Transient and cyclic characteristics of a household refrigerator using ternary hydrocarbon mixture - An experimental investigation

A household refrigerator designed to work with R134a was used as an investigation unit to assess its transient startup and cyclic characteristics using ternary hydrocarbon mixture. Twenty-five combinations of refrigerant mass (30, 40, 50, 60 and 70 g) and capillary tube length (4, 4.5, 5, 5.5 and 6 m) are tested under severe tropical environment using a mixture of propane: isobutene: n-butane of 60:26.6:13.4% by mass. Also, typical variations of compressor, condenser and evaporator temperatures during transient and cyclic operations are considered. The energy losses during off-time are addressed by comparing refrigerator power during cyclic and continuous operation. The results demonstrate that while 15 out of 25 tested combinations satisfy the required air freezer and cabinet temperatures and achieve reasonable startup transient characteristics, only 5 combinations work satisfactorily under cyclic operation. The most appropriate combination of charge and capillary tube length is identified to be 70g and 5.5m. This combination consumes the lowest energy during permanent cyclic operation and achieves reasonable cooling rate, pull-down time and startup energy. In comparison with R134a, the energy applied to this combination may save about 306.6 kWh annually for each refrigerator that would result in 36.8 TWh on the world scale.