Thermal radiation absorption is known to be an important mechanism of energy transfer in many particulate systems. In the past, radiation absorption by a particle has been analyzed mostly from an external-field viewpoint in which absorbed energy is indirectly determined from the external scattered radiant field. The purpose of the present work is to study the internal interaction of electromagnetic radiation with a small particle and the associated energy transport phenomena.; The optical constants, n and k, are essential for determining the internal electromagnetic field of an irradiated particle. Experiments were, therefore, conducted to obtain these properties. Two liquid hydrocarbon fuels, heptane (C{dollar}sb7{dollar}H{dollar}sb{lcub}16{rcub}{dollar}) and decane (C{dollar}sb{lcub}10{rcub}{dollar}H{dollar}sb{lcub}22{rcub}{dollar}), were selected as the experimental samples, as they are commonly-used fuels in droplet combustion systems and their optical constants in the infra-red spectrum are not currently available. The resulting spectral n and k of heptane and decane in the wavelength region from 2.5 {dollar}mu{dollar}m to 15 {dollar}mu{dollar}m are tabulated for convenient use.; Classical electromagnetic theory is then utilized to determine the internal distribution of absorbed radiant energy of an irradiated particle. The effects of complex refractive index and size-to-wavelength parameter on the internal absorption field are thoroughly analyzed, particularly to devise a regime map which indicates the region of the most concentrated energy absorption. A diagram which illustrates the optimum combination of the complex refractive index and the size-to-wavelength parameter for maximum local peak absorption is also constructed for thermal engineering design and application. In addition, the accuracy of the geometrical optics approach is examined by comparing results from this analysis with those obtained from electromagnetic theory. Ultimately, a criterion is established to define the applicability of geometrical optics in internal radiant absorption problems.; This work presents an analytical investigation on the transient thermal behavior of a particle with internal radiant absorption. The coupled phenomena of thermal conduction, thermocapillary convection and internal radiant absorption are analyzed here to explore the heat transfer mechanisms of an irradiated droplet. Two novel dimensionless parameters are introduced to characterize the relative importance of energy transport by both conduction and thermocapillary convection, as compared with that by radiation. Parametric studies on the transport phenomena induced by internal non-uniform radiant absorption are carried out, establishing criteria that define the circumstances in which the other two modes of energy exchange are negligible in relation to thermal radiation.
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