Cook Stove for Haiti

Project 11461

Date: February 11, 2011Location: 78:2150

Time: 10:15am – 12:15pm

Detailed Design Review

Team Members

Project LeaderRob Reid (ME)

Lead EngineerJordan Hunter(ME)

Team EngineersAlex Seidel (ME)

Brian Knight (ME)Mike Lagos (IE)

Presentation Overview

• Project Background• Project Overview• Customer Needs Assessment• Engineering Specifications• System Architecture• System Integration• Risk Assessment• Test Plan• Flow of Analysis• Design• Analysis• BOM• Plan for MSD 2

Traditional Cook Stove

Project Background

Image from feaststl.com shows a basic lump charcoal cooking stove

• The World Health Organization estimates 3 billion people use biomass cooking regularly.

• Approx. 1.5 million people die each year from stove emissions

• Our main focus is the people of Haitiwho’s main method of cookingis open flame stoves, utilizing charcoaland wood.

• We are partnering with the H.O.P.E. Organization, which works with the Haitian people to help improve theirliving conditions and save lives.

• H.O.P.E. is working with RIT to create an improved cook stove designwhich is more efficient and lesshazardous to its users.

Project Overview

Mission StatementDesign and construct all mechanical and structural aspects of a thermoelectric biomass cook stove.

The stove will utilize a blower/fan powered by thermo-electrics to significantly increase efficiency and reduce fuel consumption and emissions.

In comparison with current Haitian stoves, the project stove will have a reduction in emissions and required fuel of 50%

Deliverables• An improved RIT stove design that has been tested and validated using a working prototype.• The improved stove is to reduce fuel use and emissions by more than 50% from traditional Haitian stoves. • Build at least two prototype stoves to be sent to Haiti for field testing.• Detailed project report.• Detailed presentation for Imagine RIT.

Customer Needs

Engineering Specifications

System Architecture

Risk Assessment

Risk Assessment

Testing Plan

Testing Groups

• Non-Operational Testing Group

• Operational Testing Group

• Non Testing Group

• Destructive Testing Group

• Untestable Testing Group

Testing Plan

Non TestingES6 – Cost to ProduceES7 – Cost to Operate

Destructive TestingES5 – Pot Weight Range TestES11 – Stove Drop Test

Untestable TestingES9 – Stove Life TestES10 – Cycles without Cleaning TestES12 – Corrosion Test

Non-Operational TestingNES –Thermoelectrics Connection TestES4 – Pot Diameter Range TestES13 – Time to Replace Parts TestES14 – Stove Volume TestES15 – Stove Weight TestES16 – Lifting Index TextES21 – Assembly Time Test

Operational TestingES1 – Time to Combustion TestES2 – Time to Boil Water TestES3 – Range of Heat Output TestES8 – Tasks to Maintain Combustion TestES17 – CO Emissions TestES18 – Hazardous Emissions TestES19 – Required Fuel to Boil Water TestES20 – Maximum Temperature Test

Stove DesignImportant Dimensions: Stove base

Height: 8.5”Radius: 6”

Combustion ChamberHeight: 6” Radius: 7.25”

Stove Assembly

• Made up of 5 Components• Base• Outside combustion chamber shell• Combustion chamber• Top cover• Pot supports

Structural Analysis

Combustion

- 2 reactions occur in the combustion of charcoal -- First, a very rapid reaction between Air (Oxygen) and Charcoal (Carbon) to produce CO2 and an extreme amount of heat. -- Second, a much slower reaction that consumes the charcoal and converts the CO2 into CO while consuming heat.

- Emissions should be reduced if full combustion is achieved

- The larger the lump charcoal size, the deeper a vertical stove would have to be to ensure complete combustion (If not enough vertical space exists in the heated zone for both reactions to fully occur the charcoal will not be fully burned)

- Air Flow should be very close to the base and come in from the side -- Air flow holes should be circular unless the stove has a very wide inner diameter or has a rectangular base in which cases rectangular holes with the longest side being the horizontal should be used -- If air holes are used they need to be kept as clean and unblocked as possible

- Slower air flows velocities are preferred to ensure full combustion occurs inside of the stove without making it extremely tall/long (There is a certain point where the air flow velocity is too low)

- Preheating the air before it first enters will decrease the fuel consumption

- All data point to the fact that additional air holes at the top of the stove will not be beneficial in any way.

