Final Design

Summary of Final Design:

The purpose of this system is to provide an effective lab device OceanWell can utilize to easily test combinations of filters under different source water conditions for the company's main Reverse Osmosis device. The objective was to create a bench-top sized (1m x 1m) system that can hold at least 3 filters, allow for ease of exchanging those filters as well as not having a flow velocity greater than 0.1524 m/s (0.5 ft/s) as water passes through the filters, recirculates and maintains conditions of the source water, and can gather relative pressure, turbidity, and water flow velocity data at least once every hour for 24 hours. This system is manually operated in terms of changing out the source water, switching filters, and gathering data. 

Final Design:

This device was designed for the source water to travel through four main sections chronologically and repeatedly for roughly 24 hours. These sections are:

1. A source tank with a built in mixer that can house up to 18 L of source water. A 7.62 cm (3") PVC Flange was installed on the side of the tank along with a 7.62 cm (3") PVC valve in order to control the flow when filters are being exchanged.

2. 4 separate 7.62 cm (3") PVC piping sections connected with 3 PVC fittings in between that contain the filters used for testing. Sampling ports, pressure gauges, and turbidity sensors were installed in each of the PVC sections for constant monitoring of pressure drop and quality of the source water.

3. A T500 thruster from Blue Robotics designed to work underwater. This is used in this system as a substitute for an axial-flow pump. Filtered water from the previous section is pulled through the thruster and pushed into the final section of this cycle.

4. A 1.905 cm (3/4") flowmeter attached to a flexible PVC tube that dumps the filtered water back into the beverage dispenser, where it is made "dirty" again by mixing with the rest of the source water. A flowmeter is used here to monitor that the flow of the water is remaining below 0.1524 m/s (0.5 ft/s).

Performance of Final Design:

Initial tests of the device demonstrated a pressure drop of roughly 13.8 kPa (2 psi) from the first pressure gauge to the last one. The observed flow velocity, assuming incompressible flow within the 7.62 cm (3") pipe, from the flowmeter was initially 0.0167 m/s (1.2 gal/min reading from flowmeter), which is well within the constraint of 0.1524 m/s. When further testing was performed, now with acrylic boards installed after the thruster to prevent any swirling, the average flow velocity was 0.0623 m/s (4.5 gal/min reading from flowmeter). As for the turbidity sensor readings, source water containing pieces of chalk had a reading of 18.5 NTU within the source tank and 15.6 NTU after passing through the set of filters placed, demonstrating that this device can be used to test filters. However, while the data collected proves the device works, these tests also showed multiple points of leaking and the heatsink used to cool the thruster does not currently function correctly, preventing any long-term testing of the device. Multiple points of leaking have been resolved using water weld for pipe leaks and Teflon tape for threading leaks and the heatsink has been removed from the system temporarily until the problem has been resolved.

Future Improvements:

• Change placement of flowmeter to the center of the hose length. 

  • The leaking from the flowmeter may be caused by the weight of the hose attached to it, thus placing it in a spot where it will rest flatly on the bench should resolve this.

• Replace ports with permanent turbidity sensors for more efficient data collecting.

• Permanently fixing the hose to the side of the source tank to avoid any risk of movement.

• Adding an easier way to drain the water from the system.

  • Currently, the water must be drained entirely in order to exchange the filters.