Skip to main content
All calculators
[Natural Convection]
Free tool

Horizontal Plate, Heated Down — Isothermal

Average h and heat rate from an isothermal horizontal plate with its hot face down.

[FREE_TOOLS]
Built by our engineers
[EXPLORE]
More tools, always free
[FIELD_NOTE]

Orientation alone can halve your cooling: the same plate at the same ΔT convects about twice as well with its hot face up as with its hot face down.

[LIVE_TOOL]Results update as you type
[READ_THE_NUMBERS]

Results are indicative

Figures assume typical conditions and the stated method. For measured, guaranteed numbers on your plant, our engineers run site surveys, heat loss audits, and full process models.

[NEXT_STEP]

Send us the result — we'll tell you what it means for your plant.

[ABOUT_THIS_TOOL]

Horizontal Plate, Heated Face Down — Isothermal

Calculates the average convective heat transfer coefficient and total heat rate for a horizontal plate whose heated surface faces downward (equivalently, a cooled surface facing upward). Warm fluid is trapped beneath the plate and can only drain away at the edges, so this orientation convects much less than the heated-up case — reflected in the smaller leading coefficient (0.27 vs 0.54).

Characteristic Length

Lc=PA=2(L+W)LW

Rayleigh Number

Properties are evaluated at the film temperature Tf=(Ts+T)/2:

Ra=ν2gβ(TsT)Lc3Pr

Nusselt Number

Nu=0.27Ra1/4(105Ra1011)

Heat Transfer Coefficient and Heat Rate

h=LcNuk,Q=hA(TsT),A=LW

References

  • Hatfield, D. W. and Edwards, D. K., Int. J. Heat Mass Transfer, vol. 24, p. 1019, 1981.
  • Fujii, T. and Imura, H., Int. J. Heat Mass Transfer, vol. 15, p. 755, 1972.
  • Incropera, F. P. and DeWitt, D. P., Fundamentals of Heat and Mass Transfer.
[UPGRADE]

Need this tool, but deeper?

We build advanced versions on request — your fluids, your geometry, your standards, validated against plant data.

[REQUEST]

Missing a calculator?

Tell us what you're sizing or estimating — we build the calculators engineers actually ask for.

[FAQ]

Frequently asked questions

Average h and heat rate from an isothermal horizontal plate with its hot face down. Enter your inputs and press Calculate — the worked solution shows every step of the method with your numbers substituted in.

When there is no fan, pump or significant draught — enclosures, outdoor surfaces on still days, passive heat sinks. If there is any imposed flow, compare the two mechanisms: when Gr/Re² is well below one, forced convection dominates and the forced-convection calculators are the right tools.

No — it computes the convective part only. At typical natural-convection coefficients of 2–10 W/m²·K, radiation from a painted or oxidised surface is often the same order of magnitude, so total heat loss should add a radiative term from the Radiation calculators.