Stratification design

The persons are selected on a stratified random sampling basis, with stratifications designated according to the type of exposure, quantity of exposure, degree of hazard present, and other criteria considered important to the representativeness of the sample. The objective is to discover causal factors that are critical, that is, that have contributed to an accident or potential accident situation. The unsafe acts and unsafe conditions identified by this method then serve as the basis for the identification of accident potential problem areas and the ultimate development of countermeasures designed to control accidents at the no-loss stage [p. 304],... 

CVD reactions are most often produced at ambient pressure in a freely flowing system. The gas flow, mixing, and stratification in the reactor chamber can be important to the deposition process. CVD can also be performed at low pressures (LPCVD) and in ultrahigh vacuum (UHVCVD) where the gas flow is molecular. The gas flow in a CVD reactor is very sensitive to reactor design, fixturing, substrate geometry, and the number of substrates in the reactor, ie, reactor loading. Flow uniformity is a particulady important deposition parameter in VPE and MOCVD. 

The energy of large and medium-size eddies can be characterized by the turbulent diffusion coefficient. A, m-/s. This parameter is similar to the parameter used by Richardson to describe turbulent diffusion of clouds in the atmosphere. Turbulent diffusion affects heat and mass transfer between different zones in the room, and thus affects temperature and contaminant distribution in the room (e.g., temperature and contaminant stratification along the room height—see Chapter 8). Also, the turbulent diffusion coefficient is used in local exhaust design (Section 7.6). 

Characteristic length, / in Eq. (7.28), depends on the application e.g., for local exhaust design / equals the characteristic hood dimension, and for room air distribution design with a temperature or contaminant stratification, / equals the room height. 

In rooms where air and contaminant movement is dominated by thernnal energy of heat sources (e.g., in rooms with natural or displacement ventilation), temperature and contaminant stratification along the room height is created. Air supply and exhaust in such rooms are designed not to disturb the natural pattern of air movement created by heat sources cooled air enters the room in... 

Shilkrot, E. O., and A. M. Zhivov. 1992. Room ventilation with designed temptrature stratification. In Roomvent 92 Proceedings of the Third International Conference on Air Distrihu-timi in Rooms, vol. 1. Aalborg, Denmark. 

The mechanism of turbulent heat exchange between tbe upper and lower zones in the case of ventilation system design with temperature stratification is described in Section 7.3. 

A characteristic of many industrial halls is that zones of occupancy take up only a small portion of the room volume and height. In addition, the flows are normally buoyancy dominated. This results in a vertical temperature stratification that can be utilized for room air conditioning design in order to achieve effective climatization along with low energy consumption. 

These case examples illustrate the dependence of the stratification of temperature and contaminants on several parameters, which in some cases increase and in other cases decrease the effectiveness. Al the parameters should be included in calculations when designing the system combination of the room air conditioning methods. 

In all warm-air design applications, consideration must be given to the effects of stratification in tall buildings. Stratification increases the roof and high-wall fabric losses and the air change rate by the stack effect, and hence the ventilation loss. These effects may increase the heat loss by 25% over that of a radiant heating system. 

If a significant thermal stratification is expected inside the booth, the pressure difference between the inside and the outside ot the booth, which increases with height has to be taken into account during the design prtKcss. Appropriate design features include efficient capture devices in the ceiling o( the booth and an overall dense structure of the booth. 

Note that the recommended value for p is not always conservative. In some cases, heat input may be so high that the safety valve cannot vent all the generated vapor. In such cases, the internal pressure will rise until the bursting overpressure is reached, which may be much higher than the vessel s design pressure. For example, Droste and Schoen (1988) describe an experiment in which an LPG tank failed at 39 bar, or 2.5 times the opening pressure of its safety valve. Note also that this method assumes that the fluid is in thermodynamic equilibrium yet, in practice, stratification of liquid and vapor will occur (Moodie et al. 1988). 

The flow and return connections will be designed to suit the flow rates and temperature differentials required. The water-return connection will be fitted with either an internal diffuser or a venturi nozzle to assist mixing of the water circulating within the shell and prevent water stratification. The flow connection will incorporate the... 

Stratification and steam blanketing may add further to the insulating effects and also promote both thermal stress in excess of design limits and waterside corrosion. Over the longer term, considerable metal oxide is formed and cracking and creep develop. 

FW supply and on-off/modulation mechanisms. The on-off supply of FW tends to create cold-zone stratification within the boiler, leading to reduced steam production rates and misting (fogging) in the steam space. Boiler plant designs that provide for the continuous provision of FW through a modulated FW supply prevent these problems. 

Determine the components of variance that should be built Into the statistical design Proper stratification of the study area will allow Identification and quantification of several sources of variation. The sources of variation that can be controlled by the sampling are determined by the particular sampling design and by the pattern of sample collection superimposed over the area. An analysis of variance of the data provides estimates of the components of variance ... 

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