⚗ ChemE Tools

What The Flux

The calculator site your professors wish they built. Free tools for heat transfer, mass balance, fluids, thermo, and reaction engineering — built by a ChemE student surviving it with you.

Mass & Energy Balance
⚖
Mass Balance
Steady-state single-component balance
$$\dot{m}_{accum} = \dot{m}_{in} - \dot{m}_{out}$$
Open calculator →
🧪
Mixing Concentration
Outlet concentration for two streams
$$C_{out} = \dfrac{F_1 C_1 + F_2 C_2}{F_1 + F_2}$$
Open calculator →
⚡
Open System Energy Balance
Steady-flow heat duty
$$\dot{Q} = \dot{m} C_p \Delta T$$
Open calculator →
Fluid Mechanics
🌊
Reynolds Number
Determine flow regime
$$Re = \dfrac{\rho v D}{\mu}$$
Open calculator →
💧
Pipe Velocity from Flow Rate
Average velocity from Q and diameter
$$v = \dfrac{4Q}{\pi D^2}$$
Open calculator →
🌀
Bernoulli Equation
Pressure at point 2 from point 1 conditions
$$P_2 = P_1 + \tfrac{1}{2}\rho(v_1^2-v_2^2)+\rho g(z_1-z_2)$$
Open calculator →
📉
Darcy–Weisbach ΔP
Frictional pressure drop in a pipe
$$\Delta P = f_D \dfrac{L}{D} \dfrac{\rho v^2}{2}$$
Open calculator →
🔩
Friction Factor (Swamee-Jain)
Explicit turbulent friction factor
$$f_D = \dfrac{0.25}{\left[\log_{10}\!\left(\dfrac{\varepsilon/D}{3.7}+\dfrac{5.74}{Re^{0.9}}\right)\right]^2}$$
Open calculator →
Thermodynamics
💨
Ideal Gas Law
Solve for pressure
$$P = \dfrac{nRT}{V}$$R = 8.314 J/mol·K
Open calculator →
🔵
Van der Waals EOS
Real gas pressure from T and V
$$P = \dfrac{nRT}{V-nb} - a\dfrac{n^2}{V^2}$$
Open calculator →
🫧
Antoine Vapor Pressure
Saturation pressure from temperature
$$\log_{10} P^{sat} = A - \dfrac{B}{C+T}$$
Open calculator →
💧
Clausius-Clapeyron
Vapor pressure at a new temperature
$$\ln\!\frac{P_2}{P_1}=-\frac{\Delta H_{vap}}{R}\!\left(\frac{1}{T_2}-\frac{1}{T_1}\right)$$
Open calculator →
⚙
Carnot Efficiency
Maximum thermal efficiency
$$\eta_{Carnot} = 1 - \dfrac{T_C}{T_H}$$
Open calculator →
❄
COP — Refrigerator / Heat Pump
Coefficient of performance
$$COP_{ref}=\dfrac{T_C}{T_H-T_C}\quad COP_{hp}=\dfrac{T_H}{T_H-T_C}$$
Open calculator →
🔧
Isentropic Compression/Expansion
Outlet temperature for adiabatic process
$$\frac{T_2}{T_1}=\left(\frac{P_2}{P_1}\right)^{\!\frac{\gamma-1}{\gamma}}$$
Open calculator →
Mass Transfer
💧
Fick's Law
Molar flux from concentration gradient
$$J_A=D_{AB}\dfrac{C_{A1}-C_{A2}}{\Delta z}$$
Open calculator →
🔀
Convective Mass Transfer
Flux from mass transfer coefficient k_c
$$N_A=k_c\left(C_{A,s}-C_{A,\infty}\right)$$
Open calculator →
〽
Sherwood Number → k_c
Mass transfer coefficient from Sh
$$k_c=\dfrac{Sh\cdot D_{AB}}{L_c}$$
Open calculator →
📊
Schmidt Number
Ratio of momentum to mass diffusivity
$$Sc=\dfrac{\mu}{\rho D_{AB}}$$
Open calculator →
Unit Converter
🌡 Temperature
→
—
→
—
→
—
⚡ Pressure
→
—
→
—
→
—
→
—
💧 Volumetric Flow
→
—
→
—
⚖ Mass & Density
→
—
→
—
⚡ Energy & Power
→
—
→
—
→
—
📐 Viscosity
→
—
→
—
Formula Reference

