An apparatus for mixing and atomizing a hydrocarbon stream including coker naphta, coker gas oil, vacuum gas oil, VGO, hydro treated vacuum gas oil, hydrocracker bottom, straight run naphta, visbreaker naphtha using a diluent/dispersion stream, said apparatus comprising: an inner conduit having an inlet for receiving the diluent/dispersion stream; an outer conduit having an inlet for receiving the hydrocarbon stream and an outlet for dispensing a mixture comprising the hydrocarbon and the dispersion /diluent streams; said outer conduit concentric to the inner conduit to define at least a first annular space and a second annular space; the first annular space being located downstream of the inlet of the outer conduit, said first annular space enabling formation of a thin film of the hydrocarbon stream between an outer surface of the inner conduit and an inner surface of the outer conduit; the second annular space being located downstream of the first annular space, said second annular space having a width greater than a width of the first annular space; and the inner conduit located at the second annular space comprises a first set orifices disposed on a periphery thereof for dispensing a first portion of the dispersion/diluent stream into the thin film of hydrocarbon stream to cross-shear the thin film and form the mixture comprising the hydrocarbon and the dispersion /diluent streams; characterized in that said apparatus further comprises at least one sparging means in flow connection with said inner conduit and located downstream of said inner conduit, the sparging means being adapted to: divide the mixture into at least a first flow and a second flow; and dispense a second portion of the diluent/dispersion stream into said at least first flow and second flow of the mixture. an inner conduit having an inlet for receiving the diluent/dispersion stream; an outer conduit having an inlet for receiving the hydrocarbon stream and an outlet for dispensing a mixture comprising the hydrocarbon and the dispersion /diluent streams; said outer conduit concentric to the inner conduit to define at least a first annular space and a second annular space; the first annular space being located downstream of the inlet of the outer conduit, said first annular space enabling formation of a thin film of the hydrocarbon stream between an outer surface of the inner conduit and an inner surface of the outer conduit; the second annular space being located downstream of the first annular space, said second annular space having a width greater than a width of the first annular space; and the inner conduit located at the second annular space comprises a first set orifices disposed on a periphery thereof for dispensing a first portion of the dispersion/diluent stream into the thin film of hydrocarbon stream to cross-shear the thin film and form the mixture comprising the hydrocarbon and the dispersion /diluent streams; characterized in that said apparatus further comprises at least one sparging means in flow connection with said inner conduit and located downstream of said inner conduit, the sparging means being adapted to: divide the mixture into at least a first flow and a second flow; and dispense a second portion of the diluent/dispersion stream into said at least first flow and second flow of the mixture. divide the mixture into at least a first flow and a second flow; and dispense a second portion of the diluent/dispersion stream into said at least first flow and second flow of the mixture.