Performance assessment on a modified precision refrigeration cycle using low GWP mixtures

Abstract

Recently, with the increasing worldwide demand for low-temperature freezers, applying natural working medium hydro-carbon refrigerants for them has been widely concerned. Auto-cascade refrigeration cycle (ARC), as an efficient refrigeration technology, has been widely applications. However, the low separation efficiency of the refrigerant mixtures of the conventional ARC leads to its poor performance. Therefore, this paper presents a modified auto-cascade refrigeration cycle (MARC) using low GWP hydro-carbon refrigerants R170 and R290 for low-temperature freezer applications. In MARC, the two auxiliary separators are applied to make more low-boiling working fluid into evaporator to improve the volumetric cooling capacity (qev) and COP. The characteristics of conventional ARC and MARC are evaluated with theoretical method. The important parameters such as evaporating temperature and intermediate temperature for MARC are also detailed discussed. The theoretical research results suggest the MARC is more energy-saving and feasible. The improved cycle offers significant improvements in qev, COP and exergy efficiency. In detail, for MARC, the qev can be lifted by 40.3–91.3 % and the COP can be improved by 30.6–70.4 % compared with the ARC system. Therefore, the modified MARC shows its potential advantages for low-temperature freezer applications.

Keywords

• Low GWP mixtures
• Auto-cascade refrigeration cycle
• Performance improvement