Undergrad What is the difference between thrust and thrust density?

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SUMMARY

The discussion clarifies the distinction between thrust and thrust density in propulsion systems. Thrust is quantified in Newtons, while thrust density is defined as thrust per unit area, measured in Newtons per square metre. For example, a nozzle with a smaller area can produce higher thrust density even with the same thrust output. Thrust density is not a direct measure of efficiency, as it does not account for exhaust velocity or mass flow rate.

PREREQUISITES
  • Understanding of basic physics concepts, particularly force and area
  • Familiarity with propulsion systems and their performance metrics
  • Knowledge of units of measurement in the International System of Units (SI)
  • Basic comprehension of fluid dynamics principles
NEXT STEPS
  • Research the relationship between thrust density and exhaust velocity in various propulsion systems
  • Explore the implications of thrust density on the design of rocket nozzles
  • Learn about different propulsion technologies, including ion drives and their efficiency metrics
  • Investigate how thrust density affects overall vehicle performance in aerospace applications
USEFUL FOR

Aerospace engineers, propulsion system designers, and students studying fluid dynamics or rocket propulsion will benefit from this discussion.

AdrianHudson
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0000126.001&db_key=AST&bits=4&res=100&filetype=.gif


The picture above has thrust density as a column and I am not too sure what that is. Can anyone explain to me what the difference between thrust and thrust density? Thank you for your answers!
 

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The clue is in the table headings.
  • "Thrust" is measured in Newtons.
  • "Nozzle exit area" is measured in square metres.
  • "Thrust density" is measured in Newtons per square metre.
It shouldn't be too difficult to work it out from that.
 
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DrGreg said:
The clue is in the table headings.
  • "Thrust" is measured in Newtons.
  • "Nozzle exit area" is measured in square metres.
  • "Thrust density" is measured in Newtons per square metre.
It shouldn't be too difficult to work it out from that.

Ahh! So its the thrust produced per m2 of the nozzle area. Therefore that means that if you had nozzle "A" that has a surface area of 0.5m2 with a thrust of 10 Newtons and Nozzle "B" that has a surface area of 1m2 with a thrust of 10Newtons. Nozzle "A" is producing more thrust density?

Am I wrong in classifying thrust density as an efficiency of the given propulsion unit?
 
AdrianHudson said:
Ahh! So its the thrust produced per m2 of the nozzle area. Therefore that means that if you had nozzle "A" that has a surface area of 0.5m2 with a thrust of 10 Newtons and Nozzle "B" that has a surface area of 1m2 with a thrust of 10Newtons. Nozzle "A" is producing more thrust density?

Am I wrong in classifying thrust density as an efficiency of the given propulsion unit?
Not really. It has units of force per unit area or, equivalently, of energy per unit volume. But unless you are also given something like the density (mass per unit volume) of the exhaust stream, it cannot tell you the exhaust velocity.

You could, for instance, have an ion drive with an ultra high exhaust velocity (very mass-efficient and very energy-inefficient). The exhaust stream would also be very sparse and would likely have a low thrust density.
 
Last edited:
DrGreg said:
  • "Thrust density" is measured in Newtons per square metre.

So it's pressure?

Cheers
 
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