A STUDY ON THE IMPORTANCE OF DEPENDENT RADIATIVE EFFECTS IN DETERMINING THE SPECTRAL AND TOTAL EMITTANCE OF PARTICULATE ASH DEPOSITS IN PULVERIZED FUEL FIRED FURNACES

This paper presents the results of an experimental and theoretical inv estigation on the importance of dependent effects in determining the e mittance of ash deposits. A model has been developed to predict the sp ectral emittance (directional, normal, hemispherical) of semi-transpar ent and opaque particulate deposits without considering dependent effe cts. Predictions from this model have been presented to illustrate the effects of particle size and composition. Hemispherical transmission and reflection measurements have been performed on semi-transparent an d opaque particular deposits over a wavelength range typical of pf fir ed furnances and spectral emittance has been deduced therefrom. Well c haracterised slag particles, with composition and size similar to ash deposits formed in pf fired furnances, have been used in the measureme nts. For the opaque deposit, difference between the model predictions and measurements, in terms of emittance, have been found to be signifi cant at wavelengths up to 7 mu m. This difference is believed to be la rgely due to dependent effects. Such measurements and comparisons appe ar to be the first of its kind and more experiments are recommended to quantify the effects. (C) 1997 Elsevier Science S.A.