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Task 5: Wind-2-WaterConverting Wind Energy to

Mechanical Energy for Water TreatmentViento Agua, Duke University, WERC 2009

Task Identification

Design Criteria

Water Filtration

Harness the wind’s energy to power a water treatment process to treat brackish ground water without converting it to electricity. Applicable in a third world setting and meet all OSHA requirements Design Assumptions • Namibian village of 100 people, requiring 1000 L/day for drinking /cooking uses• Wind blows 12.5% of the day • Wind speed of 8.5 m/s, the highest distribution in Namibia

General Durability Low Cost Ease to Construct/Maintain Suitable for Developing World NoiseWind Turbine Self-start Low Cut-in Speed High Torque Accepts Wind from any Direction EfficiencyPower Transmission High Pressure Pump Adequate Flow Rate Control SimplicityWater FiltrationRejection of Organics Water Flux pH Tolerance Temperature Stability Oxidant Tolerance Compaction Tendency

Wind Turbine Pulley System Weight Pump

Rotational to Linear Force

Kinetic to Potential Energy

Potential Energy to Water Pressure

Power Transmission

Detailed Calculation for Turbine Sizing

RO membrane: -Spiral-wound, thin film composite membrane: treats high TDS with relative lowest pressure-4 in. in diameter and 40 in long with a minimum salt rejection of 98%- Tested with 2000 ppm NaCl under 150 psi; flow rate = 2700 gallons/day- Assuming 80% recovery and operation of 3 hrs/day results, flow is just over 1000 L/day.

Pre-treatment: - Granular activated carbon (GAC) filter: easy to install and only require periodic cleaning via backwash - Empty bed contact time (EBCT): bed volume divided by flow rate, 10-15 min- Volume of GAC needed: 0.05678 m3

Locally available material, such as concrete with D= 0.5 m and L = m chosen

Bench scale testing: - One liter of feed water used composed of 1390 mg Na2SO4, 3200 mg CaCl2.2H2O, and 150 mg NaHCO3 - TDS measurement was done by pipetting 10.00 mL of water sample into a pre-weighed aluminum tray and allowing the water to evaporate at 105. Then, the remaining salts were allowed to cool to room temperature in a desiccator before obtaining the weight. - WHO standard of potable water: 1000 ppm TDS

Wind Turbine

Double-hook rotor: →• From literature, optimal geometric ratios: -b:d = 0.22 -p:q = 0.4 -AR: efficiency increases with increasing AR up to

5.0. Due to stability concerns and increased material cost, AR = 2.5 was chosen.

-θ varied in bench scale test; θ =135o was optimal

tPT

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CT

100·λ(Tip Speed Percentage)

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Rotor Height (m) 4.50Radius of Curvature, q (m) 0.90Number of Rotors 2Estimated Efficiency 7.5%Power Delivered (W) 816Angular Velocity (RPM) 35Torque Delivered (N·m) 222.6Cut-In Speed (m/s) 2.5

Turbine Specifications

A: S-rotor, 0% GapB: S-rotor, 15% GapC: S-Rotor, 30% GapD: Double-hook, θ =135o E: Double-hook, θ =90o

Water Filtration

Cost Benefit Analysis: Benefits include improved health, quality of life, time Legal Considerations: Liability of injury Heath & Worker Safety: Optional safety fence surrounding area perimeter Waste Generation: Brine stream removed via a simple evaporation pond Groundwater Retrieval: Second identical system can be installed without filters for pumping water from the ground Increased Water Need: Benefit of simple ‘cookie cutter’ system. Multiple systems can be installed in separate locations for higher water volume Minimal Negative Environmental Implications Public Involvement: Involve community in decision-making processes, on-site design if necessary, and construction. Provide training sessions on operation and maintenance.

Other Considerations

← S-rotor: • Various gap sizes tested; efficiency well below double-hook in bench scale tests

Lever Arm • Torque supplied by turbine overcomes torque needed to generate pressure at pumps• As arm is lifted, pumps complete upstroke and pull water into chambers. As arm falls, pumps complete downstroke and push water through the system

Pulley System • Rope wraps around turbine shaft and through pulley system, moving as turbine spins• Cam attachment allows arm to engage and disengage at bottom and top of stroke

•High-Pressure pump has longer stroke , smaller area than low-pressure pump for equal stroke volume• Weight amount and placement can be varied for more energy storage

Water Pressure toReverse Osmosis