Emissivity Given Heat Transfer Coefficient By Radiation Calculator

Formula Used:

\[ \varepsilon = \frac{h_r}{\sigma \cdot \frac{T_{wa}^4 - T_s^4}{T_{wa} - T_s}} \]

Heat Transfer Coefficient By Radiation (h_r):

W/m²·K

Wall Temperature (T_wa):

Saturation Temperature (T_s):

Emissivity (ε):

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1. What Is Emissivity?

Emissivity is the ability of an object to emit infrared energy. Emissivity can have a value from 0 (shiny mirror) to 1.0 (blackbody). Most organic or oxidized surfaces have emissivity close to 0.95.

2. How Does The Calculator Work?

The calculator uses the formula:

\[ \varepsilon = \frac{h_r}{\sigma \cdot \frac{T_{wa}^4 - T_s^4}{T_{wa} - T_s}} \]

Where:

\( \varepsilon \) — Emissivity (dimensionless)
\( h_r \) — Heat Transfer Coefficient By Radiation (W/m²·K)
\( \sigma \) — Stefan-Boltzmann Constant (5.670367 × 10⁻⁸ W/m²·K⁴)
\( T_{wa} \) — Wall Temperature (K)
\( T_s \) — Saturation Temperature (K)

Explanation: This formula calculates emissivity based on the radiative heat transfer coefficient and temperature difference between wall and saturation temperatures.

3. Importance Of Emissivity Calculation

Details: Accurate emissivity calculation is crucial for thermal analysis, heat transfer calculations, and designing efficient thermal systems in various engineering applications.

4. Using The Calculator

Tips: Enter heat transfer coefficient in W/m²·K, wall temperature and saturation temperature in Kelvin. All values must be positive and wall temperature cannot equal saturation temperature.

5. Frequently Asked Questions (FAQ)

Q1: What is the range of possible emissivity values?
A: Emissivity ranges from 0 (perfect reflector) to 1.0 (perfect blackbody). Most real-world materials have values between 0.7 and 0.95.

Q2: Why is emissivity important in heat transfer calculations?
A: Emissivity determines how effectively a surface radiates thermal energy, which is critical for accurate thermal analysis and system design.

Q3: How does surface condition affect emissivity?
A: Surface roughness, oxidation, and contamination can significantly increase emissivity compared to smooth, clean surfaces.

Q4: Can emissivity change with temperature?
A: Yes, for some materials, emissivity can vary with temperature, though many materials maintain relatively constant emissivity over typical temperature ranges.

Q5: What are typical emissivity values for common materials?
A: Polished aluminum: ~0.04, oxidized steel: ~0.8, human skin: ~0.98, most building materials: 0.85-0.95.