The present study explores experimentally the process of melting of a phase change material (PCM) in vertical circular tubes. The study is performed with a commercially available paraffin-type material with the melting point of about 28 degrees Celsius. The experiments are conducted using vertical tubes of four different diameters, filled with the PCM and immersed in a water bath. In each tube the experiments are performed at the water bath temperatures of 10, 20 and 30°C above the melting point of the paraffin. Three different initial heights of the PCM inside the tubes are considered, thus bringing the total number of cases explored to thirty six. Each tube is thermally insulated at the bottom, and at its top open to atmosphere, to allow free expansion of the melt liquid. The tubes are transparent, and the melting process is monitored and recorded by a digital camera. The digital pictures of the melting process are analyzed, and the results are graphically presented as melt fraction vs. time, showing the effects of tube diameter, PCM height and temperature difference. Generalization of the results is attempted based on the dimensionless groups, including the Fourier, Stefan, and Rayleigh numbers. A correlation connecting the melt fraction with these dimensionless groups is suggested.