Transport phenomena occurring during the heating of a non-agitated liquid in a closed cylindrical container were studied. Existing literature on this and analogous problems is briefly reviewed. Special attention is devoted to studies on natural convection in environments of non-uniform temperature. Our experimental work revealed the existence of a boundary layer flow at the vertical sidewall of the container, together with a stratified core in the upper part and a perfectly mixed, unstratified region in the lower part of the container. For the heat transfer rate a dimensionless correlation is found revealing Nu to be approximately proportional to (GrPr)1/4. From the observed flow patterns and temperature profiles a simplified mathematical model is developed, with which the temperature stratification in the liquid during heating could be simulated. The model may be applied to conversion calculations of a first order chemical reaction (e.g. destruction of micro-organisms).