Choke points

So, when q, > q t (low subcooling, flashing before the choke print), use the compressible solution, Eq. (26-95) with q p = q,. Otherwise (for high subcooling, no flashing before the choke point), use the hquid orifice equation, Eq. (26-94). 

The increase in compressor pressure ratio decreases the operating range of the compressor. The operating range of the compressor stretches from the surge line at the low flow end of the compressor speed line to the choke point... 

The choke point is found by the usual maximization relationship ... 

Catalysts are so important in chemical industry that combinatorial-type approaches will certainly be utilized as tools in the identification and optimization of both heterogeneous and homogeneous catalysts. These are, in many cases, high value-added, commercially important materials. In any research activity it makes sense to remove any choke points that impede progress. However, many engineering considerations are important in producing commercial catalytic processes thus, combinatorial-type approaches are unlikely to be a panacea. Still, a variety of unanticipated discoveries may result from various efforts that are under way. 

In relief systems of uniform diameter, the choke point (if choking, occurs) will be at the downstream end of the pipe. However, if the relief system comprises more than one diameter, then multiple choke points are possible and it will be necessary to determine the position of the choke point that limits the flow. This can be a complex calculation, for which there are two common cases ... 

The ERM[51 assumes no flashing jin the relief system until the choke point is reached, and flashing at equilibrium rate at the point of choking. See Figure 9.3 which distinguishes between the assumptions of the ERM and HEM for the case in which saturated liquid is relieved. The simplified ERM assumes that saturated liquid rather... 

No flashing (non-equilibrium flow) until choke point... 

If the relief line contains changes in diameter, then each expansion is a potential choke point (see 9.2 and Figure 9.5). Simpsont2] suggests a calculation procedure which can be used in such cases. A number of computer codes can be used for relief lines of changing diameter (see Annex 4). 

Figure 9.5 EXAMPLE OF PRESSURE DISTRIBUTION ALONG RELIEF LINE WITH MULTIPLE CHOKE POINTS...

A discussion of the different types of assumption that can be made in two-phase flow models is given in Chapter 9. DIERS[8] recommended the use of the homogeneous equilibrium model (HEM) for relief sizing, and so, preferably, a code which implements the HEM should be chosen. The model will need to incorporate sufficiently non-ideal modelling of physical properties and provision for multiple line diameters and potential choke points, as required by the application. 

If relief is via a bursting disc, the flow capacity of the relief system will normally depend on friction and choke points in the relief system. The only exception is where friction is not important (LE/D less than about 40), where equation (A6.4) can be used.) Where friction is significant, an isometric sketch of the route of the relief system will be required to determine the capacity. If the system is to be of constant diameter, then using the sketch, the total equivalent length, LE, of the route, including the frictional resistance of bends and fittings can be determined111. This can also be expressed in terms of total frictional velocity head loss, K ... 

For a system of constant diameter (giving a single potential choke point at the end of the pipe), and if the gas is ideal, then the Design Charts for adiabatic flow of gases, given in Perry111 or the Omega method with = 1 (see Annex 8) can be used to determine the flow capacity. is a parameter within these charts. 

Let s assume that the controlling resistance to heat transfer is inside the tube. It does not matter whether this resistance is due to fouling, high viscosity, or low flow. The heat flow must still pass through the smaller surface area inside the tube. The smaller area acts as a choke point that restricts heat flow. Let s assume that 90 percent of the resistance to heat transfer is inside, and 10 percent outside, the tubes. The overall increase in the heat-transfer capacity of the exchanger would, at best, be roughly 15 percent. 

The calculated speed of sound in the gas can be thought of as that at the valve (i.e. its choke point). 

The exit Mach number M2 may not exceed unity. M2 = 1 corresponds to choked flow sonic conditions may exist only at the pipe exit. The mass velocity G in the charts is the choked mass flux for an isentropic nozzle given by Eq. (6-118). For a pipe of finite length, the mass flux is less than G under choking conditions. The curves in Fig. 6-21 become vertical at the choking point, where flow becomes independent of downstream pressure. 

Rahman SA, Schomburg D (2006) Observing local and global properties of metabolic pathways load points and choke points in the metabolic networks. Bioinformatics 22 1767-1774... 

A second form of pathway analysis is computing the potential outputs that the metabolic network might produce when supplied with a set of input metabolites (10). A third computational analysis method predicts choke points in the metabolic network, which are enzymes that if inhibited would be likely to create a major bottleneck in the metabolic network, and they are therefore likely to be good targets for developing antimicrobial... 

This logic works best for inland (fcrafon-style) kingdoms. It breaks down whenever there are strategic locations that function as natural monopolies or choke points and control of which can serve as a basis for appropriation. I have in mind the control of river mouths (the hulu-hilir distinction in the Malay world), straits, mountain passes, or deposits of vital resources. 

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