NUCLEATE POOL BOILING ON HORIZONTAL TUBES - A CONVECTION-BASED CORRELATION

Pool boiling on horizontal tubes leads to a bubbly flow layer around the lower periphery of the tube in which bubbles slide around the surface. Heat transfer is by enhanced liquid convection at the surface around the bubble and by rapid evaporation of a thin layer under the sliding bubble. Both these mechanisms are a function of the vapour flow rate and a correlation of the following form is developed: Nu = AF(p)Re(b)0.67 Pr0.4. A is a function of the critical pressure alone, F(p) is a function of the reduced pressure alone and Re(b) is based on the mean vapour mass flux from the surface and the tube diameter. The correlation applies to water, refrigerants and organics boiling on tubes of 8-50 mm in diameter. Bearing in mind the wide scatter found in pool boiling experiments the correlation fits well with the available world data and is particularly suitable for use in equipment design calculations.