Piston effect

Crosswise Airflow that takes place from one side of a space to the other. This may be achieved by one or more jets or by allowing the air to enter the whole of one side surface and extracting the air by the whole area of the opposite side. The latter arrangement provides a piston effect, ensuring good air and contaminant transport. 

Downward The supply air enters at ceiling level or high wall level and is extracted at low level. A perforated ceiling may be used to provide a piston effect. Good air mixing is achieved if cool air enters at high level at the correct temperature and velocity. 

Piston effect The ideal method of air distribution, in which uniform airflow occurs over the whole of a room, such as when the air is injected into the room over the whole surface area of one wall and extracted from the opposite wall. 

Air-vapor interface area must be kept to a minimum consistent with the warning about piston effect if the tank is too small. Various devices for reducing the area can be designed into conveyorized equipment. 

Once the molding tool has closed, the screw feeds the plastic melt axially (piston effect of the screw) into the mold step 1 injection). 

Specific for Near-Critical Fluids the Piston Effect... 

In thermally non-homogeneous supercritical fluids, very intense convective motion can occur [Ij. Moreovei thermal transport measurements report a very fast heat transport although the heat diffusivity is extremely small. In 1985, experiments were performed in a sounding rocket in which the bulk temperature followed the wall temperature with a very short time delay [11]. This implies that instead of a critical slowing down of heat transport, an adiabatic critical speeding up was observed, although this was not interpreted as such at that time. In 1990 the thermo-compressive nature of this phenomenon was explained in a pure thermodynamic approach in which the phenomenon has been called adiabatic effect [12]. Based on a semi-hydrodynamic method [13] and numerically solved Navier-Stokes equations for a Van der Waals fluid [14], the speeding effect is called the piston effecf. The piston effect can be observed in the very close vicinity of the critical point and has some remarkable properties [1, 15] ... 

The piston effect is a thermoacoustic phenomenon. Acoustic compression waves are emitted at heated boundaries, which provoke a homogeneous increase in the bulk temperature. 

The piston effect is a fourth heat transport mechanism. Depending on the applied boundary conditions, the piston effect can transport heat from one side of a thermostat-controlled container to the other on a very short time scale. As the bulk phase is homogeneously heated by the piston effect, a boundary layer is formed at the thermostat-controlled wall. 

Temperature can propagate with the speed of sound. When the critical point is approached more closely than a crossover value given by asymptote analysis, the characteristic time of the piston effect does not monotonicaUy decrease to zero, but tends to reach a constant value, which is the characteristic acoustic time. For CO2 contained in a 10 mm long container set at 1 K above its critical temperature, the crossover value is some mK. At these conditions, the... 

In order to guarantee a high reliability of the PSDs structure, it is important to evaluate the pressure load acting on PSDs due to the vehicles circulation within the system (piston effect). 

This second feature is necessary to avoid the "piston effect," where the area of the parts in the basket can act as a piston and force solvent vapor away from the parts and upward through the open cover and out into the work area (Figure 1.34). 

The pressuriser manway to be the first large opening on RCS, to prevent a rapid core uncovery by a piston effect... 

Introduction of a requirement that the first large opening of RCS is in a hot leg. This is meant to prevent a rapid core uncovery by a piston effect (when there is a opening on the cold side, while there is no opening on the hot side). 

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