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. <EOS>