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Online Training: Non-Grey Radiation Short Course

Most radiation analyses currently performed assume that grey conditions hold. That is, over the range of temperatures considered, optical properties have a nearly constant value with respect to wavelength. This reasonable approximation for systems that are near room temperature may show significant error at temperature extremes, particulary at cryogenic temperatures. Non-conductive materials typically show a drop in emissivity/absorptivity and conductive materials may also show a further complication of temperature dependence on optical values at a particular wavelength. Other areas where non-grey analysis may be appropriate is in furnace and lamp design, and in systems with specialized optical filters such as thermalphotovoltaics.

Often it is assumed that using total emissivity as a function of temperature will be sufficient to capture wavelength dependent optical behavior. This is only true in very limited cases. One such case is a system without any radiation exchange, for example a surface radiating to space with an effective temperature near 0 K. Another limited case is a system with one optical material that uniformly changes in temperature, that is, temperatures of the entire system uniformly rise or fall in close unison, such that at any point in time, greyness still holds. However, in cases where large temperature differences exist, such as a cold surface radiatively exchanging energy with a much warmer surface, a non-grey approach must be used. Using total emissivity as a function of temperature for systems that exchange radiation often leads to errors worse than assuming average grey behavior.

This short course presents the methodology and approach for performing a banded non-grey radiation analysis. Comparison results between grey and non-grey analyses are presented for several example problems. Limitations of current approaches for approximating non-grey radiation, such as approximating with temperature dependent total emssivity, are also reviewed. The class focus is not on software usage so much as on understanding the basic phenomena. Nonetheless, the types of phenomena that can be modeled and the magnitude of uncertainties involved will be noted, and demonstration models and results will be presented.

Prerequisites: Basic understanding of radiation analysis and methods.

Class Duration: 45 Minutes

This class will be limited in size so please register early. You will receive an email notification of your registration with instructions on how to log into the meeting. To participate in this class you will be logging into a web site and will need make a long distance phone call for voice conferencing. To participate in the demo your machine's internet browser must be Java enabled.

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