No abstract

No abstract

Development and performance mapping of a multi-ejector expansion work recovery pack for R744 vapour compression units, AbstractA multi-ejector expansion pack, intended as a substitute for a standard high-pressure electronic expansion valve (HPV), was designed, manufactured and experimentally investigated. Four different ejector cartridges were sized to enable a discrete opening characteristic with a binary profile for a parallel-compression R744 system. The system is rated for 70 kW at a 35 °C gas cooler outlet temperature and a -3 °C evaporation temperature. High values of ejector efficiency, exceeding 0.3 over a broad operation range, were recorded for all four of the cartridges tested under vapour compression conditions. The applicability of the multi-ejector pack as a main flashing device was verified experimentally. Similar profiles of the discharge pressure control error were recorded for both alternative options: expansion purely in the HPV vs. HPV-assisted expansion in the multiejector pack.

No abstract

Visible signs of climate change call for urgent actions on food retail industry, since such a sector is characterized by an abundant carbon footprint. Being CO2 (or R744) recognised across the world as the most promising working fluid for supermarket applications, commercial transcritical R744 refrigeration systems have emerged as leading hydrofluorocarbon (HFC)-free technologies. This study is intended to implement an in-depth review study covering the most important aspects related to the state-of-the-art pure R744 refrigeration plants for food retail applications, including the evolution of system architectures, some field measurements, the main available results from an energy, environmental and economic perspective as well as the indispensable future investigations. It could be concluded that, in spite of some persisting barriers which still prevent such technologies from a wider adoption, the usage of R744 as the only refrigerant in supermarkets is no longer open to dispute, even in warm locations.