The device has two sides, and when DC electricity flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter. The "hot" side is attached to a heat sink so that it remains at ambient temperature, while the cool side goes below room temperature. In some applications, multiple coolers can be cascaded together for lower temperature.

Dear Mohamed Sabry,

perhaps the following article of 1929 by P.W. Bridgman could be of some interest:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC522553/.

The following more recent article mentions the Peltier effect, but it is more on the Seebeck effect:

http://arxiv.org/abs/1502.05697

Sorry Mahamed, but this answer is uniquely from my cosmos and atomic models:

Atoms tend to have in balance of energy:

Law of Universal Balance:

“The cosmic energy tends to have spread along the Cosmos units (atoms, stars, etc.) in the same proportion or density.”

For it, atoms firstly tend to acquire electrons to complete their electronic balance (same number of electric charges +/-); and second atoms acquire energy in heat form till complete its required balance of total contained energy.

--When acquiring electrons, their volume increase, and also so atoms must to acquire heat energy to complete their balance of energy.

--When ceding electrons, their volume decrease, and then they must to cede heat energy to be again in balance of energy.

This case, we could consider atoms as a vessel or container that tend to be completely full of energy conserving similar density of energy all time.

Say, the cession or acquisition of energy depends on the increment or decreasing of atomic volume due to the cession or acquisition of electrons.

Then it is question of the balance of energy that atoms are obligated to conserve.

And this Law or physical principle is the one that manages all type of cessions or acquisitions of energy and electrons in atoms: firstly regulate electrons, and later on regulate calorific energy to complete the balance of total resultant energy.