Deep hole drilling is a technique used for producing holes in materials at high depth to diameter (L/D > 10) ratios. Applications demanding deep holes can be extensively found in aerospace, automotive, marine and oil & gas industries. Conventional drilling techniques such as twist drilling and gun drilling are commonly used for drilling deep holes in the aforementioned applications. However, these methods can cause problems of rapid tool degradation, chip clogging, premature tool failure and undesirable sub-surface alterations to the hole surface. Moreover, these problems get aggravated when the material is difficult-to-cut (Ni/Fe/Co based superalloys) in nature. Therefore, non-conventional machining process finds scope in order to overcome the problems associated with conventional drilling. Electrical discharge drilling (EDD) can be used for fabricating dimensionally accurate holes irrespective of hardness of the material. Nevertheless, the inefficiency in flushing of debris particles at higher depths and its subsequent accumulation is a critical challenge during EDM deep hole drilling. The reason behind flushing inefficiency based on fluid physics has not been completely explored by researchers yet. In this paper, the flow behaviour of micro debris particles in the flushing channel during EDD has been analysed using CFD simulation by employing discrete phase modelling (DPM). The developed model set up is also validated with a benchmark fluid mechanics problem. The steady state CFD analysis results show the formation of multiple recirculation zones in the flushing channel. This can be attributed to the adverse pressure gradient experienced when the dielectric fluid passes from the machining gap to annular gap. Moreover, the presence of recirculation zones reduces the flow momentum and thereby debris particle velocity. This leads to accumulation of micro debris particles in the recirculation zones over time. The results also show that the trajectory of the particles is dependent on the size of the particles generated during material removal. The outcomes of numerical analysis in the present paper can serve as a foundation for the future studies in improving the performance of EDM deep hole drilling. © 2021 Elsevier B.V.. All rights reserved.