3. Differential balances along a condenser

Given the variability of fluid composition from one point to another in a mixing condenser, it is very difficult to calculate an average overall exchange coefficient using the classic NUT (number of transfer units) or DTML (logarithmic mean temperature difference) methods. The condenser is then divided into elementary meshes, and material and energy balances are carried out in the control volume thus defined. These balances are carried out on the assumption that the main flow follows a given direction (x-direction) and that condensation takes place normally at a wall parallel to this main direction.