The paper deals with heat transfer from a horizontal heating surface to weak aqueous solutions of NaOH in order to explain whether the heat transfer in natural convection and pool boiling can be enhanced by hydrogen bubbles generated electrolytically at the heating surface. Measurements were made at liquid temperatures between 60-degrees-C and saturation temperature at atmospheric pressure. The heat flux density ranged from 4.78 . 10(4) W/m2 to 2.10 . 10(5) W/m2 and the current density from 0 to 2100 A/m2. In order not to essentially change the physical properties of water by addition of NaOH, the concentration of the solution was varied only up to 0.25 mol/l. The experiments showed an enhancement of heat transfer up to a factor of 6 due to the electrolytically produced hydrogen bubbles. The enhancement of heat transfer increases with increasing solution temperature and with increasing current density. An increasing heat flux density leads to an increase of the heat transfer coefficient alpha. At the same time the ratio alpha/alpha(0) decreases, where alpha(0) is the heat transfer coefficient without hydrogen evolution. The effect of concentration on heat transfer coefficients can be neglected in the concentration range covered by the experiments.
