Optimization of a liquid injection NH3/CO2 cascade refrigeration system. Energetic, exergetic and environmental assessment

Abstract

This article presents an in-depth numerical study on optimizing the operation of a liquid-injection cascade refrigeration system. The main objective is to determine the optimal operating point that maximizes the COP within the temperature ranges of 30°C <T_C< 60°C and −55°C<T_E< -30°C. A comprehensive mathematical model was developed to simulate the thermodynamic behavior of the system, taking into account the liquid injection processes. Optimization, based on a bio-inspired metaheuristic algorithm (Puma), was used to determine the optimal operating parameters, such as T_3L, the injection pressures and flow rates. The results show that liquid injection significantly improves system performance by reducing energy consumption, exergy destruction, and compressor discharge temperature. Additionally, an environmental analysis based on the Total Equivalent Warming Impact (TEWI) was conducted to assess the environmental impact of the system. The results show that the optimized system has a lower TEWI compared to conventional systems, highlighting its potential for reducing greenhouse gas emissions. Finally, correlations providing T_3L, injection pressures, flow ratios, and optimal COPs are provided to give valuable information for the design and operation of more efficient and environmentally friendly liquid-injection cascade refrigeration systems.