Low-Pressure Structures

For low-pressure structures that are capable of withstanding pressures of not more than 1.5 psi (0.1 bar gauge), original design techniques were based on the Runes (pronounced Roo-ness) equation16  

C ent is a constant that depends on the nature of the combustible material, 

is the smallest dimension of the rectangular building structure to be vented, 

L2 is the second smallest dimension of the enclosure to be vented, and P is the maximum internal pressure that can be withstood by the weakest member of the enclosure. 

Swift and Epstein17 presented a more detailed equation, including many important combustion features  

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The adsorption of cyclohexene, cyclohexane, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene on Pt(l 11) was studied with STM [35, 36]. Figure 7.20a shows an STM image of 2 x 10-s Torr cyclohexene on Pt(l 11). The low-pressure structure shows a hexagonal symmetry with a periodicity of approximately 7 A that is rotated approximately 18-20° with respect to the [1 1 0] direction of the Pt crystal face. From prior... 

Table 10.5 Design criteria for low-pressure structural foam...

Shallenberg, D. Low pressure structural foam molding carry the load with style. Presented at Society of Manufacturing Engineers Annual Meeting, 1999 Vol. CM99-193, 1-13. 

Molded-in stresses are minimal. The thick but hollow sections provide rigidity and do not create sink or warpage problems. The cycle time is reduced because the thick sections are hollow. As the gas is not mixed with the melt, there is no surface splay, which is typical of low-pressure structural foam molding (1). Gas injection is being used with commodity and engineering resins. 

Given a network structure, it is possible to identify loops and paths for it, as discussed in Chap. 7. Within the context of optimization, it is only necessary to consider those paths which connect two different utilities. This could be a path from steam to cooling water or a path from high-pressure steam used as a hot utility to low-pressure steam also used as a hot utility. These paths between two different utilities will be designated utility paths. Loops and utility paths both provide degrees of freedom in the optimization. ... 

The explanation of low-pressure hysteresis proposed by Amell and McDermott some thirty years ago was formulated in terms of the swelling of the particles which accompanies adsorption. The swelling distorts the structure, for example by prising apart weak junctions between primary... 

Figure 4.15. Shock pressure versus specific volume for calcia and fused quartz indicating three regimes fused quartz, low-pressure regime is fused quartz, mixed phase regime, and high-pressure regime representing stishovite. In the case of calcia, the low-pressure phase is the B1 structure, mixed phase is indicated, and the high-pressure phase regime is in the B2 structure.

At the end of the 1970s considerable interest developed in what became known as linear low density polyethylenes (LLDPE) which are intermediate in properties and structure to the high pressure and low pressure materials. While strictly speaking these are copolymers it is most convenient to consider them alongside the homopolymers. The LLDPE materials were rapidly accepted by industry particularly in the manufacture of film. The very low density polyethylenes (VLDPE) introduced by Union Carbide in 1985 were closely related. 

Pressure-tubes allow the separate, low-pressure, heavy-water moderator to act as a backup hesit sink even if there is no water in the fuel channels. Should this fail, the calandria shell ilsdf can contain the debris, with the decay heat being transferred to the water-filled shield tank around the core. Should the severe core damage sequence progress further, the shield tank and the concrete reactor vault significantly delay the challenge to containment. Furthermore, should core melt lead to containment overpressure, the concrete containment wall will leak and reduce the possibility of catastrophic structural failure (Snell, 1990). 

The shock-compression induced structural phase transformation in iron from the low pressure bcc phase to the high pressure hep phase is one of the most visible problems studied in shock-compression science, and its discovery was responsible for widespread recognition of the capabilities of the high pressure shock-compression experiment. The properties of many shock-induced phase transitions are summarized in Duvall and Graham [77D01]. 

Next we consider a molecular crystal composed of N2 molecules, (Vp = 0). Molecular N2 solids at low temperatures and low pressures are in the a structure (Pa3). Using PIMC simulations we studied the low temperature properties of N2 sohds [260] (B = 2.88 K, = 500). In Fig. 6 the temperature dependence of the molar volume is shown for our simulational as well as for experimental [289] data. We note that the classical simulations (corresponding to P = 1) lead to a nonzero slope of the volume at very low temperatures, which is in sharp contrast to the experimental behavior [289]. 

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