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ABSTRACT

The use of CO₂ in cascade refrigeration systems is increasing to achieve low temperatures, particularly in food and refrigeration industries, where understanding of the flow boiling heat transfer mechanisms is essential for heat exchanger design. This paper presents preliminary experimental results of the flow boiling heat transfer of CO₂ - lubricant mixture at low saturation temperatures varying between -30°C to -40°C, oil concentration varying between 0 - 4%, along with the effects of refrigerant vapour quality. The addition of low oil quantities to the flow (<3%) show an increase in local heat transfer coefficients at low vapour qualities (<60%), followed by a drop as the oil concentration is further increased, particularly at high vapour qualities (>80%).