The evaporator and condenser models are presented
together because they have common characteristics. The
following simpli®cations are considered: (i) the physical
properties related to refrigerant, secondary ¯uid and
pipe wall are considered uniform in the heat exchanger
transversal section, (ii) the refrigerant liquid and vapor
phases are in thermodynamic equilibrium, (iii) the heat
exchangers have a perfect thermal insulation, (iv) the
axial heat conduction in the pipes is not taken into
account (v) the refrigerant and secondary ¯uid potential
energy variations are also not considered. The model is
established by applying for each heat exchanger control
volume, the energy conservation equation (refrigerant,
secondary ¯uid and pipe wall), as well the mass and
momentum conservation equations (refrigerant). This
procedure generated the following set of dierential
equations.