Backflow

The y component of the velocity is 0 because of the symmetry of the cell. The z component is 0 because of the mass conservation and uncompressibility of the liquid crystal. The boundary condition of the velocity of the translational motion is 

The angular velocity of the liquid crystal rotating as a whole is 

The dynamic equation of the rotation of the liquid crystal director is 

Under the isotropic elastic constant assumption (Kii = K23 = K), Equation (5.154) xcos0 -Equation (5.152) x sin 0, we can get 

Comparing Equation (5.155) with Equation (5.103), we can see the extra term which is from the translational motion. For translational motion, there is only motion in the x direction. Using the dynamic equation (Equation (5.115)), we have 

---

Backflow due to high backpressure 2. Same 2. Install check valve JFL 2/93... 

Water. Water mains should be connected to plant fire mains at two or more poiats, so that a sufficient water supply can be deHvered ia case of emergency. The plant loop and its branches should be adequately valved so that a break can be isolated without affecting a principal part of the system. If there is any question of maintaining adequate pressure, suitable booster pumps should be iastaHed. Any connection made to potable water for process water or cooling water must be made ia such a manner that there can be no backflow of possibly contaminated water check valves alone are not sufficient. The municipal supply should faH freely iato a tank from which the water is pumped for process purposes, or commercially available and approved backflow preventers should be used. 

Using combustion to stimulate bitumen production is attractive for deep reservoirs and in contrast to steam injection usually involves no loss of heat. The duration of the combustion may be short (days) depending on requirements. In addition, backflow of oil through the hot 2one must be prevented or excessive coking occurs (15,16). Another variation of the combustion process involves use of a heat-up phase, then a blow-down (production) phase, followed by a displacement phase using a fire-water flood (COFCAW process). 

FIG. 17-10 Gas inlets designed to prevent backflow of solids, a) Insert tuyere (h) clubbead tuyere. Dotr-Oliver, Inc. )... 

For the gravity discharge case, the height of the fluid at maximum vacuum, which is the point at which air would begin to backflow into the tank, is determined by Eq. (26-54). Equation (26-55) calculates the corresponding vacuum in the tank s headspace at this hquid height. Since the drain nozzle is open to the atmosphere, this solution is a static force balance that is satisfied when the sum of the internal pressure and the remaining fluid head is equal to the atmospheric pressure. 

The precise flow-decay pattern will depend on the type, size, and dimensions of the pump. Flow for a typical centrifug pump will begin to decay at the NPSH point, but some additional fluid transfer will usually occur before a steady backflow of air through the pump begins. At that point, the pump s priming is completely lost. 

For these parameters, the equations predict a much higher vacuum (24.5 in Hg or 230 percent of the shortcut method) than the gravity-discharge case. Of course, different tank dimensions and pump characteristics coiild give different comparisons between cases. If conditions are such that the pump can completely empty the tank before backflow occurs, the vacuum is Rest calculated from Eq. (26-57). 

Prevent backflow from scrubber into reactor... 

This is provided to prevent reverse rotation of the pump in the event of a power failure or a deliberate shutdown due to backflow of liquid from the rising mains (pipelines). This is located immediately after the last pump stage casing/discharge outlet to prevent the shaft from rotating in the reverse direction. The provision of a non-return valve also ensures that the pump always starts in a shut-off condition, when the power requirement is at a minimum. 

The behaviour of a transient wave at a junction of two conductors, such as at junction J in Figure 18.8, is similar to that of water, when it passes through one large-diameter pipe to another of a smaller diameter. Some of the water will flow ahead and the remainder will backflow at the junction. Similarly, a transient wave will also reflect in part or in full at a junction between two conductors of different surge impedances, depending upon the surge impedance of the circuit ahead of the junction. This would give rise to two types of waves, i.e. 

Recirculating loss. This loss occurs because of backflow into the impeller exit of a compressor and is a direct function of the air exit angle. As the flow through the compressor decreases, there is an increase in the absolute flow angle at the exit of the impeller as seen in Figure 6-34. Part of the fluid is recirculated from the diffuser to the impeller, and its energy is returned to the impeller. 

Check valves must be used on each pump discharge to prevent backflow through the idle pump. On those systems where a flooded suction is not furnished, an orificed bypass around the appropriate check valve should be furnished to keep the suction line of the non-flooded suction... 

Check valves are required in the piping system at any point where backflow of gas after a shutdown has the ability to restart the compressor, running it backwards or, for that matter, even in the normal direction. Reverse rotation is totally bad, as many components of the various compressor types are not designed for reverse rotation, and there is some possibility, generally remote, that the compressor could reach a destructive over speed. Forward rotation is bad primarily because the intent was to stop the compressor, and it is now operating out of control. This is a problem, particularly if the shutdown was caused by a compressor failure indication, and the need to stop was to prevent further damage. In this mode, it is unlikely that the compressor can attain an overspeed condition. An application with a high potential for backflow is the parallel operation of two or more compressors. 

Various features may be included in a pilot-operated valve, such as backflow preventers, field testing connections, pilot line filters, manual or remote opening for depressuring purposes, etc. Details may be obtained from manufacturers literature. 

A mechanic was instructed to fit a steam supply at a gauge pressure of 200 psi to a process line in order to clear a blockage. By mistake, a steam supply at a gauge pressure of 40 psi was connected. Neither supply was labeled the 40 prsi supply was not fitted with a check valve resulting in backflow of process material into the steam supply line. Later the. steam supply caught fire when used to disperse a small leak. 

Evaluate ways to prevent backflow in critical lines between process equipment... 

Flow reversal The backflow that occurs when a fluid changes its flow direction due to an imposed pressure gradient. 

In reciprocating compressors the compressor valves themselves act as k valves, preventing backflow from high-pressure stages to lower... 

The maximum volume of hydrocarbons that could backflow from downstream equipment is significant. 

A control device in the line will effectively minimize backflow. 

---