I am in need of some help; I want to design a convergent divergent nozzle. I was wondering if someone can help me with the math to do so. I am specifically wanting the angles required to get a good expansion. Without the shocks. any help?
to start
chamber pressure = 150 psi
throat diameter = 1/4 inch
gas will be a mixture of 16.043 g/mol and 8 g/mol
and 188 J * mol * K, 29.378 J * mol * K Entropy.
discharge pressure 35 psi( to start with)
I actually need to iteratively find that base on the velocity of the jet, so I need to write a program to optimize the angles.
thanks!
Nozzle Geometry
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Nozzle Geometry
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Re: nozzle
Keep going, it looks like you're doing good work! One nice thing is that the nozzle geometry really isn't going to kill you if you don't get it perfectly optimized though. You can usually get away with cutting almost any sort of nozzle (like using a stepped bit, a chamfering tool, or even just drilling a straight hole) and from what I've seen the losses compared to a nice convergent-divergent nozzle aren't much.
If it's about optimizing performance, you might want to crank up that chamber pressure. I'm pretty sure that would give you a lot bigger boost than using a more optimal nozzle. Lots of reloadable aluminum hardware out there is good up to about 1000 psi, and that'll give you a healthy boost in your Isp. Even lots of 1" Schedule 40 PVC pipe is good up to about 1000 psi, though it's obviously not rated that high. Jumping from 150 to, say, 500 would be well worth your while if your materials can take it.
Update: here's an example for a certain AN propellant formulation. The Isp at 150 psi is 182.7. Bumping the chamber pressure up to 500 psi brings your Isp to 214.8. A thousand psi brings it to 228.9 seconds. So if you could handle 1000 psi compared to 150, it'd be like carrying 25% more propellant, but the extra wouldn't weigh anything or take up any space (keeps drag down etc).
Here's a link to Wikipedia about the nozzle shape (I'll post the relevant text as well):
http://en.wikipedia.org/wiki/Rocket_eng ... imum_shape
"The simplest nozzle shape is a ~12 degree internal angle cone, which is about 97% efficient. Smaller angles give very slightly higher efficiency, larger angles give lower efficiency.
"More complex shapes of revolution are frequently used, such as Bell nozzles or parabolic shapes. This gives perhaps 1% higher efficiency than the cone nozzle, and is shorter and lighter. These shapes are widely used on launch vehicles and other rockets where weight is at a premium. They are of course, harder to fabricate, so are typically more costly.
"There is also a theoretical optimum nozzle shape for maximum exhaust speed, however, a shorter, suboptimal bell shape is typically used due to its much lower weight, shorter length, lower drag losses, and only very marginally lower exhaust speed."
-Dave
If it's about optimizing performance, you might want to crank up that chamber pressure. I'm pretty sure that would give you a lot bigger boost than using a more optimal nozzle. Lots of reloadable aluminum hardware out there is good up to about 1000 psi, and that'll give you a healthy boost in your Isp. Even lots of 1" Schedule 40 PVC pipe is good up to about 1000 psi, though it's obviously not rated that high. Jumping from 150 to, say, 500 would be well worth your while if your materials can take it.
Update: here's an example for a certain AN propellant formulation. The Isp at 150 psi is 182.7. Bumping the chamber pressure up to 500 psi brings your Isp to 214.8. A thousand psi brings it to 228.9 seconds. So if you could handle 1000 psi compared to 150, it'd be like carrying 25% more propellant, but the extra wouldn't weigh anything or take up any space (keeps drag down etc).
Here's a link to Wikipedia about the nozzle shape (I'll post the relevant text as well):
http://en.wikipedia.org/wiki/Rocket_eng ... imum_shape
"The simplest nozzle shape is a ~12 degree internal angle cone, which is about 97% efficient. Smaller angles give very slightly higher efficiency, larger angles give lower efficiency.
"More complex shapes of revolution are frequently used, such as Bell nozzles or parabolic shapes. This gives perhaps 1% higher efficiency than the cone nozzle, and is shorter and lighter. These shapes are widely used on launch vehicles and other rockets where weight is at a premium. They are of course, harder to fabricate, so are typically more costly.
"There is also a theoretical optimum nozzle shape for maximum exhaust speed, however, a shorter, suboptimal bell shape is typically used due to its much lower weight, shorter length, lower drag losses, and only very marginally lower exhaust speed."
-Dave
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