Car refrigerator semiconductor refrigeration principle

Car refrigerator semiconductor refrigeration principle semiconductor refrigeration technology materials is one of the three pillars of industry in today's world, the material is the material basis for human survival and development, especially in recent decades with the advancement of human science and technology, the development of materials is ever-changing, the new materials come and go, of which semiconductor refrigeration materials is one of the emerging hot materials, in fact, semiconductor refrigeration technology has appeared as early as the 1830s, but its performance has been unsatisfactory, has been to the 1950s with the rapid development of semiconductor materials, hot refrigerator has gradually moved from the laboratory to the hot refrigerator. Technology as early as the 1830s has appeared, but its performance has been unsatisfactory, has been to the 1950s with the rapid development of semiconductor materials, hot spot refrigeration only gradually from the laboratory to the engineering practice, in the field of national defense, industry, agriculture, medical and daily life and other areas of application, large enough to do the air-conditioning of the nuclear submarine, small enough to be used to cool infrared detector probe, the thermoelectric cooler is usually also called the thermoelectric cooler. Therefore, the thermoelectric cooler is usually called semiconductor cooler. Semiconductor refrigeration devices can be roughly divided into four categories: (1) used to cool an object or a specific object for heat dissipation, this situation appears in a large number of electronic industrial fields; (2) used for thermostat, as small as the individual electronic devices to maintain a constant temperature, such as the manufacture of thermostat tanks, air conditioners, etc.; (3) the manufacture of complete sets of instruments and equipment, such as environmental experiments, small refrigerators, a variety of thermal properties of the test instruments; () the civil products, cold, cold, cold, cold and cold. (4) civil products, refrigerated baking box, cooling and heating fan. Application of semiconductor refrigeration: (1) in the field of high-tech and military areas of infrared detectors, lasers and photomultiplier tubes and other optoelectronic devices refrigeration. For example, the German Micropelt company's semiconductor cooler is very small, only 1 square millimeter, and lasers can be used together with the TO package. (2) Applications in the field of agriculture Too high or too low a temperature inside the greenhouse will lead to seedling necrosis, especially part of the valuable plants are more sensitive to the environment, there is an urgent need to apply the appropriate temperature detection and control system in modern agriculture. (3) in the medical field in the application of semiconductor temperature control system in medicine is more widely used. For example: for protein function research, gene amplification of high-grade PCR instrument, electrophoresis instrument and some intelligent and precise temperature control thermostat incubator, etc.; for the development of scanning probe microscope with a special temperature platform. Advantages of semiconductor refrigeration semiconductor refrigerator size is small, can be made into a volume of less than 1cm small refrigerator; light weight, miniature refrigerator can often be as small as only a few grams or tens of grams. No mechanical transmission part, no noise in the work, no liquid, gas working medium, and therefore does not pollute the environment, refrigeration parameters are not affected by the direction of space and gravity, in the large mechanical overload conditions, can work normally; through the adjustment of the size of the working current, it is convenient to regulate the cooling rate; through the switching of the direction of the current, but the refrigerant from the state of refrigeration into the state of heating; the role of the fast speed, long service life It is also easy to control. The working principle of semiconductor refrigeration device The working principle of semiconductor refrigeration device is based on the principle of Paltin, the effect is in 1834 by J.A.C Paltin first discovered, that is, the use of when two different conductors A and B composed of a circuit and DC current, in addition to Joule heat in the joints will be released in addition to some other kind of heat, while the other joints are absorbed, and the Paltin effect is caused by this phenomenon is reversible, and the effect of the Paltin effect is reversible. This phenomenon is reversible, change the direction of the current, heat release and heat absorption of the joints also changed, absorption and release of heat and current strength I [A] is proportional to the nature of the two conductors and the hot end of the temperature, that is: Qab = Iπab πab is called as a relative Peltier coefficient between the conductor A and B , the unit of [V], πab is a positive value, said that the absorption of heat, and the opposite for the release of heat, as the The heat absorption and excretion is reversible, so πab=-πab The magnitude of the Peltier coefficient depends on the nature of the material constituting the closed loop and the temperature of the joints, and its value can be derived from the Seebeck coefficient αab[V.K-1] and the absolute temperature of the joints, T[K] πab=αabT With Seebeck's effect, the Peltier system is also additive, i.e. Qac= Qab+Qbc=(πab+πbc)I Thus the absolute Peltier coefficient has πab=πa- πb The Peltier effect is weaker in metallic materials and much stronger in semiconductor materials, and thus the temperature-differential electric refrigeration devices that have found practical application are made of semiconductor materials. Development of semiconductor refrigeration materials AVIoffe and AFIoffe pointed out that among compounds of the same family of elements or the same type of plasmid, the lattice thermal conductivity Kp tends to decrease with the growth of the average atomic weight A. RWKeyes deduced experimentally that KpT approximates to be proportional to Tm3/2ρ2/3A-7/6, i.e., approximates to be proportional to the atomic weight A, and therefore, compounds made up of the heavy elements should be usually selected as semiconductor refrigeration materials. compounds composed of heavy elements as semiconductor refrigeration materials. Another great development in semiconductor refrigeration materials is the solid solution theory proposed by AFIoffe et al. in 1956, i.e., the use of homocrystalline compounds to form a mass-like isocrystalline solid solution. Solid solution doped with homocrystalline compounds introduced by the equivalent replacement atoms produced by the short-range distortion, so that the phonon scattering increases, thereby reducing the lattice thermal conductivity, while the carrier mobility is very small, so that the optimum value coefficient increases. For example, a 50% Bi2Te3-50% Bi2Se3 solid solution will have a 33% reduction in thermal conductivity compared to Bi2Te3 with only a slight increase in mobility, thus increasing the figure of merit by 50% to double. Ag(1-x)Cu(x)Ti Te, Bi-Sb alloys and YBaCuO superconducting materials, etc. used to be the object of research of semiconductor refrigeration scholars and experimentally proved that they can be better low-temperature refrigeration materials. The following will reduce these several thermoelectric properties of better semiconductor refrigeration materials, respectively. Binary Bi2Te3-Sb2Te3 and Bi2Te3-Bi2Se3 solid solutions Binary solid solutions, whether P-type or N-type, lattice thermal conductivity than Bi2Te3 have a greater reduction, but the N-type material's optimum coefficient of merit has increased very little, which may be due to the introduction of Bi2Se3 in the Bi2Te3 with the different molar content of Bi2Se3 presents two different conductive properties, which will inevitably make the two characteristics are not very strong, through the appropriate doping although it can enhance the conductive properties of the material, improve the material's superior value coefficient, but in the final analysis should be a breakthrough in the subject material. Ternary Bi2Te3-Sb2Te3-Sb2Se3 solid solution Bi2Te3 and Sb2Te3 are rhombic crystal structure, Sb2Se3 is rhombohedral crystal structure, in addition to removing the large Sb2Se3 concentration of a wide range of components, they can form a ternary solid solution. Without doping, this solid solution exhibits P-type conductive properties, which can also be transformed to N-type conductive properties by suitable doping. Adding Sb2Se3 to the binary solid solution has two advantages: firstly, it improves the forbidden band width of the solid solution material. The second is that the lattice thermal conductivity can be further reduced, so that Sb2Se3 differs greatly from Bi2Te3 and Sb2Te3 both in crystal structure and average atomic weight. When the total molar content of Sb2Te3+5% Sb2Se3 in the ternary solid solution is in the range of 55% to 75%, the lattice thermal conductivity is the lowest, which is about 0.8×10-2W/cm K, and this value is slightly lower than that of the lowest value of 0.9×10-2W/cm K in the case of the binary. However, the addition of Sb2Se3 also reduces the mobility of the carriers, which will lower the eutectic coefficients, and therefore must be controlled. the content of Sb2Se3. P-type Ag(1-x)Cu(x)Ti Te materials AgTi Te materials have a very low thermal conductivity (k=0.3 W/cm K), so if the carrier mobility μ and conductivity σ can be increased by suitable doping, it is possible to obtain a high figure of merit Z. RMAyral-Marin et al. experimentally found that AgTi Te and CuTi Te were combined in an ideal ratio to form