[FINAL EXAM] Radiation & Shape Factor | Heat & Mass Transfer

Welcome to Engineering Hack! In today's video we start solving the final exam of 2020 for the heat and mass transfer course. The first question is about radiation and view factors (how much a given body "sees" another body). It is a simple problem in the sense that there aren't any curve balls or tricks other than knowing the basic principles of radiation and reciprocity. The former will obey the zeroth law of thermodynamics and will imply that the net energy between the two bodies is going from the body with the higher temperature to the one with lower temperature. The latter says that there is a relationship between the view factor and the areas of two bodies that see each other (i.e. F12 * A1 = F21 * A2). Applying these principles should allow you to solve the question. The Stefan–Boltzmann constant is given in the formula sheet as 5.67x10^-8 W/m^2*K^4 so that no one needs to memorize any formulas to solve this during the exam. As per usual I encourage you to have a go before seeing the solution, and later compare your thought process to the one I show in the video.

Problem statement: The radiative heat transfer is taking place between two black surfaces. The area A1 is a rectangle with a length of 4 m by a width of 2 m at 1200 K, and the area A2 is a disc with 2 m in diameter at 800 K. If the view factor, F12 = 0.2, what is the view factor, F21? Also calculate the net radiation transfer between the two black surfaces.

Answer:
F21 = 51%
Qnet = 151kW

In this video:
00:00 Intro
00:28 Problem statement
01:07 Problem analysis
02:00 View factor
03:56 Net heat transfer
07:10 Final thoughts

🎓 Can you trust the answers and solutions provided? Well, you never should trust anything 100%. Make sure you are checking for yourself. When I’m solving the questions, I always solve on my own and then check the results against other sources. If there is divergence, I look for more sources. So while I can’t promise you everything will be 100% correct, I can promise I’ve done my due diligence before posting.

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[Jacopski]

youve been my guide to this unit at mq this semester, wish you were still teaching this its an amazing youtube channel

[paulatreides]

Why is there no fin efficiency problems on any of the heat transfer playlists?

[mikebandala]

Hi Pablo,
Do you plan on releasing solutions to any of the other questions also? I've attempted most and had a few hiccups that I just wanted to rectify and practice more on. Thank you!