At present, temperature distribution across the channel cross section is regarded as an adequate substitute, being both easy & cheap to measure. The accepted method of measuring the temperature distribution uses 3 triplex thermocouples, which are normally installed vertically through the roof, & are designed to provide temperature readings at 3 different levels. To allow easy comparison of various sets of readings, the 9 temperature values of a single data set are treated mathematically to give a value, which is normally quoted as a percentage. If all of these are the same the formula will give a value of 100, which is referred to as the Thermal Homogeneity Index (THI). However, there is little information concerning the practical aspects of this type of measurement & in particular, the various inaccuracies that are inherent in the measurement.
