Forced Convection Heat Transfer

Q = h × A × ΔT

Quick answer

This calculator solves Q = h × A × ΔT for Heat Transfer Rate. With Convection Coefficient 0.5 W/(m²·°C), Surface Area 100 cm², Temperature Difference 50 °C, the result is 0.25 W. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Heat Transfer Rate (W)
—

Formula

Q = h × A × ΔT

Description

Newton's law of cooling describes convective heat transfer from a surface to a moving fluid (air). The convection coefficient h depends on the fluid velocity, fluid properties, and surface geometry. Forced convection (using fans) dramatically increases h compared to natural convection, enabling much higher power dissipation from the same heatsink. This formula is fundamental to heatsink design, enclosure thermal analysis, and cooling system sizing for electronics.

Variables

  • Q — Heat transfer rate (W)
  • h — Convection heat transfer coefficient (W/(m²·°C))
  • A — Surface area exposed to airflow (m²)
  • ΔT — Temperature difference between surface and ambient air (°C)

Practical Notes

Typical h values: natural convection in air 5-25 W/(m²·°C), forced convection in air 25-250 W/(m²·°C), liquid cooling 100-20000 W/(m²·°C). Doubling airflow velocity increases h by roughly 40-50%. Fin spacing must account for boundary layer thickness to avoid diminished returns from closely spaced fins.

Symbols and units

Symbol Meaning Default unit Accepted units
Q Heat Transfer Rate W µW, mW, W, kW
h Convection Coefficient — W/(m²·°C)
A Surface Area m² mm², cm², m²
dT Temperature Difference °C °C

Step by step

  1. 1. What you know: Convection Coefficient 0.5 W/(m²·°C), Surface Area 100 cm², Temperature Difference 50 °C
  2. 2. The relation: Q = h × A × ΔT
  3. 3. Substitute: h = 0.5 W/(m²·°C), A = 100 cm², dT = 50 °C
  4. 4. Result: Heat Transfer Rate = 0.25 W

Worked examples

Minimum range

Given: Convection Coefficient 0.025 W/(m²·°C), Surface Area 10 mm², Temperature Difference 2.5 °C

Result: Heat Transfer Rate = 0.625 µW

Low range

Given: Convection Coefficient 0.25 W/(m²·°C), Surface Area 1 cm², Temperature Difference 25 °C

Result: Heat Transfer Rate = 0.625 mW

Typical

Given: Convection Coefficient 0.5 W/(m²·°C), Surface Area 100 cm², Temperature Difference 50 °C

Result: Heat Transfer Rate = 0.25 W

High range

Given: Convection Coefficient 0.8 W/(m²·°C), Surface Area 1 m², Temperature Difference 85 °C

Result: Heat Transfer Rate = 68 W

Maximum range

Given: Convection Coefficient 8 W/(m²·°C), Surface Area 10 m², Temperature Difference 850 °C

Result: Heat Transfer Rate = 68 kW

Solving for each variable

Solve for Heat Transfer Rate

Convection Coefficient 0.025 W/(m²·°C), Surface Area 10 mm², Temperature Difference 2.5 °C → 0.625 µW

Solve for Convection Coefficient

Heat Transfer Rate 10 mW, Surface Area 10 mm², Temperature Difference 2.5 °C → 400 W/(m²·°C)

Solve for Surface Area

Heat Transfer Rate 10 mW, Convection Coefficient 0.025 W/(m²·°C), Temperature Difference 2.5 °C → 0.16 m²

Solve for Temperature Difference

Heat Transfer Rate 10 mW, Convection Coefficient 0.025 W/(m²·°C), Surface Area 10 mm² → 40000 °C

How Heat Transfer Rate changes with Convection Coefficient

Convection Coefficient (input) Heat Transfer Rate (result)
0.05 W/(m²·°C) 25 mW
0.125 W/(m²·°C) 62.5 mW
0.25 W/(m²·°C) 125 mW
0.375 W/(m²·°C) 0.1875 W
0.5 W/(m²·°C) 0.25 W
0.75 W/(m²·°C) 0.375 W
1 W/(m²·°C) 0.5 W
2 W/(m²·°C) 1 W
3.5 W/(m²·°C) 1.75 W
5 W/(m²·°C) 2.5 W

The same result in other units

Unit Value
µW 250000
mW 250
W 0.25
kW 0.00025

Embed this calculator

Paste this into any page. It keeps working when this page updates, and credits the source.

<iframe src="https://vbatpower.com/embed/forced-convection/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="Forced Convection Heat Transfer"></iframe>
<p><a href="https://vbatpower.com/formulas/forced-convection/">Forced Convection Heat Transfer</a> Calculator by vbatpower.com</p>

Frequently asked questions

How do you calculate Forced Convection Heat Transfer?

Use Q = h × A × ΔT. With Convection Coefficient 0.5 W/(m²·°C), Surface Area 100 cm², Temperature Difference 50 °C, Heat Transfer Rate works out to 0.25 W.

How do you calculate forced convection heat transfer coefficient?

Rearrange for Heat Transfer Rate: with Convection Coefficient 0.25 W/(m²·°C), Surface Area 1 cm², Temperature Difference 25 °C, Heat Transfer Rate is 0.625 mW.

What is the formula for Forced Convection Heat Transfer?

The formula is Q = h × A × ΔT. Newton's law of cooling describes convective heat transfer from a surface to a moving fluid (air).

How do you find Convection Coefficient when you know the other values?

Rearrange for Convection Coefficient: with Heat Transfer Rate 10 mW, Surface Area 10 mm², Temperature Difference 2.5 °C, Convection Coefficient is 400 W/(m²·°C).

How do you find Surface Area when you know the other values?

Rearrange for Surface Area: with Heat Transfer Rate 10 mW, Convection Coefficient 0.025 W/(m²·°C), Temperature Difference 2.5 °C, Surface Area is 0.16 m².

What units does Forced Convection Heat Transfer use?

Heat Transfer Rate is shown in µW, mW, W, kW. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Thermal formulas →
Junction Temperature Full Thermal Chain Required Heatsink Maximum Power (Junction to Case) Thermal Time Constant Forced Convection Heat Transfer Power Derating (Temperature) Natural Convection Thermal Resistance

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App