Indirect methods to determine apparent position in a falling film heat transfer measurement apparatus

Report, 2008

To improve knowledge about heat transfer in evaporation of black liquor, a research evaporator (a pilot plant) was built and a method for local heat flux and heat transfer measurements in the evaporator was developed. An unexpected difference in the measured local heat transfer coefficients between different positions along the evaporator tube made it necessary to analyse the measurement system in more detail. Indirect methods were used for this investigation, and it showed that the apparent measurement position of the thermocouples varies for the different local temperature measurements. A method for calibrating the apparent position was developed. Two of the thermocouple positions were recalibrated using this method, resulting in higher accuracy and in reduced deviations of local heat transfer coefficients from 10000 to 1000 W/m2K for water experiments, and from 2000 to 800 W/m2K for black liquor experiments.