Abstract: A measuring device for determining a distribution of a heat transfer medium on an inner wall of a shaftless container which rotates when used to heat the heat transfer medium with concentrated solar radiation in a solar thermal power plant or as a rotary kiln includes a distance measuring device for determining a thickness of a film of the heat transfer medium on the inner wall of the container. The distance measuring device includes at least one optical device for detecting at least one height profile along at least one measurement line projected onto the inner wall and at least one position transducer for determining a current rotational position of the respective measurement line on the inner wall. A method for determining a distribution of a heat transfer medium on an inner wall of a shaftless container is also provided.