The well-known "zone method", treats thermal radiation in an enclosure in a global manner so that reiabile estimates of this moe of heat transfer can be obtained in systems such as gas-fired furnaces. Consequently the paper employs a two-dimensional thermal radiation model in which both the height and length of the furnace was divided into surface and volume zones. An isothermal computational fluid dynamics simulation was used to estimate the relative mass flow rates, and hence enthalpy flows, into or out of each volume zone. This simplified approach was considered to provide a ressaonable estimate of the appropriate inter-zone mass flows ince the use of small-scale experimental, near ambient temperature models have been shown in the past to given useful data on flow related behaviour of combustion systems. The computing time resulting from the coupling of a multi-zone model with a single isothermal computation of the flows are relatively short so that the transient performance of the reheating furnace can be analysed. The mathematical model was thus used topredict the fuel consumptions and load temperatures in a gas-fired furnace heating steel bars to a nominal discharge temperature of 1250 deg C over a tyhpical transient operating period of 8 hours indlucing the start-up from cold. The influences of burner geometry as well as the effects of changes to the value of the roof set point temperature which was used to control the thermal input to the burners were studied. The effects of varying t he position of the roof temperature control sensor relative to the burners and of changes in the changes in the roof construction were also investigated.
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