an AgTi Te and CuTi Te material. Te to form a solid solution by ideal ratios, and after replacing some Ag atoms by using Cu atoms, a P-type semiconductor refrigeration material, Ag(1-x)Cu(x)Ti Te, with better properties can be obtained, where the best thermoelectric properties of the material are obtained when x is around 0.3. This shows that Ag(1-x)Cu(x)Ti Te is indeed a better P-type semiconductor refrigeration material. N-type Bi-Sb alloy materials Undoped Bi-Sb alloys are currently the semiconductor refrigeration materials with the highest coefficient of merit within the temperature van 20K to 220K, which are N-type in the Bi-rich region and will be transformed to P-type when the Sb content exceeds 75%. The introduction of Sb in the single crystal of Bi does not change the crystal structure, nor does it change the concentration of carriers (including electrons and holes), but it widens the width between the conduction band and the forbidden band. 0-5% of Sb content forbidden band width of about 0eV, i.e., the conduction band and the forbidden band are connected, which belongs to the semi-metal; Sb content of 5%-40%, the forbidden band width value is basically about 0.005eV, and the value of the forbidden band width is basically about 0.005eV, and it is about 0.005eV when Sb content is 12%-15%, which belongs to the semi-metal. content is 12% to 15%, it reaches a maximum of about 0.014 eV, which belongs to the narrow-band intrinsic semiconductor. From the above, the increase of forbidden band width will surely increase the temperature difference electric potential of the material. it is Bi85Sb15 that has the highest eigenvalue coefficient in the temperature range of 80 K to 110 K, and it is Bi92Te8 that has the highest one in high temperature. YBaCuO superconducting material According to the above introduction, it can be seen that in the temperature range of 50K to 200K, the best performance of semiconductor pit-making material is n-type Bi(100-x)Sbx alloy, in which the content of Sb is 8% to 15%. At 100 K with zero magnetic field, the highest figure of merit of Bi-Sb alloy can reach 6.0×10-3K-1, while the figure of merit of p-type solid solution materials based on Bi and Te at 100 K is lower than 2.0×10-3K-1 and decreases rapidly with the decrease of temperature. Therefore, it is necessary to find a new p-type low-temperature thermoelectric material to form a semiconductor-cooling pair with n-type Bi-Sb alloys. The use of high Tc oxide superconductors instead of p-type materials as passive p-type electric arms (called HTSC arms, i.e., High Tc Supercon-ducting Legs) can theoretically improve the superiority coefficients of the electric team, and it has been proved experimentally that it is indeed feasible. Semiconductor refrigeration electric pairs in the device two arms to meet the optimal cross-section ratio of the best value coefficient is: zmax = (1) the subscripts p and n in the formula correspond to p-type materials and n-type materials, respectively. Since the temperature difference electric potential rate α of the HTSC superconducting material is almost zero, but its electrical conductivity is infinite, the ratio κ/δ of thermal conductivity κ and electrical conductivity δ is infinitely small, so that Eq. (1) can be simplified as follows: zmax(HTSC)= i.e., the optimum coefficient of the refrigeration pair consisting of the n-type thermoelectric material and the HTSC arm will be equal to the optimum coefficient of the n-type material. Mosolov A B et al. have made a single-stage semiconductor cooler utilizing YBaCuO superconducting thin films with SrTiO3 base and composite YBaCuO-Ag superconducting ceramic wafers as the passive HTSC arm materials and Bi91Sb9 alloy as the n-type material, respectively. The experimental results show that the cooler made by utilizing YBaCuO superconducting thin film can reach a maximum cooling temperature difference of 9.5 K when the hot end temperature is maintained at 85 K with zero magnetic field, and it can reach 14.4 K when 0.07 T transverse magnetic field is added; and the single-click cooler made by utilizing YBaCuO-Ag superconducting ceramic sheet can achieve a maximum cooling temperature difference of 9.5 K when the hot end temperature is maintained at 77 K with the corresponding The maximum refrigeration temperature difference is 11.4 K and 15.7 K. From the formula of maximum refrigeration temperature difference of semiconductor cooler, it can be back-calculated 80Kzuoyou this kind of refrigeration electric pair of superior value coefficient is about 6.0×10-3K-1, which can be seen that this kind of electric pair combination has a very good potential for application. With the development of high Tc superconductor materials, the hot end temperature of this refrigeration point team will gradually increase, the coefficient of merit will also gradually increase, than will get with a wide range of applications.