Team P08404

Team P08404

Team Members: Ben Johns (ME)Adam Yeager (ME)Brian T Moses (ME)Seby Kottackal (ME)Greg Tauer (ISE)

Solar Pasteurizer Project Review

2

Project Background

3

Customer Needs

Need Importance

Safely Pasteurize Enough Water 9

Cheap 9

Easy to Use 3

Easy to Assemble 3

Easy to Maintain 3

Safe 3

Environmentally Friendly 3

Distributable 3

Resistant to Unintended Uses 1

Solar Powered 9

4

Engineering Specs

5

Key Engineering Metrics

Amount of water necessary for family of five

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Key Engineering Metrics

Defining water as “Pasteurized”

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

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

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Quantifying Pasteurization

Key Engineering Metrics

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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Functional Diagram

Identified Sub-Systems

Pasteurize

Heat Back into System

Collect Solar Energy

Store Input Water

Convert to Heat

Flow Control

Heat Transfer

Transfer Heat to Water

Receive Heat

Solar Collector

Heat Recovery

Overview of Concepts Examined

A B

D E

C

Path to Pasteurization

Input BucketOutput Bucket

Co

ld

Ho

t

He

at

Exch

an

ge

rCollector Plate ValveSenses Open

Air Vent

Air

Ho

t R

ese

rvo

ir

Closed

Ch

eck V

alv

e

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

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

5. Thermostat valve opens at chosen pasteurization temperature

6. Water is held at temperature in Hot Reservoir

7. Pasteurized water flows through heat exchanger, putting heat back into incoming water

8. Pasteurized water collected in output bucket

System Components of Chosen Design

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

SENSE TEMP

CHECK VALVE

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Path to Pasteurization-Valve System

Water to hot reservoir

Inside Collector

OutsideCollector

Water from lower collector

Water to upper collector

Water from upper convective loop

Water to hot reservoir

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Path to Pasteurization-Hot Water Reservoir

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.

Reservoir Design:

Completion of Key Engineering Specifications

0

1

2

3

4

5

6

7

8

9

40

50

60

70

80

90

100

11 12 13 14 15 16 17 18 19

Flo

w R

ate

(mL

/s)

Tem

per

atu

re o

f V

alve

Time of day

Flow Rate vs Temperature

Temperature

Flow

Flow Rate:

85 C 8 mL/s

80 C 6 mL/s

75 C 3 mL/s

70 C 1 mL/s

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

Specification 1Achieve Safety Zone

Specification 1Achieve Safety Zone

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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

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

Worst Case Coliforms / 100 mlUntreated 540

Treated 8 (-5 / + 16)*

Best CaseUntreated 920

Treated 0

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

Specification 2 and 17Kill Rate of Harmful Pathogens

• Ideal Value 99.9% 0/100ml• Marginal Value 99% 5/100ml• Final Value 98.5% - 100%

Model Validation

-Air lock caused flow restriction, elevated temperatures

-Excess energy lost to boiling and higher temperatures

-Underperformed model predictions

• 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

One Year in Haiti:35,140 Liters

Yearly Average 96.2 Liters per dayDecember: 2,504 Liters (80.8 Liters / day)

Specification 3Output in Haiti from mathematical model

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

Specification 4Cost Calculation

• Ideal Value $30.00• Marginal Value $100.00• Total Cost of 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

Specification 14: Warmup Time

January 5• Sunrise 6:57

am• 500+ Watts 9:00

am• First Liter 9:52

am• Sunset 6:01 pm• Total 89 LitersApril 24• Sunrise 6:01

am• 500+ Watts 9:00

am• First Liter 9:21

am• Sunset 6:44 pm• Total 99 Liters

14 Time to reach operating temperature on average day in worst month in Haiti 3min

s 120 60

August 15• Sunrise 6:07 am• 500+ Watts 9:00 am• First Liter 9:09 am• Sunset 6:50 pm• Total 120 LitersOctober 22• Sunrise 6:20 am• 500+ Watts 9:00 am• First Liter 9:24 am• Sunset 5:57 pm• Total 104 Liters

Budget

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

• Final Prototype cost: ~$320

• Budget: $1300• Spent: $846.36• Remaining: $453.64

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.

Specification 13Operating Temperature

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Ideal Value: 70C

Marginal Value: 65C

Achieved Value: ~75C

Automotive Thermostat operates at higher temperature than expected.

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

Ideal Value MET

Specification 16Water should not flow until Desired

Temperature

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

Ideal Value MET

Automotive Thermostat Designed to open at 71C

Warm-up data showsvalve operating at 75-76C

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.

Typical Operation

• 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.

Future Work