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Propane explained

donbrown

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C3H8 - The molecular makeup of propane consists of 3 Carbon molecules and 8 Hydrogen molecules


Propane Boiling Point -44°F
Weight of 1 Gallon Liquid Propane*4.24 Lbs

BTU per Gallon of Propane Gas*91,547 so about a gallon every 3 hours for a 30k furnance
BTU per Lb. of Propane Gas 21,591
BTU per Cu Ft of Propane Gas*21,591



Propane Properties Explained

Propane Boiling Point - Water boils at 212°F meaning that it becomes a gas at this temperature whereas water is still a liquid at 200°F. Propane is a liquid at -50°F and boils at -44°F. In other words, at 10 degrees below zero, propane is well past its boiling point.

It means that propane is cold enough freeze your skin (and tissue underneath) to the point of severe damage.

Specific Gravity of Propane Gas - One cubic foot of propane weighs .1162 lbs. and one cubic foot of air weighs .07655. Dividing .1162 by .07655 equals 1.52. What does this mean? Propane is heavier than air and will seek the lowest space available.

Specific Gravity of Liquid Propane - One gallon of propane weighs 4.24 lbs. One gallon of water weighs 8.33 lbs. Dividing 4.24 by 8.33 equals .51. This means propane is less dense than water (lighter than water) and will not sink in water, so to speak.

BTU - As defined, a British Thermal Unit is the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It takes about 143 BTU, or .0016 gallons of propane, to melt one pound of ice (at 32°F).

About .33 gallons to make 30000 BTU


Ignition Temperature in Air 920-1020°F
Maximum Flame Temperature 3595°F
Octane Number Over 100

HD5 grade propane is "consumer grade" propane and is the most widely sold and distributed grade of propane in the U.S. market. HD5 is the highest grade propane available to consumers in the United States and is what propane companies ordinarily sell to their customers. HD5 spec propane consists of:

Minimum of 90% propane
Maximum of 5% propylene - propylene is used in the manufacture of plastics
Other gases constitute the remainder (iso-butane, butane, methane, etc.)

A good burn for propane is 90 plus percent efficient and rest of energy makes water.


C3H8 +5O2 --> 3CO2 + 4H2O + heat So a convection heater will dump a lot of moisture if vented into the trailer.

The gas flame appears blue because complete combustion creates enough energy to excite and ionize the gas molecules in the flame.
With complete combustion, an LPG (Propane) flame burns at a temperature of around 1,980°C.

A bad burn for propane is

A yellow color is due to incandescence of very fine soot particles that are produced in the flame at around 1000 degrees C
This type of flame only burns at around 1,000 °C.

Propane + Oxygen → Carbon Dioxide + Carbon Monoxide + Water + Heat
2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + heat

If the room fills with 1.28% CO a typical human will pass out in 2-3 minutes
 
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donbrown

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A British Thermal Unit (BTU) is an approximation of the amount of energy required to heat 1lb (one pound) of water from 39°F to 40°F (degrees Fahrenheit), and is roughly equal to 1.055 KJoules.

Simplified, 1 BTU is roughly the amount of heat produced by burning a single wooden match.
 

donbrown

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you can search for a BTU calculator to find out what BTU needed to heat area.

For an uninsulated trailer 8.5 wide 29 long and 7 feet tall with no insulation , metal sides , wood deck , no windows , no wind , Needs about 8000 BTU per hour to keep it 30F warmer above freezing. 32F will get you around 62F

Covert BTU watts 1 BTU/hr = 0.29307107 W so 8k BTU 2345watts

So 91.5k BTU per gallon will last 11 hours.

Below freezing you need more BTUS from ice forming on the walls ... to keep the water melted on the walls. I am guessing but 1 BTU per cubic foot.

and below freezing 9.8k BTU about 9 hours a gallon.

Of course this assumes the room is air tight ... which it is not.

And the hard part to calculate heat loss is wind blowing on the wall transferring heat out and cold in https://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html Which can take lots of energy to keep the thermal transfer neutral

Plus energy from the sun ! Plus color of the trailer!
 
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meathooker

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Good info.

How did you arrive at 8000 btu to keep the trailer at 62deg? Seems light

You need to account for the heater efficiency in your time calculation.
 

donbrown

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Good info.

How did you arrive at 8000 btu to keep the trailer at 62deg? Seems light

You need to account for the heater efficiency in your time calculation.

There are several "calculators" to determine required BTU . It seems most don't give the formula and you just type in the numbers.

8 feet wide 29 feet long 6 feet tall "normal" insulation for the one below Please note previous post has a larger trailer area but cant find the website to replicate the calculation here.

http://www.calculator.net/btu-calcu...=30&temperatureunit=f&calctype=heat&x=60&y=23

If select "normal" to "poor" insulation BTU goes from 8112 BTU to 17035 BTU. The formula variance does not declare why there is double the heat loss.

This formula did not take into account the fuel used and efficiency of the furnace .... so ya it is off in a real world application. So add 10% for propane to account for energy loss converting some to water? For the furnace I assume it burns 100% of the propane and has a "blue" flame.

Plus it takes much more energy to heat up the air ... this is just to maintain a 30F differential from heat transfer loss thru the walls.

Also wood is a better insulator than aluminum. Aluminum transfers heat better ... to the outside ... such as a sleds radiator
 
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Mafesto

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A little more info for comparison sake.

100,000 BTU = 1 Therm
1 Gal propane = 91,000 BTU
1 Gal gasoline = 120,500 BTU
1 Gal Diesel fuel = 138,000 (approx)
3412 BTU = 1 KW
1 lb Coal = 9811 BTU
 
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