## Characteristic analysis of TEC refrigeration cycle (III)

##### Monday, August 31, 2015 8:32:44 PM America/Los_Angeles

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 *I*_{0}≤*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*<*I*_{0} 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 meets*I*_{0}<*I*<*I*_{sat}, TEC can work normally in the cooling mode; when *I*=*I*_{0} 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, *I*_{0}<*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 *I*_{0}<*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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Keywords: TEC, thermoelectric cooler

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