The Study Of Thermoelectric Step-pulse Supercooling Characteristic Based On The Cooling System Of Semiconductor Laser

Effective heat dissipation is the development bottleneck of high heat flux semiconductor laser. In view of the requirements on packaging, the high working temperature, on-off response and precise control, although thermoelectric cooling (TEC) device to is proposed cool the semiconductor laser. But many researchers devoted to the thermal character studies of laser at the ambient temperature, few researchers paid attention to the used of thermoelectric module for cooling laser. Thermoelectric pulse cooling can be used to improve the cooling capacity of thermoelectric modules at high temperature. However how to offset the delay in increasing temperature to maintain the temperature at constant is a big challenge. Therefore, this project aims to complete the theory of thermoelectric pulse cooling and develop the reliable control strategy for maintaining temperature constant.Thermoelectric module (TEM) is the core comparent of TEC system. It’s a critical to analyze its maximum cooling capacity. This study analyzes the relationship between the maximum cooling capacity and the thermal resistance of heat exchanger at the hot-end. To explore how the critical factors influence the cooling capacity of TEC system and to simulate the real-time transient process of TEC, The steady-state and transient-state mathematical models of TEC system are built. The numerical solution is obtained by using the finite volume method and the gear algorithm. Then, the transient supercooling effect of voltage pulse is analyzed. Realistic boundary conditions, including the hot-end convection heat transfer coefficient (h) and cold-end cooling load, are considered to improve the pulse cooling performance. The miniature TEM is used to cool the high heat flux of semiconduct laser. The cooling method and cooling capacity is studied for continuous laser and pulse laser to ensure the stable temperature. The test rig for laser cooling is built, the step-cooling method and the error between numerical and experimental results are discussed.The step-changing relationship between the resonding voltage and the thermal resistance of heat exchanger at hot-end is found. A new scaling effect for the practical minimum temperature, the maximum temperature difference and the maximum cooling capacity is found. The combined effects of the three factors involving operating current, the heat exchangers at the cold and hot ends on the TEC system were discussed. It is found that the influence of electrical current is larger than the influence of heat exchangers at the cold and hot ends. The transient effects of the factors involving on-off of TEM, environment and operating temperatue on the TEC system are discussed. The test results show that the numerical model and the associated solution method can be applied to the performance prediction and optimization of Thermoelectric cooling system.The pulse superheating effect is observed by discussing the pulse supercooling effect of TEC system, and the definition of pulse supercooling effect of TEC system is extended and improved. The theoretical and experimental study shows that there is an optimal pulse amplitude. When the pulse amplitude is smaller than the optimal value, the minimum supercooling temperature decreases with the increase of the pulse amplitude, and when the pulse amplitude is larger than the optimum one, the minimum supercooling temperature increases with the increase of the pulse amplitude. The effect of pulse amplitude, heat transfer at the hot-end and the cooling load on the supercooling temperature and thermal response time are discussed. There is a cost-effective heat exchanger design at the hot end to achieve the minimum supercooling temperature. It is also demonstrated that the minimum supercooling temperature cannot approach absolute zero as reported in previous research due to the co-existence of Joule heat and Peltier effect.It is found that the miniature TEM is suitable for cooling the continuous laser when the cooling load is smaller than a constant value and the ambient temperature is equal to70℃. To decrease the pulse superheating temperature of TEC and solve the over cooling load problem, a step-pulse cooling method is introduced which can be used to cool the pulse laser. The transient response of the cold-end temperature experiences an underdamped oscillation and finally reaching a steady-state value. A curve fitting equation for the cold-end temperature is used to provide more accurate temperature and understand the temperature control strategy for pulse laser.To sum up, the scaling effect, thermal transport process and the thermoelectric effect, three new phenomena are found in this study. Firstly, the gradient of minimum temperature and temperature difference tends to be stable value as the decreasing of dimension. The voltage for getting the minimum temperature, and temperature difference as well as maximum cooling capacity step changes with thermal resistance of hot-end heat exchanger, and the step-changing phenomenon is more obvious as the decreasing of the dimension. Secondly, The random pulse superheating effect and the pulse supercooling effect of the TEC system are well defined which enhance the theory of pulse supercooling effect. It also found that the minimum supercooling temperature cannot approach absolute zero as reported in previous research. Thirdly, a step-pulse cooling method is developed to cool the pulse laser which can be used to offset the incrasing temperature by pulse super-heating effect.