Esa Muurinen

Three Phase CFD-Simulation of CAS-OB Ladle

In the production of steel, the CAS-OB process is used for composition adjustment, temperature control and removal of various dissolved impurities. In this work we have studied the CAS-OB process with CFD and focused on the behavior of the slag layer, which is produced on the top of molten steel. Dynamic mesh adaption has been applied to resolve the slag layer boundary in a detailed way. As a result the time dependent evolution of the slag layer is presented. The chosen approach to describe the process offers an effective and promising way to study this complex system. In the future this model will be validated against experimental data.

CFD-Simulation of Film Boiling at Steel Cooling Process

This paper analyzes film boiling phenomena on a flat, horizontal hot steel plate using the volume of fluid method. The influence of water delivery velocity and plate surface temperature on film boiling behaviour has been quantified for the case of a single laminar flow jet assuming two-dimensional radial symmetry. In the present study, the model includes both convection and radiation induced mass and heat transfer, where the latter was found to be more important to maintain the film layer and film boiling at high temperatures. The model estimated heat and mass transfer behaviours at impingement velocities between 1 and 5 m/s and temperatures between 500 and 1300 K were found to be qualitatively consistent with available literature. The initial results obtained with the simulation suggest that computational fluid dynamics (CFD) simulation techniques represent a promising alternative for studying complex and difficult to measure phenomena such as high temperature film boiling, and hint at a new class of experimental methods for mechanistic analysis of fluid mechanical and thermal processes using purely computational methods.

Surface Patterning of Stainless Steel in Prevention of Fouling in Heat Transfer Equipment

Fouling of surfaces is a major challenge in design and operation of many industrial heat transfer equipment. Fouling causes significant energy, material and production losses, which increase the environmental impact and decrease economic profitability of processes. Even small improvements in prevention of fouling would lead to significant savings in a wide range of heat transfer applications. In this study, crystallization fouling of aqueous calcium carbonate solutions on a heated stainless steel surface is used to investigate the prevention of fouling in heat transfer equipment by physical surface modifications. Fouling behaviour of different surface patterns are studied experimentally in a laboratory scale fouling test apparatus. CFD modelling is used to study hydrodynamic and thermal conditions near surfaces with different patterns. In addition, the effect of surface pattern on the removal of particles is studied numerically. Surface patterning is found to affect the hydrodynamic and thermal conditions near the wall, and therefore to change the conditions for fouling layer build-up and removal, when compared to a flat heat transfer surface. The most promising surface pattern includes curved shapes, and it seems to create flow conditions in which improved convective heat transfer decreases the driving force for crystallization fouling. In addition, curved surfaces increase the shear forces at the wall, which prevents adhesion of the foulants to the surface and increases resuspension.

Heat Integration of a New Formic Acid Pulping and Recovery Process

A formic acid recovery process was preliminary designed for the MILOX pulping method. The effect of various process parameters on the energy consumption of the process was studied using computer simulation. When suitable process conditions were found the overall process was heat integrated using pinch technology. Significant savings can be achieved by adjusting the amount of water fed to the process, the liquor-to-wood ratio in pulping and the concentration of formic acid in pulping liquor. The energy consumption of the process can be further decreased by about 40 % using pinch technology in heat integration.