MULTIDISCIPLINARY SENIOR DESIGNPROJECTS P12441 & P12442

2011-2012

PowerStove: Cooking for a Third of the World

Motivation

Two and half billion people depend on biomass (wood, dung, or agriculture residues) primarily for cooking

The practice of cooking with biomass has decimated many ecosystems

Biomass use requires an enormous amount of human effort to gather and process

Cooking with biomass creates considerable health problems that continue to plague the world’s poorest populations

Cookstove emissions is the second-largest global source of greenhouse gases after fossil-fuel combustion

2011-2012 Stove Project Scope

To minimize the harmful effects associated with cooking, two Rochester Institute of Technology (RIT) multidisciplinary student engineering teams in partnership with a NGO will design, build, and test a more efficient, cleaner, and socially acceptable cook stove using thermoelectrics and a simple blower. The project will result in a minimum of two working stoves that will be field tested during the summer of 2012.

Project Initial Target Customer

Borgne, HaitiPoorest country in Western

hemisphere ($420/person-year)

75% of all energy consumed is biomass

Only 4% forested land left, huge deforestation problems.

H.O.P.E (Haiti Outreach - Pwoje Espwa) partner NGO

RIT Advanced Cookstove Project Goals

This project will build on recent stove advancements to develop an improved stove for Haiti and other developing nations with the goals of:

reducing fuel use by a factor of two or greater in order to turn the tide on deforestation and diminish the time and limited financial resources spent on cooking;

creating microenterprises for assembling the advanced stoves to generate wealth and develop local expertise for maintaining the stoves in order to improve chances of sustained stove adoption;

enhancing conventional cooking techniques of traditional foods; provide an electrical power source to operate auxiliary loads such as

radio, lighting, charge cell phone batteries, and small UV water treatment technologies; and

improve the air quality to reduce the alarming rate of respiratory deaths associated with cooking while combating global climate change.

Past Projects

P10451 & 11451 – Developed testing setup and process for quantifying stove efficiencies and emissions. Benchmarked Haitian stove.

P10461, 11461, & 11462 – Developed first generation of vendor and institutional cook stoves using thermoelectrics and blower.

Project 12442Next Generation Charcoal Cook Stove for

Haiti

Build on the work done by project P11461 &11462 to develop an improved cookstove for vendors and institutional users.

The improved cook stove should substantially reduce (by more than 50%) the emissions and fuel needed for cooking compared to the traditional stoves currently used in Haiti.

Combine efficient cook stove and thermoelectric thermal system.

The stove developed by team P11461 was designed to use force draft to improve combustion and heat transfer to the pot. The stove design also made use of recycled material, attempted to reduce thermal losses by the use of radiant barriers, and increase heat transfer to pot by the use of a skirt.

Some modeling and experimentation was done, but not comprehensive.

Project 12442Preliminary Needs

Affordable (initial cost <$10 at high production quantities of 1000+) Cheaper to operate than current stove (less fuel for same cooking tasks) Significantly cleaner than current stove (reduced CO and PM emissions) Easy to operate (require little user interaction and simple and intuitive processes,

require the same or less effort than current practices for starting and cooking with stove.)

Same or improved cooking controls (control cooking conditions for traditional Haitian cooking practices). Obtain rapid boil quickly and then bring to simmer.

Be able to be fabricated and assembled using Haitian artisan practices Transportable so that a single adult can move the stove 500 meters unassisted. Rugged, can handle being dropped by user multiple times, withstand harsh conditions

such as rain and high temperatures. Durable, should operate for five or more years with a use rate of at least twice a day or

have simple, cheap, and easily replaceable parts. Thermoelectric module will not fail due to high temperature and gradients.

Safe to operate, operator should not be injured during normal use and transport of the cook stove.

Internal needs: Maintain appropriate temperature gradient across thermoelectric module Achieve desired temperature gradient quickly

Project 12442Preliminary Specifications

Production cost: <$10 for materials at 1-10K quantities, less than 3 hours of a Haitian’s craftsman labor per stove.

