CHEE2695 – Lecture 9
Transient conduction:
- Many applications involve transient conduction (unsteady state), where
temperature is dependent on time.
Biot number:
- The biot number can be used to determine if lumped system analysis can be
carried out.
- It is a measure of the resistance to heat transfer internally of an object
compared to external.
¿ V ¿ ∆x r r
L= →L = (plane wall), L¿ = 0 (cylinder), L¿ = 0 (sphere)
AS 2 2 3
- If Bi ≤ 0.1, then lumped analysis may be used.
Lumped analysis:
where T i is the initial temperature.
Analytical solutions:
- If Bi>0.1, then lumped analysis cannot be used.
- In this case, objects will have an internal temperature distribution.
- Simplifying the general conductive equation, we get:
Transient conduction:
- Many applications involve transient conduction (unsteady state), where
temperature is dependent on time.
Biot number:
- The biot number can be used to determine if lumped system analysis can be
carried out.
- It is a measure of the resistance to heat transfer internally of an object
compared to external.
¿ V ¿ ∆x r r
L= →L = (plane wall), L¿ = 0 (cylinder), L¿ = 0 (sphere)
AS 2 2 3
- If Bi ≤ 0.1, then lumped analysis may be used.
Lumped analysis:
where T i is the initial temperature.
Analytical solutions:
- If Bi>0.1, then lumped analysis cannot be used.
- In this case, objects will have an internal temperature distribution.
- Simplifying the general conductive equation, we get:
