Measurement of the temperature of the fluid inside the tube based on the temperature measurement of the thermally insulated outer surface

A new method for measuring transient fluid temperature in a tube is presented. The fluid temperature inside the tube is determined based on the measurement of time temperature changes on the external thermally insulated surface of the tube. To determine the fluid temperature, the inverse heat conduction problem is solved. The knowledge of the heat transfer coefficient at the inner surface of the tube is required. Two examples of applying the proposed method to the steam temperature measurements in a supercritical boiler are presented. In the first of these examples, the fluid temperature decreases stepwise, while in the second, it increases linearly and remains constant once the design temperature is reached. The practical application of the method is also shown by measuring the transient temperature of the steam in the tubes at the inlet to the second-stage superheater header. The advantage of the proposed method is measuring the steam temperature outside the fire zone, which greatly facilitates the temperature sensor installation and significantly extends the durability of the temperature sensor used.