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Module 5: Microfluidic Actuation Systems: Micropumps and Valves

  1. Q1(e). Which of the following is an example of an Active Microvalve? (i) Check Valve (ii) Piezoelectric Valve (iii) Flap Valve (iv) Ball Valve2025?m

    Module 5: Microfluidic Actuation Systems: Micropumps and Valves

    Which of the following is an example of an Active Microvalve?

    (i) Check Valve
    (ii) Piezoelectric Valve
    (iii) Flap Valve
    (iv) Ball Valve

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    Worked Solution

    Answer: (ii) Piezoelectric Valve

    A piezoelectric valve is an active microvalve because an external electrical signal produces mechanical deformation of the piezoelectric actuator, which opens or closes the fluid path.

  2. Q7(a). Classify micropumps. Explain the working principle and design of a Piezoelectric Micropump.20257m

    Module 5: Microfluidic Actuation Systems: Micropumps and Valves

    Classify micropumps. Explain the working principle and design of a Piezoelectric Micropump.

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    Worked Solution

    Micropump Classification and Piezoelectric Micropump

    Classification of micropumps

    Micropumps can broadly be classified as:

    1. Mechanical/non-dynamic displacement pumps: diaphragm, peristaltic and reciprocating types.
    2. Dynamic or non-mechanical pumps: electroosmotic, electrohydrodynamic, magnetohydrodynamic and other field-driven pumps.

    They may also be described as externally actuated or self-actuated, depending on the actuation mechanism.

    Piezoelectric micropump

    A piezoelectric micropump uses a piezoelectric actuator bonded to or coupled with a flexible diaphragm.

    Basic structure:
    Piezo actuator → flexible diaphragm → pump chamber → inlet valve → outlet valve

    Working

    1. Applying an alternating voltage causes the piezoelectric element to expand/contract or bend.
    2. This deflects the diaphragm and changes the chamber volume.
    3. During one stroke, chamber expansion lowers pressure and draws fluid through the inlet valve.
    4. During the opposite stroke, chamber compression raises pressure and pushes fluid through the outlet valve.
    5. Repeated electrical excitation produces continuous pumping.

    Advantages

    • Small size.
    • Fast response.
    • Low power requirements in suitable designs.
    • Precise flow control.
    • Easy electrical control.

    Applications include drug delivery, microfluidic transport, cooling and Lab-on-Chip systems.

  3. Q7(b). Differentiate between Active and Passive Microvalves. Explain the working of a Check Valve with a diagram.20257m

    Module 5: Microfluidic Actuation Systems: Micropumps and Valves

    Differentiate between Active and Passive Microvalves. Explain the working of a Check Valve with a diagram.

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    Worked Solution

    Active vs Passive Microvalves and Check Valve

    Feature Active Microvalve Passive Microvalve
    Actuation Requires external energy/control Operates mainly due to pressure/flow conditions
    Control Can be actively opened/closed Opening/closing depends on fluid conditions and geometry
    Examples Piezoelectric, pneumatic, thermal valves Check, flap, ball valves
    Complexity Generally higher Generally simpler

    Check valve working

    A check valve permits fluid flow primarily in one direction and prevents reverse flow.

    Simplified diagram:
    Inlet → [Valve seat / movable flap] → Outlet

    When inlet pressure exceeds the valve opening pressure, the movable element lifts away from the seat and fluid flows forward. When pressure reverses or falls, the element returns to the seat and blocks reverse flow.

    Advantages

    • Prevents backflow.
    • Simple construction.
    • Useful for directional fluid control in micropumps and microfluidic circuits.
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