Hi, we are having a problem with FLUENT as we are not able to have enthalpy calculated rightly. In fact we are told that in our model we have negative enthalpy fluxes and it is not possible. We are modeling a double skin facade and we are interested in finding the net heat transfer to the air flowing in the cavity. We are modeling dry air but we have decided to use a multiphase model, setting to zero the secondary phase volume in order to be able to have 0 K as the reference temperature as enthalpy should be a result of an integration starting from that temperature. Thanks in advance, Giacomo

Be careful with the conventions on fluxes in and out of the domain, any enthalpy of formation for compounds, and calculation of specific heat as a function of temperature.