BK1-5 Boiling on Tubes with Sintered Surfaces
Two bundles of tubes coated with a special porous sintered surface were tested in the HTRI kettle reboiler unit, and the performance was compared with that of a previously tested plain tube bundle of similar geometry. The sintered surfaces had a large number of relatively large nucleation cavities, and, therefore, produced significantly better performance than plain surfaces in vacuum service where large cavities are required for nucleation. At higher pressures the amount of improvement was less. Most improvement was seen at low DT where heat transfer is largely controlled by the number of active nucleation sites. At high overall DT the plain and sintered surfaces performed about the same in most cases and produced about the same maximum heat flux. Pure hydrocarbons, Freon 113, and mixtures were tested. There was seen to be an apparent decrease in the amount of improvement with increase in mixture boiling range. Performance decreased slightly with time in a test boiling pure p-xylene intermittently over a period of four weeks. Electron microscope photographs before and after the test showed that the surface had picked up some rust from the system.
In conclusion, it appears that sintered surface tubes can be very effective in kettle reboilers for clean fluids under conditions compatible with the pore sizes in the surface. An empirical correlation of surface factor was developed for these particular fluid-surface combinations showing the effect of heat flux, operating pressure, and mixture boiling range. However, the generality of such a correlation is probably very limited. Specific tests would have to be performed before making decisions regarding other applications.