Modelica.Fluid.Pipes.BaseClasses.WallFriction.Laminar

Information

This component defines only the laminar region of wall friction: dp = k*m_flow, where "k" depends on density and dynamic viscosity. The roughness of the wall does not have an influence on the laminar flow and therefore argument roughness is ignored. Since this is a linear relationship, the occuring systems of equations are usually much simpler (e.g., either linear instead of non-linear). By using nominal values for density and dynamic viscosity, the systems of equations can still further be reduced.

In UsersGuide the complete friction regime is illustrated. This component describes only the Hagen-Poiseuille equation.

Extends from PartialWallFriction (Partial wall friction characteristic (base package of all wall friction characteristics)).

Package Content

Name	Description
massFlowRate_dp	Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction
pressureLoss_m_flow	Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction
massFlowRate_dp_staticHead	Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction and static head
pressureLoss_m_flow_staticHead	Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction and static head
Inherited
use_mu=true	= true, if mu_a/mu_b are used in function, otherwise value is not used
use_roughness=true	= true, if roughness is used in function, otherwise value is not used
use_dp_small=true	= true, if dp_small is used in function, otherwise value is not used
use_m_flow_small=true	= true, if m_flow_small is used in function, otherwise value is not used
dp_is_zero=false	= true, if no wall friction is present, i.e., dp = 0 (function massFlowRate_dp() cannot be used)

Modelica.Fluid.Pipes.BaseClasses.WallFriction.Laminar.massFlowRate_dp

Information

Extends from (Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction).

Inputs

Type	Name	Default	Description
Pressure	dp		Pressure loss (dp = port_a.p - port_b.p) [Pa]
Density	rho_a		Density at port_a [kg/m3]
Density	rho_b		Density at port_b [kg/m3]
DynamicViscosity	mu_a		Dynamic viscosity at port_a (dummy if use_mu = false) [Pa.s]
DynamicViscosity	mu_b		Dynamic viscosity at port_b (dummy if use_mu = false) [Pa.s]
Length	length		Length of pipe [m]
Diameter	diameter		Inner (hydraulic) diameter of pipe [m]
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (dummy if use_roughness = false) [m]
AbsolutePressure	dp_small	1	Turbulent flow if |dp| >= dp_small (dummy if use_dp_small = false) [Pa]

Outputs

Type	Name	Description
MassFlowRate	m_flow	Mass flow rate from port_a to port_b [kg/s]

Modelica definition

redeclare function extends massFlowRate_dp 
  "Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction"

algorithm 
  m_flow :=dp*Modelica.Constants.pi*diameter^4*(rho_a + rho_b)/(128*length*(mu_a + mu_b));
end massFlowRate_dp;

Modelica.Fluid.Pipes.BaseClasses.WallFriction.Laminar.pressureLoss_m_flow

Information

Extends from (Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction).

Inputs

Type	Name	Default	Description
MassFlowRate	m_flow		Mass flow rate from port_a to port_b [kg/s]
Density	rho_a		Density at port_a [kg/m3]
Density	rho_b		Density at port_b [kg/m3]
DynamicViscosity	mu_a		Dynamic viscosity at port_a (dummy if use_mu = false) [Pa.s]
DynamicViscosity	mu_b		Dynamic viscosity at port_b (dummy if use_mu = false) [Pa.s]
Length	length		Length of pipe [m]
Diameter	diameter		Inner (hydraulic) diameter of pipe [m]
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (dummy if use_roughness = false) [m]
MassFlowRate	m_flow_small	0.01	Turbulent flow if |m_flow| >= m_flow_small (dummy if use_m_flow_small = false) [kg/s]

Outputs

Type	Name	Description
Pressure	dp	Pressure loss (dp = port_a.p - port_b.p) [Pa]

Modelica definition

redeclare function extends pressureLoss_m_flow 
  "Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction"

algorithm 
  dp := m_flow*128*length*(mu_a + mu_b)/(Modelica.Constants.pi*diameter^4*(rho_a + rho_b));
end pressureLoss_m_flow;

Modelica.Fluid.Pipes.BaseClasses.WallFriction.Laminar.massFlowRate_dp_staticHead

Information

Extends from (Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction and static head).

