MICRO PUMPS, VALVES AND MIXERS Susan Beatty Dave Ni Kunal Thaker

OUTLINE Micro pumps Micro valves Micro mixers Keypoints (conclusion)

MICROPUMPS

GENERAL TYPES OF MICROPUMPS BUBBLE PUMPS DIFUSSER PUMPS MEMBRANE PUMPS (most common) ROTARY PUMPS ELECTROHYDRODYNAMIC PUMPS ELECTROOSMOTIC/ ELECTROPHORETIC PUMPS ULTRASONIC PUMPS OPTICAL PUMPS

BUBBLE/DIFUSSER PUMP The formation and collapse of a bubble in the liquid is used to drive the flow of the liquid Allows for a valve-less diffuser design Greatly enhances mixing of the constituent phases Flow rate in the range of 4-5 μL/sec for Hz

MEMBRANE PUMPS Method of displacing the membrane –Magnetically –Electrostatically –With a piezoelectric –Thermally (SMA and thermopneumatically) Sensitive to blockage by particulates in the fluid Flow rate in the range of μL/sec

ROTARY PUMPS Very rare and not commonly researched Extremely complicated fabrication process High susceptibility to failure Very precise control of the fluid flow and direction Good for transporting high impurity liquids

ELECTROHYDRODYNAMIC PUMPS Uses an applied electric field on the fluid to be pumped to induce charge and also to electrostatically move the induced charges Not suitable for the delivery of most biological fluids, as a very specific fluid conductivity is required Extremely high voltages are required to move the fluids (~700volts) Has an equivalent magnetohydrodynamic pump

ELECTROOSMOTIC/ ELECTROPHORETIC PUMPS Electrophoretic pumping relies on the presence of ions in the fluid –The ions are manipulated through the application of an electric field and flow is induced Electroosmotic flow relies on the presence of ions on the surfaces of the fluidic channel Example- between glass and organic fluids –An applied electric field allows for the movement of the bulk fluid Flow rate on the order of 15 μL/sec No moving parts

ULTRASONIC/OPTICAL PUMPS Ultrasonic pumps use piezoelectric networks to actuate on a cyclical basis to produce predictable fluid motion –Most applicable to mixing, not pumping In optical pumps, heat is introduced to the fluid by way of optical absorption –Gradients in the fluids heat result in viscosity and surface tension gradients, which in turn lead to fluid flow by way of the thermocapillary effect –Most applicable to mixing, not pumping

VALVES

VALVE CLASSIFICATION Non-moving valve Passive valves Actuated valves

NON_MOVING VALVES Diffuser Valve –Provides directional resistance

PASSIVE VALVES Cantilever Disc Membrane Shoji, Journal of micromechanics and microengineering 1994

PASSIVE VALVES (cont) Piston Gas controlled Quake, Science 2000

ACTIVE VALVES Valve types based on actuation –Electromagnetic –Piezoelectric –Pneumatic –Shape memory alloy –Thermopneumatic –Chemical

MICROMIXERS Definition: The controlled micro- mixing of two or more fluids

GENERAL TYPES OF MIXERS Laminating Mixers Plume Mixers Active Mixers Micrograph of Silicon-glass -- Copyright, Meinhart, Bayt

LAMINATING MIXERS At the microscopic scale the use of laminating mixers is try to laminate two or more fluids together to increase the contact area and enhance diffusion (0.5 to 12 l/min) Two fluids entering the inlet ports laminate at the first horizontal junction, producing two side-by-side fluid streams. Successive vertical separation and horizontal reuniting of fluid streams increases the number of laminates with each stage and, thus, the contact area between the two fluids.

PLUME MIXERS Takes advantage of the behavior of a fluid leaving a narrow nozzle (15 m) Generates a small plume which increases the contact area of two liquids Homogeneous mixing in 1.2 secs in a 0.5 l volume at a 45 l/min flow rate

ACTIVE MIXERS The use of external energy –Ultrasonic traveling wave pumps moving fluids in a circulating path –Bubble pumps – two large pumps used to generate push & pull forces

KEY POINTS Membrane pumps are the most common type of micro pumping device currently fabricated An attempt is being made to phase out check valves and other mechanisms that slow down the frequency response of the pumping system. –Drive toward diffuser valves More flow loss, but increase in frequency. Pumps with non-moving parts are preferred due to higher reliability, etc. Bubble, electroosmotic, and electrophoretic pumps tend to be the direction in bio-micro fluidics applications.

KEY POINTS (cont) Passive valves are commonly used because they are easier to fabricate and are smaller that actuated valves The easier and cheaper the valve is to fabricate the more likely it will be used Chemically reactive valves are ideal for bio-microfluidics because they are easy to make, they are small and they behave as an active valve

KEY POINTS (cont) Laminating Mixers – to laminate fluids together Plume Mixers – plume is generated to increase contact area of two liquids Active Mixers – uses external energy to mix fluids