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Solar Pasteurizer . Performance Review. Team P08404 . Team Members: Ben Johns (ME) Adam Yeager (ME) Brian T Moses (ME) Seby Kottackal (ME) Greg Tauer (ISE). Project Background. Customer Needs. Engineering Specs. Key Engineering Metrics. Amount of water necessary for family of five.

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Team p08404 l.jpg

Solar Pasteurizer

Performance Review

Team P08404

Team Members:

Ben Johns (ME)

Adam Yeager (ME)

Brian T Moses (ME)

Seby Kottackal (ME)

Greg Tauer (ISE)

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Key Engineering Metrics

Amount of water necessary for family of five

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Key Engineering Metrics

Defining water as “Pasteurized”

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

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)

Team meeting with Dr. Jeffrey Lodge (Microbiologist, RIT) suggested above graph is conservative

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Key Engineering Metrics

Quantifying Pasteurization

A “Multiple-Tube Fermentation Technique” was used to verify pasteurization had occurred. This is the same test used by the U.S. EPA when analyzing drinking water.

This technique involves attempting to culture Coliform organisms in various dilutions of treated water. Results are measured by a Most Probable Number (MPN) Index of organisms per 100 ml.

Coliforms organisms themselves are not dangerous but indicate the presence of other, more dangerous, micro organisms.

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

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Path to Pasteurization

System Components of Chosen Design

  • Input bucket stores incoming water at elevation for pressure

  • Water is pre-heated in Tube-in-Tube counter-flow Heat Exchanger

  • Water enters solar collector and convective loop subsystem

  • As water comes to temperature, air is released through air vent

  • Thermostat valve opens at chosen pasteurization temperature

  • Water is held at temperature in Hot Reservoir

  • Pasteurized water flows through heat exchanger, putting heat back into incoming water

  • Pasteurized water collected in output bucket

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Path to Pasteurization- Collector

Collector constructed from 1/16” aluminum sheeting attached to a serpentine path of 5/16” aluminum tubing.

Original attachment method used Trans-A-Therm thermally conductive putty. This product proved to dry very brittle and porous. This created a weak bond, and the large air pockets prevented heat transfer.

Final attachment solution utilizes a bead of approx. 4oz of heat transfer paste. Tubing is held flat on collector by wire tie downs every 3 inches.

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Path to Pasteurization-Heat Exchanger

Tube in a tube counter flow heat exchanger. Inside tube 5/16” OD Aluminum tubing, which carries the hot water. The outside tube is made of FDA approved Santoprene 1/2” ID tubing. Approx. 0.063”/ thick flow annulus.

Wrapping the cooler incoming water around the hot water minimizes the losses and maximizes the efficiency.

A counter flow heat exchanger was chosen for higher temperature change.

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Path to Pasteurization-Convective Loop/Solar Collector

Upstream Temperature Regulation (UTR)

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


Convective Loop Flow

Water outside of collector is not being heated. This temp differential will drive a change in density between the cooler and hotter areas of the loop. This, combined with the vertical displacement of the angled collector will drive flow through the collector.

This flow can reduce the warm up time of the system.

Check Valve prevents backflow through valve


Path to pasteurization valve system l.jpg

Water from upper convective loop

Water to upper collector

Path to Pasteurization-Valve System

Water from lower collector

Water to hot reservoir

Inside Collector



Water from upper convective loop

Water to upper collector

Water from lower collector

Water to hot reservoir



Inside Collector

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Path to Pasteurization-Hot Water Reservoir

Reservoir Design:

Pasteurization is a function of temperature and time.

Since temperature at which the valve opens can be controlled, a system was designed to hold the water at 71C for 6 minutes

This is accomplished through a well insulated reservoir where high temperature water is held for the necessary amount of time.

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Specification 1Achieve Safety Zone

Reservoir Size: 1030 mL

Dwell Time

2.2 min 85 C

2.8 min 80 C

5.7 min 75 C

17 min 70 C

Flow Rate:

85 C 8 mL/s

80 C 6 mL/s

75 C 3 mL/s

70 C 1 mL/s

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Specification 1Achieve Safety Zone

This graph shows reservoir coming to temperature and operating at steady state. The insulation of the reservoir prevents significant thermal losses. The dip in the graph shows when the input bucket ran empty.

