Immersed coil heat transfer
Overall heat transfer coefficient for a coil or pipe submerged in a tank, with free convection on the tank side, forced convection inside the coil, and the effect of splitting into parallel pipes.
Inputs
Results
Heat Exchanger Excel kit
Shell and tube performance, fouling, LMTD and NTU rating, condenser and reboiler performance, plate exchanger — with print-ready reports, any units and visible formulas.
Join PlantCalcKit — free
Be first to hear about new calculators, Excel tools and field guides — one short email when something new is ready. The calculators stay free with or without an account.
By joining you agree to our privacy policy. Unsubscribe or delete your details any time.
You are a PlantCalcKit member
Signed in as . We will email you when new tools and guides are ready.
How this calculator works
A coil or bundle of pipes submerged in a tank is a simple way to heat or cool a batch. The overall U depends on three resistances in series: the forced-convection film inside the coil, the pipe wall conduction, and the natural-convection film on the tank side. The tank side often controls because free convection is slower than forced flow, but a laminar-flow coil side can be worse.
The tank-side HTC uses the Churchill–Chu correlation for free convection around a horizontal cylinder, which covers the full Rayleigh-number range from laminar to turbulent. The coil side uses Dittus–Boelter (turbulent) or Sieder–Tate entry-length (laminar). Splitting one long coil into N parallel shorter pipes divides the flow: the velocity and Reynolds number drop, so the coil-side HTC falls, but the pressure drop falls much faster (roughly as 1/N²). The comparison shows the trade-off.
Limits: the Churchill–Chu correlation assumes the tank is large enough that the coil does not block the convection currents (coil OD small compared with the tank diameter). For tightly wound coils, multiply the tube-side h by approximately 1 + 3.5×(d/Dcoil) for the Dean-number effect — not applied here. Fouling resistances are not included: add them to 1/U if needed. References: Incropera & DeWitt, Fundamentals of Heat and Mass Transfer; Kern, Process Heat Transfer; Churchill & Chu, Int. J. Heat Mass Transfer, 18, 1049 (1975).