Inputs

Type	Name	Default	Description
Pressure	dp		Pressure loss (dp = port_a.p - port_b.p) [Pa]
Density	rho_a		Density at port_a [kg/m3]
Density	rho_b		Density at port_b [kg/m3]
DynamicViscosity	mu_a		Dynamic viscosity at port_a (dummy if use_mu = false) [Pa.s]
DynamicViscosity	mu_b		Dynamic viscosity at port_b (dummy if use_mu = false) [Pa.s]
Length	length		Length of pipe [m]
Diameter	diameter		Inner (hydraulic) diameter of pipe [m]
Real	g_times_height_ab		Gravity times (Height(port_b) - Height(port_a))
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (dummy if use_roughness = false) [m]
AbsolutePressure	dp_small	1	Turbulent flow if |dp| >= dp_small (dummy if use_dp_small = false) [Pa]

Outputs

Type	Name	Description
MassFlowRate	m_flow	Mass flow rate from port_a to port_b [kg/s]

Modelica definition

redeclare function extends massFlowRate_dp_staticHead 
  "Return mass flow rate m_flow as function of pressure loss dp, i.e., m_flow = f(dp), due to wall friction and static head"

protected 
  Real k0inv = Modelica.Constants.pi*diameter^4/(128*length) "Constant factor";

  Real dp_grav_a = g_times_height_ab*rho_a 
    "Static head if mass flows in design direction (a to b)";
  Real dp_grav_b = g_times_height_ab*rho_b 
    "Static head if mass flows against design direction (b to a)";

  Real dm_flow_ddp_fric_a = k0inv*rho_a/mu_a 
    "Slope of mass flow rate over dp if flow in design direction (a to b)";
  Real dm_flow_ddp_fric_b = k0inv*rho_b/mu_b 
    "Slope of mass flow rate over dp if flow against design direction (b to a)";

  Real dp_a=max(dp_grav_a,dp_grav_b)+dp_small 
    "Upper end of regularization domain of the m_flow(dp) relation";
  Real dp_b=min(dp_grav_a,dp_grav_b)-dp_small 
    "Lower end of regularization domain of the m_flow(dp) relation";

  SI.MassFlowRate m_flow_a "Value at upper end of regularization domain";
  SI.MassFlowRate m_flow_b "Value at lower end of regularization domain";

  // Properly define zero mass flow conditions
  SI.MassFlowRate m_flow_zero = 0;
  SI.Pressure dp_zero = (dp_grav_a + dp_grav_b)/2;
  Real dm_flow_ddp_fric_zero;
algorithm 
/*
  dp = 0.5*zeta/(A^2*d) * m_flow * |m_flow|
     = 0.5 * c0/(|m_flow|*(4/pi)/(D_Re*mu)) / ((pi*(D_Re/2)^2)^2*d) * m_flow*|m_flow|
     = 0.5 * c0*(pi/4)*(D_Re*mu) * 16/(pi^2*D_Re^4*d) * m_flow*|m_flow|
     = 2*c0/(pi*D_Re^3) * mu/d * m_flow
     = k0 * mu/d * m_flow
  k0 = 2*c0/(pi*D_Re^3)
*/

  if dp>=dp_a then
    // Positive flow outside regularization
    m_flow := dm_flow_ddp_fric_a*(dp-dp_grav_a);
  elseif dp<=dp_b then
    // Negative flow outside regularization
    m_flow := dm_flow_ddp_fric_b*(dp-dp_grav_b);
  else
    m_flow_a := dm_flow_ddp_fric_a*(dp_a - dp_grav_a);
    m_flow_b := dm_flow_ddp_fric_b*(dp_b - dp_grav_b);

    // Include a properly defined zero mass flow point
    // Obtain a suitable slope from the linear section slope c (value of m_flow is overwritten later)
    (m_flow, dm_flow_ddp_fric_zero) := Utilities.regFun3(dp_zero, dp_b, dp_a, m_flow_b, m_flow_a, dm_flow_ddp_fric_b, dm_flow_ddp_fric_a);
    // Do regularization
    if dp>dp_zero then
      m_flow := Utilities.regFun3(dp, dp_zero, dp_a, m_flow_zero, m_flow_a, dm_flow_ddp_fric_zero, dm_flow_ddp_fric_a);
    else
      m_flow := Utilities.regFun3(dp, dp_b, dp_zero, m_flow_b, m_flow_zero, dm_flow_ddp_fric_b, dm_flow_ddp_fric_zero);
    end if;
  end if;
/*
  m_flow := if dp<dp_b then dm_flow_ddp_b*(dp-dp_grav_b) else
              (if dp>dp_a then dm_flow_ddp_a*(dp-dp_grav_a) else
                Modelica.Fluid.Utilities.regFun3(dp, dp_b, dp_a, dm_flow_ddp_b*(dp_b - dp_grav_b), dm_flow_ddp_a*(dp_a - dp_grav_a), dm_flow_ddp_b, dm_flow_ddp_a));
*/
end massFlowRate_dp_staticHead;

Modelica.Fluid.Pipes.BaseClasses.WallFriction.Laminar.pressureLoss_m_flow_staticHead

Information

Extends from (Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction and static head).

