Thermodynamic Properties of Black Powder - Graybeard Outdoors
 
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post #1 of 5 (permalink) Old 11-11-2010, 12:03 AM Thread Starter
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Default Thermodynamic Properties of Black Powder

I have just completed testing for the thermodynamic properties of black powder using a bomb calorimeter. The results are presented below:

Density - 454 grains per inches cubed

Energy - 13.65 ft-lb(f)/grain

Co-Volume - 0.00395 inches cubed/grain

Gamma - 1.268

Average Mol. Wt - 59.25

With this data it is possible to calculate muzzle velocity and pressure.

For a people who are free, and who mean to remain so, a well-organized and armed militia is their best security. (Thomas Jefferson)
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post #2 of 5 (permalink) Old 11-11-2010, 12:33 AM
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Default Re: Thermodynamic Properties of Black Powder

Have you a short example for "Dummies"

As in how you use the information given . ???

Left Handed people are in their right mind .
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post #3 of 5 (permalink) Old 11-11-2010, 12:39 AM
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Default Re: Thermodynamic Properties of Black Powder

Er nie,

He is building a ballistics program for black powder cannons...
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post #4 of 5 (permalink) Old 11-11-2010, 02:12 PM
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Default Re: Thermodynamic Properties of Black Powder

Do these values change with the grade of powder, or an I missing something?
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post #5 of 5 (permalink) Old 11-11-2010, 04:36 PM Thread Starter
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Default Re: Thermodynamic Properties of Black Powder

The values do not change with granulation. However, the burning rate and ratio of the surface area (So) to volume (Vo) of the black powder do change with the granulation. The burning rate is also effected by the pressure. A simple equation for velocity would look like this:

Velocity = (2*Grains.Burnt*13.56*32.2/Projectile.Weight)^0.5

Grains.Burnt = Powder.Charge * So *Burn.Rate*Time/Vo

Time - is the time from ignition to the projectile leaving the barrel

Burn.Rate = Alpha * Pressure ^ Beta

This equation assumes the temperature of the gases are constant - not correct - the gas temperature changes form 2038 to about 1200 for cannons but are almost constant for mortars.

That Beta is constant for all pressures - it is not - Beta is also a function of pressure - and the relationship is sigmoid. The general sigmoid function shape is shown in the attachment. The sigmoid is very common in science. If you have ever measured the velocity or range of a projectile over a series of powder charges say 30 grains to 120 grains in a golfball mortar you will have noticed the sigmoid effect. At around 80 grains their is a shift in the distance or velocity acheived - what happens - the Beta value changes because pressure changes do to the faster burn.



Attached Images
File Type: jpg Sigmoid.jpg (32.0 KB, 7 views)
File Type: jpg Sigmoid.jpg (32.0 KB, 7 views)
File Type: jpg Sigmoid.jpg (32.0 KB, 7 views)

For a people who are free, and who mean to remain so, a well-organized and armed militia is their best security. (Thomas Jefferson)
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