Absorption system based on the refrigerant R134a
The possibility of using 1,1,1,2-tetrafluoroethane (R134a) as a refrigerant in combination with different organic absorbents, such as dimethylether tetraethyleneglycol (DMETEG), N-methyl ϵ-caprolactam (MCL) or dimethyl-ethyleneurea (DMEU), in absorption units was investigated. The procedures in this paper are presented for the model working pair R134a-DMETEG. Temperature-pressure-concentration curves were constructed on the basis of vapour-liquid equilibrium measurements. Excess thermodynamic properties of the mixture were calculated, and enthalpy-concentration diagrams were constructed. The density and viscosity of the working fluids were measured. Thermostability testing of R134a-DMETEG showed that no changes were found in either of the phases over the course of the test. The performances of the investigated working fluids were compared in terms of the coefficient of performance (COP) and circulation ratio (f), which were evaluated by a computerized simulation program based on a single-stage absorption cycle containing a jet ejector as a mixer and preabsorber. The values of the COP for the three combinations were similar (R134a-DMEU reached 0.49, R134a-MCL 0.47 and R134a-DMETEG 0.46), but the value of f for R134a-DMTEG was lower than for the other two pairs. R134a-DMETEG was therefore the best of the three candidate working pairs.