Measurement of Transient Fluid Temperature in the Heat Exchangers

Abstract

In the chapter, a method for measuring the transient temperature of the flowing fluid based on time temperature changes of the thermometer is described. In the presented method, the thermometer is considered as an inertial system of first and second order. To reduce the influence of random errors in the temperature measurement, the local polynomial approximation based on nine points is used. As a result, the first and second derivatives of a temperature, which indicate how the temperature of the thermometer varies over time, are determined very accurately. Next, the time constant is defined as a function of fluid velocity for sheathed thermocouples with different diameters. The applicability of the presented method is demonstrated on real data in the experiment. The air temperature is estimated from measurements carried out by the three thermocouples having different outer diameters when the air velocity varied in time. A comparison of the computed temperatures of air gives confidence to the accuracy of the presented method. The method presented in this chapter for measuring the transient temperature of the fluid can be used for the online monitoring of fluid temperature change with time.