| OCR Text |
Show • 3 a = ratio of the recirculated heat to the total heat contained in the recirculated gas flow and the subscripts are; in : input, rec : recirculation, exh : exhaust, cold: initial state, f : fuel, ev : excess value, m : heated materials, loss : loss Based on this equation, the characteristics of the improved heating method with heat and combustion product recirculation, particularly in the thermal field where radiation controls heat transfer, were studied by changing major parameters affecting furnace temperatures and thermal efficiencies of furnaces. 2.2 Heat Balance in the System 2.2.1 Gross Heat Input The quantities of heat transferred from the hot flue gases to the fuel and air by a counter type of heat exchanger can be given by equation (2). { Qev = ~h (Cm )in (Tout - TCOld) ~h = (LK/(Cm)in)/(l + LK/(Cm)in) (2) where Tcold = initial temperature of fuel and air Tout = flue gas temperature at the furnace outlet (Cm)in = sum of heat capacity of fuel and air ~h = heat exchange coefficient L = Length of the heat exchanger K = gross heat transfer coefficient of the heat exchanger The temperature at the exit of the heat exchanger, Yin!' and the temperature after the mixer, Yin2 ' are given in equation (3) and (4) respectively. Ratio of mass recirculation to the inlet mass is defined in equation (5). 1'; - T, + Qev inl - cold (Cm)in Yin! + a Qrec/(Cm)in lin 2 = ......:.:..:.,;~-l-+.:...:::R=-=---~ R = (m,.ec/~n) (3) (4) (5) |
