Overall Heat Transfer Coefficient Calculator

1/U = 1/h_i + R_f,i + R_wall + R_f,o + 1/h_o — combines convection, conduction, and fouling resistances in series for flat walls or cylindrical tubes.

Heat Transfer · HX Design

Inputs

Wall geometry:

Inner convection coefficient hi (W/(m²·K))

Outer convection coefficient ho (W/(m²·K))

Wall thermal conductivity k (W/(m·K))

Wall thickness t (mm)

Inner fouling resistance Rf,i (m²·K/W)

Outer fouling resistance Rf,o (m²·K/W)

Theory

Flat wall — resistances in series:

1/U = 1/h_i + R_f,i + t/k + R_f,o + 1/h_o

U = 1 / ΣR [W/(m²·K)]

Cylindrical tube — based on outer area:

1/U_o = 1/h_o + R_f,o + (r_o/k)·ln(r_o/r_i) + (r_o/r_i)·R_f,i + (r_o/r_i)/h_i

For thin-walled tubes (r_o/r_i ≈ 1), the cylindrical formula reduces to the flat-wall equation. The radius-ratio corrections become important for thick-walled tubes.

Typical U values for common HX types:

Service	U [W/(m²·K)]
Gas-to-gas	10 – 50
Gas-to-liquid	15 – 250
Liquid-to-liquid (light)	200 – 1000
Water-to-water	800 – 2500
Steam condenser (water-cooled)	1000 – 6000
Boiling water (reboiler)	500 – 2500
Oil cooler (water-cooled)	150 – 500

TEMA fouling resistance guidelines (m²·K/W):

Steam, treated water, light organics: 0.0001 – 0.0002

River water, hard water: 0.0002 – 0.0006

Crude oil (mild): 0.0003 – 0.0005

Fuel oil / heavy residuals: 0.0005 – 0.0009