Surface Convection Heat Transfer

Evaluate convective heat flow and thermal resistance using a supplied film coefficient.

How this calculation works

Use this relation when the convection coefficient is already known or supplied from another analysis. Enter that coefficient in W/(m²·K), the exposed surface area, the surface temperature and the surrounding bulk-fluid temperature. Their temperature difference sets the heat flux through Newton's cooling relation. The area then converts flux into total duty, while the reciprocal of coefficient times area gives the film's thermal resistance in K/W. A positive duty denotes heat leaving the surface for the fluid; a negative duty denotes heat entering it. Equal temperatures give zero net convection even though the film resistance remains finite. The calculation assumes a uniform coefficient and surface temperature and does not estimate the coefficient from geometry or flow, or add conduction and radiation.

Inputs and units

Convection coefficient (W/(m²·K))
Exposed area (m²)
Surface temperature (°C): Must be above absolute zero
Bulk fluid temperature (°C): Must be above absolute zero

Method and formula

q = h(Tsurface − Tfluid); Q = qA/1000 kW; R = 1/(hA).

Worked example

Example inputs

Convection coefficient: 10 W/(m²·K)
Exposed area: 5 m²
Surface temperature: 60 °C
Bulk fluid temperature: 20 °C

Calculation steps

Find the surface-to-fluid temperature difference: 60 − 20 = 40 K.
Calculate heat flux: q = 10 × 40 = 400 W/m².
Calculate total convection duty: Q = 400 × 5/1000 = 2 kW, from the surface to the fluid.
Calculate film resistance: R = 1/(10 × 5) = 0.02 K/W.

Example results

Signed surface-to-fluid flux: 400 W/m²
Signed convection duty: 2 kW
Convection resistance: 0.02 K/W

Assumptions

Uniform supplied film coefficient and surface temperature

Limitations

Does not determine h or include radiation or conduction

Sources

U.S. DOE Fundamentals Handbook: Heat Transfer, Volume 2: HT-02 pp. 18–19, Newton cooling relation