Gravity head

The upward flow of gas and Hquid in a pipe is subject to an interesting and potentially important instabiHty. As gas flow increases, Hquid holdup decreases and frictional losses rise. At low gas velocity the decrease in Hquid holdup and gravity head more than compensates for the increase in frictional losses. Thus an increase in gas velocity is accompanied by a decrease in pressure drop along the pipe, a potentially unstable situation if the flows of gas and Hquid are sensitive to the pressure drop in the pipe. Such a situation can arise in a thermosyphon reboiler, which depends on the difference in density between the Hquid and a Hquid—vapor mixture to produce circulation. The instabiHty is manifested as cycHc surging of the Hquid flow entering the boiler and of the vapor flow leaving it. 

Feedwater pipework will normally be gravity head suction from the hotwell or feed tanks to the pumps and at a pressure in excess of the boiler working pressure from the pumps to the boiler. Few problems occur on the pipework between pumps and boilers. However, inadequately sized suction lines can give rise to cavitation at the feed pump with subsequent boiler shutdown. The feed tank should always be positioned to suit the temperature of the feed-water and the pipework sized to give free flow at that head, taking account of bends, valves and filters. 

Piping systems often involve interconnected segments in various combinations of series and/or parallel arrangements. The principles required to analyze such systems are the same as those have used for other systems, e.g., the conservation of mass (continuity) and energy (Bernoulli) equations. For each pipe junction or node in the network, continuity tells us that the sum of all the flow rates into the node must equal the sum of all the flow rates out of the node. Also, the total driving force (pressure drop plus gravity head loss, plus pump head) between any two nodes is related to the flow rate and friction loss by the Bernoulli equation applied between the two nodes. 

The proper location of the heavy liquid weir (r2) can be determined by a balance of the radial pressure difference through the liquid layers, which is analogous to the gravity head balance in the gravity separator in Fig. 12-5. The radial pressure gradient due to centrifugal force is... 

Both scrubbers will be supplied with three sources of electrical power - the main grid supply, a back-up grid supply from a different substation and an emergency diesel generator. In the emergency chlorine scrubber, critical equipment items will be backed-up by automatic start-up of stand-by equipment. A gravity head tank of caustic soda and a nitrogen ejector will also be provided to allow safe neutralisation of chlorine vents in the event of total power failure. 

Hydraulic hammer from sudden closing of valve downstream of hose (primarily when loading with substantial gravity head or at high flow rates)... 

The in-conlainmeni refueling water storage tank provides 500,000 gallons (about 1900 cubic meters) of water with a gravity head above the core. This water inventory is sufficient to flood the containment above the level of the reactor core and provide decay heat removal by natural circulation. 

As shown in Fig. 18.23, dry liquid feed containing olefins and isobutane is charged to a combined reactor-settler. In this example, the reactor uses the principle of a differential gravity head to circulate through a cooler before contacting a highly dispersed hydrocarbon feed in the reactor pipe. The hydrocarbon phase, generated in the settler, is sent to a fractionator, which separates LPG-quality propane, isobutane recycle, n-butane, and alkylate products. A small amount of dissolved catalyst is also removed from the propane product by a small stripper tower. 

Analyze a set of pump and system characteristic curves for the following conditions friction losses without static head, friction losses with static head, pump without lift, system with little friction and much static head, system with gravity head, system with different pipe sizes, system with two discharge heads, system with diverted flow, and effect of pump wear on characteristic curve. 

FIGURE 6.26 Negative lift (gravity head). (Peerless Pumps.)... 

Flood. This condition occurs at high vapor and/or liquid rates when the gas pressure drop is higher than the net gravity head of the liquid, which then backs up through the column. 

Type A The grout eolumn is not pressurized. Sand-eement mortars as well as neat cement grout is plaeed under gravity head only. 

In fluid dynamics fluids are in motion. Generally, they are moved from place to place by means of mechanical devices such as pumps or blowers, by gravity head, or by pressure, and flow through systems of piping and/or process equipment. The first step in the solution of flow problems is generally to apply the principles of the conservation of mass to the whole system or to any part of the system. First, we will consider an elementary balance on a simple geometry, and later we shall derive the general mass-balance equation. 

A specially constructed lower containment volume that collects the liquid break flow, as well as any condensate from the containment, in a cavity where the reactor vessel is located. Following a LOG A, the cavity floods above the core level, creating a gravity head of water sufficient to provide coolant makeup to the reactor vessel through the DVI lines. This cavity also assures that the lower outside portion of the RV surface is or can be wetted following postulated core damage events. 

In the first capillary rheometer, Hagen (1839 Figure 6.1.1) controlled pressure by a gravity head. This is still the case with the common glass capillary viscometers. As indicated in Figure... 

We assume that the gravity head of the liquid column to be negligible as the height of the microchannel is very small. Therefore, the pressure at the entrance of the microchannel has a constant value. 

In Section 2 several nuclear reactor designs as well as natural circulation applications have been described.The single phase natural circulation flow is driven by a gravity head induced by coolant density differences the mass flow is established according to the balance between driving head and flow resistance losses. Because the (one component) density is a ftinction of the temperature there is a functional interaction between heat exchange and natural circulation flow. 

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