The Effects of Subcooled Temperatures on Transient Pool Boiling of Deionized Water under Atmospheric Pressure

Abstract

Pool boiling heat transfer and critical heat flux (CHF) were experimentally studied in subcooled temperatures ranging from 0oC to 20oC and under transient power conditions. A chromealuminum- iron alloy wire was used as the heating element. The heating rate in the test section was increased linearly depending on time by applying voltage control for 1s to 1000s. The transient boiling heat transfer coefficient (TBHTC), transient wire superheat temperature, transient heat flux and transient CHF were also obtained. The results showed that in the case of all subcooled temperatures and periods, the TBHTC increased in the nucleate boiling region because of the growth, separation, motion and turbulence of the bubbles. The TBHTC also decreased in the transition from nucleate boiling to film boiling because some part of the wire covered by temporary thin vapor film. The TBHTC again increased in film boiling due to the increment of radiation heat transfer. The TBHTC decreased in the second part of the film boiling due to the heat flux and the vapor film thickness around the wire had increased. Relative to the saturation condition, the timely average of the wire superheat temperature for subcooled temperatures of 10oC and 20oC , respectively, decreased by 9.23% and 9.29% in the nucleate boiling region and in a time period of 1000s.