Flow reversal devices

In all static surge-detection devices, the actual plienonemon of flow reversal (surge) is not directly monitored. What is monitored are other conditions related to surge. Control limits are set from past experience and a study of compressor characteristics. 

Cowl A roof-mounted device designed to provide airflow out of a building with the minimum of flow reversal. 

Check valves and other reverse-flow prevention devices, if their failure can affect the safety of the plant. 

A flow direction switch occurs at r/2 for a cycle period r set by the plant operator, or it may be initiated by the reactor or recuperator outlet temperature. Startup of the flow-reversal system requires a heating device to bring the catalyst bed or at least the frontal portion up to ignition temperature. This temperature is about 350°C for S02 oxidation using conventional catalysts. 

The piston is directly attached to a device that is pushed inside a cylinder by means of a constant speed rotating motor. The pump delivers a constant flow (without any pulsation) and check valves are not needed. The performance of a syringe pump is dependent on flow rate, syringe size and the architecture involved [24], In the more sophisticated models, the motor speed and rotation can be varied, which offers real advantages for analytical applications involving multi-reagents, sample stopping or flow reversal. 

The ReviveFlow system (ReviveFlow, Inc., Quincy, MA) is a novel method of cerebral flow reversal in which a balloon guide catheter is placed in the cervical internal carotid arteries and jugular veins on one or both sides of the neck. The balloons are subsequently inflated and blood is aspirated via an external pump system from the proximal 1C A and infused in the distal internal jugular vein. The end result is total reversal of the cerebral circulation and perfusion of the venous system with arterial blood into the capillary bed, which is now physiologically proximal to the occluded artery. This device is currently undergoing precliifical smdies. 

The idea of utilizing the centrifugal force for separation of liquid from gas also finds application in gas-oil hydrocyclone separators (Fig. 2.9). In order to create a centrifugal stream inside these separators, an attached unit - a hydrocyclone - is installed on their lateral surface (Fig. 2.9, a, b, c). A hydrocyclone is usually a vertical device with a fiat tangential input and directing branch pipe for gas flow reversal in the top part, and a liquid cross-flow section in the bottom part. The technological reservoir is made in the form of a horizontal separator with various devices for additional separation of liquid from gas that are typical for oil-gas separators. 

Gas-liquid (gas dominated) separation done by axial-and reverse-flow cyclonic devices operating at 20-200 g. These are also used for polishing at gravity separator gas outlets. 

Sand-liquid separation done by reverse-flow cyclonic devices operating at 10-500 g. These have been commercially available in the mining industry for a long time, and are extensively used for sand cleaning in the offshore industry... 

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