ECT imaging of thin liquid film in thermosyphons

This paper reports for the first time the investigation into the measurement of the thickness of the liquid film in a two phase closed thermosyphon using electrical capacitance tomography (ECT). The main challenge is the spatial resolution for extremely thin film, in the order of 100 μm. For image reconstruction, the Linear Back Projection (LBP) algorithm and the Landweber iteration with the optimal step length are applied and the images reconstructed using the different algorithms are compared. It was found that the former is able to provide qualitative indications of the working conditions inside the thermosyphon, but unable to achieve sufficient spatial resolutions for the measurement of the film thickness. The Landweber iteration algorithm with the optimal step length is able to reconstruct high-resolution images with enhanced spatial resolution. The capability of ECT for measuring such thin film has been demonstrated. Experimental results are compared with the established theory, i.e. the Nusselt's equation, on the film thickness. The agreements with, and discrepancies between, the measured data and the theory are discussed.