###### Abstract  
The interfacial area between two phases plays a crucial role in the mass transfer rate of gas-liquid processes such as absorption. In this context, the droplet size distribution within the flow field of a droplet-based absorber significantly affects the surface area, thereby influencing the absorption efficiency. This study focuses on developing a computational fluid dynamics (CFD) model to predict the size and distribution of water droplets free-falling in a transparent square tube. This model serves as a digital twin of our experimental setup, enabling a comparative analysis of experimental and computational results. For the accurate measurement of droplet size and distribution, specialized experimental equipment was developed, and a high-speed camera along with Fiji software was used for the capturing and processing of droplet images. At the point of injection and at two different heights, the sizes and distributions of falling droplets were measured using this setup. The interaction between the liquid water droplets and the gas phase within the square tube was modeled using the Eulerian-Lagrangian (E-L) framework in the STAR-CCM+ software. The E-L multiphase CFD model yielded approximations with errors ranging from 11 to 27% for various average mean diameters, including \(d_{10}\), \(d_{20}\), \(d_{30}\), and \(d_{32}\), of the liquid droplets at two distinct heights (200 mm and 400 mm) for both nozzle plates. This comprehensive approach provides valuable insights into the dynamics of droplet-based absorption processes. d pacs: date 000-0001-5284-4, 2000-0001-5284-4, 2000-0001-5284-4, 2000-0001-5284-4, 2000-0001-5284-4, 2000-00 Different studies have focused on the CFD simulation of spray-based equipment using different approaches. The use of CFD for the assessment of evaporative cooling by water spray systems, particularly in urban settings, was highlighted by [PERSON] et al. (2015), who also demonstrated the precision of the Lagrangian-Eulerian approach when tested against wind-tunnel results [6]. [PERSON] et al. (2006) compared the Eulerian and Lagrangian modeling approaches for turbulent dispersion and droplet coalescence within a spray, and they came to the conclusion that the Lagrangian approach was more feasible in terms of implementation and applicability [7]. An axisymmetric population balance model for spray drying was created by [PERSON] et al. (2014), who emphasized the importance of capturing the precise droplet size distribution and how it relates to drying kinetics [8]. [PERSON] et al. (2022) argued for a well-balanced combination of both CFD and experimental methodologies to improve spray releases [9], whereas [PERSON] et al. (2017) investigated the influence of parameters such as droplet size distribution on CFD simulations and computing time [10]. Together, these works highlight the expanding body of evidence supporting the usefulness of CFD in understanding and predicting droplet behavior, as well as the necessity of incorporating experimental data for strong validations. Applications ranging from combustion systems to environmental controls depend heavily on monitoring the distribution of droplet sizes. To simulate urea-water sprays in selective catalytic reduction systems, [PERSON] et al. (2020) used CFD, demonstrating the skill of air-assisted nozzles in obtaining the best ammonia homogenization [11]. A novel technique was developed by [PERSON] et al. (2022) to measure the median diameter of water-mist spray droplets, a crucial factor that affects fire extinguishing procedures [12]. To mimic the aerodynamic breakage of droplets, [PERSON] and [PERSON] (2022) introduced a hybrid Volume of Fluid (VOF)-Lagrangian technique, providing a thorough response to the problems associated with liquid fragmentation [13]. The importance of accurate droplet measurements and the possibility of CFD validations in improving industrial applications are both emphasized by these works. Understanding droplet size and distribution in various flow regimes is crucial for optimizing industrial processes.