Investigation of flow boiling in narrow channels by thermographic measurement of local wall temperatures

Abstract

Flow boiling heat transfer characteristics of water and hydrocarbons in mini and microchannels are experimentally studied. Two different test section geometries are employed; a circular channel with a hydraulic diameter of 1,500 lm, and rectangular channels with height values of 300-700 lm and a width of 10 mm. In both facilities, the fluid flows upwards and the test sections, made of the nickel alloy Inconel 600, are directly electrically heated. Thus, evaporation takes place under the defined boundary condition of constant heat flux. Mass fluxes between 25 kg/m 2 s and 350 kg/m 2 s and heat fluxes from 20 kW/m 2 to 350 kW/m 2 at an inlet pressure of 0.3 MPa are examined. Infrared (IR) thermography is applied to scan the outer wall temperatures. These allow the identification of different boiling regions, boiling mechanisms, and the determination of the local heat transfer coefficients (HTC). Measurements are carried out in initial, saturated, and post-dryout boiling regions. The experimental results in the region of saturated boiling are compared with currently available correlations and with a physically founded model developed for convective boiling.

An investigation into the influence of different parameters on the onset of boiling in minichannels

“…Wambsganss et al identified the flow patterns occurring in flow boiling in minichannels, both circular and rectangular [23][24][25]. In [26], the authors investigated flow boiling heat transfer characteristics of water and hydrocarbons in mini-and microchannels. Infrared (IR) thermography was employed for determining wall temperatures.…”

An accurate wall temperature measurement using infrared thermometry with enhanced two-phase flow visualization in a convective boiling system

“…Consequently, high-speed photography (Klausner et al, 1993;Situ et al, 2008;Chu et al, 2011) and a laser-based flow visualization technique (Estrada-Perez and Hassan, 2010) have been utilized to study the hydrodynamics of liquid/vapor phases in a boiling system. For a wall heat transfer study, the thermal patterns under boiling conditions can be also visualized, for which liquid crystal thermography (Kenning et al, 2001;Bayazit et al, 2003;Muwanga and Hassan, 2006) and infrared (IR) thermometry (Hapke et al, 2000;Theofanous et al, 2002a;Theofanous et al, 2002b;Diaz et al, 2006;Jung et al, 2014) have been employed.…”