Modelling a solar absorption chiller using positive flash to estimate the physical state of streams and theoretical plate concept for the generator

Publication date: August 2017Source:Renewable Energy, Volume 109
Author(s): Sabine Sochard, Lorenzo Castillo Garcia, Sylvain Serra, Yann Vitupier, Jean-Michel Reneaume
In this paper a general model for the steady state simulation of a solar absorption chiller is proposed. The novelty of this model is to calculate the physical state of all the streams rather than fix them (especially at the outlet of the condenser and evaporator). The thermodynamic properties of the mixture can be calculated by suitable predictive thermodynamic models, hence the working pair can be changed easily. Using this thermodynamic model, a general Positive Flash model is able to describe all the possible states (sub-cooled, super-heated, biphasic) of the various streams which are all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions. Another originality of the present study is that the generator is modelled as a distillation column, using the theoretical plate concept: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) were written for each stage. Despite the modular structure of the software, a global solution strategy was implemented, using a Newton-Raphson method. This model is successfully compared to an example in the literature which deals with a GAX (Generator-Absorber heat eXchange) configuration absorption chiller using ammonia/water as the working pair.

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