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We present results from direct numerical simulations of two types of technologically important phase change processes: directional solidification of a binary alloy and film boiling. We use a two-dimensional finite-difference/front-tracking method which allows us to accurately follow the evolution of the interface between the phases. The method is general in the sense that discontinuities in material properties between the phases as well as topological changes are easily handled. In the directional solidification problem the fully coupled solute and energy equations for a dilute binary alloy without fluid flow are solved. The effects of latent heat, unequal material properties between liquid and solid and unsteady effects are completely taken into account. We demonstrate the evolution of a cellular interface with rejection of solute ahead of the advancing interface and in the intercellular grooves. The numerical results for the transition from a planar to a cellular interface are in excellent agreement with linear stability theory. The film boiling problem couples the phase change with fluid flow. This requires the solution of the Navier-Stokes and energy equations with interphase mass transfer. We study the growth and dynamics of a vapor layer adjacent to an upward facing, flat, heated surface. Vaporization of the liquid at the liquid-vapor interface continually replenishes the vapor lost due to bubble departure from the interface. 1. Introduction Phase change plays a central role in energy systems and materials processes. However it is usually the combination of phase change with fluid flow and heat transfer that determines, for exam

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In this paper, hourly terrestrial radiation: direct beam, diffuse and global solar radiation are modelled and calculated based on daily measured data for a horizontal surface. In addition, the same parameters were modelled for inclined surfaces. Most of the parameters modelled in this work represent a part of the input data required by building thermal simulation and solar energy systems software. Important trends of the solar radiation on tilted surfaces as a function of time and direction are being presented and discussed. The comparison of some of the results with measured data from other sources shows good agreement. The effect of tilt angle and orientation on the incident solar radiation fluxes arepresented along with optimum surface tilt angles and directions for maximum solar radiation collection in Muscat area. The results presented in this paper are quite useful for quick estimation of solar radiation for calculations of cooling load and solar collector performance. Also, the models and the computer code developed in this work form the backbone of any computer-aided building thermal design and solar systems design calculations.