Heat Transfer [email protected]

Human Development Index vs. Energy Consumption 1 0.9 0.8 0.7

Africa Asia Europe N America Oceana S. America Large

HDI

0.6 0.5 0.4 0.3 0.2 0.1 0

0

5000

10000

15000

20000

Annual Energy per Capita (kg oil)

25000

Human Developm 1 0.9 0.8 0.7

Integrated Problem Application

Fuel

Stove

What is Heated? Air Thermal Mass/Storage Water Direct Grill Grill Through Metal Steam Chemical Processes Bricks/Kilns Smelting

Gathering Storage Drying Processing Densification

Insulate Heat to Application Support Pot/Application Mix Fuel & Air Hold Structural Integrity Fuel in Ash out Embers out

Light?

[email protected]

Flue Exhaust Poisons Channel waste heat Provide air motive force Damp excessive flow Accommodate cleaning Prevent Fire/Explosion

Application What is Heated? Air Thermal Mass/Storage Water Direct Grill Grill Through Metal Steam Chemical Processes Bricks/Kilns Smelting Light?

The Flue is Key • The heat to the application is generally carried primarily in the flue gas • The flue’s draft draws the inflow of air

• The hotter the exhaust, the more heat you just wasted

Flue Exhaust Poisons Channel waste heat Provide air motive force Damp excessive flow Accommodate cleaning Prevent Fire/Explosion

It’s Easy to Screw up the Flue: • Too little draft and the fire chokes – And it can burn or blow up

• Too much draft and heat exchange is reduced • Flue gas is not good for people – Seals are very hard, leaks are easy

• Flues need to be cleaned

The Chimney Equation

The Stove • The most difficult materials problem • • • •

Seals Insulation Cyclic Thermal stresses Nothing flamable

• Lots of integrated structure issues • • • • •

Support Access to application Fuel loading Flue cleaning Ash, ember management

Stove

Insulate Heat to Application Support Pot/Application Mix Fuel & Air Hold Structural Integrity Fuel in Ash out Embers out

Materials: Metals • Sheet metal • Iron Pipe • Galvanized roofing • Cans • Metal rods • Aluminum foil • Wire mesh

• Bolts & Nuts – Not sheet metal screws

Ceramics/Insulators • Refractory brick • Brick • Tile • Stone • Pumice • Cement • Vermiculite/Perlite • Fiberglass • Char • Ash/Cinders • Sand • Boric-Acid treated fabric

It’s Easy to Screw up the Stove: • Incomplete combustion – Many noxious/toxic gasses

• Too much air and your flue gas cools • Thermal stresses, corrosion are common failure modes • Wear and tear on the fuel inlet

Integrated Problem Application

Fuel

Stove

What is Heated? Air Thermal Mass/Storage Water Direct Grill Grill Through Metal Steam Chemical Processes Bricks/Kilns Smelting

Gathering Storage Drying Processing Densification

Insulate Heat to Application Support Pot/Application Mix Fuel & Air Hold Structural Integrity Fuel in Ash out Embers out

Light?

Flue Exhaust Poisons Channel waste heat Provide air motive force Damp excessive flow Accommodate cleaning Prevent Fire/Explosion

Fuel Gathering Storage Drying Processing Densification

Hydrocarbon

Biologic

Solid

Liquid

Gas

Alcohol CnH2n+1OH

H2 123 Methane CH4 55.6 Ethane C2H6 51.9

Carbohydrate 17 Protein 16.8 Dung 15.5 Cellulose 17.6 Algae Seaweed Wood: -logs -branches/sticks -pellets -shoots/straw -cardboard/paper/scrap -leaves -grass -sawdust (Burn or Pyrolyze) Char 14 Peat 12.8

Ethanol C5H11OH 30 Methanol CH3OH 19.7 Best used in liquid state to make digestion products for gasses

Carboxylic acids: (R)-C(=O)OH xx* *These don’t like oxygen (They are Acids…)

•With hydrogenation, turn

Fossil

Other trace Biologic: Propane C3H8 49.6 Butane C4H10 49.1 CO 10.1 etc..

into alcohols •With Bacteria, turn into methane

Compound Megajoules/Kg

Solid … Wood: 17.6 -logs -branches/sticks -pellets -shoots/straw -cardboard/paper/scrap -leaves -grass -sawdust …

It All Burns…

Integrated Problem Application

Fuel

Stove

What is Heated? Air Thermal Mass/Storage Water Direct Grill Grill Through Metal Steam Chemical Processes Bricks/Kilns Smelting

Gathering Storage Drying Processing Densification

Insulate Heat to Application Support Pot/Application Mix Fuel & Air Hold Structural Integrity Fuel in Ash out Embers out

Light?

Flue Exhaust Poisons Channel waste heat Provide air motive force Damp excessive flow Accommodate cleaning Prevent Fire/Explosion

C

C

1.25’ curve at 2.5’ radius 1.25’ curve at 0.5’ radius 5’ section at 24 deg to vertical

C 5.33’ section at vertical

1. 5’ curve at 1’ radius 2.33’ section at 9 deg 3” cut allows swing-out of foot during replacement

1’ vertical section

Everything Goes in Cycles…

Final Thoughts • Designing the stove is only one of the hard parts for the engineer • Processing the fuel and handling the waste stream are usually the hard parts for the customer

• Work the flue first, then build around that • Materials selection and maintenance is huge – Refractory materials need attention

Heat Transfer.pdf

0.8. 0.9. 1. 0 5000 10000 15000 20000 25000. Annual Energy per Capita (kg oil) HDI. Africa. Asia. Europe. N America. Oceana. S. America. Large. Page 2 of 40 ...

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