Abstract
Under steady-state conditions when fluid temperature is constant,
temperature measurement can be accomplished with high degree of accuracy
owing to the absence of damping and time lag. However, when fluid
temperature varies rapidly, for example, during start-up, appreciable
differences occur between the actual and measured fluid temperature. These
differences occur because it takes time for heat to transfer through the
heavy thermometer pocket to the thermocouple. In this paper, a method for
determinig transient fluid temperature based on the first-order
thermometer model is presented. Fluid temperature is determined using a
thermometer, which is suddenly immersed into boiling water. Next, the time
constant is defined as a function of fluid velocity for four sheated
thermocouples with different diameters. To demonstrate the applicability
of the presented method to actual data where air velocity varies, the
temperature of air is estimated based on measurements carried out by three
thermocouples with different outer diameters. Lastly, the time constant is
presented as a function of fluid velocity and outer diameter of
thermocouple.
Go to article