Influence of flow rate and surface thickness on heat transfer characteristics of two consecutively impinging droplets on a heated surface

•Numerical model is implemented in OpenFOAM to simulate the droplet impingement on a heated surface in open atmospheric conditions.•Contact line evaporation and dynamic contact angle motion is considered during the simulations.•Solver is successfully validated against in-house experimental observations.•Effects of droplet flow rate and surface thickness on spreading and heat transfer characteristics are examined.•Numerical results are in good agreement with available analytical models of maximum spreading diameter and input heat transfer. Understanding the droplet-hot wall interaction is crucial in industrial applications such as spray cooling, desalination and refrigeration, and IC engines. The present study focusses on simulations of two consecutively impinging concentric droplets on a heated surface in ambient conditions. A numerical model with fluid-solid coupling is implemented in opensource CFD software OpenFOAM considering contact line evaporation and dynamic contact line motion. The implemented numerical solver is assessed by validating it against the sessile droplet evaporation case available in the literature, followed by in-house experimental results of a single droplet impact. Consequently, the validated solver is used to conduct the simulations of consecutive droplet impingement on a hot surface, considering the droplet flow rate (i.e., the time interval between the two droplets) and surface thickness as parameters. The droplet flow rate is chosen in the order of 102−103 droplets per second (time interval is in the range of 3 - 100 milliseconds), and two variants of the surface thickness of 0.025 and 2 mm are used. The spread and heat transfer dynamics of each droplet are calculated in terms of spread factor, dimensionless input and evaporation heat transfers, respectively, and compared at all parametric conditions. The study reveals that the selected droplet flow rate affects the spread dynamics of the two droplets, resulting in various droplet heat transfer patterns. Moreover, it is observed that a surface with higher thickness results in more droplet heat transfer due to large thermal inertia. The numerical results are in good agreement with theoretical calculations of maximum spread factor and corresponding droplet heat transfer.