The article presents the results of experimental studies of mixed convection during the upflow of liquid metal in a duct with homogeneous (two-sided) and inhomogeneous (one-sided) heating of the channel walls. The results are presented in comparison with the data of previous studies in round pipes and ducts. The data are relevant for the design of cooling systems for fast reactors, as well as for the verification of design codes, whose models often do not take into account the effect of mixed convection on heat transfer. The measurements were carried out on a mercury loop using an immersion probe at the end of which a microthermocouple sensor was installed. It consisted of four thermocouples that make up two correlation pairs, allowing both the longitudinal component of velocity and temperature to be measured. The probe had the ability to move to any point of the cross-section under study using coordinate mechanisms and allowed detailed measurement of temperature, velocity fields and obtaining data necessary to determine heat transfer coefficients. As a result of the study of an extensive map of modes in a wide range of parameters (in terms of coolant flow and heating), a picture was obtained describing the behavior of heat transfer in the described configuration. A significant increase in heat transfer compared to turbulent heat exchange was found (1.5 times with one-sided heating and 3 times with two-sided heating), as well as qualitative similarity with the results related to a round pipe. Thus, the parametric analysis provides a key insight into the prediction of heat transfer in the geometry under study and discusses the differences in the formulation of the problem and the subsequent results of the experimental approach.