An algorithm based on the equations mentioned above has been developed and implemented in a Matlab [24] code. The main steps of the algorithm are reported in Fig.2. The initial step establishes the variable parameters, both geometric and thermodynamic, at the fixed simulated condition listed in Table 1. At the first elementary section (z=1), the local temperature of the working fluid is set equal to the temperature in the state 3 inFig.1(b), whereas the local temperature of the hot water is set equal to the hot source temperature. The overall heat transfer coefficient Uand the pressure drop of both fluids for each elementary volume is evaluated with the mentioned prediction methodsfrom Eq. (6) to Eq. (12). Then, the elementary heat power ̇ is obtained from Eq. (3). By considering the heat exchanger adiabatic through its surroundings, the energy balances in Eq. (4) and (5) allow the calculation of the specific enthalpies for the subsequent integration steps (z+1). This procedure must be repeated until the heat power target is achieved. Finally, the total surface heat exchange A can be evaluated, for each investigated geometric configuration and boundary condition.