Inputs

Type	Name	Default	Description
MassFlowRate	m_flow		Mass flow rate from port_a to port_b [kg/s]
Density	rho_a		Density at port_a [kg/m3]
Density	rho_b		Density at port_b [kg/m3]
DynamicViscosity	mu_a		Dynamic viscosity at port_a (dummy if use_mu = false) [Pa.s]
DynamicViscosity	mu_b		Dynamic viscosity at port_b (dummy if use_mu = false) [Pa.s]
Length	length		Length of pipe [m]
Diameter	diameter		Inner (hydraulic) diameter of pipe [m]
Real	g_times_height_ab		Gravity times (Height(port_b) - Height(port_a))
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (dummy if use_roughness = false) [m]
MassFlowRate	m_flow_small	0.01	Turbulent flow if |m_flow| >= m_flow_small (dummy if use_m_flow_small = false) [kg/s]

Outputs

Type	Name	Description
Pressure	dp	Pressure loss (dp = port_a.p - port_b.p) [Pa]

Modelica definition

redeclare function extends pressureLoss_m_flow_staticHead 
  "Return pressure loss dp as function of mass flow rate m_flow, i.e., dp = f(m_flow), due to wall friction and static head"

protected 
  Real k0 = 128*length/(Modelica.Constants.pi*diameter^4) "Constant factor";

  Real dp_grav_a = g_times_height_ab*rho_a 
    "Static head if mass flows in design direction (a to b)";
  Real dp_grav_b = g_times_height_ab*rho_b 
    "Static head if mass flows against design direction (b to a)";

  Real ddp_dm_flow_a = k0*mu_a/rho_a 
    "Slope of dp over mass flow rate if flow in design direction (a to b)";
  Real ddp_dm_flow_b = k0*mu_b/rho_b 
    "Slope of dp over mass flow rate if flow against design direction (b to a)";

  Real m_flow_a=if dp_grav_a >= dp_grav_b then m_flow_small else m_flow_small + (dp_grav_b-dp_grav_a)/ddp_dm_flow_a 
    "Upper end of regularization domain of the dp(m_flow) relation";
  Real m_flow_b=if dp_grav_a >= dp_grav_b then -m_flow_small else -m_flow_small - (dp_grav_b - dp_grav_a)/ddp_dm_flow_b 
    "Lower end of regularization domain of the dp(m_flow) relation";

  SI.Pressure dp_a "Value at upper end of regularization domain";
  SI.Pressure dp_b "Value at lower end of regularization domain";

  // Properly define zero mass flow conditions
  SI.MassFlowRate m_flow_zero = 0;
  SI.Pressure dp_zero = (dp_grav_a + dp_grav_b)/2;
  Real ddp_dm_flow_zero;
algorithm 
/*
  dp = 0.5*zeta/(A^2*d) * m_flow * |m_flow|
     = 0.5 * c0/(|m_flow|*(4/pi)/(D_Re*mu)) / ((pi*(D_Re/2)^2)^2*d) * m_flow*|m_flow|
     = 0.5 * c0*(pi/4)*(D_Re*mu) * 16/(pi^2*D_Re^4*d) * m_flow*|m_flow|
     = 2*c0/(pi*D_Re^3) * mu/d * m_flow
     = k0 * mu/d * m_flow
  k0 = 2*c0/(pi*D_Re^3)
*/

  if m_flow>=m_flow_a then
    // Positive flow outside regularization
    dp := (ddp_dm_flow_a*m_flow + dp_grav_a);
  elseif m_flow<=m_flow_b then
    // Negative flow outside regularization
    dp := (ddp_dm_flow_b*m_flow + dp_grav_b);
  else
    // Regularization parameters
    dp_a := ddp_dm_flow_a*m_flow_a + dp_grav_a;
    dp_b := ddp_dm_flow_b*m_flow_b + dp_grav_b;
    // Include a properly defined zero mass flow point
    // Obtain a suitable slope from the linear section slope c (value of dp is overwritten later)
    (dp, ddp_dm_flow_zero) := Utilities.regFun3(m_flow_zero, m_flow_b, m_flow_a, dp_b, dp_a, ddp_dm_flow_b, ddp_dm_flow_a);
    // Do regularization
    if m_flow>m_flow_zero then
      dp := Utilities.regFun3(m_flow, m_flow_zero, m_flow_a, dp_zero, dp_a, ddp_dm_flow_zero, ddp_dm_flow_a);
    else
      dp := Utilities.regFun3(m_flow, m_flow_b, m_flow_zero, dp_b, dp_zero, ddp_dm_flow_b, ddp_dm_flow_zero);
    end if;
  end if;
end pressureLoss_m_flow_staticHead;