Measurements of local heat flux to membrane water walls of combustion chambers

摘要

Three different tubular type instruments (flux tubes) were developed to identify steady-state boundary conditions in water wall tubes of steam boilers. The first meter is constructed from a short length of eccentric smooth tube containing four thermocouples on the fire side below the inner and outer surfaces of the tube. The fifth thermocouple is located at the rear of the tube on the casing side of the water-wall tube. The second flux tube has two longitudinal fins which are welded to the eccentric smooth tube. In the third solution the fins are attached to the water wall tubes not to the flux tubes as in the second variant of the flux tubes. The first instrument is used to measure the heat flux to water walls made from bare tubes, while another two heat flux tubes are designated for measuring the heat flux to membrane walls. In contrast to the existing devices, the flux-tube is not attached to adjacent water-wall tubes. The boundary conditions on the outer and inner surfaces of the water flux-tube are determined from temperature measurements at interior locations. Temperature dependent thermal conductivity of the flux-tube material was assumed. An inverse problem of heat conduction is solved using the least-squares method. Three unknown parameters are estimated using the Levenberg-Marquardt method. At every iteration step, the temperature distribution over the cross-section of the heat flux meter is determined using the ANSYS/CFX software.