Total Emissivity Method — Lesson 9

This lesson covers the concept of emissivity and absorptivity of gases, and how these properties can be calculated based on information from each of the absorption bands of the gas. It further delves into how these calculations can be applied to solve real-world problems. The lesson explains how emissivity depends on the path length of the absorbing gas and the gas temperature. It also discusses how this information can be utilized in radiative heat transfer. The lesson provides an example of how to convert a problem defined in terms of absorption co-efficient to one in terms of emissivity. It also discusses the concept of 'lifted minimum', a phenomenon observed in the atmosphere, and how it can be explained using the emissivity model.

Video Highlights

02:51 - Discussion on the spectral values and the Kernel approximation.
12:38 - Explanation of the phenomena called lifted minimum observed in the atmosphere.
22:38 - Discussion on the emissivity and non-homogenous path followed by radiation as it goes from the surface to very high altitudes.
31:38 - Understand the mathematical treatment behind the lifted minimum phenomenon.
41:56 - Explanation of how to solve the combined conduction radiation problem to understand the occurrence of lifted minimum.
49:33 - Discussion on the importance of accurate data for emissivity in explaining the lifted minimum phenomenon.

Key Takeaways

- Emissivity of a gas depends on the path length of the absorbing gas and the gas temperature.
- Emissivity can be utilized in solving real-world problems related to radiative heat transfer.
- The 'lifted minimum' phenomenon observed in the atmosphere can be explained using the emissivity model.
- Accurate data for emissivity is crucial for understanding and explaining certain atmospheric phenomena.
- Emissivity data can be used in estimating the efficiency of a power plant or a boiler furnace.