Experiment On Effect Of Rotation On Thermocapillary Convection Of Silicone Oil In Shallow Annular Pool

In order to understand the effect of system rotation on stability and wave patternof thermocapillary convection a series of experiments of thermocapillary convection ina slowly rotating shallow annular pool (Ri=20mm, Ro=40mm, and depth H=1mm) ofsilicone oil were conducted on-ground. The critical temperature differences (ΔTc`s) forthe incipience of oscillatory flow for two kinds of silicone oil (KF-96L-0.65CS andKF-96L-1CS) were measured at two cases of heat direction, i.e., heated from outer walland heated from inside wall. The hydrothermal waves (HTWs) under differenttemperature differences and rotational speeds were observed by a shadowgraph method.The temperature fluctuation on the pool surface was measured by an IR camera.The experimental found that, the ΔTcis about6K for0.65cSt silicone oil underdifferent rotational speed, and it is11K for1cSt silicone oil. Heating direction gives avery little effect on the ΔTc`s for the two kinds of silicone oils.The characteristics of HTWs changes with the rotational speed for0.65cSt siliconeoil when heated from outside wall. There are two groups of HTWs which propagate inopposite azimuthal direction when rotational speed is less than3rpm; There only existone group of HTWs which propagates in clockwise direction when3rpm n6rpm.When rotational speed is larger than7rpm another group of HTWs appears near theinside wall, which propagates along the counterclockwise direction. For1cSt silicone oilheated from outside wall, a kind of steady multi-cellular pattern appears near the outsidewall in the stationary pool as well as in the rotating pool when the temperaturedifference is slightly less than ΔTc. When the temperature difference exceeds the ΔTc,two groups of HTWs propagate in opposite directions in non-rotating pool. But inrotating pool when the temperature difference slightly exceeds ΔTc, only one group ofHTWs remains in the pool and propagates in azimuthal direction opposite to that ofpool rotation. With the increase of imposed temperature difference, the propagatingdirection of the HTWs is partly or totally reversed. Temperature amplitude on liquidsurface decreases with the increase of the rotational speed. However, it increases withthe increase of temperature difference. The oscillatory frequency increases with theincrease of rotational speed and also increases with the temperature difference.When heated from inside wall, a kind of flower-like waves appears near the insidewall for both0.65and1cSt silicone oil under a slightly higher temperature difference. Its propagating direction is as same as the HTWs. In a stationary liquid pool, there aretwo groups of HTWs propagating in opposite azimuthal direction. However, only onegroup of HTWs remains in rotating pool. For1cSt silicone oil, a kind of steadymulti-cellular pattern appears near the inside wall when the temperature difference isslightly less than the ΔTc.The experiment also found that, when heated from inside wall the propagatingdirection of HTWs is same as the bending direction of HTWs. However, they areopposite each other when heated from outside wall. Either for the case heated fromoutside wall or that heated from inside wall the HTWs always start at the hot wall, andextend to the cold wall.