1.When a current is made to flow through a junction composed of materials A and B, heat is generated at the upper junction at T2, and absorbed at the lower junction at T1. This is called Peltier effect.
Joule's heating the heat that is generated whenever a voltage is applied across a resistive material.
2. peltier effect is thermally reversible. Joule's effect is thermally irreversible.
3. the heat absorbed or liberated at a junction is found to be proportional to the first power of current where as in Joule effect that is proportional to the square of current.
4. in Joule's heating heat is generated through out the wire.
In Peltier effect heat is generated at one junction and absorbed in another.