AbstractThe zone method for analysing radiative heat transfer has been widely applied for furnace modelling, and is extensively reported in the open literature. The main reason for the application of this method lies in the accuracy with which it solves the radiant transfer in hot enclosures. Thus, it is generally the preferred method when it is essential to predict accurately the temperature distribution in the furnace. Its application, however, has been limited in most cases by the need to over-simplify the furnace conditions. These simplifications include the need to modify the furnace shape and zoning arrangement, the load representation, and the simulation of convection. Another significant feature of most applications of the zone method is the restriction of the simulation to steady-state conditions.
This Ph.D. project aims to eliminate some of these constraints and, therefore, improve application of the zone method to furnaces. Hence, full transient conditions were simulated for different zone models, which varied in complexity from a single gas zone model to a full 3D multi-zone version. The exchange factors required in the zone method were calculated by a Monte-Carlo method using RADEX, a suitable computer code which enabled the furnace geometry to be accurately represented as well as the load, which could be simulated by a series of individual components instead of a single big slab covering the entire hearth surface area. Two different furnaces were modelled, namely a steel reheating furnace and a heat treatment furnace. Experimental data from production were used to validate the heat treatment system mathematical model. Parametric studies were then performed for both furnaces. The predictions clearly demonstrate the need for multi-zone transient models since the load temperature-history was significantly different from that predicted by a simpler long-furnace model.
Another aim of the project was to produce reliable data concerning the convective heat transfer in furnaces. This parameter is often ignored in furnace modelling, or if included has been restricted to a crude single empirical value (usually 5 - 10 W/m2K). This can produce erroneous results in applications where the flame and combustion products temperatures are low, as in heat treatment furnaces. In these cases convection may play a more important role than is currently assumed. A mass transfer technique was employed in order to determine heat transfer coefficients for the heat treatment furnace for a variety of load arrangements and firing conditions. These coefficients which were significantly higher (25 - 45 W/m2K) than the usually assumed crude values were subsequently used in the mathematical models of the furnace performance.
|Date of Award
|Robert Tucker (Supervisor)