Ideal Value MET


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Specification 2 and 17Kill Rate of Harmful Pathogens

  • Ideal Value 99.9% 0/100ml

  • Marginal Value 99% 5/100ml

  • Final Value98.5% - 100%

* 95% Confidence Interval on test result of 8 Coliforms / 100 ml

Two coliform density tests performed:

  • One test run on output from coldest, worst case, test day.

  • Second test run on output from hottest, best case, test day.

  • Kill rates of 98.5% and 100%

    • Too much uncertainty to prove statistical significance

  • Marginal Value MET

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    -Air lock caused flow restriction, elevated temperatures

    -Excess energy lost to boiling and higher temperatures

    -Underperformed model predictions

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    Specification 3Output in Haiti from mathematical model

    • Jan 1 to March 31

    • 8,234 Liters in 90 Days

    • Average of 91.5 Liters per day

    • July 1 to September 30

    • 9,725 Liters in 92 Days

    • Average of 105.7 Liters per day

    • Apr 1 To June 31

    • 9,219 Liters in 91 Days

    • Average of 101.3 Liters per day

    • October 1 to December 31

    • 7,962 Liters in 92 Days

    • Average of 86.5 Liters per day

    Marginal Value Met, Ideal Value Met in spring and summer months

    One Year in Haiti:

    35,140 Liters

    Yearly Average 96.2 Liters per day

    December: 2,504 Liters (80.8 Liters / day)

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    Specification 4Cost Calculation

    • Ideal Value $30.00

    • Marginal Value $100.00

    • Total Costof prototype ~$320.00

    • Estimated Mfg Time for one unit: 5 Hours

    • U.S. Manufacturing Cost: Valve manufactured in US

      $30 for one hour estimated to construct valve assembly

    • Haiti Manufacturing Cost: All other assembly operations

      $20 for 4 hour estimated to construct

    • Bulk Materials Cost: $270

    • Final Manufactured Cost: $320

    • Ideal and Marginal Cost Values NOT MET

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    • P08404 was successful in creating a fully functional prototype well below budget.

    • Final Prototype cost: ~$320

    • Budget: $1300

    • Spent: $846.36

    • Remaining: $453.64

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    Specification 5Maintenance Cost

    • Ideal Value $0.00

    • Marginal Value $25.00

    • Final Value$0.00

    Automotive thermostat

    • Unit may need to be disassembled and periodically cleaned ($0)

    • No expected replacement parts will be required ($0)

    • One moving part: Valve Thermostat

      • Replacement cost should it break: $3.98

    • Ideal and Marginal Values MET

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    Specification 6Requires no Consumables

    • Ideal Value NO

    • Marginal Value NO

    • Final ValueNO

    The unit runs on solar power only, requiring no chemicals or other fuel sources.

    Ideal and Marginal Values MET

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    Specification 7Median Set up time

    • Ideal Value 15 min

    • Marginal Value 60 min

    • Final Value~1 min

    • Set up requires:

      • Add water to input bucket

      • Hang bucket on stand

      • Verify air purge lines are secure

    • This does not include time to get water to system or to carry system to usable location.

    • Ideal Value MET

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    Ergonomic Considerations

    • Approximately 7% of population can complete bucket lifting task unassisted (Height limited).

      • Nearly 100% if bucket is used as step-stool.

    • Around 30% of females will not be strong enough to lift the 5-gallon bucket above head level.

      • Failure most likely at shoulder joint.

      • 50% of females strength capable for 4.5 gallons of water.

    • OSHA / NIOSH Lifting Index: 1.50

      • Task would be considered inappropriate for U.S. industry.

      • Not a large concern, given tough US standards and low frequency of bucket lifting task.

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    Specification 8Time between maintenance operations

    • Ideal Value 30 days

    • Marginal Value 7 days

    • Final ValueAt least 30 days

    The device was tested and operated regularly for the entire month of April.

    During this time, no maintenance was required except for cleaning the surface of the glass

    It is possible that over time detritus and corrosion buildup will require the system to be flushed and the valve housing cleaned. The team did not have enough time to test these phenomena

    Based on the behavior of the prototype during testing, the Ideal Value was MET

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    Specification 9Highest Temp of External Housing

    • Ideal Value 60 C

    • Marginal Value 86 C

    • Final Value58

    • Highest glass temperature recorded as 58°C on 4/8/08.

