Different Technologies:

There are several different approaches to changing the way people cook in poor urban and rural areas. These include (in order of environmental friendliness) solar cooking, switching to another fuel, and making wood stoves more efficient. However, there are many areas where wood stoves are going to be used anyway unless there are other major changes in the social and economic areas.

Solar cooking ovens:

http://solarcookers.org/

http://solarcooking.org/

acceptance issues

Biogas cooking:

http://www.seedtree.org/index.html

http://www.seedtree.org/biogas.html

http://asofenix.org/projects/complementary-projects/

Improved wood stoves

Aprovecho Research Center - research on stoves to improve indoor air, reduce deforestation and address climate change

Rocket stove - wikipedia

make a rocket stove

WoodGasTM Campstove - see how it works

Energy calculations for wood stoves

For the purposes of this lab we will focus on a practical way to address the efficiency of using different stoves: how much wood does it take to heat water to boiling and how long does it take?

Heating 200 mL of water from 25 degrees to 100 degrees would require approximately 1500 calories = 15 kcal of energy to be absorbed by the water (200 mL * 75 degrees). Since 1 Kcal = 70 Watt*min, this equals 1050 watt*min of energy. The power absorbed if it takes 5 minutes to boil is 210 watts.

We are following the power absorbed not what is put out by these different configurations and fuels.

Compare 4 configurations:

1) an electric hotplate

2) a gas stove

3) wood in an open flame

4) a high-efficiency twig stove

For the electric hotplate and possibly the gas stove we can calculate the amount of energy used by using a watt meter or by weighing the gas cansiter before and after cooking. For the wood stoves, it is possible but a little messy.

For the electric hotplate:

• set to 700 watts = 10 Kcal/min
• once the hotplate is heated (which takes the first amount of energy)
• 200 mL of water * 75 deg Celsius requires 15000 cal (15 Kcal)
• 15 Kcal/(10 Kcal/min) = 1.5 minutes if the heat transfer were perfect

For the propane stove:

• propane contains about 12 kcal/gram of fuel
• this is equal to 840 watts*minute/gram
• at full flow the gas stove burns about 2 grams/minute = 1680 Watts
• At 24 kcal/minute it would take minutes to heat 200 mL of water * 75 degrees (15 kcal of heat, only about 40 seconds if the heat transfer were perfect)
• since it takes X minutes, that means the heat transfer is (.66 minutes)/(X minutes) efficient

For the wood stoves:

• wood is about 4.3 kcal/gram
• 15 kcal required to heat 200 mL water to boiling
• should require (at the minimum) 15/4.3 = 3.5 grams of wood

 

• The high efficiency WoodGas stove is supposed to have a power of 3 KWatts (or the equivalent of a big burner on a home stove top).
• This amount of power should be able to boil 1 quart of water in 8 to 9 minute.
• 1 quart = 946 mL
• 200 mL should take less than 2 minutes if the stove is working under full power.

 

wood has 18 MJ/kg = 18/3.6 Watt*hr/kg = 5 Watt*hr/kg = 0.083 Watt*min/kg = 4.3 kcal/gram

propane = 49.6 MJ/kg = 11.8 kcal/gram