Development of CO₂ dry ice heat pump system

A refrigeration temperature below −50.0°C is highly required for the storage of vaccines and fishery catches
using natural refrigerants such as CO₂ (carbon dioxide). In this study, we have proposed and developed a
unique refrigeration system using solid-state CO₂ (dry ice) to achieve ultra-low temperatures below −70°C.
The initial challenge was the evaporator blockage due to dry ice aggregation, causing system instability. A
stainless-steel spiral coil (swirl promoter) was introduced at the evaporator/sublimator inlet to enhance heat
transfer and alleviate the blockage problem. The system, which operates effectively at the triple point of
approximately −60°C and 0.5 MPa, is further advanced to its limits by using a cyclone separator/evaporator
in its latest stage. By integrating a cold recovery heat exchanger in a cylindrical vessel, the system can
maintain ultra-low temperatures of approximately −70°C inside the recovery section, achieving a coefficient
of performance of this system (COPsystem) of 1.2.
Keywords: Natural Refrigerant, CarbonDdioxide, CO₂ Refrigeration System, Dry Ice, Ultra-low Temperature