New environment friendly working pairs of dimethyl ether and ionic liquids for absorption refrigeration with high COP

To overcome the limitations of absorption refrigeration system brought by commercial working pairs of NH₃/H₂O and H₂O/LiBr for the utilization of low-grade heat, a new class of working pairs consisting of dimethyl ether (DME) and ionic liquids (ILs) are developed. The solubilities of DME in three ILs [BMIM][BF₄], [BMIM][PF₆] and [BMIM][Tf₂N] were firstly measured and correlated. Then, COPs of the single-effect absorption refrigeration system (ARS) and absorption-compression hybrid refrigeration system (ACRS) using DME/IL were calculated under different conditions. The maximum COP of ARS using the three DME/IL working pairs can be up to 32.0% larger than that using NH₃/H₂O, while the maximum COP of ACRS using the three DME/IL working pairs can be up to 38.3% larger than that using NH₃/H₂O under studied conditions. The three DME/IL working pairs also show much better cooling performance than HFC/IL and HFO/IL working pairs which are R152a/[HMIM][Tf₂N] and R1234ze(E)/[HMIM][Tf₂N]. In ACRS, DME/ILs can drop the optimal generation temperature in ARS by more than 10 K. DME/ILs are very promising alternative absorption refrigeration working pairs due to the high COP, wide applicability and environmental friendliness.