[gensuruthebomber]

Hi, a school mate present to me the following question and I was incapable of answer to him, there is it:
Situation: A heat exchanger, vapor in one side, liquid in the other.
In the basic analysis  we wil write, Q=UALMTD  (Q=heat, U= Heat transfer coefficient, A=Area, LMTD=logaritmic mean temperature, by a correction factor if apply) and for the balance in the vapor side Q=m*Lambda  ( m= mass condensing over time, Lambda=Enthalpy of condensation), a common assumption is that the resistance to heat transfer in the condensation side is very small compared to the liquid side, so an increase in the vapor flow has practically no effect in the overall heat transfer coeficcient, this togheter with the energy balance for the vapor in terms of the mass condensing, gives the result that no extra mass is condensed, in conclusion no effect is observed. This contradicts the industrial and perhaps intuitive procedure of rise the flow of vapor to improve heat transfer to the liquid side. So my question is what is the process variable affected when we rise the flow of vapor, or what  of the assumptions in the analysis above is the more weak , and consequently gives wrong results. thanks in advance.