Biot Number Calculator
Calculate the Biot number for transient heat conduction from thermal conductivity, convection coefficient, and characteristic length.
Biot Number in Heat Transfer
The Biot number compares internal conduction resistance to external convection resistance. It tells you whether a solid can be treated as having uniform temperature during transient heating or cooling.
Formula
$$Bi = \frac{h L}{k}$$Where \(h\) is the convection coefficient (W/m²·K), \(L\) is a characteristic length (m), and \(k\) is thermal conductivity (W/m·K).
Interpretation
- Bi < 0.1: Lumped capacitance model is valid; internal gradients are small.
- Bi ≥ 0.1: Temperature varies inside the body; spatial analysis is required.
Frequently Asked Questions
What is a characteristic length?
For a slab, use half-thickness. For a sphere, use radius. For a long cylinder, use radius. It is the distance heat must diffuse from the center to the surface.
Why is Bi < 0.1 the lumped threshold?
When Bi is small, convection dominates and the interior stays nearly uniform. The 0.1 criterion is a common engineering rule of thumb for lumped analysis.
How is Bi related to Nusselt number?
During external flow, Nu and Bi both involve convection at a surface, but Bi compares internal conduction to convection while Nu compares convection to conduction in the fluid.
What units must I use?
Use SI units: h in W/m²·K, L in meters, k in W/m·K. Bi is dimensionless.
Related Tools
JSON to One Line
Dice Average Calculator
Density to Mass Calculator
FEUrea Calculator
Lumen To Candela Calculator
Change Image Base Color
Octal to IP Converter
Random Fractions Generator
HTML Emphasize Text Generator
Lever Calculator
XML Diff
Minutes to Seconds Converter
Lightning Distance Calculator
State Tax Calculator
Heaviness of Smoking Index Calculator
Particle Acceleration in Electric Field Calculator
Ideal Gas Pressure Calculator
Moon Sign Calculator
Text to CSV Converter
Ratios of Directed Line Segments Calculator