pneumatic chamber

Hello, I'm creating new pneumatic chamber with inlet and outlet. for such a chamber mass continuity equation would be like this:

mas accumulation rate within chamber = inlet mass flow rate - outlet mass flow rate

as I understand, expression for mass accumulation rate in chamber is the same as in constant volume pneumatic chamber already created in simscape foundation library. I modified the code of constant volume penumatic chamber:

component chamber1

nodes
  A = foundation.pneumatic.pneumatic; % A:top
  B = foundation.pneumatic.pneumatic; % B:top
end

variables
  gas_flow   = { 0, 'kg/s' };
  heat_flow   = { 0, 'J/s' };
  pressure     = { 0, 'Pa' };
  temperature  = { 0 , 'K' };
end

parameters
  Volume = { 1e-3, 'm^3' };  % Chamber volume
  p0     = { 101325, 'Pa' }; % Initial pressure
  T0     = { 293.15, 'K' };  % Initial temperature
end

function setup
  through( gas_flow,   A.G, B.G );
  through( heat_flow,  A.Q, B.Q);
  across( pressure,    A.p, B.p );
  across( temperature, A.T, B.T );

    % Initial conditions
    pressure = p0;
    temperature = T0;
  end
equations
  gas_flow == Volume/A.R/temperature * (pressure.der - ...
      pressure* temperature.der/temperature);

    heat_flow == A.c_v * Volume / A.R * pressure.der;
  end

end

it works when I conect pressure source, new chamber, orifice and atmospheric reference, but I have doubts about the results. And it won't work when I connect pneumatic pump made of rotational pneumatic converter (this pump works when I don't use my new chamber). maybe I missunderstood something, and that somebody will help me with this.

P.S. if my question is unclear, please wright to me and i will clarify it.

Answer 1

[Arnaud Miege]

I don't think it's as simple as this. You need the concept of orifices for the inlet and oulet of the chamber. A better way would be to use the Constant Volume Pneumatic Chamber block from the Foundation Library as a building block for a 2-port pneumatic chamber. A simple way to do this is to use 2 Constant Area Pneumatic Orifice blocks with their B ports connected to the Constant Volume Pneumatic Chamber block.

HTH,

Arnaud

[Tomas Iesmantas]

could you please clarify: what is the role of reversed orifice? since if I connect two orifices with both B ports at the chamber one orifice models negative flow rate, or mybe I'm wrong at this?

thanks in advance for your always fast responses.

[Arnaud Miege]

One orifice would represent the inlet orifice, while the second orifice would represent the outlet orifice. I think they need to be connected back to to back so that the same convention for the flow rate is used, but I could be wrong. I'd suggest trying with the orifices back-to-back and also in the same direction to see the impact on the simulation results. It should be clear which one is incorrect.