Concepts

A searchable glossary of the ideas behind the tools. Each concept links to the calculator that applies it once that tool ships. This is the starting set — the glossary grows alongside the curriculum.

23 concepts

Bond number (Bo): The ratio of gravitational to interfacial forces. At the microscale Bo is tiny, so surface tension dominates gravity.
Capillary number (Ca): The ratio of viscous to interfacial forces, Ca = μv/γ. It governs droplet formation regimes in two-phase microfluidics.
Diffusion: Spreading of molecules driven by concentration gradients. Mixing time scales as t ≈ L²/2D, so it is slow across wide channels.
Droplet microfluidics: Generating and manipulating discrete droplets in an immiscible carrier, each a tiny isolated reactor — the basis of single-cell workflows.
Flow-focusing: A droplet generator where a central stream is pinched by two side streams through a narrow orifice, giving fine control of droplet size.
Hydraulic diameter (Dₕ): An effective diameter for non-circular channels, Dₕ = 4A/P (for a rectangle, 2wh/(w+h)). It lets circular-pipe formulas apply to other shapes.
Hydraulic resistance (R): A channel's resistance to flow, R = ΔP/Q. Channels combine in series and parallel exactly like electrical resistors.
Hydraulic–electrical analogy: A modelling shortcut mapping pressure↔voltage, flow rate↔current, and hydraulic resistance↔resistance, so a chip can be analysed as a circuit.
Lab-on-a-chip: A device that integrates one or more laboratory functions onto a single microfluidic chip.
Laminar flow: Smooth, orderly flow in parallel layers with no cross-stream mixing. It is the norm at the microscale, where viscous forces dominate inertia.
Microfluidics: The science and engineering of manipulating tiny volumes of fluid in micrometre-scale channels.
Newtonian fluid: A fluid whose viscosity is constant regardless of shear rate (e.g. water). Most microfluidics formulas assume Newtonian behaviour.
PDMS: Polydimethylsiloxane — the workhorse elastomer for soft lithography: transparent, gas-permeable, and easy to mould and bond.
Péclet number (Pe): The ratio of advective to diffusive transport, Pe = vL/D. High Pe means flow carries species faster than diffusion can mix them.
Poisson loading: Cell encapsulation follows Poisson statistics, P(k)=λᵏe⁻λ/k!. To keep doublets rare, most droplets must be empty (low λ).
Pressure drop (ΔP): The pressure difference needed to drive a flow through a channel. For laminar flow it is linear in flow rate (Hagen–Poiseuille).
Reynolds number (Re): The dimensionless ratio of inertial to viscous forces, Re = ρvDₕ/μ. Low Re (≪2000) means laminar flow; microchannels almost always sit here.
Soft lithography: Casting an elastomer (usually PDMS) against a micro-patterned mould to replicate channels — the most common rapid-prototyping route.
Stokes–Einstein relation: Estimates a particle's diffusion coefficient, D = k_BT/(6πμr), linking diffusion to temperature, viscosity, and particle size.
Surface tension (γ): The energy per unit area of a liquid interface. It dominates microscale behaviour, driving capillary filling and droplet formation.
T-junction: A droplet generator where the dispersed phase meets the continuous phase at a right angle; droplet size is set by the flow-rate ratio.
Weber number (We): The ratio of inertial to interfacial forces. It helps predict droplet breakup and jetting behaviour.
Wetting & contact angle: How a liquid spreads on a surface, quantified by the contact angle. It sets whether channels fill spontaneously and how droplets behave.