Ph.D. Thesis: Design and Fabrication of a Ferrofluidic Miniature pump
This thesis presents the prototype design and fabrication of magnetically actuated miniature pumps which utilize self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The contactless external actuation feature of the design enables integration of the pump with other PMMA-based microfluidic systems with low cost and disposability. The body of the 1<sup>st</sup> fabricated prototype pump consists of three nozzle/diffuser elements and two pumping chambers connected to the ends of a flat-wall pumping cylinder. A cylindrical permanent magnet placed inside the pumping cylinder acts as a piston which reciprocates by using an external magnetic actuator driven by a motor. The magnetic piston is covered by a ferrofluid to provide self-sealing capability. Three-dimensional numerical simulations are also carried out to study the performance of the pump. In the 2<sup>nd</sup> design, the valving action is performed by employing one active valve along with two nozzle/diffuser elements. Two cylindrical permanent magnets are placed inside the flat-wall channels; one magnet acts as the active valve and the other one serves as a reciprocating piston actuating the working fluid. In order to seal the gaps between the channel walls and the permanent magnet of the valve/piston, ferrofluid is used to cover the surfaces of both magnets. The valve and the piston are actuated using external permanent magnets driven by two separate stepper motors. In the 3<sup>rd</sup> pump, the minichannel consisting of a cylindrical pumping chamber, a check valve, an inlet and an outlet, comprises six bonded layers of PMMA. A cylindrical permanent magnet that is placed inside the chamber and is externally actuated by a motorized off-center permanent magnet, functions as a revolving piston which sweeps the perimeter of the cylinder. Ferrofluid is used to cover the gaps between the magnetic piston and the channel walls, also serves as a separating plug between the inlet and the outlet of the chamber preventing recirculation of the pumped fluid inside the chamber. This novel revolving piston design eliminates the need for an inlet valve. Pressure head is maintained using one ball check valve at the outlet of the pump. With total volume of about 6 cm<sup>3</sup>, the pumps are capable of pumping the water at flow rates of up to 1000 µL/min and backpressures of up to 1 kPa.
Ferrofluidic Diffuser Micropump
The pumping effect is the result of the reciprocating motion of a piston inside a cylinder. The valving function is based on the flow-rectifying effect of nozzle/diffuser elements. The pump body consists of a pumping cylinder with its both ends connected to a pumping chamber, three nozzle/diffuser elements, an inlet, and an outlet. The pumping cylinder has a rectangular cross-section and contains a cylindrical permanent magnet which acts as the piston. The magnetic piston is covered with a ferrofluid. The ferrofluid fills the gaps between the permanent magnet and the channel walls to maintain sealing and provide lubrication. The reciprocating motion of an external actuator displaces the piston. The actuator is also a permanent magnet which is driven by a motor.
The CFD simulation of the presented micropump was performed by solving the three-dimensional Navier–Stokes equations using a finite volume method. Volume of Fluid (VOF) model is used to solve the two-phase flow. The video is slowed down by a factor of 100.
Revolving Piston Miniature Pump
The pumping mechanism is based on the peripheral sliding motion of a disk inside a cylinder. The pump consists of a cylindrical chamber with one inlet port and one outlet port, one passive valve at the outlet, and a revolving disk piston inside the chamber. The disk piston is a permanent magnet which is externally actuated using another cylindrical permanent magnet driven by a motor. The rotating shaft of the motor has its axis of rotation that matches the centerline of the chamber; however, it is eccentric with respect to the revolving piston. The magnetic piston is fully covered with ferrofluid which is held to the surface of the disk by its magnetic force. The ferrofluid fills the gaps between the cylindrical magnet and the chamber walls to maintain sealing. Serving as the sliding vane in a “roller compressor”, a narrow plug of ferrofluid which is held by an external stationary permanent magnet is always present in the upper section of the chamber between the inlet and the outlet ports.
Nozzle pump with an extra ferrofluidic valve
The pumping mechanism is based on the reciprocating motion of a cylindrical permanent magnet inside a minichannel of rectangular cross-section. The two ends of the pumping minichannel are linked by an active valve containing a cylindrical permanent magnet which controls the route of the fluid flow. Both cylindrical permanent magnets are covered with a ferrofluid which is held by their magnetic forces. The ferrofluid fills the gaps between the cylindrical magnets and channel walls to maintain sealing and provide lubrication.
The pump consists of a pumping cylinder, one active valve, and two nozzle/diffuser elements. The pumping cylinder has a rectangular cross-section and contains a magnetic piston displaced by the reciprocating motion of an external actuator. The cylindrical permanent magnet inside the valve is also activated by another external actuator. The two external actuators are permanent magnets which are driven by two motors.