In a boiler, heat is transferred from the products of combustion to the steam. the temperature of the products of combustion decreases from 1100oc to 550oc while the pressure remains constant at 0.1 mpa. the average constant pressure specific heat of the products of combustion is 1.09 kj/kg-k. the water enters at 0.8 mpa, 150oc and leaves at 0.8 mpa, 250oc. determine the exergy destroyed for this process per kilogram of water evaporated.