Enhancement of the heat transfer is done, in many industrial applications, by permanent change of the fluid flow, as in spiral, compact or coiled tube heat exchangers. The Dean vortices, which appear as a result of the secondary flow, are responsible for the increase of local turbulence, and thus, the decrease of prob-ability of stagnant zone development, which, in turn, lower the chance for the solids to sediment. A new patented heat exchanger was studied whose both cold and hot fluids flow along paired helical path. The ratio heat transfer aria/equipment volume is sufficiently high to classify it as compact. The experiments proved its capacity to deal with important thermal duties even for small driving forces, due to the high partial heat transfer coefficients obtained for low Reynolds numbers. Also, good values for the exergetic coefficient were acquired. A mathematical model for this heat exchanger was developed, its solutions permitting a better understanding of the impact that the design parameters like spiral step or wall thickness have upon its performance. This model consists of a system of ODEs, resulted from the spatial periodicity of the helical channels. The technique used to solve it has an iterative nature, because the temperature map must be assumed. The convergence is obtained if two successive maps are close enough. A fairly good agreement between the experiments and the model was observed.
展开▼