    • Ideal Value MET

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    Specification 10Percentage of Dry Mass Recyclable/Reusable

    • Ideal Value 100%

    • Marginal Value 75%

    • Final ValueMET (exact value not calculated)

    • The largest mass proportion of the device consists of the wood frame, the aluminum plate, the aluminum tubing, the valve housing, and the glass. These are all recyclable or reusable materials.

    • Remaining weight of device is in rubber tubing, insulation, and plastic fittings. The fittings and tube can be reused. The tubing and insulation can not be recycled.

    • It can therefore be assumed that the Marginal value has been MET

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    Specification 11Number of units to fit on shipping pallet

    • Ideal Value 4

    • Marginal Value 2

    • Final Value2

    With legs removed, and the units positioned vertically, two collector units and their corresponding four buckets with bundled legs can fit on a standard 48”x40” shipping pallet.





    Bucket stand may be constructed on site, or any means of maintaining head pressure employed on location.

    Marginal Value MET

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    Specification 12Resists Undesired Repurposing

    • Ideal Value YES

    • Marginal Value YES

    • Final ValueYES

    • Unit was designed to resist undesired repurposing

      • Potentially reusable parts:

        • Glass Pane – Potentially useful, however low quality and fragile glass

        • Aluminum Plate – Many holes drilled through, would make poor construction surface

        • Plywood Frame – Production model assembled with tamper-resistant screws and hardware

        • Thermostat Valve – This valve was modified in such a way as to prevent it’s use in automotive applications

    • Ultimately, if a user wishes to repurpose the device they probably could. Need to focus on end user education to prevent desire for repurposing.

    • Ideal and Marginal Values MET

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    Specification 13Operating Temperature

    Ideal Value: 70C

    Marginal Value: 65C

    Achieved Value: 79C

    Automotive Thermostat opens and operates at higher temperature than expected.

    This adds safety to pasteurization, but results in lower than expected output.

    Ideal Value MET


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    Specification 14Time to reach operating temperature in Haiti

    • Ideal Value 60 min

    • Marginal Value 120 min

    • Final Value ~180 min

    January 5

    • Sunrise 6:57 am

    • First Liter 9:52 am

    • Sunset 6:01 pm

    • Total 89 Liters

      April 24

    • Sunrise 6:01 am

    • First Liter 9:21 am

    • Sunset 6:44 pm

    • Total 99 Liters

    • August 15

    • Sunrise 6:07 am

    • First Liter 9:09 am

    • Sunset 6:50 pm

    • Total 120 Liters

    • October 22

    • Sunrise 6:20 am

    • First Liter 9:24 am

    • Sunset 5:57 pm

    • Total 104 Liters

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    Specification 15Expected Lifetime of Device

    • Ideal Value 15 years

    • Marginal Value 5 years

    • Final Value Not Calculated

    • Unfortunately, the team did not get a chance to test the device under normal conditions for 5-15 years. Ideally, the device would be put through some sort of accelerated testing and the device life would be statistically computed.

    • The components that were selected are anticipated to be able to withstand the stress of the environment and operation. For example, the tubing to the buckets is UV resistant, the material exposed to water is either aluminum, Santoprene, or stainless steel, and the wood is pressure treated.

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    Specification 16Water should not flow until Desired Temperature

    Automotive Thermostat Designed to open at 71C

    Warm-up data shows

    valve opening at 75-76C

    Valve opens at higher than expected temperature; adds additional safety to level of pasteurization.

    Ideal Value MET

    When conditions are such that after passing through the heat exchanger and the lower 2/3 of the collector the water has not yet reached temperature, the valve will restrict flow. This appears in the data as an oscillating temperature at the valve, as well as a “cycling” of output.

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    Future Work

    • Unit cost likely too high for target market.

      • Investigate alternative materials and construction techniques.

    • Opportunities exist for increased output

      • Thermostat opens at higher temperature than rated

    • Human Factors

      • Steps on stand for hanging buckets should be considered

      • Hold more than five gallons at a time

      • Guard or enclose air vent.