Thermoelectric module introduction

1.Terms
1-1 Semicon cooling--Thermoelectric cooing--Electronic cooling.
1-2 They are completely different from the compressive type and absorption type in the fields of principle of refrigeration and equipment.
1-3 Semicon refrigeration is named after the direct refrigeration by power-on and the refrigerating parts are made of special semicon materials instead of refrigerant.

1-4 Peltier Effect--in 1834,French scientist Peltier discovered the phenomenon of thermoelectric refrigeration and heating--e.g. The Metal Thermoelectric Inverse Effect. One pair of thermocouple made by two different metals. when DC current is inputted, due to the input different direction DC power, endothermic and exothermic phenomenon will be produced at nodes of the electric couple, this is called Peltier Effect.
1-5 This Peltier Effect was discovered 200 Years ago,But the history of application in refrigerating field is only several tens of years. From 1956, China started her study on semicon cooler, which was one special branch in the fields of semicon technology．
1-6 N-type and P-type semicons:special N-type and P-type con-ductors make up semicon cooler.
1-7 N-type semi-conductor:Any matter is made up by atoms and an atom is made of nucleus and electrons. Due to the abstraction of nucleus, electrons rotate around the nucleus at a high speed. Since there exists certain limitation, electrons could only revolve at the limited orbit and
could not leave freely. Because electrons at orbits of each layer possess different energy(electronic potential energy). The electrons at the farthest orbit from the nucleus may often break away from the absorption of nucleus and move among atoms. Because its electronic energy is maximum, free electrons are formed to take part In conduction under the action of electric field, this Is called conductor, If electrons coud not be separated from the orbit and form free electrons, they can not take part in conduction. This is called insulator. The conduction capability of semicon is between the conductor and insulator.It is called semicon.
The important characteristic of semicon is that, after mixed with certain numbers of impurity, not only the conduction capability are greatly increased, but also semicons may be produced with different properties and functions according to the varieties and volumes of the impurities mixed up, Mix one kind of impurity into semicon, it could release free electrons to increase the conduction capability, this semicon is called N-type semicon.
1-8 P-type semicon is conducted by "hole".Under the action of external electric field, the flowing direction of "hole" is opposite to that of electrons, that is "hole" flows from positive electrode to negative electrode. This is the principle of P-type semicon.
1-9 Carrier phenomenon:both the free electrons within N-type semicon and the "holes" within P-type semicon are taking part in conduction, they are called "charge carrier", which are specifically possessed by semicon and caused by the impurity mixed up.
1-10 Semicon refrigerating materials:In accordance with not only the characteristics of N-type and P-type semicon are needed,but also different impurities, the thermoelectric potential energy ratio，conduction ratio and heat conduction ratio of the semicon should be changed to satisfy the requirement of refrigerating ma-terials with this special semicon. At presen,common materials in domestic is the Ternary Solid Solution Alloy,which takes Bismuth Telluride as the base. Among them,the P-type is Bi2Te3-Sb2Te3 and N-type is Bi2Te3-Bi2Se3,crystal materials are extracted with the method of vertical zone melting.

2.Principle of Refrigeration
2-1 The Principle of Semicon Refrigeration:weld one particle of N-type semicon with another P-type one with oneconnecting metal sheet into one electric couple pair. When DC current flows from electrode N to electrode P, Ends 2 and 3 will produceendothermic phenomenon, this end is called Cold End. While following Ends 1 and 4 produce exothermic phenomenon. this end is called Thermal end.If the directions of current are reversed accordingly, the Cold End and Thermal End will be changed,Since the thermal effect produced by one electric couple is very small (commonly about 1 Kcal/h) ,actually,one thermopile is formed by tens of, even hundred pairs of electric couples connected in series.Therefore, the refrigeration of semicon-endot- hermic and exothermic process are the energy trans-mission of potential energy caused by carrier(electrons and holes)flowing through nodal points,this is the nature of semicon refriaeration.

2-2 Process of semicon refrigeration:electron starts from the negative pole.through metal sheet-flowing to P-point-4-reach to P-type then flowing to P-point-3-Node metal sheet-from Node 2-reach to N-type-then return to Node l-reach to metal sheet and return back to the positive electrode of the power supply. Since the left half is of P-type,the conduction type is hole, the flowing direction of hole is opposite to that of the electron.Therefore, the hole is that Node 3 metal sheet-P-type-Node4 metal sheet-reach to the negative direction of electrode.Energy possessed by the hole inside Node 4 metal is lower than that of the hole in P-type. Under the action of electric field, if hollow is from 3 to P-type, the energy must be increased and these parts of energy should be converted into the potential energy of the hole,therefore, the metal sheet at Node 3 is cooled down. When the hole is flowing to 4 because the hole energy of P-type is larger than that in metal, the metal sheet should release its excessive potential energy by heat-releasing, so the 4-metal Sheets are heate.The right half is of N-type, the connection with metal sheet depends on the conduction of free electrons. But under the action of electric field,electric potential energy of free electrons in metal is lower than that in N-type, the potential
energy of electrons must be increased as reaching to N-type through Node.

2. These parts of potential energy could only be obtained from that of metal sheet.Meanwhile, it will inevitably cool down Node 2 metal sheet. When electrons flow from N-type to Node 1 metal sheet, due to the flowing of electrons from high potential energy to lower parts, it will release its excessive potential energy and change it into thermal energy to heat the metal sheet at Node 1, it is the Thermal End.

3.Characteristics of Semicon Refrigeration
3-1 No noise, no abraslon, reliable operation and easy for maintenance.
3-2 Fast cooling speed. Adjusting the working current, which is easy for manual and automatic control,could control the coolinq speed.
3-3 Small volume,lightweight,greatly save con-struction area.
3-4Both refrigerating and heating could be reached by changing the direction of current.
3-5 Free of refrigerant and no pollution to environ-ment.