Pool boiling of R-11 refrigerant and water on oxidized enhanced tubes

The effects of oxidation on pool boiling on an oxidized enhanced boiling tube (GEWA-SE) have been studied. Water and a refrigerant R-11 were boiled at subatmospheric pressure. Oxidation increases the pool boiling heat transfer coefficient for both fluids. The pool boiling heat transfer coefficient increased as much as a factor of 2.4 for water, and 1.5 for the refrigerant. For the R-11 refrigerant, a highly wetting fluid, the boiling heat transfer coefficient increases with increase in the level of oxidation. The increase in the heat transfer coefficient with increasing level of oxidation for water as the boiling fluid was slightly less than that recorded fro R-11. This study includes contact angle measurement and its influence on oxidation. The contact angle of different levels of oxidation and various surface grades of copper and aluminum in contact with water, and refrigerants were measured. Contact angles can be used as a rough guide or indicator of the level of surface oxidation or the degree of wettability of fluids on a surface. With the depth of the roughness below 0.5 μm, no surface roughness effect on contact angle were observed.