Method for non-intrusively determining the temperature of a fluid flowing through a conduit portion

A system for determining a temperature of a fluid flowing through a pipe section, the system comprising:

• an evaluation unit;
• and
• a first temperature sensor,
• wherein evaluation unit is configured:
• to obtain a temperature of the pipe section,
• to obtain a reference temperature measured by using the first temperature sensor at a distance from a surface of the pipe section,
• to determine a heat transfer behavior, comprising a thermal resistance, of a boundary layer of the fluid on an inner wall of the pipe section based on at least one material property and at least one value of a state variable of the fluid,
• to determine the temperature of the fluid based on the heat transfer behavior of the boundary layer, a heat transfer behavior, comprising a thermal resistance, of the pipe section, the temperature of the pipe section, and the reference temperature.