Calculation of Temperature Distribution in Boiler Water Wall Tube

The temperature distribution of boiler water wall tube regarding the pressure drop along the tube is calculated. In this work water enters the riser as compressed liquid and leaves at low vapor quality values, whereas uniform heat source supplies the heat flux required to the evaporation process. Temperature rises before the flow boiling process, may lead to the failure of heated tube; hence we should control the temperature along the tube to not exceed the allowable temperature. While calculating the water wall in vertical tubes, we should note that the pressure drop effect on flow and fluid properties cannot be neglected, as the pressure drop is comparable to operating pressure. Twophase flow pressure drop and two-phase properties such as void fraction are also investigated in this study. The tube length is divided into small cells that the flow and fluid properties in each cell can assume to be uniform. Two main thermal regions and three sub regions are initiated in flow boiling; hence different correlations should apply to each region to calculate the heat transfer coefficient which is prerequisite of calculating the wall temperature. A computer program has been written to divide the tube length to small equal length cells and calculate pressure drop of each cell and update the flow properties in that. It also implies the appropriate heat transfer correlation to calculate heat transfer coefficient and wall temperature of each cell. The wall temperature distribution in the pressure of 22.7 KPa is compared to experimental results, and a system in the pressure of 150 KPa is numerically analyzed.

Keywords:

Water flow boiling , Two-phase flow pressure drop , wall temperature , sub atmospheric pressure