Samuel F. Yana Motta

A visual study of R-404A/oil flow through adiabatic capillary tubes

The present study explores the potential of using visualization techniques to investigate refrigerant/oil flow through adiabatic capillary tubes. A literature review shows that these techniques have been used before for capillary tube investigations, but none of these studies focused on the refrigerant/oil phenomena. Therefore, the main objective is to investigate the flow of a refrigerant/oil mixture through a glass capillary tube, with special emphasis on the behavior of the vaporization point. The test fluids are R-404A (a near azeotropic blend) and a polyolester-type oil. Experimental data cover oil concentrations ranging from 5.6 to 6.9% (by mass), degrees of subcooling ranging from 6.2 to 21.5 °C (11.2 F to 38.7 F), and a condensing pressure of 1825 kPa (250 psig). The results show trends of mass flow rate, and give some useful insights about the location of the vaporization point for various oil concentrations and operating conditions.

LOW GLOBAL WARMING REFRIGERANTS FOR RESIDENTIAL AIR CONDITIONING APPLICATIONS

Due to the growing global concerns around the use of refrigerants with relatively high global warming potential, new refrigerants with the positive attributes of both high thermal performance and low environmental impact are currently in development by Honeywell. These new refrigerants exhibit promising performance when compared with refrigerants currently used in stationary AC systems such as those that use R-410A, R-407C, and R-134a, for example. These new refrigerants also show significantly lower flammability characteristics than the much more flammable hydrocarbons. Replacements of common HFC refrigerants such as R-410A and R-407C are discussed for residential air conditioning applications. Thermal properties as well as experimental results in representative air conditioning systems are presented, showing the benefits of using these new refrigerants.

Experimental evaluation and field trial of low global warming potential R404A replacements for commercial refrigeration

R404A refrigerant is widely used for various refrigeration applications ranging from centralized refrigeration systems for supermarkets to transport refrigeration for truck/trailer. Various environmental regulations have been proposed in the United States and Europe that phase out the use of high global warming potential refrigerants like R404A (global warming potential = 3943) in these applications. This article presents an evaluation of two low global warming potential R404A replacements: A nonflammable refrigerant R448A with global warming potential of 1273 and a mildly flammable refrigerant R455A with global warming potential of 146. Tests carried out with a commercially available R404A self-contained freezer showed that the compressor run time of R448A and R455A are similar to R404A due to similar capacity. The 24-h energy consumption of the compressor is 9% lower for R448A and 6% lower for R455A compared to R404A. Tests were also performed with R448A in a commercially available walk-in freezer/cooler. R448A matches the capacity with 4 to 8% higher efficiency compared to R404A. This indicates that R448A and R455A can reduce both the direct and indirect emissions significantly in these systems. Finally, this study presents the performance results conversion of an actual supermarket refrigeration system from R404A to R448A, which resulted in energy savings from about 9 to 20% depending on outdoor ambient temperature.