About PRNDTL of temperature

H.P.LIU

In POLIS, Phoenics has provided the following information: PRNDTL(phi).... if positive, sets the laminar Prandtl number of variable phi. If it is negative, but not equal to GRND, GRND1, etc, the LAMINAR DIFFUSIVITY of variable phi is set equal to ABS(PRNDTL(phi)), with dimensions: length**2/time. For TEM1 andTEM2, negative values denote conductivities. When Temperature is represented by the solved-for variables TEM1 and TEM2 and PRNDTL(TEM1) is set for negative values, PRNDTL(TEM1) denotes heat conductivity ( Standard Unit: W/m/K),but as above mentioned, it also stands for heat diffusivity (Standard Unit: m**2/s), why has it different concept and unit when the same negative PRNDTL(TEM1) is set? How does PHOENICS formulate the energy equation in terms of temperature rather than enthalpy when the variable TEM1 is a solved-for variable? Thank you for your kind help!