Abstract: A shell-and-tube heat exchanger for heating viscous fluids, in particular, for heating liquid fuel in thermal power stations, comprising a shell with external tubes located therein which contain heating elements constructed in the form of internal tubes plugged at one end and auxiliary tubes contained therein for supplying a heating medium to the heating elements, the viscous fluid flowing between the external and the internal tubes, tube plates for fixing the external and internal tubes to the shell, and partitions for dividing the bundle of external tubes into sections, the number of external tubes in each section being different and proportional to the viscosity of the heated fluid flowing in the appropriate section.