Exploring heat transfer augmentation in slug flow through converging channels: A study on enhancement strategies

Using OpenFOAM CFD software, this study conducts a numerical investigation of the heat transfer enhancement in slug flows within converging channels. The research incorporates both gas-liquid and liquid-liquid slug flows, with air, water, and hexadecane serving as the working fluids. The volume of fluid (VOF) method is employed to capture all gas/liquid and liquid/liquid interfaces, and the finite volume method on a structured mesh is used to solve governing conservation laws. The effects of channel inlet-to-outlet aspect ratio and fluid flow rates are examined on the heat transfer rate and the overall pressure drop across the converging channels. The obtained results confirm that using a convergent channel enhances the heat transfer rate for slug flows compared to a conventional rectangular channel. This trend is partly attributed to the decrease in the liquid film thickness surrounding the primary phase bubble/droplet with decreasing channel diameter. Moreover, the channel with a 3:2 aspect ratio demonstrates the highest Performance Evaluation Criteria (PEC) with a maximum value of around 1.4. Additionally, an escalation in the heat transfer augmentation is observed with an increase in the fluid flow rate.