Passive system

In an electrochemical polarization experiment on a passive system tire onset of localized dissolution can be detected by a steep current increase at a very distinct anodic potential (tire pitting potential, —see figure... 

L. D. Martin and W. P. Banks, "Electrochemical Investigation of Passivating Systems," Proceedings of the 35th International Water Conference,... 

These three passive systems are important in the technique of anodic protection (see Chapter 21). The kinetics of the cathodic partial reaction and therefore curves of type I, II or III depend on the material and the particular medium. Case III can be achieved by alloying additions of cathodically acting elements such as Pt, Pd, Ag, and Cu. In principle, this is a case of galvanic anodic protection by cathodic constituents of the microstructure [50]. 

Instead of the human being conceptualized as a passive system element, to be treated in the same way as a pump or valve, the cognitive approach emphasizes the fact that people impose meaning on the information they receive, and their actions are almost always directed to achieving some explicit or implicit goal. 

The fifth type of passive system is the natural convective loop, in which the collector is placed below the living space and the hot air that is created rises to provide heat where it is needed. This same principle is nsed in passive solar hot water heating systems known as thermosiphons. The storage tank is placed above the collector. Water is heated in the collector, becomes less dense, and rises (converts) into the storage tank. Colder water in the storage tank is displaced and moves down to the collector where it is heated to continue the cycle. 

The third approach is called the thermodynamic theory of passive systems. It is based on the following postulates (1) The introduction of the notion of entropy is avoided for nonequilibrium states and the principle of local state is not assumed, (2) The inequality is replaced by an inequality expressing the fundamental property of passivity. This inequality follows from the second law of thermodynamics and the condition of thermodynamic stability. Further the inequality is known to have sense only for states of equilibrium, (3) The temperature is assumed to exist for non-equilibrium states, (4) As a consequence of the fundamental inequality the class of processes under consideration is limited to processes in which deviations from the equilibrium conditions are small. This enables full linearization of the constitutive equations. An important feature of this approach is the clear physical interpretation of all the quantities introduced. 

Passive systems to decrease temperature fluctuations. The PCM is integrated into building materials or building components and increases the thermal mass of the building. 

Of the study homes mentioned in the previous section, some passive systems seemed sufficient to lower the radon concentrations, while in all cases, active systems resulted in significantly lower concentrations. Table 31.1 summarizes the findings of these particular projects.9... 

Overall Design Considerations Active and Passive Systems... 

When designing an active or passive system, many design considerations are common to the two systems. For example, some provision for removal of condensation that forms in the exhaust pipe will be required. Routing of the pipes from the basement to the roof must be considered when the house is being designed. Placement of the exhaust is extremely important. 

Removal of condensation is an important consideration. Water collecting in an elbow or other low point of the system can effectively block the pipe, and reduce or disable the system. Builders should strive to design a pipe system that will allow condensation to run back through the pipe to the subslab aggregate. This can be accomplished by ensuring that the pipe run is vertical to the entire distance from the basement to the exhaust. A completely vertical pipe run with no bends or elbows will also provide a pipe system with lower static pressure losses that will enhance the effectiveness of both active and passive systems. If elbows or a low point is incorporated into the... 

Some builders prefer laying perforated PVC piping in the gravel before the slab is poured and connecting the perforated pipe to the exhaust pipe of the system. The use of perforated pipe may not be necessary in active systems but probably will assist a passive system. Membranes beneath the slab help us to keep a continuous radon barrier in the event of slab cracking. 

A passive system is much the same as an active system with the exception of the fan. A passive system relies only on stack and wind effects to produce the pressure field. As can be seen in Table 31.1, passive systems do not always reduce radon concentrations to acceptable levels, but careful design and installation may improve the effectiveness of a passive system. 

It is probably beneficial to a passive system to lay a network of perforated drainage pipes in the gravel bed beneath the slab prior to the pour. The use of horizontal pipe runs and elbows in a passive system may greatly lessen the effectiveness the system and should be a voided. Some builders use a 6-in. PVC pipe in a passive system to help lessen the pressure drop. 

This paper presents data from a passive system implemented to treat the mine water from the abandoned mining site of Jales, in North Portugal. The layout of the plant comprises initial oxidation and neutralization in a limestone channel. The present work is focused on the resulting products that are generically named ochre-precipitates. 

This study, focused on ochre-precipitates from a passive system, can be summarized in the following items ... 

Site conditions favorable for the construction of these systems are generally those that are suitable for agricultural drainage. Most functioning passive recovery systems are based on the principles of drainage design. Typically, passive systems are constructed where ... 

All passive systems rely on the natural hydraulic gradient to transport LNAPL to the recovery location. Under most circumstances, the flow of LNAPL into this type of system is very slow. At open surface recovery sites (trenches and ponds) constructed in low-permeability soils, the LNAPL migrates in so slowly that free volatile product often evaporates before it accumulates sufficiently to be collected. High-permeability soils typically are subject to a low hydraulic gradient, which limits the rate of flow into the system. Conditions that are more favorable to passive recovery, shown schematically in Figure 7.1, include ... 

Additional information on active and passive systems is contained in Chapter 7. 

Measures to reduce the impact of fire include active and passive systems. Active systems include automatic sprinkler, water deluge, water mist, gaseous agent, dry chemical, foam, and standpipe handle systems. Passive protection is provided by fire resistive construction, including spray-applied or cementitious fireproofing of steel, concrete/masonry construction, and water-filled steel columns. Chapter 7 provides details on the design of fire protection systems. 

This chapter provides the fundamentals of design for passive and active fire protection systems. A passive system should be used wherever possible, as this is an inherently safer approach than an active system. 

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