Heat Transfer Coefficient Calculator — Convection Coefficient Converter
Convert between heat transfer coefficient units including W/m²·K, Btu/h·ft²·°F, cal/s·cm²·°C, and more. Essential for convection analysis, heat exchanger design, and thermal engineering. See also our Thermal Conductivity Calculator and Thermal Resistance Calculator.
How to Convert Heat Transfer Coefficient
- Enter the heat transfer coefficient value to convert.
- Select the source unit from the dropdown.
- Click Calculate to see the value in all other units.
- Higher coefficient means better convective heat transfer.
Heat Transfer Coefficient Formula
Newton's Law of Cooling:
Q = h × A × ΔT
Where:
Q = Heat transfer rate (W)
h = Heat transfer coefficient (W/m²·K)
A = Surface area (m²)
ΔT = Temperature difference (K)
Thermal resistance for convection:
R = 1 / (h × A)
Nusselt number relationship:
Nu = h × L / k
Where:
Nu = Nusselt number (dimensionless)
L = Characteristic length (m)
k = Thermal conductivity of fluid (W/m·K)
Overall heat transfer coefficient:
1/U = 1/h₁ + R_wall + 1/h₂Example Calculation
Problem: Air convection has h = 25 W/m²·K. Convert to Btu/h·ft²·°F.
Given: h = 25 W/m²·K
Solution: h = 25 ÷ 5.678 = 4.40 Btu/h·ft²·°F
Answer: The heat transfer coefficient is 4.40 Btu/h·ft²·°F.
Typical Heat Transfer Coefficients
| Heat Transfer Mode | h (W/m²·K) | h (Btu/h·ft²·°F) |
|---|---|---|
| Free convection - air | 5-25 | 0.9-4.4 |
| Forced convection - air | 25-250 | 4.4-44 |
| Free convection - water | 500-1000 | 88-176 |
| Forced convection - water | 1000-15000 | 176-2640 |
| Boiling water | 3000-100000 | 528-17600 |
| Condensing steam | 5000-100000 | 880-17600 |
| Liquid metals | 5000-40000 | 880-7040 |
| Supercritical fluids | 1000-8000 | 176-1408 |
Technical Details
The heat transfer coefficient quantifies convective heat transfer between a surface and fluid. It depends on fluid properties (viscosity, thermal conductivity, density), flow conditions (velocity, turbulence), surface geometry, and temperature difference. Higher coefficients indicate more effective heat transfer. The coefficient is used in Newton's law of cooling and is fundamental to heat exchanger design. It's related to the Nusselt number, which characterizes the enhancement of heat transfer by convection compared to conduction. Values vary widely depending on the heat transfer mechanism and operating conditions.
Frequently Asked Questions
What is the heat transfer coefficient?
The heat transfer coefficient quantifies how effectively heat transfers between a surface and fluid by convection. It's the proportionality constant in Newton's law of cooling.
What factors affect the heat transfer coefficient?
Fluid properties (viscosity, thermal conductivity, density), flow velocity, surface roughness, geometry, temperature difference, and whether flow is laminar or turbulent all affect the coefficient.
Why is boiling heat transfer so effective?
Boiling involves phase change, which transfers large amounts of latent heat. Bubble formation and departure create intense mixing and high heat transfer coefficients (3,000-100,000 W/m²·K).
How is the overall heat transfer coefficient calculated?
For composite systems: 1/U = 1/h₁ + R_wall + 1/h₂, where U is overall coefficient, h₁ and h₂ are convection coefficients, and R_wall is wall thermal resistance.
What's the difference between h and k?
h (heat transfer coefficient) describes convection between surface and fluid. k (thermal conductivity) describes conduction within materials. Both have different units and physical meanings.