Acoustic separation of T cells

A method for separating biological cells from a host fluid, comprising:

• chilling a mixture of the host fluid and the biological cells;
• flowing the cooled mixture of the host fluid and the biological cells through a first acoustophoretic device, the first acoustophoretic device comprising:
• a flow chamber including at least one inlet and at least one outlet;
• at least one ultrasonic transducer coupled to the flow chamber, the at least one ultrasonic transducer including a piezoelectric material configured to be driven to create a multi-dimensional acoustic standing wave in the flow chamber;
• and
• a reflector opposite to the at least one ultrasonic transducer;
• and
• driving the at least one ultrasonic transducer to create the multi-dimensional standing wave in the flow chamber, such that at least some of the biological cells are trapped in the standing wave, and agglomerate, aggregate, clump, or coalesce together, and settle out of the host fluid due to enhanced gravitational settling forces.