Introduction: The cost of electricity on the island of Vinalhaven is $0.28 /kWh, which is triple the Maine state average. To reduce the power bought from the grid the idea of installing tidal turbines has been purposed. Because there is no scientific data regarding the site a flow meter has been designed and fabricated to be used at the Vinalhaven site to record the flow data.

Vane Anemometer Flow Meter for Vinalhaven Micro Turbine Site

Objectives: The objective of this project is to research, design, fabricate, and test a flow meter than can be used to measure flow velocities at the Vinalhaven site. The flow meter must be mobile so flow data for both the free channel and the channel obstructed by the cisterns can be recorded. The device must also work reliably in the salt water conditions.

Fabrication:A polyethylene housing block was chosen and three concentric holes were drilled to fit a shaft, sleeve bearings, and thrust screw. Two other holes were tapped into the block to mount the photoelectric sensor and the mounting/handling apparatus.

Figure 1. View of the Cisterns at the Proposed Site

Results:After testing the anemometer in the University of Maine tow tank an equation for the velocity of the tow tank carriage, and an equation relating the velocity of flow to the frequency of the propeller were determined.

Figure 2. Exploded view of Fabricated vane anemometer

Testing:To test the designed flow meter the University of Maine tow tank was used. The apparatus was mounted to the tow tank carriage and the sensor was wired into the power supply and data logging system. The carriage than pulled the sensor through the tank to simulate water flowing over the sensor. The speed of the carriage was calculated and related to the frequency of the propeller. A velocity – frequency relationship was established.

Figure 4. Designed Vane anemometer mounted in tow tank

Figure 5. Carriage Output Voltage – Carriage Velocity

Figure 6. Propeller Frequency – Flow Velocity

Future Work:With the fabricated and calibrated anemometer flow meter actual flow data from the Vinalhaven site can now be recorded. It is recommended that a future design group travel to Vinalhaven to measure the actual flow at this site. From this data power evaluations can be performed, tidal turbines sized, and a feasibility report can be created to determine the solution is cost efficient.

The velocity of the carriage was calculated by using the above equation to convert the carriage voltage output to a velocity in feet per second.

ageOutputVoltinches

ft

volts

pulses

revolution

inches

pulses

revolutionVelocity

12

1

5

sec/1000

1

)94(.2

100

1

With the velocity of the carriage determined the frequency of the propeller was recorded at the same carriage speeds.

Background:Back in the early 1900’s Vinalhaven was a major exporter of granite. A mill was located on the island that used turbines driven from the tides to polish the granite. All that remains of this mill are three large granite cisterns where the turbines were placed. The cisterns are placed in a channel that leads to a saltwater pond called Carvers Pond. There are two channels leading into the pond, one is unobstructed and the other has the cisterns in it. In operational days, a butterfly dam was placed in the open channel so that once the tide changed, the dam would shut, causing all of the trapped water to flow out of the pond through the cisterns. However, the butterfly dam has been disabled and cannot be used. The cisterns are the proposed site for a tidal turbine.

Team Members: Derek Bruno & Nathaniel House

Figure 3. Wiring Diagram of vane anemometer

Theory: The flow of the water will turn the propeller blades at different speeds due to changes in the waters velocity. Mounted on the vane anemometer is a photoelectric sensor that creates a pulse every time the blade passes by it. These pulses create frequencies that are dependent on the velocity of the water. The frequency can be converted to a voltage which is read by a data logger. Through calibration we can relate these voltages to water velocities.

Acknowledgements:We would like to thank the following people that contributed to our project:Michael “Mick” Peterson, Richard Kimball, Patrick Bates, Phil Crossman, Murray Callaway, Meg Smith, and The Mechanical Engineering Department.