Thermoelectric Effects in Thermodynamic Conversion of Heat

The various thermoelectric effects in relation to thermodynamic conversion of heat to work are as follows: 1. Seebeck Effect 2. Peltier Effect 3. Thomson Effect 4.Joule Effect.    

1. Seebeck Effect:

If two dissimilar materials are joined to form a loop and two junctions maintained at different temperatures, an e.m.f. will be set up around the loop. The magnitude of current depends on the materials (1 and 2) and the temperature difference between the junctions (Fig. 9.1.).  

The magnitide of e.m.f. (E) is given by:

E = α_s ΔT …(9.1)

where, α_s = Seebeck coefficient, and

ΔT = Temperature difference between hot and cold junctions.

This effect has been used in “Thermocouples” to measure temperatures.

2. Peltier Effect:

Refer to Fig. 9.2.

Peltier Effect States:

“When an electric current flows across an isothermal junction of two dissimilar materials, there is either an evolution or absorption of heat at the junction”.

Peltier’s coefficient a₁₂ is defined as the heat evolved or absorbed as the junction per unit current flow, per unit time.

3. Thomson Effect:

Refer to Fig. 9.3.

Thomson Effect States:

“Any current carrying conductor with a temperature difference between two points will either absorb or emit heat, depending upon the material”.

The ‘Thomson’s coefficient’ is defined as the heat absorbed (or evolved) per unit time per unit electric current and per unit temperature gradient.

The Seebeck, Peltier and Thomson effects are more pronounced in “semiconductors” as compared to metals.

The relations between seebeck, peltier and thomson coefficients as derived by Kelvin are as follows:

1. The relation between seebeck effect and peltier effect:

2. The relation between seebeck effect and thomson effect:

4. Joule Effect:

Joule Effect States:

“In a closed electric circuit if the current I flows through a resistance R, the heat generated (Q) by the resistance is equal to I²R”:

Mathematically, Q = I²R …(9.8)