Investigating the Effect of Heating Method on Pool Boiling Heat Transfer

Pool boiling experiments are generally conducted with electrically heated surfaces in laboratories to obtain the heat transfer coefficient data. In many process applications however, a fluid stream is employed as the heating medium. The heat transfer data generated with the electrically heated test sections therefore raises the question of their applicability to practical equipment design. Similar concerns have been expressed in literature for flow boiling heat transfer. The present investigation focuses on generating experimental data using two identical stainless steel tubes in pool boiling with water at atmospheric pressure. The tubes are made of stainless steel, 3.2 mm outer diameter, 0.1 mm wall thickness, and 152 mm long. One of the tubes is heated electrically using direct current from a power supply, while the other is heated by circulating pure ethylene glycol. Under comparable conditions, the heat transfer coefficients are seen to be considerably different for the two heating methods. A numerical analysis is also performed in the region of the wall in the vicinity of a bubble for both heating methods. The numerical analysis shows the temperature profiles of the surface under and around a bubble being considerably different for the two heating methods. The mechanism causing a localized reduction of temperature in the wall underneath the bubble seems to be the primary reason for the differences in the heat transfer coefficients for the two heating methods.