Data from: The mastery and uses of fire in antiquity By J. E. Rehder

Combustion

Combustion

0

20

40

60

80

100

120

140

160

CFM Required Variance vs Variables

Energy per Volume FoodVolume FoodRequired Energy to Heat FoodEfficiency 1Efficiency 2Specific Energy of Charcoal 1Specific Energy of Charcoal 2Air to Fuel Ratio 1Air to Fuel Ratio 2Cooking Time 1Cooking Time 2Density of Air 1Density of Air 2Max Fan Flow

Arbitrary Range

Volu

met

ric F

low

Rat

e (C

FM)

Combustion

0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.4500

10

20

30

40

50

60

70

80

Efficiency vs. Volumetric Flow Rate

System Efficiency 1Max Fan Flow

System Efficiency : Combustion to Food

Requ

ired

Volu

met

ric F

low

Rat

e (C

FM)

Combustion

38.00000 40.00000 42.00000 44.00000 46.00000 48.00000 50.00000 52.000000

5

10

15

20

25

30

35

40

45

50

Air to Fuel Ratio vs. Volumetric Flow Rate

Air to Fuel Ratio 1Max Fan Flow

Air to Fuel Ratio

Requ

ired

Volu

met

ric F

low

Rat

e (C

FM)

Combustion

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.5000

20

40

60

80

100

120

140

160

Cooking Time vs. Volumetric Flow Rate

Cook Time vs Volumetric Flow Rate 2Cook Time vs. Volumetric Flow Rate 2Max Fan Flow

Cooking Time (Hours)

Requ

ired

Volu

met

ric F

low

Rat

e (C

FM)

Combustion

23000000 25000000 27000000 29000000 31000000 33000000 35000000 37000000 39000000 4100000020

25

30

35

40

Specifc Energy in Lump Charcoal vs. Volumetric Flow Rate

Specific Energy in Lump CharcoalActual Specific Energy ValuesMax Fan Flow

Specific Energy in Lump Charcoal

Requ

ired

Volu

met

ric F

low

Rat

e (C

FM)

Analysis Process : Combustion Chamber

• Heat require to meet specs is calculated

• Heat gain to sustain boiling is estimated from heat lost

• Combustion chamber spectrum analyzed with various possible efficiencies and charcoal energy contents

• Stoichiometric Ratio of the varying charcoals is calculated

• Calculated : - Heat Output Range - Fuel Consumption - Air Flow

• Combustion chamber dimensions calculated from estimated density of charcoal

www.fao.org/docrep/x5328e/x5328e0b.htm

Charcoal Specs

0 10 20 30 40 5075

80

85

90

95

100

105

Heat Lost From Pot Over Time

Time (min)

Tem

p (C

elsiu

s)

Fuel Consumption, Air Flow, & Chamber Size

Fuel Consumption, Air Flow, & Chamber Size

Fuel Consumption vs Time to Complete Boil

8 9 10 11 12 13 14 150

1

2

3

4

5

6

7

8

9

10

11

12

K-36%

K-28%

K-18%

K-14%

D-36%

D-28%

D-18%

D-14%

W-36%

W-28%

W-18%

W-14%

Time to Complete Boil (min)

Char

coal

Con

sum

ption

(gra

ms/

min

)

Stoichiometric Air Flow vs Time to Complete Boil

1 2 3 4 5 6 7 80.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

K-52%K-41%K-38%K-30%D-52%D-41%D-38%D-30%W-52%W-41%W-38%W-30%

Time to Complete Boil (min)

Min

imum

Air

Flo

w (C

FM)

Air Flow Analysis• Pressure drops due to

– Rapid Expansion when air enters outer stove chamber– Orifice – Charcoal Bed – Annulus

• Pressure Rises due to– Head supplied by fan– Heating of air in combustion chamber

• Pressure drops through the system are determined to ensure the fan is not supplying more than 1W of power to the air entering the system.

Flow SchematicAnnulus

Fan

Pot & Water

Packed Bed of Charcoal

Orifices

Combustion

Air Flow Air Flow

Major Equations

Assumptions• Rapid Expansion coefficient

– K=0.85• Determine from Area ratio=A1/A2

– Used Figure 8.15 in Introduction to Fluid Mechanics by Fox, Pritchard, McDonald

– Velocity is determined from fan volumetric flow rate• Orifice has a square edged inlet

– K=0.5 from Area Ratio=A2/A1– a=0.5

• Pressure drop across packed bed of charcoal– Assumed particle size is approximately 1.5”-2.0”– ε (Void Ratio)=Void Volume/Total Volume

• Power supplied by fan cannot exceed 1W

Parameters

Spreadsheet Layout

Effects of Varying Orifice Size

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.0180

1000

2000

3000

4000

5000

6000

7000

8000

9000 Effect of Varying Orifice Size on System Pressure

1/4" Hole Radius

1/2" Hole Radius

3/8" Hole Radius

5/8" Hole Radius

Volumetric Flow Rate (m3/s)

Pres

sure

(Pa)

Effects of Varying Particle Diameters

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.0180

100

200

300

400

500

600Effects of Number of Orifice Holes on System Pressure

8 Holes

6 Holes

10 Holes

12 Holes

Volumetric Flow Rate (m3/s)

Pres

sure

(Pa)

Thermal Analysis

• A Thermal analysis of the stove system was then completed in order to help understand the affects of different forms of heat transfer.

