[Saketh Bharadwaj]

The idea is to simulate a double glazed window exposed to solar radiation and see the maximum temperature in the glass. This temperature should be less than the maximum permissible temperature of the adhesive used. We have boundary conditions and the spectral properties of the glass defined as shown in the picture attached.

Information provided by manufacturer: Wavelength dependent Reflectivity and Wavelength dependent Transmissivity.
a. Reflectivity is defined on front side and back side of the glass pane. If there is no coating(thermal protective layer) on the glass, then the reflectivity on both sides of the glass will be same.
b. Transmissivty is defined for the complete glass but not on each surface.

In COMSOL, the spectral properties are defined on each side (upside and downside) of each boundary. Within the glass, there should not be any emissivity (only conduction and transmission). The manufacturer defines transmissivty for complete glass. But in COMSOL I have to provide transmissivity values for each boundary (semi-transperent surface). As of now, we assume that tau value of 1 for in following places.

1. “1. Downside”
2. “2 Downside”
3. “3 Upside”
2. “4 Downside”

This assumption helps mathematically, 1. to achieve the tau values provided by the manufacturer since the total transmissivty of first glass provided by manufacturer is understood as product of tau on semi-transperent surfaces and 1 and 4. 2. to make sure sum of spectral properties is unity on semi-transperent surfaces and 1 and 4 on both sides.

With these assumptions, we end with zero internal reflections inside the glass and hence not shown in the image. For example looking at far left surface, the incident radiation is factored out by wavelength dependent tau value. So the part of radiation going through is completely transmitted onto second boundary without any reflection or absorption loss.

So how can I model this in COMSOL? Is the assumption correct? If not, How to adjust the transmissivity such that the values can be defined on both surface 1 and surface 2 at the same time achieving the values provided by the glass manufacturer?

Thanks in advance.

Best Regards,
Saketh Bharadwaj