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This paper presents results of an experimental investigation carried out to determine the effects of surface material on nucleate pool boiling heat transfer of refrigerant R113. Experiments were performed on horizontal circular plates of brass, copper and aluminum. The heat transfer coefficient was evaluated by measuring wall superheat and effective heat flux removed by boiling. The experiments were carried out in the heat flux range of 8 to 200kW/m2. The obtained results have shown significant effect of surface material, with copper providing the highest heat transfer coefficient among the samples, and aluminum the least. There was negligible difference at low heat fluxes, but copper showed 23% better performance at high heat fluxes than aluminum and 18% better than brass.

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The present research focuses on the simulation of encased stone columns in a 2D state by utilising the coupled finite difference method (FDM) and discrete element method (DEM). The stone column material was modelled by DEM using irregularly shaped particles, and the geotextile used as the encasement of the stone column was simulated using parallel-bonded particles. The surrounding clayey soil was modelled by FDM. Two models were combined by employing a direct coupling method. After validating the coupled DEM-FDM model through comparisons with experimental results, the encased stone column was investigated at the micro and macro scale. The results indicated that the coupled model can imitate the behaviour of the encased stone column to a reasonable degree. Furthermore, the encased stone column exhibited different deformation behaviour than the ordinary stone column. The use of the encasement decreased the stress deviation at the top and bottom of the column. Also, the soil surrounding the encased stone column displayed different displacement behaviour than the soil surrounding the ordinary stone column. In addition, the effect of encasement length on stone column responses was examined.

Combination of the continuum-based numerical methods and the discrete element method (DEM) could be a powerful way of simulating complex problems. This approach benefits from the capabilities of both methods. The main feature of the discrete element method is that the soil grains are considered as individual particles without need to impose any behaviour law in modelling the medium. The limitation of this method is, however, its high computational demand. In continuum based methods, on the other hand, it is impossible to trace micro scale phenomena. According to these facts, combining continuum and discrete methods is an optimal way in approaching geotechnical problems which deal with granular soils. In this approach, the coarse grain zone (medium) is modelled using DEM and the surrounding media are modelled using the continuum methods. Stone columns that are widely used for improving and/or increasing the strength of weak soils could be modelled using this type of coupled simulation. The Coarse aggregates present in the stone column make it appropriate for the coupled modelling. In this paper, the ordinary and encased stone columns have been simulated by combining 2D DEM and finite difference method (FDM). Clump technique was employed to achieve the interlocking of aggregate particles in DEM, and the surrounding cohesive soil was modelled using FDM. The obtained results were validated by the reported experimental results in the literature, indicating that the coupled DEM-FDM method is a robust way to simulate stone columns.