The drying process consumes large amounts of energy in industrial and agricultural production. Research and practical applications show that compared with other drying technologies

the heat pump drying technology has better energy-saving potential and economic benefits. As a natural working medium

CO2 is environmentally friendly. The transcritical CO2 cycle has a clear temperature glide

which is more suitable for heat pump drying than the subcritical cycle with a constant condensing temperature of a conventional working fluids. In this paper

the research status of the transcritical CO2 heat pump drying systems is described. The feasibility of the application

system model establishment and key parameter analysis

experimental research

and system optimization of CO2 heat pump drying system are discussed in depth. The advantages and disadvantages of various CO2 heat pump drying system optimization methods are summarized. Existing limitations in the current research of transcritical CO2 heat pump drying systems are proposed

thereby providing a reference for future research applications of CO2 heat-pump-drying technology.