Fluid circulation simulation in heat exchanger pipes of double tube: from cylindrical smooth surface to finned tubes

Abstract

Nowadays, and increasingly common, numerical methods using computers are setting up, both industry and teaching, to solve problems in the field of chemical engineering. The classical resolution of these problems was subject to empirical expressions adjusting the available data with a simple model that can be easily solved, said colloquially, “pencil and paper”. The resolution of the problems based on the microscopic balances of mass, energy and momentum without computer implies high computation time and inherent human mistakes. Society evolves and progresses and the technology too. The use of computers is too globalized and this is something unavoidable, so it is interesting to take advantage of this technological advance, and the increased power of these machines, to resolve microscopic balances much more quickly and accurately. There is a branch of fluid mechanics, Computational Fluid Dynamics (CFD), capable of using numerical methods and algorithms to solve and analyse problems related to fluid flow. The use of these CFD methods allows simulating the behaviour of fluid media. As the mass and energy conservation balances must be fulfilled and there are good models based on empirical data that takes into account the energy lost in the momentum balances, hence quite reliable results are obtained by CFD. CFD, therefore, presents an opportunity to have a “virtual laboratory”, where it is possible to study, simulate and obtain solutions that provide insights and better understanding of the unit behaviour. A “virtual laboratory” in all its entirety, where to test and simulate aspects that otherwise based only on experiments would require more time and resources. This project shows that the CFD tools widely used in other engineering fields such as the aeronautics is also useful for the chemical engineering purposes. This project, taking advantage of continuous research and incorporation of software in the engineering world, gives small touches of these aspects using the simulation program ANSYS®, used to resolve microscopic balances of mass, energy and momentum, focusing on the fluid flow through pipe heat exchanger: from double pipe to another complex geometry such as finned tubes. The analysis of all possibilities raised allow to obtain a general understanding of the unit. The results obtained provide an overview of the differences between units, helping the understanding of how the fluid behaves inside them. A comparison between the simulations results and the classical equation results is also provided.