A closed disposable multiple sterile blood bag system for fractionating blood, said system comprising: - a fluid collecting bag (B.00) comprising at least one outlet port; - first and second sampling bags (B.10, B.12), each comprising at least one inlet port and at least one outlet port; - first means for transferring fluid from the fluid collecting bag (B.00) to the first and second sampling bags (B.10, B.12); wherein the first means for transferring fluid comprises: - a channel extending along a longitudinal axis, the channel having a cross section with a width measured along a first transverse axis and a thickness measured along a second transverse axis (z) perpendicular to the first transverse axis, the width being greater than or equal to the thickness, the channel having first and second walls along the second transverse axis (z); - at least one inlet in fluid communication with the channel; - at least first and second outlets in fluid communication with the channel, the first outlet being separated, on the second transverse axis (z), from the second outlet; - at least one acoustic wave generator configured to generate a volumetric acoustic standing wave having a wavelength λ over the thickness and over the width of the channel for sorting and fractionating a fluid; and wherein thickness of the channel of the first means for transferring fluid is equal to λ/2 or is equal to a multiple of λ/2; wherein the at least one outlet port of the fluid collecting bag (B.00) is fluidly and sterilely connected to the at least one inlet of the first means for transferring fluid and the at least first and second outlets of the first means for transferring fluid are fluidly and sterilely connected to the at least one inlet port of respectively the first and second sampling bags (B.10, B.12). - a fluid collecting bag (B.00) comprising at least one outlet port; - first and second sampling bags (B.10, B.12), each comprising at least one inlet port and at least one outlet port; - first means for transferring fluid from the fluid collecting bag (B.00) to the first and second sampling bags (B.10, B.12); wherein the first means for transferring fluid comprises: - a channel extending along a longitudinal axis, the channel having a cross section with a width measured along a first transverse axis and a thickness measured along a second transverse axis (z) perpendicular to the first transverse axis, the width being greater than or equal to the thickness, the channel having first and second walls along the second transverse axis (z); - at least one inlet in fluid communication with the channel; - at least first and second outlets in fluid communication with the channel, the first outlet being separated, on the second transverse axis (z), from the second outlet; - at least one acoustic wave generator configured to generate a volumetric acoustic standing wave having a wavelength λ over the thickness and over the width of the channel for sorting and fractionating a fluid; and - a channel extending along a longitudinal axis, the channel having a cross section with a width measured along a first transverse axis and a thickness measured along a second transverse axis (z) perpendicular to the first transverse axis, the width being greater than or equal to the thickness, the channel having first and second walls along the second transverse axis (z); - at least one inlet in fluid communication with the channel; - at least first and second outlets in fluid communication with the channel, the first outlet being separated, on the second transverse axis (z), from the second outlet; - at least one acoustic wave generator configured to generate a volumetric acoustic standing wave having a wavelength λ over the thickness and over the width of the channel for sorting and fractionating a fluid; and wherein thickness of the channel of the first means for transferring fluid is equal to λ/2 or is equal to a multiple of λ/2; wherein the at least one outlet port of the fluid collecting bag (B.00) is fluidly and sterilely connected to the at least one inlet of the first means for transferring fluid and the at least first and second outlets of the first means for transferring fluid are fluidly and sterilely connected to the at least one inlet port of respectively the first and second sampling bags (B.10, B.12).