evaporation modeling - have problem with temperature field
 

Hi everybody

I'm involved in two phase flow modeling of water and vapor through risers tubes in HRSG including evaporation, however I have some serious problems.
I have captured the chorn and dispersed flow regime, but after looking at the variable contours, I found that the udf is working in an awkward manner, and also the temperature field looks like a disaster. the walls are at the convection boundary condition with a flow of 840K hot gas and h=10 W/m2K but yet the temperature has a sudden drop (about 200K drop) in the middle of the field. I am really confused about that.
It would be appreciated if someone helps me