Fluid device and method for controlling fluid device

A method for controlling a fluid device, the fluid device including:

• a flow path through which a fluid containing fine particles flows;
• a separation module having a module inflow port, a first module discharge port, and a second module discharge port along the flow path, the fluid flowing into an inside space of the separation module via the module inflow port and flowing out from the first and second module discharge ports, the inside space being surrounded by a first wall, a second wall facing the first wall, and a side wall having the module inflow port and the first and second module discharge ports;
• an ultrasonic transmitter including:
• a vibrator formed in a part of the first wall of the separation module;
• and
• a piezoelectric element provided on the vibrator and configured to transmit an ultrasonic wave to the fluid in the flow path by vibrating the vibrator in response to an input of a drive signal;
• and
• a flow velocity measurement unit configured to measure a flow velocity of the fluid in the flow path, the method for causing a processor to execute a process, the method comprising executing on the processor the steps of:
• setting an amplitude of the drive signal according to the flow velocity;
• and
• inputting the drive signal having the set amplitude to the ultrasonic transmitter to converge the fine particles in the fluid by the ultrasonic wave, and
• the fluid having the converged fine particles is discharged from the first module discharge port, and the fluid without having the converged fine particles is discharged from the second module discharge port.