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Name | Description |
---|---|
dp_suddenChange |   |
dp_thickEdgedOverall |   |
This function shall be used within the restricted limits according to the referenced literature.
The local pressure loss dp is generally determined by:
dp = 0.5 * zeta_LOC * rho * |v_1|*v_1
with
rho | as density of fluid [kg/m3], |
v_1 | as average flow velocity in small cross sectional area [m/s]. |
zeta_LOC | as local resistance coefficient [-], |
The local resistance coefficient zeta_LOC of a sudden expansion can be calculated for different ratios of cross sectional areas by:
zeta_LOC = (1 - A_1/A_2)^2 [Idelchik 2006, p. 208, diag. 4-1]
and for sudden contraction:
zeta_LOC = 0.5*(1 - A_1/A_2)^0.75 [Idelchik 2006, p. 216-217, diag. 4-9]
with
A_1 | small cross sectional area [m^2], |
A_2 | large cross sectional area [m^2]. |
The local resistance coefficient zeta_LOC of a sudden expansion in dependence of the cross sectional area ratio A_1/A_2 is shown in the figure below.
The local resistance coefficient zeta_LOC of a sudden contraction in dependence of the cross sectional area ratio A_1/A_2 is shown in the figure below.
Extends from Modelica.Icons.Information
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This function shall be used within the restricted limits according to the referenced literature.
The pressure loss dp for a thick edged orifice is determined by:
dp = zeta_TOT * (rho/2) * (velocity_1)^2
with
rho | as density of fluid [kg/m3], |
velocity_1 | as mean velocity in large cross sectional area [m/s], |
zeta_TOT | as pressure loss coefficient [-]. |
The pressure loss coefficient zeta_TOT of a thick edged orifice can be calculated for different cross sectional areas A_0 and relative length of orifice l_bar =L/d_hyd_0 by:
zeta_TOT = (0.5*(1 - A_0/A_1)^0.75 + tau*(1 - A_0/A_1)^1.375 + (1 - A_0/A_1)^2 + lambda_FRI*l_bar)*(A_1/A_0)^2 [Idelchik 2006, p. 222, diag. 4-15]
with
A_0 | cross sectional area of vena contraction [m2], |
A_1 | large cross sectional area of orifice [m2], |
d_hyd_0 | hydraulic diameter of vena contraction [m], |
lambda_FRI | as constant Darcy friction factor [-], |
l_bar | relative length of orifice [-], |
L | length of vena contraction [m], |
tau | geometry parameter [-]. |
The geometry factor tau is determined by [Idelchik 2006, p. 219, diag. 4-12]:
tau = (2.4 - l_bar)*10^(-phi) phi = 0.25 + 0.535*l_bar^8 / (0.05 + l_bar^8) .
The pressure loss coefficient zeta_TOT of a thick edged orifice in dependence of a relative length (l_bar = L /d_hyd) with different ratios of cross sectional areas A_0/A_1 is shown in the figure below.
Incompressible case [Pressure loss = f(m_flow)]:
The pressure loss DP of an thick edged orifice in dependence of the mass flow rate m_flow of water for different ratios A_0/A_1 (where A_0 = 0.001 m^2) is shown in the figure below.
And for the compressible case [Mass flow rate = f(dp)]:
Extends from Modelica.Icons.Information
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Generated 2018-12-12 12:13:30 EST by MapleSim.