A Computational Fluid Dynamics Model for Designing Heat Exchangers based on Natural Convection

A computational fluid dynamics model was created for the design of a natural convection shell-and-tube heat exchanger with baffles. The flow regime proved to be turbulent and this was modelled using the image–image turbulence model. The features of the complex geometry were simplified considerably resulting in an almost two-dimensional mesh with only 30 000 mesh cells. The effect of black-body radiation was investigated. The modelling results were validated experimentally and a model neglecting the effect of radiation turned out to be sufficiently accurate, reducing calculation times with a factor 60. Different meshes were used to check that the solution did not depend on the mesh chosen. The measurements indicated that the cross-flow caused by the baffles improved the heat-flux dramatically. The heat exchanger in this case study was intended to be used in an experimental greenhouse. The usefulness of the heat exchanger model was demonstrated by applying it to relevant variations of the experimental arrangements. The model calculations resulted in many recommendations on the dimensions and the operation of the heat exchanger.