Beyond the Classroom Aquarium – A Prototype Laminar Flow Fountain Design & Modeling Project for STEM Students to Replicate/Modify and Install as Part of a Recirculating Aquatic Ecosystem Display

3 Oct

Have you ever considered how to bend a beam of light? A simple demonstration may be done using a stream of water. This demonstration illustrates the similar mechanism by which strands of glass-like fiber optic cable are used to carry messages. The description below is based on a description of this process published by Melvin Berger (1987, Lights, Lenses and Lasers, G.P. Putnam’s Sons, pp. 67-68)

Begin by punching two holes in the cap of a jar – one hole at the center the other near the rim. Fill the jar with water and screw the cap on tightly. Wrap a piece of dark cloth or paper around the jar. Extend the wrapping beyond the end of the jar – like a sleeve.

Hold the jar over a sink in a darkened room. Place a flashlight against the bottom of the jar – within the sleeve – and turn it on. Then tilt the jar so water from the jar flows out of the hole near the rim; with the center hole above it.

People who do this (in a darkened room) will likely view the curved stream of water glow with light. They may see the spot where the water strikes the sink as illuminated. And another person standing by the sink may place their hand in the glowing stream and see their own hand glow from the light in the curved stream of water.

The stream of water is like cladding in a woven-glass fiber optic cable. It reflects back straight rays of light so the light follows the curve of the water flowing from the jar.

The laminar flow fountain project explanation below guides students to design and assemble a fountain system that has three primary components: a

  1. cylinder housing assembled to remove turbulence from water injected into it
  2. Red/Green/Blue (RGB) light-emitting-diode (LED) and wire – to illuminate the laminar stream of water exiting the fountain, and
  3. stepper motor driven cutter mechanism to interrupt to flow of water exiting the fountain – operated in this case, though a driver connected to an activating button wired to an Arduino MEGA (Thanks to Mr. Dick Irish of Wilmington, NC – whom I first met at an Arduino/Raspberry Pi Meetup).

An ultimate goal of this project is for students to successfully install their own prototype laminar flow fountain in an existing recirculating aquatic ecosystem display within their classroom or beyond; tapping into the recirculating ecosystem flow so that the fountain has an unending and clean source of water (including organized descriptions and documentation of educational objectives mastered throughout the process).

“Laminar” implies an absence of turbulence. Thus the first objective in creating an aquatic laminar flow fountain is to create a fountain cylinder that removes turbulence from water as it passes through the cylinder.

The first set of photos show a cylinder used for the laminar fountain prototype. The cylinder is clear. Has a hole at one end to allow water to escape (the top of the fountain). At the other end (the bottom of the fountain) are two holes; one through which turbulent water may be pumped into the cylinder, the second (and smaller) hole in the center is used to hold the RGB/LED assembly and wiring.

The cylinder itself is divided into three parts a) water entry section (at the bottom), b) turbulence removal section (straws, screens and coarse fiber pads), and c) a section in which all water is under pressure and moving in laminar (non turbulent direction) towards the outlet of the cylinder (containing the tip of the RGB/LED assembly).

Many YouTube videos feature laminar fountains. Some incorporate light others do not. Most of these videos illustrate how to create the three sections within a cylinder. As you see from photos of this prototype, I used screen, scrub pads, straws (and some superglue and plastic ties to help hold the screens in place). The initial 120 Volt AC pump I used for this prototype was rated at about 295 gallons per hour. I want to use a 12V DC pump with a much higher output for the next iteration of this fountain. The water inlet from the pump to the cylinder was a half-inch push-to-connect fixture. The inlet hole for the LED and wiring was the diameter of a straw – connected through another push-to-connect assembly through the center of the bottom of the cylinder. In future iterations of this assembly, I would not drill the exit hole through the plastic seam of the cylinder. The outlet hole was a bit larger than 1/4 inch. I believe avoiding the seam would make the edge of the exit hole a bit smoother thereby further reducing interference with the laminar flow of the water exiting the fountain.

The next set of photos illustrate how light was incorporated into this fountain prototype (a second component of the system).

In order to include light in this fountain design I positioned the 1/2 inch push-to-connect water inlet to the side of the fountain’s base and placed a 1/4 inch push-to-connect fixture (for the light and wiring) in the center of the base. A four stranded wire was threaded through the center hole within a central straw where each wire was soldered to one of the four leads of  a RGB light-emitting-diode (LED). The straw holding the wires was then fitted into the connector and somewhat filled with aquarium silicone to minimize expose of wires to the water. Each soldered connection was encased in shrink-wrap tubing and the entire set of four wires were further encased in a wider shrink wrap tube and smothered in aquarium silicone.

In previous projects in Beyond the Classroom Aquarium, students were guided to use programmable logic controllers, sensors and coding. In this prototype project, the LEDs are controlled through an Arduino MEGA. The RGB bulb cycles through many colors and the program can be revised by anyone who wants to do some coding. Students will find many open source sites where code may be obtained.

The final system component in this laminar fountain prototype involves creating a stepper motor driven cutter mechanism that will also be controlled by the Arduino MEGA code. The cutter serves to abruptly interrupt to flow of water from the fountain diverting it directly from the nozzle exit of the fountain directly into the water in the fountain’s reservoir. The flow may be resumed instantaneously – based on the code sent to the motor through the Arduino MEGA (and the driver of the stepper motor).

Design of the cutter mechanism used here was based on the use of a flat topped 4″ diameter PVC cylinder. Each of the three pieces of the cutter mechanism were designed by using OnShape online software. These three pieces include the:

  1. base that attaches to the 4 inch diameter fountain cylinder, featuring the exit hole for the laminar flow of water and also containing grooves through which water will be channeled when the cutter is interrupting the flow of water;
  2. stepper motor housing assembly attached to the base featuring a hole through which the stream of laminar water may flow when it is uninterrupted, a housing for the stepper motor where the cutter blade will be attached, and
  3. cutter blade to be contained between the base and the stepper motor housing.

The pieces were 3D printed. Photos & videos of this mechanism – running the stepper motor through an arduino MEGA show how it is intended to operate. The code used to operate the stepper motor was obtained as open source code.

The fountain actually works. It has been assembled from a range of inexpensive (free whenever possible) materials. Students who want to tinker with this prototype will have unlimited opportunities to apply their own ideas (and budget) to improve it; an open-ended assignment/activity.

For my part, after acquiring a more powerful 12V DC pump it will be relatively simple to configure a PVC cylinder to serve as the body of the fountain. I will share the results of my updated prototype here. I also plan to include a simple low-pass filter (for pressure regulation) in the next iteration.

By the way, I am currently unable to show videos of the fountain in operation while using this basic level of WordPress.

Before going any further, I want to assure students who might want to take on a project of this kind that they will learn a lot! Beyond the Classroom Aquarium students spend a lot of time working with aquatic ecosystem components like pumps, pipes, hoses, sensors, reservoirs, sumps, drains, and Programmable Logic Controllers (even Arduinos & Raspberry Pi’s) so this challenging project allows them to explore additional ways to apply their understanding of these technologies.  Whoever takes this project on can expect to derive great satisfaction from sharing their fountain at public events, and in on-site installations in school and beyond…. Using the fountain to perhaps even transform a small piece of their own school environment into a mini Epcot Center or Disney World.

I will post updates (to include PVC cylinder, a stronger 12V DC pump, more smoothly edged fountain outlet, and a pressure regulating low-pass filter) as they become available.

Comments / Feedback are invited. Inquiries from teacher/students who might like to collaborate are also always welcome.

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