Flow Control

1. Flow Control Creativity without a trip Variations on a drip Giving head loss the slip

2. Overview • Why is constant flow desirable? • Reflections on Creative Design • Constant head devices • Overflow tanks • Marriot bottle • Floats • Float valve • Orifices and surface tension • Flow Control Valve • If you had electricity • Variable head loss in the unit process

3. Why is constant flow desirable? • Slow constant treatment can use a smaller reactor than intermittent treatment • It isn’t reasonable to expect to treat on demand in a household • Flow variations are huge • System would be idle most of the time • Use a mini clearwell so that a ready supply of treated water is always available

4. Applications of Constant Flow • Make a POU SSF that works • Reagent addition for community treatment processes • Alum • Calcium or sodium hypochlorite • Could you make a meter that increased the dose in proportion to the main flow? UV disinfection, clay pot filters, arsenic removal

5. Hypochorinator Fix http://web.mit.edu/d-lab/honduras.htm

6. Reflections on Creative Design • Experience as Fuel for the Fire (or a prison that inhibits new ideas) • Be a Free Thinker • Be an Extremist (variations over the domain) • List all the possible parameters that you could vary • Vary them to the extreme (0 to infinity!) • Be a Reductionist • Tear the problem apart • Identify the essential components and the role of each of the components • Organize your ideas into a scheme showing relationships • Evaluate your ideas • Go back to the problem statement 3 ideas that are as unrelated as possible Pick one How will performance vary? Is there something else that could fill the role?

7. Constant Head: Overflow Tanks Surface tension effects here What controls the flow?

8. orifice Supercritical open channel flow! VERY Flexible hose Constant Head: Floats Head can be varied by changing buoyancy of float Unaffected by downstream conditions!

9. A simple constant head device Why is pressure at the top of the filter independent of water level in the Marriot bottle? What is the head loss for this filter? Constant Head: Marriot bottle

10. Constant Head: Float Valve Float adjusts opening to maintain relatively constant water level in lower tank (independent of upper tank level) ? Describe sequence of events after filling

11. Hole in a Bucket Vena contracta Orifice

12. Fs= Fp= Surface Tension Will the droplet drop? Is the force of gravity stronger than surface tension? 2prs

13. 0.080 0.075 0.070 Surface tension (N/m) 0.065 0.060 0.055 0.050 0 20 40 60 80 100 Temperature (C) Surface Tension:(droplet radius larger than Dh)

14. Surface Tension:(droplet radius smaller than Dh) No flow!

15. Flow Control Valve (FCV) • Limits the ____ ___ through the valve to a specified value, in a specified direction • Calculate the sizes of the openings and the corresponding pressures for the flows of interest flow rate

16. Variable Process Head Loss • How do you design the system so that increasing head loss in the unit process does not result in decreasing flow rate? • Goal is no communication between process and flow control device! • Of course, eventually high head loss will cause some sort of failure (but you can make this be a pleasant failure!)

17. If you had electricity… • Metering pumps (positive displacement) • Pistons • Gears • Peristaltic • Valves with feedback from flow sensors • So an alternative would be to raise the per capita income and provide electrical service to everyone… • But a simpler solution would be better!

18. Reflections on Creative Design • Experience as Fuel for the Fire (or a prison that inhibits new ideas) • Be a Free Thinker • Be an Extremist (variations over the domain) • List all the possible parameters that you could vary • Vary them to the extreme (0 to infinity!) • Be a Reductionist • Tear the problem apart • Identify the essential components and the role of each of the components • Organize your ideas into a scheme showing relationships • Evaluate your ideas • Go back to the problem statement 3 ideas that are as unrelated as possible Pick one How will performance vary? Is there something else that could fill the role?

19. Be a Reductionist • Tear the potential solutions apart • Identify the essential components and the role of each of the components • Identify substitutes • Constant head • Head loss that changes with flow

20. Integrate Flow Control Device (FCD) into the Bigger Project • What are the options for where you place the FCD? • Before • After • Up flow • Down flow • How is the FCD affected by changes upstream and downstream?

21. Identify the Failure Modes • Moving parts • Wear • Corrosion • Precipitation • Incompatible materials • Clogging • Design errors…

22. Flow Control of Dirty Water • Come up with at least 3 very different ways to get around the clogging problem (may be context specific) • Why are you trying to control the flow of dirty water? • How could you eliminate the possibility that a single particle could clog the FCD? • How could you make your FCD able to handle more particles? • How could you make a FCD that could be easily cleaned?

23. How could you reduce cost? • Size! • Use commonly available materials (tire tubes, PVC pipe, bottles) • Eliminate precision components • Or use components that are already mass produced (and cheap)

24. Water Tight Connections!!!! • O’ring seals • PVC glue • Pipe threads • Duct tape

25. Budget and Machining • CEE is able to pay up to $30 per team for supplies • Paul Charles, Tim Brock or I can order supplies for you • Your team must keep track of your expenses • Tim Brock is willing to supervise/assist you with simple machining or fabrication tasks in the CEE shop (basement of Hollister) • Call (5-4201) or email ( teb4) to set up a time (between 1 and 4 pm) This information is at the website

26. Where do you get supplies? • Lab supplies • 4” filter columns • ¼”, 3/8”, ½” flexible tubing • Connectors • Online Hardware store (McMaster) http://www.mcmaster.com/ • Lab/medical supplier (Fisher Scientific) https://www1.fishersci.com/ • Home Depot! This information is at the website

27. Progress Report (1) • Classify your flow control schemes according the fundamental principles that each flow control device uses. Represent this classification of flow control devices in an outline form or (even better) as a graphic. • Evaluate the strengths and weaknesses (failure modes) for each of the schemes. Explain what strategies you will use to mitigate the failure modes.

28. Progress Report (2) • If you are designing your flow control device for a particular application, describe how that application is influencing the design. In any case, explain how your flow control device will be used and include a sketch showing how it will be connected to the treatment process. • Show design calculations that you used to determine the sizes of the various components of your flow control device. Explain what constrained the size and what would fail if it were made smaller.

29. Progress Report (3) • Sketch to scale the most promising designs that you are investigating. • Pick the design that you plan to build and explain why it is the best choice. • Calculate the range of flow rates that your device will be able to produce. • List the materials that you will need to construct the device including supplier, part numbers, and cost. • Describe any machining or fabrication assistance that you will need.

30. Reflections • Engineered design (not just trial and error!) • Explore as many possibilities as you can on paper and assess which ones are the most promising to succeed • Can you make a simple module that can be used in many applications?