z, Δz_Nn = z_Nn − z_Nn−1

m

Local position, SC node length (z_Nn−1 = z_CE at n = 0)

m

BC and SC outlet and entrance positions, total length

z_BB, z_ML, z_SPC

m

Boiling boundary, mixture level resp. supercritical boundary within a BC

α

-

Void fraction

α_TWk

Heat transfer coefficient along a BC wall surface

Δ

-

Nodal differences

ε_DPZ

-

Coefficient controlling the additional friction part

ε_QTW

-

Correction factor with respect to Q_NOM,0

ε_TW

m

Abs. roughness of tube wall (ε_TW/d_HW = rel. value)

-

Two-phase multiplier

Φ_ZG

-

Angle between upwards and flow direction

ρ, ρ^P, ρ^T

Density and their partial derivatives with respect to (system) pressure and temperature

s

Time constant

-

Partial derivative