#surface-tension

Surface-tension dimensionless numbers for droplets, sprays, atomization and two-phase flow as an API, computed locally and deterministically. The weber endpoint computes the Weber number We = ρ·v²·L/σ — the ratio of inertia to surface tension — and classifies the secondary-droplet-breakup regime (no breakup below We≈12, then bag, multimode, sheet-thinning and catastrophic breakup), the key number for atomization and spray formation. The capillary endpoint gives the Capillary number Ca = μ·v/σ, the ratio of viscous to surface-tension forces used in coating and microfluidics. The bond endpoint computes the Bond (Eötvös) number Bo = Δρ·g·L²/σ, gravity versus surface tension, which governs whether a drop stays spherical or is flattened by gravity. The ohnesorge endpoint gives the Ohnesorge number Oh = μ/√(ρ·σ·L) = √We/Re, viscosity versus inertia and surface tension, plus the inkjet printability number Z = 1/Oh whose sweet spot is roughly 1 < Z < 14. All quantities are SI: density kg/m³, velocity m/s, length m, surface tension N/m, viscosity Pa·s (water σ ≈ 0.0728 N/m at 20 °C). Everything is computed locally and deterministically, so it is instant and private. Ideal for microfluidics, inkjet, spray, atomization, coating, lab-on-a-chip and fluid-physics-education app developers, droplet-regime and printability tools, and research software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 4 endpoints. These are the dimensionless ratios; for capillary rise (Jurin) and Young-Laplace pressure use a capillary/surface-tension API.

api.oanor.com/weber-api

Surface-tension and small-scale fluid-physics maths as an API, computed locally and deterministically. The capillary-rise endpoint applies Jurin's law, h = 2γ·cosθ / (ρ·g·r), to give the height a liquid climbs (or, for a contact angle above 90° like mercury, is depressed) in a narrow tube from its surface tension, the tube radius, the liquid density and the contact angle — and can solve the surface tension back from a measured rise. The laplace-pressure endpoint computes the Young-Laplace excess pressure across a curved interface: a liquid droplet ΔP = 2γ/r, a soap bubble ΔP = 4γ/r (two surfaces) and a cylindrical jet ΔP = γ/r. The poiseuille endpoint applies the Hagen-Poiseuille law, Q = π·r⁴·ΔP / (8·μ·L), for laminar flow in a pipe, returning the volumetric flow rate, the average velocity and the peak centreline velocity (twice the average) from the radius, the pressure drop, the fluid viscosity and the length. Surface tension is in N/m, lengths in m, density in kg/m³, viscosity in Pa·s and pressures in Pa; water is γ ≈ 0.0728 N/m at 20 °C. Everything is computed locally and deterministically, so it is instant and private. Ideal for microfluidics, fluid-engineering, lab-on-a-chip, inkjet and coating app developers, capillary-action and wicking tools, and physics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is surface tension and capillarity; for incompressible Bernoulli flow use a Bernoulli API and for pipe friction a Darcy API.

api.oanor.com/capillary-api