Fuel use: 50% of traditional Haitian rebar fuel use for both Full Water Boil Test (WBT) and established Controlled Cooking Test (CCT).

CO emissions: 25% of tradition Haitian rebar stove emissions for both WBT and CCT PM emissions: 25% of tradition Haitian rebar stove emissions for both WBT and CCT Time to boil during WBT using traditional starting practice is ¾ the time currently

achieved with the Haitian rebar stove. Surfaces of the stove that will be contacted by stove operator should not exceed 50°C. Less than 15 minutes to start and bring 2.5 liters of water to boil using traditional

starting techniques. Range of heat output 1-6 kW (heat transferred to pot). Capable of using with pot diameters from 20-60 cm. Withstand pot mass up to 25 kg. Five or less tasks to maintain fire throughout a CCT after initial stove start. Any part that will need to be replaced within a three year stove life should:

Be less than $3. Require less than 60 minutes to replace. Be able to be replaced with no or simple hand tools.

Project 12442Preliminary Specifications

Stove weight should be less than 8 kg. Stove volume should not exceed 0.2 m3. Stove construction should be possible using basic Haitian fabrication capabilities Survive 20x 2-meter drop tests. Egonomics metrics?

Internal Specifications: Keep a minimum temperature gradient of 200°C across a Thermonanic TE (TEP1-1264-

3.4) thermoelectric module under peak power conditions (i.e. electrically loading module with the internal resistance of the module.)

Reach desired temperature gradient within 20 minutes of starting the fire. Consume less than 0.6 W (i.e. ideal case, 1 W absolute max) to operate all stove internal

electrical loads (i.e. fan and controls). Thermoelectric module never exceeds max operating temperature (380°C continuously

and 400°C intermittently on hot side and 200°C on cold side). Thermoelectric module is mechanically loaded evenly and loading does not exceed

module failure limit.

Project 12442Project Deliverables

An improved RIT stove design that has been tested and validated using a working prototype and shown to reduce fuel use and emissions by more than 50% from traditional Haitian stoves and is affordable and user friendly.

Stove must be tightly coupled to thermoelectric power unit prototype being developed by P12441

Two prototype stoves to be sent to Haiti for field testing. Full and easy to follow documentation on how to fabricate and

assemble the stove. Intuitive end-user operation manual with instruction of how to start,

maintain, and operate the stove at optimal performance.

Project 12441Thermoelectric Power Pack for Next Generation Cook

Stove

Build on the work done by project P10462 & P11462 to develop power pack for that is electrically coupled to P12442 stove and will supply sufficient power for fan and auxiliary charging.

Needs: Affordable (<$10 at high production quantities) Easy to operate: require little user interaction and simple and intuitive processes. Compact, should be small so it does not extend too much from stove body. Rugged, can handle being dropped by user multiple times, withstand harsh conditions

such as rain and high temperatures. Heat resistant, can be mounted on stove framing with minimal loss in lifetime. Durable, should operate for five or more years with a use rate of at least twice a day. Able to charge multiple cell phones and other typical 5V USB loads over the course of a

typical institutional or vendor single stove use. Minimize stove use for sole purpose of electric power generation: unit should be able to

charge one typical cell phone when no power is provided by thermoelectric to the fan. Power fan used for a force air stove during entire stove operation. Able to start fan multiple times in cases where there are multiple stove restarts. Safe to operate: operator should not be injured during normal use and transport of the

thermoelectric power pack.

Project 12441Preliminary Specifications

Production cost: <$10 for materials and fabrication plus thermoelectric module at 1-10K

Operate 1.2W fan continuously during stove operation with a draw of 4-12VDC.

Power load using a Thermonanic TE Module (TEP1-1264-3.4) with a 20 minute warm-up period with cold side of TE going from 30 to 100°C and the hot side from 30 to 300°C. This is followed by steady state temperatures of 100°C and 300°C for 2.5 hours.

