High surface temp. oscillating flow

UNAL

Hello. I m studying oscillating flow in vertical annular gap with VOF model. There are two fluids (phases)in the gap which is water and air. The gap filled with water a known level and opened the top end of the gap to atmosphere. I have interface between water and air or free boundary. The fluid is moving oscillatory motion in the gap and exposed to constant heat flux by a heater at wall section. The heater contact with two phases simultaneously.The heater surface temperature is normal contact with water but the air contact section surface temperature not normal, this section surface temp.is very high for example 1000K my interval is 350 K. Why the air section is very high, How can I correct it, What is your opinion to decrease normal level, help please?!!!......,