Cheat sheet

Every key formula, in canonical order, at a glance. Each formula links to the lesson that derives it.

1 — The liquid state

Lennard-Jones 12-6 potential

U(r)=4ε[(σ0/r)12(σ0/r)6]U(r) = 4\varepsilon\left[(\sigma_0/r)^{12} - (\sigma_0/r)^{6}\right]

Equilibrium separation

req=21/6σ0r_\text{eq} = 2^{1/6}\sigma_0

Bulk modulus

K=VpVTK = -V\left.\dfrac{\partial p}{\partial V}\right\rvert_T

Linear compressive response

ΔVV=ΔpK\dfrac{\Delta V}{V} = -\dfrac{\Delta p}{K}

Born cohesive estimate

pcoh0.235Kp_\text{coh} \approx -0.235\,K

Spinodal (metastability limit)

pVT=0\left.\dfrac{\partial p}{\partial V}\right\rvert_T = 0

Elastic work to tension pp

Wp2V2KW \approx \dfrac{p^2 V}{2K}

2 — Nucleation

Bubble Gibbs free energy

ΔG(R)=43πR3(pvp)+4πR2σ\Delta G(R) = -\tfrac{4}{3}\pi R^3(p_v - p_\infty) + 4\pi R^2\sigma

Critical radius

R=2σΔpR^* = \dfrac{2\sigma}{\Delta p}

Barrier height

ΔG=16πσ33(Δp)2\Delta G^* = \dfrac{16\pi\sigma^3}{3(\Delta p)^2}

Homogeneous nucleation rate

J=J0exp ⁣(ΔGkBT)J = J_0\exp\!\left(-\dfrac{\Delta G^*}{k_B T}\right)

Young–Laplace at meniscus

pgp=2σRmp_g - p_\infty = \dfrac{2\sigma}{R_m}

Crevice stability condition

θ+β>90\theta + \beta > 90^\circ

Crevice critical tension

p,crit=pg2σrccos(θ+β90)p_{\infty,\text{crit}} = p_g - \dfrac{2\sigma}{r_c}\cos(\theta+\beta-90^\circ)

Nucleus size distribution

N(R)R4N(R) \sim R^{-4}

Free-microbubble equilibrium

pg+pvp=2σR0p_g + p_v - p_\infty = \dfrac{2\sigma}{R_0}

Cavitation susceptibility

f(p)=Rcrit(p)N(R)dRf(p_\infty) = \displaystyle\int_{R_\text{crit}(p_\infty)}^{\infty} N(R)\,dR

Henry’s law

cg=kHpg,gas-phasec_g = k_H\,p_{g,\text{gas-phase}}

Cavitation inception number

σi=ppv12ρU2=Cp,min\sigma_i = \dfrac{p_\infty^* - p_v}{\tfrac{1}{2}\rho U_\infty^2} = -C_{p,\text{min}}

3 — The Rayleigh–Plesset equation

Incompressible velocity field

u(r,t)=R2R˙r2u(r,t) = \dfrac{R^2\dot R}{r^2}

Rayleigh–Plesset equation

ρ[RR¨+32R˙2]=pBp2σR4μR˙R\rho\left[R\ddot R + \tfrac{3}{2}\dot R^2\right] = p_B - p_\infty - \dfrac{2\sigma}{R} - \dfrac{4\mu\dot R}{R}

Young–Laplace at wall

pBpliq,wall=2σRp_B - p_\text{liq,wall} = \dfrac{2\sigma}{R}

Bubble internal pressure

pB(t)=pv+pG,0(R0R)3κp_B(t) = p_v + p_{G,0}\left(\dfrac{R_0}{R}\right)^{3\kappa}

Clausius–Clapeyron

dpvdT=LρvT\dfrac{dp_v}{dT} = \dfrac{L\rho_v}{T}

Gas thermal time

τthR2αgas\tau_\text{th} \approx \dfrac{R^2}{\alpha_\text{gas}}

Static equilibrium relation

p=pv+KR32σRp_\infty = p_v + \dfrac{K}{R^3} - \dfrac{2\sigma}{R}

Blake radius

RB=3K2σR_B = \sqrt{\dfrac{3K}{2\sigma}}

Blake threshold pressure

p,crit=pv432σ33Kp_{\infty,\text{crit}} = p_v - \dfrac{4}{3}\sqrt{\dfrac{2\sigma^3}{3K}}

Minnaert frequency

ω0=1R03κpG,02σ/R0ρ\omega_0 = \dfrac{1}{R_0}\sqrt{\dfrac{3\kappa p_{G,0} - 2\sigma/R_0}{\rho}}

Rayleigh collapse velocity

R˙2=2p3ρ[(RmaxR)31]\dot R^2 = \dfrac{2p_\infty}{3\rho}\left[\left(\dfrac{R_{\max}}{R}\right)^3 - 1\right]

Rayleigh collapse time

τRayleigh0.915Rmaxρp\tau_\text{Rayleigh} \approx 0.915\,R_{\max}\sqrt{\dfrac{\rho}{p_\infty}}

Rayleigh growth velocity

R˙=2p3ρ\dot R_\infty = \sqrt{\dfrac{2\lvert p_\infty\rvert}{3\rho}}