Package size for entire power pack except thermoelectric module is restricted to 3”x3”x1.5”

Unit should be less than 3 lbs. Package should prevent damage or significant reduction in product life to

electrical components during a downpour. A minimum of 7.0 Wh of charging capacity to auxiliary loads such as cell

phones through a standard USB connection over the course of a 3 hour cooking cycle

Sustain surface mounting temperatures up to 350°C. Handle some sort of dynamic crush test Survive 20 2-meter drop test. Safety metrics?

Project 12441Project Deliverables

Two working thermoelectric power packs that are to be sent to Haiti for field testing. The power pack must be nicely packaged and rugged. These power packs must be fully coupled with the stove being developed by P12442.

Full set and intuitive set of documentation on how to fabricate and assemble power pack units including necessary engineering pcb layouts files.

Intuitive operation manual should be provided for the end-user.

Instructions on how to adjust fan voltage so future teams can adjust design for different fans.

Classification of Cook Stoves

Open Fire Rocket Stove

http://wings.interfree.it/html/Elbow.html

http://picasaweb.google.com/lh/photo/_D6z6UiS0hupX2pf1LIP5A

Classification of Cook Stoves

Gasifier Stove Forced Draft Fan Stove

http://www.treehugger.com/files/2006/03/philips_smokele.php

http://www.vrac.iastate.edu/ethos/files/ethos2009/Stove%20Developments/TLUD%20Gasifier.pdf

Classification of Cook Stoves

Charcoal Stove Liquid or Gas Fuel Stove

http://picasaweb.google.com/lh/photo/VhARzq11pifTNUljR09z6g?feat=embedwebsite

http://www.bioenergylists.org/stovesdoc/Ezzati/New%20Folder/metal.jpg

Stove Innovation

Outer pressurized make-up cavity

Thermoelectric module

Adjustable skirt to improve heat transfer

Inner combustion chamber

Inlet air perforations for improved combustionAir flow

Heat Sink

Small fan

Power storage and conditioning/control

Potential auxiliary power supply

Why Forced Air?

Why Forced Air?

Why Forced Air?

Stove Testing

Water Boiling Test

Bring 5 L of water to a boil for a “Cold Start”

Bring a fresh 5 L of water to a boil from a “Hot Start”

From the “Hot Start,” allow the water to continue to boil for 45 minutes

Provides feedback on fuel consumption and thermal efficiency

Stove Testing

RIT Modified Water Boiling Test

Bring 2.5 L of water to boil from a “Cold Start”

Hold the boil for one minute

Simmer Stage: Allow the water to continue boiling for 20 minutes

Allows to quickly verify repeatability

Results

0 5 10 15 20 25 30 35 40 450

100

200

300

400

500

600

11.8

12

12.2

12.4

12.6

12.8

13

13.2

13.4

13.6

Water Temperature, Carbon Monoxide and Total Weight

During Modified Water Boiling Test

Temperature (°C)CO (ppm)Total Weight (kg)

Time (min)

Results

Thermoelectric Benefits

Modular, scalableSolid-state, no moving partsOperate over a range of temperaturesTransient thermal sourcesMinimal maintenanceNo noise, vibration

Resources

Category Source Description Resource Available

(mark with X)

Faculty

Rob Stevens ME Expertise in thermoelectrics and heat transfer X

John Wellin ME Expertise in DAQ, fluids, and fan characterization X

Brian Thorn ISE Product Sustainability X

George Slack EE Power electronics X

Jim Myers Center for Multidisciplinary Studies

Haiti expert X

Environment

Sustainable Energy Lab

ME-Stevens Lab for testing thermoelectric modules and subsystems. Lab does have ventilation and some DAQ resources

X

Equipment

DAQ system ME-Stevens A USB based DAQ system, laptop, thermocouples, etc. are available through the Sustainable Energy Lab

X

Cook stove test stand

SEL X

Several stoves

SEL X

Advise

Identify the key hurdles and address them earlier rather than later.

Identify and focus on the critical parts and do not get caught up with the trivial things.

Test early and test often. Test components and subsystems before the entire system.

Learn from the past. Pick the brains of those with experience.

Define your boundaries before you design, but be flexible.