L5 - Microfluidics Flashcards
(14 cards)
What is microfluidics?
MEMS for fluids. Provides the means to deliver small quantities of fluid to MEMS devices.
Allows us to seperate, move, position and mix small samples.
List the areas that microfluidic devices could be used in?
Medical (faster results, portable equipment, new possibilities)
Industrial (Food safety, sampling)
Environmental (Water and soil sampling)
Define viscosity
A fluids resistance to flow
High viscosity = high resistance (thick)
Define surface tension
Surface tension is defined as the tendency of a liquid’s surface to resist external forces and minimize its surface area.
What is the Reynolds number?
What is its significance in MEMS?
The Reynolds number is a dimensionless quantity in fluid mechanics that represents the ratio of inertial forces to viscous forces within a fluid. It is used to predict flow patterns in different fluid flow situations, indicating whether the flow is laminar, transitional, or turbulent.
Re < 2000 leads to laminar flow.
At high velosity flow is unstable (turbulent). In microfluidics velocity is low (scales with L) and the considered length is small so flow in microfluidics is almost always laminar unless we create turbulance.
What is laminar flow?
Laminar flow is a type of fluid motion characterized by smooth, parallel layers of fluid that move without significant mixing or turbulence.
What is diffusion?
Diffusion is the process by which particles of one substance spread out through the particles of another substance. Diffusion is how smells spread out through the air and how concentrated liquids spread out when placed in water.
True of false forces such as Gravity, momentum and buoyancy can largely be ignored in microfluidics?
True
They have very little effect at this scale
As proven by the Bond Number (The ratio of the gravity force to the capillary force)
What is surface energy?
Surface energy measures the excess energy at a material’s surface compared to its bulk. Molecules at the surface of a material are in a higher energy state and experience therefore net inward forces that tend to minimize the surface area. These forces are balanced by the resistance of the material to deformation leading to a state of tension similar to a stretched elastic band.
This results in surface tension in liquids, driving phenomena like droplet formation where the liquid assumes a spherical shape to minimize surface area.
Tight droplet = high surface energy
What forces are in play in a soap bubble?
Surface tension and air pressure.
The two are in equilibrium for the bubble to be stable.
What is fluidic resistance?
Fluidic Resistance opposes Flow.
∆P = Q⋅R
∆P Pressure Difference
Q Flow
Analogous to V = IR
What is fluidic capacitance?
The volume of fluid in a channel can change just because of a change in pressure: this is either due to fluid compressibility or channel elasticity.
How can membrains help stabilise flow in a channel?
By acting as capacitors.
A channel with a membrain will bulge under normal flow. If pressure drops the membrain will flex inwards discharging its accumulated fluid maintaining flow.
What is Fluidic rectification?
Resistance to flow in one direction
