Influences of wall superheat and channel width ratio on bubble behaviors and heat transfer within a heated microchannel T-junction

Abstract

Despite many studies conducted to reveal the bubble behaviors and associated heat transfer within straight microchannels, those within heated microchannel T-junctions are relatively few. In this paper, the ANSYS Fluent 17.0 enhanced by user-defined functions (UDFs) is utilized to perform 2D simulations on an evaporating bubble passing through the heated T-junction. The influences of wall superheat (ΔT) and channel width ratio (W*) are investigated. Four typical breakup regimes (Non-breakup, “Tunnel” breakup type one, “Tunnel” breakup type two, and obstructed breakup) are observed and the corresponding phase diagram is drawn. The heat transfer characteristics for different heated walls are quantitatively assessed. The bubble behaviors have great impact on the heat transfer characteristics of T-junction. The oscillation of relatively small bubble produces obvious local heat transfer enhancement. The occurrence of tunnel is found to weaken the heat transfer enhancement. It should be noted that the serpentine flow structure occurring at larger W* also significantly influences the heat transfer of branching channel. Generally, the overall heat transfer performance tends to increase with increasing ΔT or decreasing W*. This study contributes to a better understanding of bubble behaviors within microchannel T-junctions.