A direct observation of gas bubbles in non-transparent liquid metals is impossible by optical means. Despite of the substantial technical effort, the use of high energy radiation (g-ray or X-ray) allows also investigations of liquid metal two-phase flows.

We have used X-ray measurements to directly observe the formation of gas bubbles in mercury and InGaSn, respectively. However, due to the high attenuation of the liquid the experiment is restricted to narrow flow domains. The thickness of the fluid, which can be screened by X-ray, depends of the atomic number of the liquid metal.

In the experiments a 450kV industrial X-ray tube was employed for the inspection of liquid metal contained in rectangular cell made from Perspex. Due to the high mercury atomic number of 80, the thickness of the liquid metal layer along the beam direction has to be very narrow. Otherwise, the quality of the real time image becomes poor. Flow sequences were recorded in mercury layers with a depth of 6 mm at 450 kV and 10 mm for InGaSn at 147 kV. Experiments with InGaSn would allow an enlargement of the fluid domain, whereas for mercury the limit has been reached.

Experimental configuration of the X-ray screening technique

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