Biot Number Using Heat Transfer Coefficient Calculator

Biot Number Formula:

\[ Bi = \frac{h \times \delta}{k} \]

Heat Transfer Coefficient (h):

W/m²·K

Thickness of Wall (δ):

Thermal Conductivity (k):

W/m·K

Biot Number (Bi):

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1. What is the Biot Number?

The Biot Number is a dimensionless quantity that represents the ratio of internal conduction resistance to the surface convection resistance. It is used in heat transfer analysis to determine if a body can be treated with the lumped capacitance method.

2. How Does the Calculator Work?

The calculator uses the Biot Number formula:

\[ Bi = \frac{h \times \delta}{k} \]

Where:

\( h \) — Heat Transfer Coefficient (W/m²·K)
\( \delta \) — Thickness of Wall (m)
\( k \) — Thermal Conductivity (W/m·K)

Explanation: The formula calculates the ratio of convective heat transfer at the surface to conductive heat transfer within the material.

3. Importance of Biot Number Calculation

Details: The Biot Number is crucial in heat transfer analysis. When Bi < 0.1, the temperature gradient within the body is negligible, and the lumped capacitance method can be applied. For higher values, spatial temperature variations must be considered.

4. Using the Calculator

Tips: Enter heat transfer coefficient in W/m²·K, thickness in meters, and thermal conductivity in W/m·K. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What does a high Biot Number indicate?
A: A high Biot Number (Bi > 0.1) indicates that internal conduction resistance is significant compared to surface convection resistance, meaning temperature gradients within the material cannot be neglected.

Q2: What does a low Biot Number indicate?
A: A low Biot Number (Bi < 0.1) indicates that internal conduction resistance is negligible compared to surface convection resistance, allowing the use of lumped capacitance method.

Q3: What are typical values for heat transfer coefficients?
A: Heat transfer coefficients vary widely: natural convection of air (5-25 W/m²·K), forced convection of air (10-200 W/m²·K), water (500-10,000 W/m²·K), and boiling/condensation (2,500-100,000 W/m²·K).

Q4: How does material thickness affect the Biot Number?
A: For a given material and heat transfer coefficient, increasing thickness increases the Biot Number, making internal temperature gradients more significant.

Q5: Can the Biot Number be applied to non-rectangular geometries?
A: Yes, but the characteristic length changes. For spheres it's radius/3, for cylinders it's radius/2, and for cubes it's side length/6.