NUCLEATE POOL BOILING OF R-134A ON ENHANCED HORIZONTAL SURFACES HAVING PORES ON SUB-TUNNELS

Enhanced surfaces having circular pores and rectangular sub-tunnels were made and nucleate boiling tests were conducted using R-134a under horizontal positions. Nine samples had pore diameters from 0.1 mm to 0.3 mm and pore pitches from 0.75 mm to 3.0 mm. The heat transfer coefficient increased as the pore size increased, at least for the investigated test range. The reason was attributed to the increased bubble departure diameter with the pore diameter. The heat transfer coefficient also increased as the pore pitch decreased, while the number of pores increased approximately in proportion to the square of pitch ratio. Increased nucleate site density at smaller pore pitch appears responsible for the high heat transfer coefficient. Existing theoretical models did not adequately predict the present data. A new model was proposed, which predicted 70% of the present data within ± 50%.