Calculating Air Bag Inflation Rate for Exhaust Powered Vehicle Jack

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Discussion Overview

The discussion focuses on calculating the inflation rate of an air bag designed for an exhaust powered vehicle jack. Participants explore the necessary equations and considerations for both the inflation process and the stresses the air bag must endure. The scope includes fluid mechanics and thermodynamics related to gas behavior and material stresses.

Discussion Character

  • Technical explanation, Conceptual clarification, Experimental/applied

Main Points Raised

  • One participant seeks equations to calculate the inflation time of an air bag based on exhaust gas flow rates and stresses involved in lifting a vehicle.
  • Another participant suggests using the ideal gas law, PV = nRT, as a relevant equation for the calculations.
  • A subsequent reply questions how to determine the number of moles (n) for the ideal gas law in this context.
  • Further clarification is provided regarding the composition of exhaust gases, noting that it primarily consists of unburnt nitrogen (80%), carbon dioxide, and water vapor, which may condense within the air bag.
  • There is an acknowledgment of the complexity introduced by the presence of water vapor in the exhaust and its phase change behavior.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the specific equations to use or the method for determining the number of moles in the ideal gas law. Multiple viewpoints and uncertainties remain regarding the calculations and the behavior of exhaust gases.

Contextual Notes

Limitations include the need for assumptions about the chemical composition of exhaust gases and the potential effects of water vapor condensation, which may not be fully resolved in the discussion.

Who May Find This Useful

Individuals interested in automotive engineering, fluid mechanics, or thermodynamics may find this discussion relevant.

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I am designing an exhaust powered vehicle car jack air bag. I have calculated the mass flow rate and velocity of the exhaust gases leaving the vehicles exhaust pipe. I need to calculate the amount of time it will take to inflate an air bag of a particular size. What equations do I need to be using in order to calculate the rate of inflation? Also I need to calcuate the stresses the air bag will have to withstand in order to lift the vehicle. I have taken fluid mechanics but I am having trouble figuring out which equations to use.

Thanks for the help...
 
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PV = nRT
 
how would I get (n) for the above equation?
 
n is the number of moles.
Mostly coming out of the exhaust is unburnt N2 (80%) of air, CO2 an H2O
You said you know the mass flow of exhaust, you can probably lookup the chemical composition of exhaust (it's probably in the clean air act etc) otherwise just assume air.
The tricky part is probably water, it will come out as a gas but condense in the bag.
 

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