Computational simulations of spray flows typically start with bulk liquid flow, bulk-to-droplet conversion algorithm for primary atomization, then tracking of discrete particle motion. The key step is the atomization criterion and subsequent drop size conversion. To facilitate this process, we consider the Weber number, based on strain rate (We<sub><i>st</i></sub>), as the local atomization condition in computational simulations of spray flows. This atomization criterion is tested within the computational protocol developed in this laboratory, which uses the integral theory as the primary atomization algorithm. Based on this definition, We<sub><i>st</i></sub> ~ 10<sup>7</sup> appears to work quite well in specifying the location of primary atomization, across different spray geometries. Therefore, the conservation equations of mass and energy in integral forms can be effectively coupled with the CFD-based momentum solver to simulate spray flows, by using the current atomization criterion.