When an electromagnetic wave interacts with participating media (e.g. particulate media); the intensity of the radiation may be changed by the absorption, emission and scattering phenomena . Subsequently, the incident radiation will be attenuated and/or aug mented under the effect of these phenomena. Light scattering and absorption by small particles are quite important in a wide range of applications such as meteorology, biomedicine, biophysics, astronomy, combustion, fire and flame and solar thermal applic ations. Particulate media have been introduced as a working medium to improve the efficiency of thermal systems such as solar thermal power plants. The efficiency of the direct absorption solar thermal collectors (DASC) can be improved by using particulate media because of the unique thermo optical properties , which in turn leads to enhance the thermal performance. The main objective of the present study is to investigate the effect of the participating media in the volum etric heat generation under the concept of photo thermal energy conversion.