The demonstrator is an ultra-low temperature CO2 direct expansion unit for food blast freezing, to be used in freezing tunnels, conveyors, spirals, etc. Fast freezing is assured by extremely low evaporation temperatures (close to -50 °C) and high air volume flow. State-of-the-art technologies are applied for optimal use of the heat transfer surface, capacity control, suitable compressor and lubricant, defrosting and unit control. The possibility of improving the performance by applying a two-phase ejector is being evaluated. The demonstrator is suitable for hot climate (South Europe) and heat recovery is included. The demonstrator combines use of natural working fluids (NWF) with improved energy efficiency and reduced freezing time.
Different tests have been conducted to assess the reliability of a prototype refrigerant unit. Initial challenges with the refrigerant level sensor led to its replacement, and subsequent tests aimed to address charge instability that allowed to improve the control system of the system. The tests demonstrated the unit now can operate stably for indefinite period of time. Further investigations are ongoing to resolve minor issue. Based on Enex’s demonstrator unit, a numerical model for a single-stage compression subcritical brine-to-water unit has been developed by using software Simcenter Amesim. After this first round of tests, the demo went under few modifications to install additional instruments.
Blast freezer built at Enex’s testing facility (CO2 unit and secondary loop)
A second experimental campaign was conducted to evaluate the unit’s performance under different condensation temperatures, with evaporation temperature from -42 °C to -10 °C. Numerical simulations were also performed by CNR under the same conditions to validate the numerical set up. This model will be then extended to match the layout of the final standard application of demo in the field i.e. dual stage compression air-air and used to map the expected performances under the expected working conditions.
The Coefficient of Performance (COP) and the cooling power for the low stage unit, as a function of the evaporation temperature, are reported in in the figure below.
Coefficient of performance and cooling power of the of the prototype unit
To effectively measure key performance indicators (KPIs) of the demonstrator, proper instruments and monitoring systems have been identified and installed. Benchmarking will be performed based on corresponding traditional application (HFC, -30/-40 °C evaporation) as the field installation is identified. In the meantime, numerical modelling is used to compare ENOUGH technology to traditional blast freezer cabinet.
Interest in the demo extends beyond fish products. A key activity for the final year is mapping potential applications across the supply chain, including power requirements, temperature control, and product type management. Synergistic efforts within the task will focus on comparing various fish freezing techniques and identifying best technology based on end-user requirements.
