Cooling liquid flow boiling heat transfer in an annular minigap with an enhanced wall

^1,2 Faculty of Mechatronics and Mechanical Eng., Kielce University of Technology, Al. 1000-lecia P.P. 7, 25-314 Kielce, Poland
³ Circle of Health Tourism, Dabrowa 2, 26-001 Maslow, Poland

^* Corresponding author: tmpmj@tu.kielce.pl

Published online: 28 June 2019

Abstract

The paper focused on flow boiling heat transfer in an annular minigap. This gap of 1 mm width was created between the metal pipe with an enhanced surface contacting fluid and the external glass pipe positioned along the same axis. The heated element for the HFE-649 flowing in the minigap was a cartridge heater. Thermocouples were used to measure the temperature of the metal pipe in the contact surface with a fluid. The local values of the heat transfer coefficient for stationary state conditions were calculated using an one-dimensional method in which the multilayer cylindrical wall was assumed to be planar. The results were presented as a function of the heat transfer coefficient along the minigap length and as boiling curves, prepared for selected values of mass flow rate and five types of the enhanced heated surface and a smooth one. Observations indicated that the highest local values of heat transfer coefficient were obtained with using the enhanced surface produced by electromachining process (spark erosion) at the saturated boiling region. The boiling curves generated for two distances from the minigap inlet have similar plots without a drop in the temperature of the heated surface characteristic for nucleation hysteresis.