Tutorial 7 Summary of Week 7 lecture
HOW SHOULD I WRITE THE ENERGY BALANCE EQUATION FOR RADIATIVE HEAT TRANSFER?
I have received queries from students on how to write up the energy balance equation for radiative heat transfer. Specifically, the query is about when to use eq (1) and when to use eq (2)
𝑞!”#,%&’ = 𝐴(𝐽 − 𝐺) (1) 0r
Copyright By PowCoder代写 加微信 powcoder
𝑞!”#,%&’ = 𝐴(𝐺 − 𝐽) (2)
Eq (1) is given as the definition of the net rate of radiant heat transfer. qnet,rad, is defined as net radiant heat transfer from an object to the surroundings in absence of any specific irradiation. However, the energy balance equation should be written with a proper drawing, which identify the directions of all processes of heat transfer.
Your lecture notes also offered a derivation, which shows that eq (1) can also be written in the form of
𝑞 = 𝐴𝜀𝜎(𝑇) − 𝑇) ) (3) !”#,%&’ ( (*%%
The symbols have their usual meanings. This equation has the instruction on how we write the energy balance. If the surface temperature of the object is higher than the surroundings, heat will transfer from the object surface to the surroundings, we write the energy balance in the form of eq (2) (see Figure 1). If, however, the surface temperature of the object is lower than that of the surroundings, such as an esky in outdoor summer, heat will transfer from the surroundings to the surface of the object. Then we either use eq (1) (see Figure 2).
Hope this clarifies. Wei
程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com