ENHANCEMENT OF SUBCOOLED FLOW BOILING HEAT-TRANSFER ON CYLINDERS USING INTERFERENCE SLEEVES

This paper describes a experimental study of subcooled how boiling of water on a horizontal stainless steel tube with an interference sleeve (a sleeve with perforations). The flow of water is in the annular sec tion between the sleeve surface and a outer glass tube. Six sleeves we re used with different hole geometries (hole diameters and the pitch o f holes) and the clearance between the sleeve and the boiling tube. Re sults show that sleeves with larger values of clearances and pitch nee ded lower temperature driving forces for a given heat flux, but with t he disadvantage of an early transition to film boiling. However, inter ference sleeves with hole diameters of 1 mm and those with a combinati on of 1 mm and 2 mm holes on alternate rows required high heat fluxes for transition to film boiling. The level of inlet sub-cooling showed a marked effect of the two phase heat transfer coefficient. A subcooli ng of 20 K gave heat transfer coefficients that were two to three time s lower than that obtained with a sub-cooling of 5 K. An increase in t he inlet mass velocity of the liquid showed a significant increase in the wall superheat accompanied by a greatly increased heat flux requir ed for transition to film boiling. A correlation has been proposed for the two phase heat transfer coefficient and the importance of the par ameters in the correlation is discussed in terms of the physics of the process.