• The key pieces of information needed from this analysis are:

• Heat Loss Through stove walls• Surface Temperatures of the various

chambers. (Shown to Right)• Affects of different insulations and barriers.

• This data would then help us to optimize the stove in terms of heat transfer and minimize thermal loses throughout the stove.

Thermal Analysis

Equations Used to Calculate Losses due to Conduction, Convection, and Radiation. Radiation Within Combustion Chamber & To Atmosphere

qrad = Ac* ε *σ* (T1^4 – T2^4) [Large Cavity]

Radiation Within Annulusqrad = (Ac* σ *(T1^4 – T2^4)) [Annulus] ((1/ ε1)+((1- ε2)/ ε2)*(r1/r2))  

Conduction Within Insulation Layerqcond =(2*Pi*L*K*(T1-T2)) / ln(r2/r1) Convection Within Combustion Chamber, Annulus, & To Atmosphereqconv = h*A*(T1-T2)

Energy Lost in Air

qforced = mdot*Cp*(T1-T2) 

Thermal Circuit Diagram

TfireTs1

Ts2Ts3

Combustion Chamber

Air Annulus

1” Ceramic Insulation Blanket

Thermal AnalysisEnergy Balances Were used to optimize the system using Excel Solver.

Energy Balance Surface 1qconv-fire + qrad-fire – qconv-annulus1– qrad-12 = 0

Energy Balance Surface 2qrad-12 + qconv-annulus2 – qcond-ins = 0

Energy Balance Surface 3qcond-ins + qrad-amb – qconv-amb = 0

Energy Balance Airqconv-annulus1 + qconv-annulus2 – qforced = 0

Energy BalancesLocation Balance Abs ValSurface 1 0.018 0.0183671 WSurface 2 3.390 3.38960141 WSurface 3 -0.450 0.45022206 WAir 0.01261 0.01260974 WTotal Error 3.871 WTotal Heat Loss 120.076 W

The energy balances were used in conjunction with the heat transfer equations to solve for the air and surface temperatures in and around the stove.

Heat Lossqconv-fire 467.248 Wqrad-f ire 845.560 Wqconvannulus1 442.720 Wqconvannulus2 -747.054 Wqrad1-2 870.069 Wqforced 1189.761 Wqcond-ins 119.626 Wqconv-amb 103.636 Wqrad-amb 16.441 W

Thermal Analysis

Surface Data (Optimized)In Celcius Kelvin

Tf ire 1000.000 1273TS1 971.538 1244.54Tforced 30.000 303Torafice 99.155 372.16TS2 893.150 1166.15TS3 46.505 319.51Tamb 30.000 303

• Using the constants to the left, I was able to calculate the approximate surface temperatures.

• According to these results we exceed our target spec of having a 50 C outside stove wall (TS3).

• These values were found using 1” thick layer of ceramic insulation (L=1”, K=0.29 W/m KL), From Thermal Ceramics Corp.

• The inner stove wall is also made of a polished steel, which acts as a radiant barrier.

ConstantsL 0.025 mK 0.290 W/m KLmdot 0.017 kg/scp 1009.000 kJ/kg Ksigma 5.67E-08epsilon 1 0.800epsilon 2 0.300rho 1.150nu1 14.074Reynolds1 580.988nu2 14.074Reynolds2 580.988Dh out 0.760 mKinematic V 0.000062 m^2/sReynolds out 61.290nu out 4.644Velocity 0.204 m/sRcomb 0.092 mRinner 0.127 mRoutside 0.152 mHcomb 0.142 mHinner 0.190 mHouter 0.190 mCFM 30.000 cfm

Thermal Analysis

Convection

• Insert 1” thick ceramic insulation blanket between combustion chamber and outside wall.

• Secondary wall of polished steel to promote fluid flow and act as a radiant barrier.

Radiation

ConductionThis combination yields a theoretical total heat loss through the stove walls of ~ 120 W.

BOM

Project Plan

Order handles

Order Insulation

Finalize Design

Build Stove

Cut Design out of Drum

Build base

Build outside Chamber

Build Combustion Chamber

Build Top Cover

Build pot supports

Assemble Stove

Testing

Prepration for Imagine RIT

Imagine RIT

3/3 3/7 3/11 3/15 3/19 3/23 3/27 3/31 4/4 4/8 4/12 4/16 4/20 4/24 4/28 5/2 5/6 5/10

Thermo-Electric Cook Stove #2: MSD II Project Plan

Questions?