2.2 Peltier effect The direction of current flow and the material combination determines whether heat is liberated or removed. This is a reversible process, unlike irreversible Joule heating (Terasaki, 2016).
Contrary to Joule heating, the Peltier effect is reversible and depends on the direction of the current.
Disadvantages of Peltier Systems
Can't provide low temperatures (below 10°C) Not very energy-efficient compared to compressor-based systems (although control technology means cooling can be more accurately measured than with a compressor, so these systems can be energy-efficient for small temperature gradients)
The Seebeck effect and its resultant thermoelectric effect is a reversible process. If the hot and cold junctions are interchanged, valence electrons will flow in the other direction, and also change the direction of the DC current.
The joule effect is irreversible, i.e., the heat in a conductor is always evolved whatever be the direction of current. Peltier effect on the other hand is reversible. If on passing the current in one direction, heat is evolved at a junction, then on reversing the current, heat is absorbed at the same junction.
Heating or cooling an object will always change its temperature and may alter other properties as well. The temperature change is reversible, but changes to other properties might be irreversible. Heating, in particular, often causes chemical changes in which atoms alter their bonding to form new substances.
2) In the Peltier effect the heat is generated at one junction and absorbed at another junction. While in Joule effect the heat is generated throughout the wire. Note: While comparing both the effects, the Joule effect will have more heat generated hence it is square of current.
The Seebeck effect is the conversion of temperature differences into electricity, the Peltier effect is the conversion of electricity to temperature differences, and the Thomson effect is heat produced by the product of current density and temperature gradients.
There is no such thing as reversible heat in thermodynamics, though there is a process called reversible heat transfer. This process involves transfer of thermal energy from one system to another along a reversible path.
A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat (driven by temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect).
The most common failure mechanism of Peltier modules is mechanical fracturing of the semiconductor pellets or the associated solder joints. These fractures initially do not propagate completely through the pellet or solder joint and can be detected by a rise in the series resistance of the device.
To obtain the maximum efficiency when cooling with Peltier elements, there are the three golden rules. I / Imax when dT < 25 K. I / Imax should be in the lower third (0 - 0.33 x Imax) I / Imax when dT > 25 K. I / Imax should be in the middle third (0.33 - 0.66 x Imax)
The Peltier effect is the reverse phenomenon of the Seebeck effect; the electrical current flowing through the junction connecting two materials will emit or absorb heat per unit time at the junction to balance the difference in the chemical potential of the two materials.
A Peltier-induced reverse heat flow has the advantage of easy tunability using an external current source, in contrast with previously proposed circuits, using external electrical coils21,24 and natural convection22,23.
Peltier modules efficiency heavily depends on the temperature differential. If you try to make both sides too different in temperature, the COP will reach zero, meaning your peltier is wasting electricity and outputting heat without actually doing work (i.e. cooling).
An example of an irreversible process is electric current flow through a conductor with a resistance. An example of an irreversible process is magnetization or polarization with hysteresis. An example of an irreversible process is inelastic deformation.
Although this energy doesn't actually disappear, some amount of the initial energy turns into forms that are not usable or we do not want to use. Some examples of these losses include: Heat energy, potentially as a result of air drag or friction. Heat energy is the most easily dissipated form of energy.
It is due to friction, and similar hysteresis features are necessary for reversible processes. If it takes place readily, the system would be set up with pressure changes and limited temperature gradients, leading to irreversible loss and heat flow.
The large construction cost comes from the power supply and the heat exchanger part, and the large operating cost comes from the fact that the Peltier coolers require a lot of current.
Such a module, powered by a current, will have a temperature difference between its two sides; one side will be cold side and the other hot. This is the Peltier effect. The opposite application can also be achieved with this type of module: a difference in temperature between the two sides will generate electricity.
Peltier systems typically excel in lower temperature ranges (e.g., -20°C to +70°C), while compressor systems are more efficient across wider temperature ranges, including sub-zero. Additionally, compressor systems can cover a wider temperature delta than Peltier systems, making them more flexible overall.
The Peltier–Seebeck and Thomson effects are thermodynamically reversible, whereas Joule heating is not.
The major disadvantage of the Peltier effect is low efficiency. The flowing current itself tends to generate a significant amount of Joule heating which adds to the overall heat dissipation requiring some form of active cooling system.
In Joule effect, the heat produced H=I2Rt. Thus, when the current flows the heat is produced. But we can not get the conduction current by heating. Thus, Joule effect is not reversible.