Where 〖∆α〗^nom is the air in-leakage at the nominal steam power (D_sh^nom = 45 t/h) This parameter, 〖∆α〗^nom , was previously determined for all boilers tested and yielded a roughly constant value of 0.2.
Finally, to calculate the exhaust gases heat loss, q_2 , the exhaust gas enthalpy, I_b ,needs to be known. This enthalpy depends on the stack temperature T_eg . The experimental data show a linear dependence of T_eg on the stoichiometric ratio, as seen in Fig. 4. As in Fig. 3, errors bars are only depicted for the lowest and highest values of the steam power (20 and 50 t/h). Fitting a curve to the measurements relating T_eg to ∝_f and D_sh , the following equation is obtained