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Concentric well screen filter design
Offset filter bed design
55 gallon barrel filters around a shared clear well
Single 55 gallon barrel filter schematic
Height required to attain backwash velocity (with headloss calculations)
We've attempted to model the headloss through the pipes and orifices:
We have modeled a siphon filter system for a plant similar in size to Aguateca. The design is based on a 55 gallon drum, a commodity known to be accessible and cheap in Honduras. We wished to experiment with a well screen filter below the sand in place gravel, which is more commonly used. A basic schematic of the siphon filter system is shown below:
We modeled the filter in regular down-flow mode to size the system and determine the necessary pressure drops. By calculating the head loss across the filter system, we will determine the necessary height difference from the sedimentation tank to the filter. We have generated a model in Mathcad using the relations below:
The sand bed pressure drop was modeled with the Carman Kozeny equation:
The pressure drop across the well screen was modeled with the orifice equation (for summation of holes):
The head loss across the piping and fittings was calculated using parameters from Morton M. Denn's Process Fluid Mechanics (page 93):
Viscous Losses due to fittings 2/s^2
Where is the "velocity heads lost" Coefficent, Kf
Factors to control
a. Sand level monitoring
b. Pressure across filters
c. Flow distribution during backwash
d. Bypass entire system
Discussion topics
a. 7 backwash 1 problems/feasibility
b. Inclusion of clear well
c. Backwash with raw water
Future work
a. Bench top modelAfter initial calculations with typical parameters from well screen manufacturers, we calculated a head loss on the order of 8 meters across the screen. This amount of head is too large to proceed, therefore we have abandoned the use of a well screen and will use the traditional solution, gravel. Our next step will be to model the siphon back wash mechanism.