Study Of Laser Irradiation Effects On Liquid Tank

Liquid tank is a potential part by laser irradiation. In this paper, laser irradiationeffects on liquid tank are investigated by experimental research, theoretical analysis andnumerical simulation. The main contents and conclusions are given as follows.1、Experimental system is set up to study the laser irradiation effects on liquid tank.For the experiment that the liquid is in a natural convection state, an effective method isdeveloped to measure the temperature of the wall which is in contact with liquid, and atwo-dimensional digital particle image velocimetry system is constructed to measure thevelocity field in a plane. For the experiment that boiling occurs, a mid-infrared camerais calibrated to measure the temperature of the irradiation surface of the aluminum plate.2、After some reasonable assumptions, it is found that a3-D unsteady conjugateconduction-natural convection model can be utilized to study the flow physics and heattransfer characteristics during laser irradiation on a liquid tank. The numerical results ofthe temperature variation of the aluminum plate and the velocity field variation of theliquid are shown to be in well agreement with the ones obtained by experiment.Utilizing the numerical model, the influences of the laser power density, the dimensionof the liquid along the direction of laser incidence, the water level in the tank on thetemperature rise of the aluminum plate and the velocity field of the liquid areinvestigated.3、Laser irradiation effects on a water tank are investigated by experiments andnumerical simulations when the water is in a natural convection state. The irradiationmechanisms can be described as follows: at the initial stage of laser irradiation, thecenter region of the aluminum wall has an obvious temperature increase due to laserheating, and the temperature of the water near the wall also has a slight increase. Withthe time evolution, the water temperature becomes larger and larger and the magnitudeof the max velocity vmaxon the line LC, which is perpendicular to the plate and passesthrough the laser spot center, keeps on increasing in response to the temperatureincrease, thus the heat transfer intensity continues increasing. With the increase of theheat transfer intensity, the temperature rise rate of the aluminum wall decreasesgradually. When the energy absorbed by the wall can be taken away by the water naturalconvection, the temperature rise rate of the plate center approaches to zero. If the flowfield near the velocity boundary layer doesn’t change obviously, the vmaxalso keepsconstant nearly. For the model used in this paper, during the laser irradiation, the flowfield and the temperature near the plate center doesn’t change obviously. Bigger theIabsorb, which is the absorbed power density by the plate, and quicker the temperaturerise rate approaches to zero. The temperature of the plate center and the vmaxat the endof laser irradiation increases linearly with the increase of Iabsorb. Based on the relationship, the threshold value of Iabsorbfor the nucleate boiling of water is estimated.4、Laser irradiation effects on a water tank are investigated by experiments whenboiling occurs. Utilizing the experimental data, the time needed for the occurrence ofboiling, which is donated by tB, is correlated with Iabsorb. It is found that the relationshipbetween tBand Iabsorbcan be characterized by equilateral hyperbola, which indicates twophenomena. Firstly, as Iabsorbdecreases and approaches to a threshold power density I0,tBwill approach to infinity and boiling phenomenon will not occur. This is due to thefact that the liquid temperature outside of the thermal boundary layer near the spotcenter has no obvious increase when Iabsorbis less than I0, and the energy absorbed bythe aluminum plate is totally taken away by the water natural convection, thus a heatbalance state will be reached before the wall temperature satisfies the demand thatboiling can occur. Secondly, as Iabsorbis sufficiently large, tBapproaches to a minimumvalue t0. This is due to the fact that the heat diffusion from the front surface of thealuminum plate to the back surface needs some time, and the growth and detach ofbubbles also needs some time. After the occurrence of boiling, the heat balance in thecenter region of the plate is reached quickly and the temperature rise rate approaches tozero. The balance temperature, which is donated by TC, increases with Iabsorbaccordingto the Iabsorb0.21law.5、It is found that there are two different modes for the burn-through of thealuminum plate. The first mode is described as follows: during the laser irradiation,nucleate boiling occurs firstly and lasts for a long time. With the time evolution, moreand more bubbles accumulate in the water. After the volume percentage of the bubblesincrease to a certain degree, the heat transfer intensity near the wall will drop, whichleads to the temperature increase of the plate. Then the boiling state will jump fromnucleate boiling to film boiling, which leads to burn-through. The laser burn-throughtime tmof this mode is dependent on water quantity. The second mode is described asfollows: when Iabsorbis high enough, the boiling state near the wall will jump fromnucleate boiling to film boiling without the accumulation of bubbles, which leads to asharp temperature increase of the plate and burn-through occurs. For our model, thelaser burn-through time tmdecreases linearly with the increase of Iabsorb.