 ## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

• snr1
Subscriber

I am writing mixture properties and its constituent species properties in a material.scm file.

What will be units of formation-enthalpy and formation-entropy in material.scm file.

• Rob
Ansys Employee

Open the materials panel and it should be listed there. It'll be SI units in Fluent.

• snr1
Subscriber

Formation-enthalpy and specific enthalpy both are the same or different? If these two are different, how we can calculate the formation-enthalpy for a particular material?

• Rob
Ansys Employee

What is shown in the materials panel? Note, there's a reference temperature there too which may be important.

• snr1
Subscriber

For material properties, i am writing a material.scm file. In this file, we need to mention the formation-enthalpy value of that material. Now, my query is whether the specific enthalpy and formation-enthalpy are same or not?

If these two are different, how we can calculate the formation-enthalpy of a particular material. For example: see below for ammonia properties.

(ammonia-liquid  fluid

(chemical-formula . nh3 (density (constant . 610) (compressible-liquid 101325 610 2.1e+09 7 1.1 0.9))
(specific-heat (constant . 4758))
(thermal-conductivity (constant . 0.493))
(viscosity (constant . 0.000152))
; Critical Properties from Polling et al.
(critical-pressure (constant . 11.3530e6))
(critical-temperature (constant . 405.40))
(acentric-factor (constant . 0.257))
(critical-volume (constant . 0.00426))
)

(ammonia-vapor  fluid
(chemical-formula . nh3)
(density (constant . 0.6894))
(specific-heat (polynomial piecewise-polynomial (300 1000 1076.164 4.9380262 -0.0071534199 7.0653986e-06 -2.601377e-09) (1000 5000 1201.9011 2.9580837 -0.00097882914 1.5309961e-07 -9.4628597e-12)) (constant . 2158))
(thermal-conductivity (constant . 0.0247))
(viscosity (constant . 1.015e-05))
(molecular-weight (constant . 17.03061))
(absorption-coefficient (constant . 0.5) (polynomial piecewise-linear (550 . 3.14) (890 . 1.93) (1220 . 0.95) (1550 . 0.5)))
(formation-enthalpy (constant . -45915740))
(reference-temperature (constant . 298.15))
(thermal-accom-coefficient (constant . 0.9137))
(velocity-accom-coefficient (constant . 0.9137))
(formation-entropy (constant . 192612.34))
; Critical Properties from Polling et al.
(critical-pressure (constant . 11.3530e6))
(critical-temperature (constant . 405.40))
(acentric-factor (constant . 0.257))
(critical-volume (constant . 0.00426))

)
• Rob
Ansys Employee

If you open the materials panel up & turn on both species and anything with a phase change you'll see most of the above. If you're poking around in the materials files you'll note that some values are missing: not all materials have all data available. You'll also find a more useful description of both the name & units in the Materials panel. Assuming you've not altered any units these should be what's needed in the file you're writing. 