The heart part of semiconductor refrigeration application products is semiconductor refrigeration chip. According to the characteristics of semiconductor temperature difference, weakness and application range, the following problems should be determined when selecting semiconductor refrigeration chip:
1. Determine the working state of the semiconductor cooling sheet. According to the direction and size of the working current, the refrigeration, heating and constant temperature performance of the semiconductor refrigerator can be determined. Although the refrigeration method is commonly used, its heating and constant temperature performance should not be ignored.
2. Determine the actual temperature of the hot end during refrigeration. In order to achieve the cooling effect, the semiconductor cooling plate must be installed on a good radiator. According to the heat dissipation conditions, the actual temperature of the hot end of the semiconductor cooler is determined. It should be noted that due to the influence of temperature gradient, the actual temperature of the hot end of the semiconductor cooler is always higher than the surface temperature of the radiator, usually less than a few degrees, and more is higher Several degrees, more than ten degrees. Similarly, in addition to the thermal gradient at the hot end, there is also a temperature gradient between the cooled space and the cold end of the semiconductor cooler.
3. Determine the working environment and atmosphere of the semiconductor cooling sheet. This includes whether working in vacuum or in normal atmosphere, dry nitrogen, static or flowing air and ambient temperature, so as to consider insulation measures and determine the effect of heat leakage.
4. Determine the working object and thermal load of the semiconductor refrigeration chip. In addition to the influence of the temperature at the heating end, the low temperature or large temperature difference that the semiconductor cooling sheet can reach is determined under the conditions of no-load and thermal insulation. In fact, the semiconductor cooling plate can not be truly insulated, and it must have a thermal load, otherwise it is meaningless.
5. Determine the number of stages of the cooling plate. The selection of the series number of the semiconductor refrigeration chip must meet the requirements of the actual temperature difference, that is, the nominal temperature difference of the semiconductor refrigeration piece must be higher than the actual temperature difference required, otherwise it can not meet the requirements, but the number of stages can not be too much, because the price of the semiconductor refrigeration chip increases greatly with the increase of the number of stages.
6. Specification of semiconductor refrigeration sheet. After selecting the number of stages of the semiconductor cooling sheet, the specification of the semiconductor cooling sheet can be selected, especially the working current of the semiconductor cooling sheet. There are several kinds of semiconductor cooling chips that can meet the temperature difference and cooling at the same time. However, due to the different working conditions, the stack with small working current is usually selected. At this time, the cost of supporting power is relatively small. However, the total power of stack is the decisive factor. If the same input power is reduced, the voltage must be increased (0.1V per pair of components), so the number of components has to be increased.
7. Determine the number of semiconductor cooling sheets. This is determined by the total cooling power of stack which can meet the requirements of temperature difference. It must ensure that the sum of cold production of stack is greater than the total power of thermal load of working object at working temperature, otherwise it can not meet the requirements. The thermal inertia of the stack is very small, which is less than one minute under no-load. However, due to the inertia of the load (mainly due to the thermal capacity of the load), the working speed when the stack reaches the set temperature is far greater than one minute, which can last for several hours. If the working speed is higher, the number of stacks will be more. The total power of thermal load is the total heat capacity plus heat leakage (the lower the temperature, the greater the heat leakage).
The seven aspects mentioned above are the general principles to be considered when selecting the semiconductor refrigeration chip. According to the above-mentioned, the original user should first put forward the requirements to select the semiconductor refrigeration chip according to the needs. General requirements:
① The given ambient temperature is th ℃
② The cooling space or object reaches the low temperature Tc ℃
③ Known thermal load Q (thermal power QP, heat leakage QT) w
When th, TC and Q are known, the required stack and the number of stacks can be estimated according to the characteristic curve of the semiconductor cooler.
1. Determine the model and specification of the cooling plate
2. After selecting the model, consult the thermoelectric refrigeration characteristic curve of the model.
3. The temperature th at the hot end of the semiconductor cooler is determined by using the ambient temperature and heat dissipation mode, and the similar TC is obtained.
4. Find out the cooling capacity of the cold end QC in the corresponding characteristic curve.
5. By dividing the required cooling capacity Q by the cooling capacity QC of each semiconductor cooling chip, the required number of semiconductor cooling sheets is obtained, n = q / QC
