Method for determining a state of a heat exchanger device which has means for transferring heat with the aid of at least one process flow, a) wherein a thermohydraulic simulation of the at least one process flow is effected by at least one passage in the heat exchanger device for determining temperature and/or heat transfer coefficient profiles of the means for transferring heat, b) wherein time-variable temperature boundary conditions are ascertained during the thermohydraulic simulation; and c) wherein the state of the heat exchanger device is determined with the aid of a finite element method for a structural-mechanical calculation of the state as a function of the variable temperature boundary conditions; d) wherein, for the thermohydraulic simulation, a respective passage with a coupled means for transferring heat is mapped onto a one-dimensional model system having a process flow infeed, a heat transfer path, and a process flow outfeed, wherein a one-dimensionally extended body having a heat capacity lies along the heat transfer path, e) wherein, for the thermohydraulic simulation, a respective passage is described with the aid of one-dimensional Navier-Stokes equations; and wherein the method further includes the steps of: detecting several passages of the heat exchanger device, each having a start point and an end point, wherein a respective start point or end point corresponds to a process flow infeed or a process flow outfeed; detecting nodes between the detected passages, wherein several start and/or end points converge at a node; associating a one-dimensional model with every detected passage; determining pressures of the process fluid at process flow outfeeds and the nodes; and performing a spatially and temporally discretized, computer-implemented calculation of the respective one-dimensional model for determining the temperature and/or heat transfer coefficient profiles. a) wherein a thermohydraulic simulation of the at least one process flow is effected by at least one passage in the heat exchanger device for determining temperature and/or heat transfer coefficient profiles of the means for transferring heat, b) wherein time-variable temperature boundary conditions are ascertained during the thermohydraulic simulation; and c) wherein the state of the heat exchanger device is determined with the aid of a finite element method for a structural-mechanical calculation of the state as a function of the variable temperature boundary conditions; d) wherein, for the thermohydraulic simulation, a respective passage with a coupled means for transferring heat is mapped onto a one-dimensional model system having a process flow infeed, a heat transfer path, and a process flow outfeed, wherein a one-dimensionally extended body having a heat capacity lies along the heat transfer path, e) wherein, for the thermohydraulic simulation, a respective passage is described with the aid of one-dimensional Navier-Stokes equations; and wherein the method further includes the steps of: detecting several passages of the heat exchanger device, each having a start point and an end point, wherein a respective start point or end point corresponds to a process flow infeed or a process flow outfeed; detecting nodes between the detected passages, wherein several start and/or end points converge at a node; associating a one-dimensional model with every detected passage; determining pressures of the process fluid at process flow outfeeds and the nodes; and performing a spatially and temporally discretized, computer-implemented calculation of the respective one-dimensional model for determining the temperature and/or heat transfer coefficient profiles. detecting several passages of the heat exchanger device, each having a start point and an end point, wherein a respective start point or end point corresponds to a process flow infeed or a process flow outfeed; detecting nodes between the detected passages, wherein several start and/or end points converge at a node; associating a one-dimensional model with every detected passage; determining pressures of the process fluid at process flow outfeeds and the nodes; and performing a spatially and temporally discretized, computer-implemented calculation of the respective one-dimensional model for determining the temperature and/or heat transfer coefficient profiles.