A thermodynamic analysis of carbon dioxide–ammonia (R744–R717) cascade refrigeration system is presented in this paper to optimize the design and operating parameters of the system. The design and operating parameters considered in this study include (1) condensing, subcooling, evaporating and superheating temperatures in the ammonia (R717) high-temperature circuit, (2) temperature difference in the cascade heat exchanger, and (3) evaporating, superheating, condensing and subcooling in the carbon dioxide (R744) low-temperature circuit. A multilinear regression analysis was employed in terms of subcooling, superheating, evaporating, condensing, and cascade heat exchanger temperature difference in order to develop mathematical expressions for maximum COP, an optimum evaporating temperature of R717 and an optimum mass flow ratio of R717 to that of R744 in the cascade system.

Thermodynamic analysis of an R744-R717 cascade refrigeration system

Exergoeconomic and environmental analyses of CO 2 /NH 3 cascade refrigeration systems equipped with different types of flash tank intercoolers

Exergetic, economic and environmental (3E) analyses, and multi-objective optimization of a CO2/NH3 cascade refrigeration system

Thermoeconomic optimization and exergy analysis of CO2/NH3 cascade refrigeration systems

A prototype of a cascade refrigeration system using NH 3 and CO 2 as refrigerants has been designed and built. The prototype is used to supply a 9 kW refrigeration capacity horizontal plate freezer at an evaporating temperature of −50 °C as design conditions. The prototype includes a specific control system and a data acq*uisition system. The experimental evaluation started with the real conditions within the design operating parameters. Subsequently, several tests were performed fixing four CO 2 evaporating temperatures (−50, −45, −40 and −35 °C). At each one of the evaporating temperatures evaluated, the CO 2 condensing temperature was varied from −17.5 to −7.5 °C and an experimental optimum value of CO 2 condensing temperature was determined. The discussions on the experimental results include the influence of the operating parameters on the cascade system’s performance. In addition, the experimental results are compared with two common double stage refrigeration systems using NH 3 as refrigerant.

Experimental evaluation of a cascade refrigeration system prototype with CO2 and NH3 for freezing process applications

This paper presents modeling and experimental analyses of evaporators in “in situ” frozen-food display cabinets at low temperatures in the supermarket industry. Extensive experiments were conducted to measure store and display cabinet relative humidities and temperatures, and pressures, temperatures and mass flow rates of the refrigerant. The mathematical model adopts various empirical correlations of heat transfer coefficients and frost properties in a fin-tube heat exchanger in order to investigate the influence of indoor conditions on the performance of the display cabinets. The model is validated with the experimental data of “in situ” cabinets. The model would be a good guide tool to the design engineers to evaluate the performance of supermarket display cabinet heat exchangers under various store conditions.

H.M. Getu

Papers

Thermodynamic analysis of an R744-R717 cascade refrigeration system

Modeling and performance analyses of evaporators in frozen-food supermarket display cabinets at low temperatures