Piston Strategy

The highest effectiveness can be achieved with the piston strategy. The contaminant concentration, temperature or humidity, and the local effectiveness are functions of the location and the power of the sources in relation to the supply and exhaust openings. With a homogeneous distribution 

To create unidirectional air flow field over the room area by supply air 

To support flow field created by density differ enecs by replacing the airtiaw our from th room arCci wuh iir 

To control air i.ondi witliin selected xune 111 the roam hy the supply a r and allow stratification of heat and contain Hants Ml che orher room arCcTH 

7o provide Lriifonn c Olid It ions through out the vcntilatcti space 

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FIGURE 8.10 Examples of air distribution and exhaust methods for the piston strategy. 

The design criterion of the piston strategy is to overcome all the air currents opposite to the directional airflow created within the room. 

Srratification is a desirable strategy to provide efficient room air condi-noning with much less effort than using the piston strategy. Its mam application in room air conditioning is the thermal replacement method. However, it can also be applied for contaminants without any thermal buoyancy sources that have different density from the room air. Examples of different air distribution methods to create thetma teplacement are presented in Fig. 8.12. 

A similar temperature and contaminant distribution throughout the room is reached with stratification as with a piston. The driving forces of the two strategies are, however, completely different and the distribution of parameters is in practice different. Typical schemes for the vertical distribution of temperature and contaminants are presented in Fig. 8.11. While in the piston strateg) the uniform flow pattern is created by the supply air, in stratification it is caused only by the density differences inside the room, i.e., the room airflows are controlled by the buoyancy forces. As a result, the contaminant removal and temperature effectiveness are more modest than with the piston air conditioning strategy. 

Coring Strategy. Sediment cores were collected with a thin-walled polycarbonate tube fitted with a piston and operated from the lake surface by rigid drive rods (30). This device recovers the very loose uncompacted sediment surface as well as deeper strata without disturbance or displacement (core-shortening, cf. refs. 31 and 32). Core sections were extruded vertically from the top of the tube into polypropylene collection jars, transported on ice to the laboratory, and stored at 4 °C until analysis. 

It is important to describe how fluids are propelled, as well as the main liquid drivers such as peristaltic pump [1], piston pump [89], reciprocating pump [154], gas propeller [25] or other strategies for this task, e.g., kinematic focussing [155] or gravity [156]. The peristaltic pump is by far the most common device for propelling fluids in flow analysis therefore, the absence of any information assumes the use of such a pump. Characteristics of the pump tubing are mentioned in most publications, but this information is not needed unless there is an incompatibility with the propelled fluids. 

Another strategy for exploiting piston movements in flow systems involves the attachment of the piston to a diaphragm. The moving piston then acts as a pivot and its movements press and release the diaphragm. The wetted surface of the pump is normally made of PEEK or Viton [28]. One-way directional check valves (usually ball-style valves) are required. 

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