Thermoelectricity
Thermoelectricity, also called Peltier-Seebeck effect, direct conversion of heat into electricity or electricity into heat through two related mechanisms, the Seebeck effect and the Peltier effect.
In 1821 Thomas Seebeck, a German physicist discovered that when two dissimilar metal ( Seebeck used copper and bismuth) wires are joined at two ends to form a loop, a voltage is developed in the circuit if the two junctions are kept at different temperatures. The pair of metals forming the circuit is called a thermocouple . The effect is due to conversion of thermal energy to electrical energy.
The existence of current in the closed circuit may be confirmed by the deflection of a magnetic needle caused by the magnetic field of the current Joule heating produced in the wires closing the circuit with a capacitor to accumulate measurable charge
placing a sensitive ammeter or a galvanometer in the circuit measuring the amount of chemiucal deposit at the electrodes of an electrochemical cell.
The open circuit potential difference in the circuit whose junctions are maintained at temperatures `T_h`
and `T_c( < T_h)` is given by
`DeltaV = S_(AB) (T_h - T_c)`
where the coefficient of proportionality is known as the thermoelectric power or the Seebeck coefficient. The term thermoelectric power is a misnomer because it does not measure any power and is measured in volt/ K. By convention, Seebeck coefficient's sign is the sign of the potential of the cold end with respect to the hot end. Thus if `S_(AB)` is positive, convertional current flows from A to B at the hot junction. Seeback coefficient is not a constant but is dependant on temperature. The temperature dependence of a commercial thermocouple is usually expressed as a polynomial expansion in powers of temperature . For instance, for a thermocouple with Platinum as one of the metals and an alloy of Pt - Rh (90:10) the open circuit voltage is given approximately by a quadratic.
`V = c + aT + aT^2`
so that the thermoelectric power is given by
`(dV)/(dT) = a + 2bT`
The relationship between V and T and is a parabola. The temperature `T_n = -a/(2b)` at which the thermoelectric power is maximum is called the neutral temperature . The temperatures `T_i = T_o` and `T_i = T_o - a/b` at which a small change in the difference of the junction temperatures leads to a change in the sign of emf is called the inversion temperature.
In 1821 Thomas Seebeck, a German physicist discovered that when two dissimilar metal ( Seebeck used copper and bismuth) wires are joined at two ends to form a loop, a voltage is developed in the circuit if the two junctions are kept at different temperatures. The pair of metals forming the circuit is called a thermocouple . The effect is due to conversion of thermal energy to electrical energy.
The existence of current in the closed circuit may be confirmed by the deflection of a magnetic needle caused by the magnetic field of the current Joule heating produced in the wires closing the circuit with a capacitor to accumulate measurable charge
placing a sensitive ammeter or a galvanometer in the circuit measuring the amount of chemiucal deposit at the electrodes of an electrochemical cell.
The open circuit potential difference in the circuit whose junctions are maintained at temperatures `T_h`
and `T_c( < T_h)` is given by
`DeltaV = S_(AB) (T_h - T_c)`
where the coefficient of proportionality is known as the thermoelectric power or the Seebeck coefficient. The term thermoelectric power is a misnomer because it does not measure any power and is measured in volt/ K. By convention, Seebeck coefficient's sign is the sign of the potential of the cold end with respect to the hot end. Thus if `S_(AB)` is positive, convertional current flows from A to B at the hot junction. Seeback coefficient is not a constant but is dependant on temperature. The temperature dependence of a commercial thermocouple is usually expressed as a polynomial expansion in powers of temperature . For instance, for a thermocouple with Platinum as one of the metals and an alloy of Pt - Rh (90:10) the open circuit voltage is given approximately by a quadratic.
`V = c + aT + aT^2`
so that the thermoelectric power is given by
`(dV)/(dT) = a + 2bT`
The relationship between V and T and is a parabola. The temperature `T_n = -a/(2b)` at which the thermoelectric power is maximum is called the neutral temperature . The temperatures `T_i = T_o` and `T_i = T_o - a/b` at which a small change in the difference of the junction temperatures leads to a change in the sign of emf is called the inversion temperature.