| OCR Text |
Show 4 The maximum temperature in the furnace, Tfmax' is given by equation (6) as it is assumed to be equal to the adiabatic flame temperature neglecting the effect of dissociation. (6) 2.2.2 Heat Transfer in Furnace A simple heat transfer model is introduced to express the relationship between combustion gas and the materials to be heated without taking into account the details of the actual heat transfer process taking place in a furnace. The amount of heat, Qm ' gained by the heated materials is expressed by equation (7) as the sum of the radiation, Qrad , and the convection heat transfer, (konv, from the combustion gas, using f representing heat transfer ratio Qrad / ~onv here. Qm = Qrad + ~onv = (konv C1 + f) (7) Equation (8) is given by rewriting f as a function of temperature ratio, rT' of combustion gas, Tg , and materials, Tm , and coefficient, Cr' ¢CG . aCTi - T~) ,...3 ( 2 3) I CrT ) = = Cr lg 1 + rT + rT + rT h(Tg - Tm) (8) where a = Stefan-Boltzmann constant ¢CG = over-all thermal absorption coefficient h = convection heat transfer coefficient In a furnace, fCrr) generally is affected by flow condition, the temperature profile of the combustion gas and of the heated surface configuration or furnace shape. The following three assumptions were used in order to simplify this heat balance calculation . • C r is constant ' O.17 x lO- 9 defined under the condition of Tgr tf =2000K ,Tmr tf =600K \ |
