A heat exchanger, providing indirect heat transfer between a first fluid and at least one second fluid, comprises a jacket enclosing a jacket space for accommodating the first fluid and a tube bundle arranged in the jacket space and having a plurality of tubes for accommodating the at least one second fluid. The tubes form multiple tube layers. A shroud arranged in the jacket space encloses an outermost tube layer of the tube bundle. Spacers extending along the longitudinal axis are arranged between the shroud and the outermost tube layer. An interspace is present between any two spacers adjacent in the circumferential direction of the shroud, and between the shroud and the uppermost tube layer. A flow obstruction is arranged in the respective interspace and is designed to prevent or suppress a flow of the first fluid in the respective interspace, at least over a part section thereof.