Boiling Heat Transfer during Flow in Vertical Mini-Channels with a Modified Heated Surface

Abstract

The process with change of phase during flow in mini-channels plays a significant role in many industrial applications, such as microelectronics. Furthermore, methods for heat transfer intensification during flow in channels of small cross-section are still being sought. In this work, studies of the effect of using a modified heated surface on intensification boiling heat transfer in rectangular mini-channels during upward and downward flow are performed. The test section of a group of seven parallel mini-channels 1 mm deep was investigated during the subcooled and saturated flow boiling of FC-72. The temperature of the outer heated wall surface was measured using an infrared camera. During the experiments, two-phase flow structures were captured with a quick camera. Local heat transfer coefficients at the contact surface between the working fluid and the heated surface were determined with the use of a one-dimensional calculation method. To present the results, local temperature measurements and heat transfer coefficients, boiling curves and two-phase flow patterns are shown and analyzed. The results concerning two directions of vertical flow along mini-channels are discussed. Several modified heated surfaces and one smooth were tested for comparison. The main objective was to find out how the modified surface of the heated wall can intensify boiling heat transfer with upward and downward refrigerant flow in mini-channels of rectangular cross-section.