Getting the condensation temperature of steam in a gas mixture

[David Kaeser]

Hi there 

I need to get the condensation temperature of steam from my gas mixture but I am unable to do so... Until now I try to get the partial pressure of H2O of my mixture, multiply it with my pressure and then try to set my gas mixture to this pressure. In my mind the resulting temperature of this gas mixture should be then my condensation temperature. However I get a temperature of 1221.0 K at a pressure of 391776.29460509267 Pa. What did I do wrong and how could I arrive to the correct temperature? Sorry I still a newbie in chemistry as well as cantera... 

My setup is as follow:

p= 1500000.0

T = 1221.0

steam_CH4_CO2 = ct.Solution('gri30.cti')

steam_CH4_CO2.X = {"CH4": nCH4 , "H2O": nH2O, "CO2": nCO2}

steam_CH4_CO2.TP = T, p

feedstock = ct.Mixture([(steam_CH4_CO2, nH2O+nCH4+nCO2)])

steam_pressure = steam_CH4_CO2.X[steam_CH4_CO2.species_index("H2O")]*p

feedstock.P = steam_pressure

T_condense = feedstock.T

What do I need to change to get the correct T_condense?

Any help is greatly appreciated :D

best,

David

[Bryan Weber]

Hi David,

I think the key thing is that you always need to set two independent state variables to have a completely specified state. In your case, the condensation temperature is the temperature at which this particular partial pressure of water reaches the vapor dome. Therefore, you can actually use a pure-water phase, as long as it includes the vapor dome. Fortunately, Cantera includes such a phase:

p = 1500000.0

T = 1221.0

steam_CH4_CO2 = ct.Solution('gri30.cti')

steam_CH4_CO2.X = {"CH4": nCH4 , "H2O": nH2O, "CO2": nCO2}

steam_CH4_CO2.TP = T, p

steam_pressure = steam_CH4_CO2("H2O").X[0] * p

water = ct.Water()

water.PQ = steam_pressure, 1.0

T_condense = water.T

Hope that helps,

Bryan