The fluid flow patterns and associated concentration fields in Y-mixers are investigated using lattice Boltzmann method-based models. The focus lies on the impact of the mixing angle on the flow and concentration fields, with the mixing angle varying between acute (theta = 10 degrees) and obtuse (q = 130 degrees) angles. Residence time distributions are determined to study the effect of the angles on the mixing and velocity patterns, in particular, different flow regimes, i.e., stratified laminar, vortex, and engulfment flow. The results from the simulations are validated with literature data and found to be in good agreement. Maximum mixing occurs in the 100 degrees obtuse-angle Y-mixer, attributed to the extensive engulfment of flows in the mixing channel.