Heat Transfer

$Q=mC_p\Delta T$
Sensible heat
$Q=UA\Delta T_{lm}$
HX duty
$q=kA\Delta T/L$
Fourier conduction
$q=hA(T_s-T_\infty)$
Newton's cooling
$h=Nu\cdot k/L_c$
Nusselt → h
$Pr=\mu C_p/k$
Prandtl number
$q=\varepsilon\sigma A(T_1^4-T_2^4)$
Radiation
$Bi=hL_c/k$
Biot number
$T(t)=T_\infty+(T_i-T_\infty)e^{-t/\tau}$
Lumped cap.

Fluid Mechanics

$Re=\rho vD/\mu$
Reynolds number
$v=4Q/(\pi D^2)$
Pipe velocity
$\Delta P=f_D(L/D)\rho v^2/2$
Darcy-Weisbach
$f_D=64/Re$
Laminar friction
$P_2=P_1+\tfrac{1}{2}\rho(v_1^2-v_2^2)+\rho g\Delta z$
Bernoulli

Thermodynamics

$PV=nRT$
Ideal gas
$P=nRT/(V-nb)-an^2/V^2$
van der Waals
$\log P^*=A-B/(C+T)$
Antoine
$\eta=1-T_C/T_H$
Carnot efficiency
$T_2/T_1=(P_2/P_1)^{(\gamma-1)/\gamma}$
Isentropic

Reaction Engineering

$X=(F_{A0}-F_A)/F_{A0}$
Conversion
$V=F_{A0}X/(-r_A)$
CSTR design eq.
$V=(F_{A0}/kC_{A0})\ln(1/(1-X))$
PFR 1st order
$k_2=k_1e^{-E_a/R(1/T_2-1/T_1)}$
Arrhenius
$C_A=C_{A0}-kt$
0th order batch
$C_A=C_{A0}e^{-kt}$
1st order batch
$1/C_A=1/C_{A0}+kt$
2nd order batch
$Da=\tau k$
Damköhler

Mass Transfer

$J_A=D_{AB}(C_{A1}-C_{A2})/\Delta z$
Fick's law
$N_A=k_c(C_{A,s}-C_{A,\infty})$
Convective flux
$k_c=Sh\cdot D_{AB}/L_c$
Sherwood → k_c
$Sc=\mu/(\rho D_{AB})$
Schmidt number

Dimensionless Numbers

$Re=\rho vL/\mu$
Reynolds
$Nu=hL/k$
Nusselt
$Pr=\mu C_p/k$
Prandtl
$Bi=hL_c/k$
Biot
$Sh=k_cL/D_{AB}$
Sherwood
$Sc=\mu/(\rho D_{AB})$
Schmidt
$Le=Sc/Pr=\alpha/D_{AB}$
Lewis
$Da=\tau k$
Damköhler
👤 About

Why I Built What The Flux

I'm a ChemE senior at UConn. Throughout four years of general education courses up to the higher-echelon of chemical engineering coursework I've noticed a disparity in the quality of teaching. I always rely heavily on my ability to gather information and learn through the use of outside resources and independent study, and while some courses had incredible professors with helpful resources, there were many lacking the capability or interest to provide material beyond textbook definitions.

While I've excelled in my classes, things never felt easy or stepwise in the way I learned my coursework. I've wasted hours hunting for the right explanation, the right formula, the right example — often perusing numerous online forums and consulting AI interpretations. While there are slivers that can be helpful, I hope to give every student resources that can inspire learning, not simply information.

What The Flux is what I wish existed when I started. Fast calculators, clean equations, and the context and derivations that actually make them make sense. Built by someone who just went through it, not someone who taught it thirty years ago. I hope to let my resources evolve with the demand and topic concentrations of my audience. If it saves you an hour before your next exam, it did its job.

© 2026 What The Flux
HomeAboutContactPrivacyTerms