Sieve tray internals are a well-known method for reducing liquid phase backmixing in bubble columns. In the soaker mode of visbreaking, cracked hydrocarbon vapors increase in volume as we move up in a soaker drum because of more vapor generation due to cracking as well as reducing hydrostatic head on the gas bubbles. The free flow area in sieve trays is gradually increased as we move up in the soaker drum because of this increase in volume. A CFD analysis is presented on a soaker drum with two set of sieve tray internals with same free flow area on corresponding sieve trays, but different configuration of holes. The liquid and vapor properties have been taken identical to the hot short residue and hydrocarbon vapors, respectively. The size of flow domain for simulation has been taken equivalent to a real soaker drum, for realistic simulations. It was found that increasing of flow area in sieve trays by increasing the size of holes is more effective way for reducing liquid phase back mixing, as compared to increasing number of holes.