Generalized component design model by combined heat and mass transfer analysis in NH₃-H₂O absorption heat pump systems

This paper develops a generalized design model using combined heat and mass transfer analysis for components used in absorption heat pump systems. The model can be applied to the design of an absorber, desorber, rectifier, condenser, or evaporator in NH₃-H₂O absorption heat pump systems. The physical significance of the ammonia composition in the absorbing/desorbing vapor, z, was studied. A composition map was generated by solving the diffusion and mass balance equations simultaneously for each component. It was found that the ammonia concentration in the absorbing/desorbing vapor cannot be found using only the liquid concentration or vapor concentration but must be determined using combined heat and mass transfer analysis. The composition of ammonia, z, should be z < x₁ for the rectifier, x₁ < z < x_vb for condensers, x_vb < z for absorbers, x_vi < z for desorbers, and x₁ < z < x_vi for evaporators. The results show that the mass transfer of ammonia and water is in the same direction for the rectifier, evaporator, and condenser, while it may be in the opposite direction for the absorber and desorber. The generalized design model developed in this paper can be used to investigate the effects of variable parameters, such as the heat transfer coefficient in each region, the vapor velocity, and the temperature deviation from the equilibrium, on the performance of each component.