Advanced two-stage cascade configurations for energy-efficient -80 °C refrigeration

Area of Science:

• Thermodynamics
• Refrigeration Engineering
• Sustainable Energy

Background:

• COVID-19 vaccine distribution necessitates ultralow-temperature refrigeration.
• Traditional cascade cycles for ultralow temperatures exhibit poor energy performance.
• Increased global demand for ultralow-temperature freezers drives the need for energy-efficient solutions.

Purpose of the Study:

• To analyze the operational and energy performance of various two-stage cascade refrigeration cycles for ultralow-temperature freezers.
• To optimize the intermediate cascade temperature for maximizing the coefficient of performance.
• To evaluate the use of ultra-low global warming potential natural refrigerants like R-290 and R-170.

Main Methods:

• Thermodynamic analysis of 42 different two-stage cascade configurations.
• Comparison of single-stage, vapor injection, liquid injection, and parallel compression cycles.
• Optimization of the intermediate cascade temperature for each configuration.

Main Results:

• Vapor and liquid injection cascade configurations demonstrated the highest energy efficiency.
• Vapor injection in the low-temperature stage achieved a coefficient of performance of 0.89, a 40% improvement over traditional cycles.
• Internal heat exchangers were found to be unnecessary for energy performance at ultralow temperatures.
• Optimal intermediate temperatures varied widely (-37 °C to 2 °C) across different cycles.
• Parallel compression offered moderate energy improvements (20-30%) compared to single-stage cycles.

Conclusions:

• Cascade cycles with vapor or liquid injection are the most energy-efficient for ultralow-temperature refrigeration.
• Natural refrigerants like R-290 and R-170 are suitable for these applications.
• Single-stage high-temperature stages can be effectively employed in many ultralow-temperature cascade systems without compromising performance.