J. Alberto Dopazo

Experimental Analysis of the Freezing Process in a Horizontal Plate Freezer With CO2 as Refrigerant in a Cascade Refrigeration System

An experimental evaluation of a cascade refrigeration system prototype using NH3 and CO2 as refrigerants has been performed. The prototype is used to supply a 9-kW refrigeration capacity to a horizontal plate freezer at an evaporation temperature of –50°C as design conditions. The prototype includes a specific control system and a data acquisition system. The article describes the prototype and the experimental program carried out to study the freezing process in the horizontal plate freezer. The experimental results include the freezing time, the temperature evolution in the product to be frozen, the refrigeration capacity of the facility, the electric power of the compressors, the coefficient of performance (COP) of the low- and high-temperature systems, and the overall system COP. The results obtained would confirm that the use of CO2 in plate freezers represents a viable alternative to refrigerants currently in use.

Condensation of R22 Retrofit Substitutes R417A, R422A, and R422D on Horizontal Smooth Tubes

This article reports on the experimental research conducted to study the condensation of R22 retrofit refrigerants R417A, R422A, and R422D on Cu smooth tubes of 18.85 mm outside diameter. These retrofit substitutes are three-component mixtures. Experiments were carried out at vapor saturation temperature of 40°C and wall subcooling from around 1.8 to 16.7°C. The results clearly show the difference in behavior of the mixtures during condensation from that of a pure substance. A rapid increase of the heat transfer coefficients for low wall subcoolings was found. Comparisons of the condensation performance among the different refrigerant mixtures are also shown in the article.