Pool boiling heat transfer of R134a outside reentrant cavity tubes at higher heat flux

An experimental investigation on the pool boiling heat transfer of refrigerant R134a outside three enhanced tubes is conducted. The heat flux is from 10,000 to 370,000 W/m². The heat transfer is substantially enhanced at the heat flux less than 200 kW/m². An increase of heat transfer coefficient up to 330% above the plain tube is observed. However, at the heat flux higher than 200 kW/m², it is found that the heat transfer coefficient of enhanced tubes is even lower than the plain tube. The same features are also observed for other enhanced tubes in the literature.