model TwoTanks_basic
  //Constants
  constant Real pi = 3.14;
  constant Real g = 9.81;
  //Parameters

  parameter Real A1=1.0 "Area of tank1";
  parameter Real A2=2.0 "Area of tank2";
  parameter Real L=0.1 "Pipe length";
  parameter Real D=0.2 "Pipe diameter";
  parameter Real rho = 0.2 "Fluid density";
  parameter Real mu = 2e-3 "Fluid dynamic viscosity";

  //variables
  Real p1 "pressure in tank1";
  Real p2 "pressure in tank2";
  Real h1( start=0) "liquid level in tank1";
  Real h2( start=50) "liquid level in tank2";
  Real q( start=0) "Volume flow rate between tanks";

equation
   //relation pressure and height
   p1=h1*g*rho;
   p2=h2*g*rho;

   //Flow between tanks(positive out of tank1)
   q=(p1-p2)*(pi*D^4/(128*mu*L));
   //Mass Balances for each tank
  A1*der(h1)=-q;
  A2*der(h2)=q;
 annotation (Icon(coordinateSystem(preserveAspectRatio=false)), Diagram(
        coordinateSystem(preserveAspectRatio=false)));
end TwoTanks_basic;