OCR Text |
Show 6 4n = length of the heat exchanger bm = the sum of reciprocal of the heat capacity 2.2.3 Heat Output The amount of heat flowing out of the furnace, Qout ' and flowing out of the counter type heat exchanger, Qexh' are given by equation (12) and (13) respectively. (12) lQexh = (kut - Qev T -T, (1v exh - out (Cm)in (13) 2.3 Equation Arrangement Through the above heat balance analysis, a relationship between combustion gas temperature at the furnace outlet, Tout, and other variables were obtained as equation (12). Another relationship in terms of the quantity of the heat transferred from combustion gas to the heated materials in the furnace, Qm' were also obtained as equation (7) by estimating the convection and radiation heat transfer rate based on the same assumptions which simplifies the actual heating process. Equations (7) and (12), can be rewritten with the use of the basic variables shown in equations (14) and (15) respectively. These equations can be calculated as two simultaneous equations numerically when specific values are given to those variables except for two arbitrary variables. It is necessary to provide initial conditions for heat input with fuel, Qf' heat loss in furnace, Qloss' and temperature of fuel and air, Teold' For example, Qm and Tout are calculated from these two equations by giving certain values to other variables, R, a, ~a' ~m' 'r, (Cm)in' (Cm)m' (14 ) (15) \ |