usually referred to as a Coanda effect. The attached jet or, as it is commonly called, wall jet, can result from air supply through an outlet with one edge coincident with the plane of the wall or ceiling fFig. 7.27). Jets supplied at some distance from the surface or at some angle to the surface can also become attached (Fig. 7.28)... 

Coanda effect When a jet becomes and remains attached to a surface due to static pressure differences, as in the case of a wall jet. 

Jet, wall A jet that attaches itself to a surface. See also Coanda effect. 

Interestingly, the film behavior was much more predictable when it flowed over the disc surface containing the raised lips arising from the punching operation. Film flow on the alternate side tended to leak through the disc, particularly at lower liquid flows, presumably due to the Coanda effect as liquid negotiated the rounded edge of the holes. 

Recycle-flow Coanda-effect Mixing Based on Taylor Dispersion Most Relevant Citations... 

The use of the Coanda effect is based on the desire to have a second passive momentum to speed up mixing in addition to diffusion [55, 163], The second momentum is based on so-called transverse dispersion produced by passive structures, which is in analogy with the Taylor convective radial dispersion ( Taylor dispersion ) (see Figure 1.180 and [163] for further details). It was further desired to have a flat ( in-plane ) structure and not a 3-D structure, since only the first type can be easily integrated into a pTAS system, typically also being flat A further design criterion was to have a micro mixer with improved dispersion and velocity profiles. 

Relying on the knowledge of flow pattern generated by the Coanda effect inplane micro valves and micro pumps, it was envisaged to transfer this technique to a micro-mixer device [55], In the latter case, using a Tesla structure (see [163] for geometric details), the flow is redirected and collision of streams occurs. 

Mixer 87 [M 87] Coanda-effect Micro Mixer with Tesla Structures... 

Figure 1.181 Schematic of the action of the Coanda effect on the fluid flow, expressed by major stream directions [163] (by courtesy of RSC).

Mixer type Coanda-effect micro mixer with Tesla structures Angle of turn for the main passage 90°... 

A novel in-plane passive micromixer using coanda effect, in Ramsey, J. M., van den Berg, A. (Eds.), Micro Total Analysis Systems, Kluwer, Dordrecht, 2001, 31-33. 

V. Sidiropoulos and J. Vlachopoulos, An Investigation of Venturi and Coanda Effects in Blown Film Cooling, Int. Polym. Process., 15, 40 (2000). 

Among the areas not covered here is that of intrinsic instabilities associated with chemical-kinetic mechanisms, as exhibited in cool-flame phenomena, for example these subjects are touched briefly in Section B.2.5.3. Intrinsic instabilities of detonations were considered in Section 6.3.1 and will not be revisited. Certain aspects of intrinsic instabilities of diffusion flames were mentioned briefly in Section 3.4.4 diffusion flames appear to exhibit fewer intrinsic instabilities than premixed flames, although under appropriate experimental conditions their effects can be observed, as indicated at the end of Section 9.5.2. Certain chamber instabilities that are not related to acoustic instabilities (such as Coanda effects—oscillatory attachment of flows to different walls) will not be discussed here, but reviews are available [1]. 

In the cross-flow air classifier (Figure 5.7) the main air is introduced at (a,) and secondary air at ( 2)- Both streams are bent round a solid wall (b) and the resulting flow follows the bend without leaving the wall or forming vortices. The so-called Coanda effect helps to maintain the flow round the bend for approximately 90° and this is enhanced by the application of suction. 

The flow instability shows up at high liquid superheats. A jet may be entrapped by the wall of the channel superimposed flange and spread out in the plane perpendicular to the direction of its motion (the Coanda effect ). The force of the jet recoil R acting on a chamber with a liquid increases with saturation pressure in the chamber, but on attaining conditions of explosive boiling-up and a jet collapse (spread along the surface of the operating chamber) the value of R decreases (Fig. 8). 

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