Team P08404

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

Solar Pasteurizer Project Review

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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

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Project Background

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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

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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

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Engineering Specs

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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

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Key Engineering MetricsAmount of water necessary for family of five

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Key Engineering MetricsDefining 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” will be used to verify pasteurization has occurred. This is the same test used by the U.S. EPA when analyzing drinking water.

This technique will involve 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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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

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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

Col

d

Ho

t

He

at E

xch

ang

erCollector Plate ValveSenses Open

Air Vent

Air

Hot R

eserv

oir

Closed

Che

ck 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

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Path to Pasteurization: Water Storage

5 gallon buckets chosen for water storage

By mounting a mesh screen across the fill hole, large particulates will be filtered out.

UV resistant tubing for water delivery

Design Review Feedback / Risk Assessment:Stand design and bucket size chosen to minimize cost

Life cycle failure of cantilevered supports / bucket handle mount analysis planned for SDII

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Path to Pasteurization-Heat ExchangerTube 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 3/8” ID. Approx. 0.03” 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.

Risk Assessment:Stagnation Temperature: Temperature inside flat plate solar collectors can reach 400 F. Materials outside of collector area must withstand boiling temperatures.

Tube in Tube Apex: Flow annulus will not be uniform due to Al tubing apexing the arcs in the santoprene tubing.

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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

Path to Pasteurization-Venting of Excess Air

Heating water results in the release of previously dissolved air.

A method was devised for releasing this excess air through a vent tube coming from a T-fitting at the highest point of the collector.

Design Review Feedback / Risk Assessment:

This method will result in a tall column of coldwater that may flow back into, and contaminate, the system.

Other methods of venting air, such as a floating ball valve, being examined.

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Path to Pasteurization-Valve System

Inside Collector

OutsideCollector

Water from lower collector

Water to upper collector

Water from upper convective loop

Water to hot reservoir

Design Review Feedback / Risk Assessment:

Seal at thermostat and O-ring angled seal difficult

Extensive testing necessary

Spring clearance value

New concepts for sealing being finalized as of Design Review on 2/18/07

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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.

Design Review Feedback / Risk Assessment:

Thermal losses can reduce efficiency of heat exchanger

Reservoir Design:

Cost Calculation• Total Cost $217.98• Marginal Value $100.00

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Subsystem Cost of MaterialsCollector $86.52HX $31.00Valve $30.88Buckets $27.11Box $14.42Misc $9.53Loop $6.87Plenum $6.69Vent $4.96Total $217.98

Shown: the raw material cost necessary to build a prototype. More complete high volume manufacturing costs will be calculated in SDII

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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

Mathematical Model

Purpose of the Cost Model:Model assumes a worst case scenario for incident solar radiation and calculates heat transfer to the water, modeled as finned tubes. It also calculates the efficiency of the heat exchanger.

The model approximates the dimensions of the system: the plate size and tubing length for both HX and collection area.

The model also optimizes dimensions based on cost inputs for the tubing, glazing, and plating materials

Design Review Feedback / Risk Assessment:Verify output by modeling hourly weather data for a range of environments, calculating total daily output.

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Discussion Content

• Project Overview

• Customer Needs

• Key Engineering Metrics

• Design Overview

• Mathematical Model

• Risk Assessment

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Fault Tree Diagram