2nd Generation

Solar Pasteurizer

Team Members Left to Right

Ben Johns (ME)Brian T Moses

(ME)Seby Kottackal

(ME)Greg Tauer (ISE)

Adam Yeager (ME)

Objective

Design

Testing

The purpose of this project was to continue the work of the previous solar pasteurizer team in designing, building and testing a solar water pasteurizer. The design must provide enough clean water daily for a family, be easy to assemble, and affordable for use in the third world.

The project focuses on areas of the world where populations have low access to drinking water. Most of these areas are ideally located for the use of solar energy.

Key Engineering Metrics

Choosing the customer area:Haiti was chosen as the customer nation. This is because Haiti has a large population without access to safe drinking water, and the climate there is comparable to Puerto Rico, where detailed weather and solar incidence data are available. This data is necessary in validating the mathematical model, and in turn scaling test data acquired in Rochester to other areas. This is the basis of providing accurate predictions of pasteurized water output based on seasonal weather data.

Amount of water necessary for a family:

Standards from the World Health Organization define “basic access” to drinking water as 20 liters per capita per day. 100 liters for a family of five was chosen for the optimal output.

Shown is a conservative water pasteurization curve for a group of particularly resilient pathogens, Enteroviruses. Other sources propose that this curve is conservative: ex: 65C for 6 minutes. (Stevens, 98) A team meeting with Dr. Jeffrey Lodge (Microbiologist, RIT) also suggested above graph is conservative.

Feachem, Richard G - Sanitation and disease: Health aspects of Excreta and Wastewater Management

Defining water as “Pasteurized”:

Quantifying Pasteurization:A “Multiple-Tube Fermentation Technique” will be used to verify pasteurization has occurred. This is the same test used by the U.S. EPA when analyzing drinking water.

Ideal value: Zero Coliform organisms per 100ml given input water with an initial concentration of > 200 MPN per 100ml.

According to the World Health Organization report “Water for life,” 5000 children die daily of incidents directly related to poor drinking water quality.

AcknowledgementsDr. Stevens (Advisor)Dr. Lodge (Coliform Testing)Dr. Thorn (Sustainability)

Input BucketOutput Bucket

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Air Vent

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At Temp

Pasteurized

System Flow SchematicP8404 – Solar Water Pasteurizer

1. Input bucket stores incoming water at elevation for pressure

2. Water is pre-heated in Tube-in-Tube counter-flow Heat Exchanger

3. Water enters solar collector and convective loop subsystem. Heated water in collector drives convective loop from insulated tube outside collector area.

4. As water comes to temperature, air is released through air vent

5. Thermostat valve opens at 71° C6. Water is held at temperature in Hot Reservoir

for 5 minutes, reaches “safety zone”7. Pasteurized water flows through heat

exchanger, putting heat back into incoming water

8. Pasteurized water collected in output bucket

Inside Collector

OutsideCollector

Water from lower collector

Water to upper collector

Water from upper convective loop

Water to hot reservoir

SENSE TEMP

CHECK VALVE

Heat Exchanger:• Tube in a tube counter flow heat exchanger. Inside tube 5/16” OD Aluminum tubing carries the hot water. The outside tube is FDA approved Santoprene 1/2” ID. Approx. 3/16” thick flow annulus.• Wrapping the cooler incoming water around the hot water minimizes the losses and maximizes the efficiency. Heat Exchanger and insulation

(Pro/E Model)

Upstream Temperature Regulation:Automotive Thermostat Valves can react slowly to temp change. Sensing temperature upstream from where valve opens prevents leaking of unpasteurized water past valve.

Final Prototype

Collector with plumbing (Pro/E Model)

Thermostatic Valve Assembly:

Automotive Thermostat

actuates piston at 71° C

Mathematical Model:A mathematical model was constructed and implemented in Matlab to both calculate heat exchanger and plate dimensions, as well as predict flow rates and outputs based on different weather data. This model was validated through testing, shown below.

Warm-Up Time:On this test day, first output occurred at 10:12 AM. Solar input was insufficient to maintain steady state until 10:21. The saw tooth pattern shows the valve regulating temperature. As water in the collector warms up, the valve opens, and a new rush of colder water enters the sensing region, indicated by the blue line. The red line indicates water as it leaves the valve into the reservoir. As the valve closes, water below the pasteurization temperature of 71°C is never allowed to leave the valve. Steady state flow rate 4.5 mil/sec

Heat Exchanger Efficiency:On this test day, output occurred at 10:52 AM. As the system reached steady state, efficiency of the heat exchanger averaged 79% ± 0.1%

Thermal Losses:Hottest plate temps measured at top of plate, lowest on bottom. Glass temperature was measured above top of plate.

Prototype Cost: $300.00Estimated Production Cost: TBD

Insulating the Heat Exchanger

First generation design

Shown without spring

Validating the Mathematical Model:This graph plots predicted output based on the mathematical model against measured output. Validating the predictions of the model make it possible to predict outputs for Haiti solar irradiance and temperature data. Because detailed weather data was not available for Haiti, Puerto Rico data will be used to predict output for its similar climate.

Kill Rate:Kill rate tests completed as of this writing are as follows:

Untreated: 540 coliforms/100ml water sample Treated: 8 coliforms/100ml water sample (98.5%)

Untreated: 920 coliforms/100ml water sample Treated: 0 coliforms/100ml water sample (100%)