Gravity Driven

For over 2000 years, the hourglass has used gravity-driven granular flow to keep time. The flow rate in an hourglass is independent of depth [112,113] making it 

Two related gravity-driven flows are chute flow [3,33,146-155] and vertical tube flow [156-159]. Chute flow generally differs from hopper discharge in that the chute is opened so that the flow experiences a free surface. Vertical tube flow is similar to hopper flow, but there is no narrowing of the flow chamber at the outlet. A similar flow-rate scaling holds for vertical tubes [156] but the velocity profile tends to be plug like [157] for slow flows. For faster flows, density waves have been observed [159]. 

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The innovative features, such as passive, gravity-driven ECCS, simplified RCS, digital I C, optimized plant arrangement, and modular construction methods, characterize the AP600 design. These changes result in fewer systems, equipment, operations, inspections, maintenance, and QA requirements (Table 6.1-7). Features of the AP-6(K) are as follows ... 

Flooding the reactor with low pressure gravity-driven flow from the elevated... 

GDCS- Gravity driven cooling system (SBWR feature). 

An intuitive beginning point is to examine the self-weight deflections of a stmeture. These are gravity-driven. Consider the simplest of systems, a mass on a spring. In this system the responses are given by... 

Thus, if 5 = 1mm, / = 15.8 Hz. This very simple result is quite useful for approximately evaluating the gravity driven deflections of a stmeture given its natural frequency, or visa versa. Of course this was derived for a specific and very simple system, so it does not perfectly apply to more complex systems. Still it is a very useful rule of thumb. For a mass on the end of a cantilever beam, the above formula is correct. The lowest natural frequency of a massive cantilever beam is about 1.2 x the prediction of the above formula. 

No physical interpretation of the criterion was provided, but it can be regarded as the ratio of the square of the velocity of a gravity-driven "free fall bubble," of diameter equal to the flame thickness, to the square of the laminar flame speed. This leads to the conclusion that quenching occurs when a flame element quenched at the wall moves ahead of the flame, as observed and as described by Jarosinski et al. [4] (see Fig. 5 in the paper referred to) for downward propagating flames in tubes. 

Generally, the behavior of a gas (or vapor) cloud during dispersion can be either buoyant or gravity driven. The former is regarded with heavier-than-air gases and the later with lighter-than-air gases. Currently, dispersion estimations can be performed via the use of semiempirical one-dimensional models (the so-called box models) and the CFD codes. 

The selection of the appropriate dispersion model in an accidental release scenario requires the behavior of dispersing gas to be known since each model is specialized on one kind of release (buoyancy or gravity driven). 

Figure 3.22 Two realizations of cross-stream cutter solutions to process sampling involving significantly heterogeneous aggregate materials (broken ore, raw material, powders, intermediates, cement, waste, soil, other). The gravity-driven, rotating cross cutter [left] does not comply with TOS requirements (highly detrimental IDE and lEE), while the automated cross-stream cutter implemented at the terminal end of a conveyor belt [right] can be easily optimized to eliminate all ISEs. See [3,14] for a broad discussion of all issues related to process industry cross-stream sampler principles, and [11,21] for particular details.

Physical Metallurgy. One obstacle to Ihc processing of alloys on earth is dial components of a given mixture are olien immiscible. As a result, density differences cause the components to separate as the bulk inch cools. By eliminating this gravity-driven separation, the manufacture of alloys can benclit from a nucrogravily environment. 

Various new devices that have been used in soil sampling include a gravity-driven, hydraulically sampled multi-piston corer for fine-grained soils [11] and time-series trap that can collect 21 samples of soil at programmed intervals [12]. 

Heat transfer involving non-Newtonian fluids has not been studied in rotating devices. Models have been developed for gravity-driven heat transfer for power-law fluids (46). These models may be useful as a starting point to evaluate performance in higher-gravity fields. 

Shang D-Y, Anderson HI. Heat transfer in gravity-driven film flow of power-law fluids. Int J Heat Mass Transfer 1999 42 2085-2099. 

Gray, J.M.N.T., Wieland, M. and Hutter, K. (1999) Gravity-driven free surface flow of granular avalanches over complex basal topography. A Proceedings of Royal Society London 455, 1841-1874... 

The volume flow in a typical miniplant is of the order of 101 h 1. The limiting factor is the gravity-driven flow in the separation units, for example, a rectification column. As separation units usually accompany a chemical process, this flow limit dominates the overall capacity of a miniplant. It is surprising that the flow rate is not limited here by the pressure loss. 

In a microstructured reactor plant, in contrast, the flow rate will be dominated by the pressure loss. Typical pressure losses in micro devices are of the order of 1 bar at a flow of 11 h 1 (water) [50,93], If sufficient pump capacity is available, the pressure loss in a micro structured device is limited by the mechanical stability of the reactor housing, which is often made of steel and hence a loss of several bar is certainly acceptable. Even the combination of up to 10 different micro devices only amounts to about 10 bar in this example. The main advantage of a micro structured reactor plant is that the flow rate can be adjusted more freely because the flow is pressure driven and not influenced by a single gravity-driven device as in a miniplant. 

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