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 NeedImportance Safely Pasteurize Enough Water9 Cheap9 Easy to Use3 Easy to Assemble3 Easy to Maintain3 Safe3 Environmentally Friendly3 Distributable3 Resistant to Unintended Uses1 Solar Powered9

4 Engineering Specs

5 Key Engineering Metrics Amount of water necessary for family of five

6 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

7 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.

8 Functional Diagram

Overview of Concepts Examined A B D E C

Path to Pasteurization 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.

12 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 ”/ 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.

13 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

14 Path to Pasteurization-Valve System Inside Collector Outside Collector Water from lower collector Water to upper collector Water from upper convective loop Water to hot reservoir Inside Collector Outside Collector Water from lower collector Water to upper collector Water from upper convective loop Water to hot reservoir

15 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

Flow Rate: 85 C8 mL/s 80 C6 mL/s 75 C3 mL/s 70 C1 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 1 Achieve Safety Zone

18 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 CaseColiforms / 100 ml Untreated540 Treated8(-5 / + 16)* Best Case Untreated920 Treated0 * 95% Confidence Interval on test result of 8 Coliforms / 100 ml Specification 2 and 17 Kill Rate of Harmful Pathogens Ideal Value99.9%0/100ml Marginal Value99%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 Liters per day Apr 1 To June 31 9,219 Liters in 91 Days Average of 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 day December: 2,504 Liters (80.8 Liters / day) Specification 3 Output in Haiti from mathematical model Marginal Value Met, Ideal Value Met in spring and summer months

Specification 4 Cost Calculation Ideal Value$30.00 Marginal Value$ Total Cost of prototype ~$ 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 Sunrise6:57 am 500+ Watts9:00 am First Liter9:52 am Sunset6:01 pm Total89 Liters April 24 Sunrise6:01 am 500+ Watts9:00 am First Liter9:21 am Sunset6:44 pm Total99 Liters 14Time to reach operating temperature on average day in worst month in Haiti3mins12060 August 15 Sunrise6:07 am 500+ Watts9:00 am First Liter9:09 am Sunset6:50 pm Total120 Liters October 22 Sunrise6:20 am 500+ Watts9:00 am First Liter9:24 am Sunset5:57 pm Total104 Liters

Budget P08404 was successful in creating a fully functional prototype well below budget. Final Prototype cost: ~$320 Budget: $1300 Spent: $ 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 13 Operating Temperature 27 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 16 Water 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 shows valve 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