Application Of Dual Frequency Laser Interferometry System In Study Of Surface Fluctuation In Thermocapillary Convection

Thermocapillary convection is a form of convection caused by the Marangoni effect.It is the main convection mode in space environment.With the increasing frequency of outer space activity,the research on the thermocapillary convection has drawn more and more attention.Research on hot capillary convection can help people to adapt to the space environment better.Meanwhile there also exist thermocapillary convection in industrial production such as the crystal growth and thin film process,which has an influence on the quality of production.Under the conditions of constant gravity,the gravity-dominated buoyancy convection is the main form of convection.Although the thermal capillary convection is relatively weak,it can not be neglected.The weak physical signals such as temperature and velocity in thermocapillary convection have been studied in detail.However,in the field of fluid mechanics,the change of free surface in thermocapillary convection is a very important physical phenomenon.Aiming at the deformation displacement of the free surface of the thermocapillary convection,a dual-frequency laser interferometry system was developed.We combined optical interferometry with phase meter and obtained the signal from the measurement system that reflects the surface deformation.The principles and devices of this photoelectric detection system such as phase meter are described in detail.A dual-frequency laser heterodyne interferometry system was set up to measure the moving objects driven by the PI motor.We collect the data and calibrate the performance characteristics of the system.At the same time,the laser displacement sensor is used to verify the accuracy of the measurement system that we developed.Calibration results show that the developed dual-frequency laser heterodyne interferometry system has better measurement performance than the laser displacement sensor.A thermo-capillary convection free surface measuring system of rectangular liquid pool was set up to realize real-time measurement of free-surface oscillation in liquid pool.The system includes temperature control unit,measurement unit and data acquisition unit.The temperature of the side wall of the tank is controlled to create a temperature gradient.The free surface oscillations of the liquid layer was measured by the developed measuring system.It was found that the liquid reservoirs of different thicknesses could oscillate at different temperatures,and the oscillation frequency of the free surface was basically the same.The feasibility of using heterodyne interferometry to measure free surface of hot capillary convection was verified.At the same time,the influence of environment on dual-frequency laser heterodyne interferometry system is analyzed to find out the factors that influence the measurement and take measures to reduce the impact on the measurement results.