Quiz 10

Question 1

Which processes take place when a monochromatic ray travels in a participating medium?

Answer 1

o Absorption
o out-scattering
o emission
o in-scattering

Question 2

What are the dominant species in the combustion products in regard to radiation?

Answer 2

o CO2
o (CO)
o Water (H20)
o Soot
o (Fuel)

Question 3

Why does FDS not necessarily use the exact amount of solid angles that the end user specify? How does FDS calculate the amount (reference is ok) and what criteria must be fulfilled?

Answer 3

o Problems at poles, angles to tight

o Divisible by 4 on each axis, as moving closer to poles the number decreases by 6.13 in tech ref guide

Question 4

What makes semi-transparent materials challenging when it comes to radiation? Can FDS take these things into account?

Answer 4

They reflect, emit and transmit, transmission all of which are wavelength dependent.

Question 5

Why does FDS use RADIATIVE_FRACTION (when not doing DNS) and where in the computational domain is it used?

Answer 5

o To conserve energy expected radiative energy since depending on temperature prediction quickly leads to the wrong radiation term (T^4)
o It is used in the “flaming region” defined as where the nominal radiative loss is greater than 10 kW/m^3.

Question 6

At what typical dimensions/HRR does radiation become dominant over convection in regards to heat flux feedback/pyrolysis?

Answer 6

Pool fire 20 cm approx., so maybe 50-100 kW

Question 7

How can you see in Smokeview that the FDS radiation solver has been given too few solid angles?

Answer 7

Clear cold and hot-spots on in boundary files. Patterns in the integrated intensity slice files close to solid objects.

Question 8

Out of the following options, what is a fire safety engineer typically interested of when it comes to radiation?

Answer 8

o Self-absorbing scenarios
o Optically thin ignores smoke layer
o Optically thick treats smoke layer almost as a solid.