In absorption technology a fluid with high volatility is used as refrigerant, whereas a second fluid which less volatility but strong affinity to the former is used as absorbent. The processes in the absorption cycle are based on absorption and separation between refrigerant and absorbent. Working fluids properties are key factors in the performance of the absorption chillers. Problems in using aqueous solutions of lithium bromide are crystallization and corrosion. Various organic chemicals as alternatives to the conventional working fluids have been reported. The main drawbacks of these organic working pairs are thermal instability, absorbent volatility and low process efficiency. ILs are excellent candidates as absorbents for absorption systems, as they have great solvent character, good thermal stability and very low vapour pressure. As a drawback, the ILs are moderately to highly viscous, especially at low temperature, restricting the flow of the absorbent in the machine. A careful choice of the IL or the addition of a molecular solvent that can reduce dramatically the viscosity, can overcame this problem. Therefore, an adequate design of a mixture IL + molecular solvent can lead to more efficient cycles.
The main objective of this project is to identify new ionic liquid + molecular solvent absorbing pairs considering the following characteristics:
– non-toxic and biodegradable for absorption refrigeration;
– more efficient in closed cycle work;
– with high excess enthalpy;
– density and viscosity adequate for refrigeration closed cycle work;
– capable of replacing water + LiBr and water + ammonia highly corrosive and toxic absorbers;
– with good coefficient of performance
– high mass circulation ratio.
The experience obtained in NARILAR (Project PIRSES-GA-2010-269321) and the collaboration with Prof. Alberto Coronas (Consultant from CREVER, URV, Tarragona, Spain) will facilitate the achievement of this objective.
The project will have the following objectives:
1)To measure thermophysical properties (density, viscosity, heat capacity and thermal conductivity), and properties related with thermodynamic and transport processes, like solubility, heats of mixing/solution, heat transfer coefficients, thermal degradation, water activity, ecotoxicity.
2)To identify the physical/chemical interactions cation/anion/molecular solvent, by modelling selected systems
3)To test the efficiency of the chosen IL pairs in heat transfer equipment at a pilot level, for several types of heat exchangers (shell and tube, parallel plates and hair-pin).
4)To propose new models/correlations for the prediction of the thermophysical properties of ionic liquids and heat transfer coefficients of these novel fluids in flowing and phase-change systems with the support of experimental results.
5)To perform toxicity and biodegradability tests of the products developed, both in aquatic media and ambient plant operation.