Experimental studies have been undertaken to examine the flow in long
vertical conduits with particular reference to the design of storm
water drop shafts. A distinguishing characteristic of such flow is the
potential cavitation regime. Its existence depends upon the design of
the structure. The cavitation regime will develop when the conduit is
sufficiently long and the head sufficiently large. It can also be
generated at a lower head if a control valve is installed in the supply
line so that the net head can be negative. The cavitation region consists of a rather finely divided mixture of water and water vapor at a constant cavitation pressure of about -32.0 ft of water throughout the
region and for all discharges. The cavitation region terminates with
a shock front whose location is also a function of the discharge. The
concentration of vapor, while relatively constant throughout the cavitation region, decreases with increasing discharge.
If a small amount of air is introduced into the system, the cavitation
region is eliminated, the pressure gradient is more uniform, and the
flow consists of a uniform mixture of air and water.
This report was submitted in fulfillment of Project Number 11034 FLU,
Contract EPA 14-12-861, under the sponsorship of the Water Quality
Office, Environmental Protection Agency.
Anderson, Alvin G.; Vaidyaraman, P.; Chu, C..
Hydraulics of Long Vertical Conduits and Associated Cavitation.
St. Anthony Falls Hydraulic Laboratory.
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