ABk m² BC cross sectional area (at BC node boundary k) ANn, AMn m² SC cross sectional area (at SC node boundary n, mean value) ATWMn m² Surface area of a (single) tube wall along a node n C C0, - - Dimensionless constant Phase distribution parameter and its slope at α = 0 dHY m Hydraulic diameter f(z, t), fNn, fMn - General and nodal (boundary and mean) solution functions fLIMCA - Upper or lower limit of the approx. function f(z,t) Mass flow Mass flux h, hP, cP = hT Specific enthalpy and its partial derivatives with respect to pressure and temperature (=specific heat) hSW = h// − h/, h//, h/ Latent heat, saturation steam and water enthalpy KEYBC - Characteristic key number for each channel (BC) within an overall design LFTYPE = 0, 1, 2 or 3 - SC with saturated water/steam mixture, sub-cooled water, superheated or supercritical steam LFTBE (=LFTYPE of 1-st NSC) LHEATB = 0 or = 1 - - LFTYPE of 1-st SC within BC Non-heated or heated wall LNOCCF = 0 or = 1 - Eventual CCF situation allowed or not allowed NBT = NBCA − NBCE + 1 - Total number of BC nodes NBCA = NCT + NBCE − 1, NBCE - BC node numbers containing BC outlet or entrance NCT = NCA − NCE + 1 NCA, NCE, NCT = NCA − NCE + 1 - Total number of SC nodes BC node number containing SC outlet and entrance and total number of SC nodes NSC = NSCE, NSCA - Characteristic number of each SC, setting NSCE = 1, 2, 3 or 4 if LFTYPE = 0, 1, 2 or 3. Then NSCA = NSCE + NSCT − 1 P, ΔPT = PA − PE Pressure and pressure difference (in flow direction) QBT, QBMk W Total and nodal power into BC node k Mean nodal BC power density into the fluid (=volumetric heat transfer rate) Heat flux from (heated) wall to fluid at BC node k Linear power along BC node k Mean nodal SC power density into fluid (=volumetric0 heat transfer rate) T, t C, s Temperature, time UTW m Perimeter of a heated (single) tube wall m3 Mean nodal SC volume Water velocity Steam velocity - Steam quality (extended to single-phase flow too)