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Time : Apr 30 2015Source :analogtechnologies Author : Analog Click :

From (3), (13) and (14), it is shown that when T_h -T_c>△T_max, the cooling capacity q_c<0. At the same time, TEC cannot cool, but start heating, which is not allowed in practical work. So the working current should be controlled in range of I₀≤I≤I_sat, which can ensure the cooling capacity q_c≥0. Although based on the analysis of the cooling capacity q_c, the general range of working current can be determined, but in practical work, the refrigeration coefficient is still an important indicator. From (9), when the working current of TEC satisfies the following relations, the TEC can reach the maximum refrigeration coefficient β_max:



Where, I_opt is the working current in the condition of meeting the optimal refrigeration coefficient; Z is the figure of merit, .The relationship among current I, cooling capacity q_c and β is shown in the figure 3. When I_sh<I<0 and W<0, TEC is in the power generation mode. When I<I_sh、0<I<I₀ and I>I_sat, the cooling capacity of TEC q_c<0 and it will heat the cold load, which should be avoided as far as possible in practical work. When 0<I<I_sat, the amount of heating load is small because there exists the Peltier effect reducing the impact of heat resistance in the cold end. Only when the current meetsI₀<I<I_sat, TEC can work normally in the cooling mode; when I=I₀ or I=I_sat, it cannot cool. The cooling capacity q_c is a quadratic function about current I, so q_c is symmetric in the two interval, I₀<I<I_sat and I_max<I<I_sat. However, when considering that the refrigeration coefficient β increases with the current increasing in the range of I₀<I<I_opt and decreases with the current increasing in the range of I_opt<I<I_sat, so he refrigeration coefficient should be considered at the same time with improving cooling capacity and the working current in I_max<I<I_sat is not selected in general. Obviously, TEC has two extreme ways of working, the maximum refrigeration coefficient operation mode and the maximum cooling capacity operation mode. The former is the operation mode of variable voltage and variable operating current; the latter is the operation mode of constant working voltage and working current. But in the actual work, the hot and cold end temperature of thermoelectric cooler is changing, and it generally works between the maximum refrigeration coefficient and the maximum refrigeration capacity, so the current needs to be regulatedaccording to the actual situation.

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