# 3 Mechanisms for Heat Transfer

Let's go back to our example of the cup
filled with hot tea left in a room at 25oC.

We have already discussed how heat flow will transfer the energy from the tea to the surrounding air until the system reaches

#### thermal equilibrium

.
Hot Cup
of Tea
Surrounding Air
T = 25oC
Q
We have not discussed the mechanisms involved in heat transfer.
In what ways can heat be transferred?
Mechanisms for Heat Transfer
1. #### Conduction

- Fourier's Law
2. #### Convection

- Newton's Law of cooling

- Stefan-Boltzmann Law
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### Ch4, Lesson B, Page 14 - 3 Mechanisms for Heat Transfer

• In the next few pages, we will use our cup of hot tea to guide our discussion of the three mechanisms for heat transfer.
• As long as the tea is hotter than its surroundings, the system is not at thermal equilibrium and heat will continue to be transferred from the tea to the surroundings.
• Here we list the three mechanisms for heat transfer and the key equation that we will use to calculate the heat transfer rate due to each mechanism.
• The total heat transfer rate is the SUM of the three rates.
• In the next few pages, we will look at each mechanism more closely.