Abstract:
Selective withdrawal from stratified fluid system is a technique of water quality management.
St;lgnant water in most of the reservoirs are stably stratified throughout most or all of the year .
.This stratification is caused primarily by temperature variation with depth, and secondarily by a
variable concentration of dissolved or suspended solid. Selective withdrawal is one, where one can
select the strata of the fluid at the sink level. Here the flow in the horizontal direction is restricted
and thus enables the water to be withdrawn in horizontal layers. This method of reservoir fluid
quality management is becoming popular day by day. This method is used in cooling ponds, solar
ponds, salt producing industry.
The flow from different layers in a stably stratified fluid system depends on many parameters. .
They are; nature of stratification, thickness of the interface, flow rate, shape of the sink, location
of the sink, rotation etc.. The change in any of this parameter effect the drawdown significantly.
By changing these variables effectively one can efficiently control fluid quality from a stably .
stratified fluid system.
Starting from the middle of this century, still today, numerous experimental and analytical work
has been done on this topic. Location of sink effects the percentage drawdown significantly. It is
found from theexperjment that when the sink is elevated to a certain height Densimetric Froude
number becomes the governing parameter in controlling the drawdown history of the stratified
fluid ,system and all other parameter becomes less significant. From the experimental data a
generalized equation is developed which can predict drawdown efficiently.
