Trouble calculating effective exhaust velocity

In summary, the conversation discusses the calculation of effective exhaust velocity for an engine using a simplified version of the specific impulse formula. The main issue is determining the correct value for the Universal Gas Constant, with difficulties arising from using different units for atomic weight. The individual provides the values and equations used for their calculations and requests assistance in identifying any errors.
  • #1
Swartz55
1
0
So I'm trying to calculate the effective exhaust velocity of an engine which burned aluminum oxide and hydrogen gas at a barebones minimum temperature of 973.15 degrees Kelvin (700 C, the ignition temperature) The formula I have for specific impulse is TcxRgas, where Tc is combustion chamber temperature and Rgas is the specific exhaust velocity. It's a simplified version of the whole equation, and you can see where I got it here. First off, I believe my problem is in my equation for the Universal Gas Constant. The only one I've found that I know how to use is 8.3144621x(Tc/M) where M is the atomic weight. I've seen where the Universal Gas Constant is listed as 8.3144621x(J/mol K), but I don't know what the J, mol or K stand for, and have yet to find a definition.

When I use the weight in amu's, I get a number for the Isp ranging in the thousands (which I doubt), and when I use the weight in kg (1.66053982x10^-27) I get numbers to the power of 32, 40, 60 and so on. Another main issue is that I have been unable to get the same number twice. I know I'm doing something horribly wrong, but I don't know what. Here is everything that I know that I use for my calculations:

Exhaust total weight (amu): 43.98853
Exhaust average weight (amu): 14.66284
R: 8.3144621(Tc/m)
Tc: 973.15 degrees Kelvin
Ve (effective exhaust velocity): Rgas x Tc
Rgas: R/MM (total exhaust gas weight)
 
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  • #2
At this point, I'm not sure if I'm using the correct formula or even the correct values. Any help would be greatly appreciated!
 

Related to Trouble calculating effective exhaust velocity

1. What is effective exhaust velocity?

Effective exhaust velocity is a measure of the average velocity of all the exhaust gases leaving the rocket engine, taking into account both the speed and mass of the exhaust particles.

2. How is effective exhaust velocity calculated?

Effective exhaust velocity is calculated by dividing the thrust force of the rocket by the rate of mass flow of the exhaust gases. This can be expressed mathematically as Ve = F/m_dot.

3. Why is it important to calculate effective exhaust velocity?

Effective exhaust velocity is an important factor in determining the performance and efficiency of a rocket engine. It can help determine the amount of thrust generated and the amount of fuel needed for a successful launch.

4. What are the common challenges in calculating effective exhaust velocity?

The main challenges in calculating effective exhaust velocity include accurately measuring the thrust force and mass flow rate of the exhaust gases, as well as taking into account any external factors that may affect these values, such as atmospheric conditions.

5. How can the calculated effective exhaust velocity be used in rocket design?

The calculated effective exhaust velocity can be used to determine the specific impulse, or fuel efficiency, of a rocket engine. It can also be used to optimize the design of the engine and determine the ideal fuel mixture and nozzle size for optimal performance.

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