Convergent-divergent design of fins for simultaneous thermo-hydraulic improvement assisted by dual-flow topology optimization

Ahmad Fawaz$^{1,\star}$, Yuchao Hua$^{1}$, Steven Le Corre$^{1}$, Lingai Luo$^{1}$, Yilin Fan$^{1}$
$^{\star}$ : ahmad.fawaz@univ-nantes.fr
$^{1}$ Nantes Université, CNRS, Laboratoire de thermique et énergie de Nantes, LTeN, UMR6607
Mots clés : Topology optimization, Plate heat exchanger, Convergent-divergent, Conjugate heat transfer, thermo-hydraulic performance, Synergy field.
Résumé :

Reducing the energy consumption has been widely considered an essential topic in energy systems. In most of heat recovery systems, heat exchangers (HXs) play a crucial role to benefit from the energy carried by the emitted gases leading to a significant cost savings. Categorically, plate heat exchangers (PHEs) are extensively employed in heat transfer applications that works under low-to-medium pumping power. Equipped with lightweight and highly effective heat transfer surfaces, PHEs provide superior thermal performance when compared to other heat exchangers. In recent decades, numerous active and passive methods were involved to improve the efficiency of HXs. Although the passive techniques such of using extended surfaces as fins has, in practice, been well-demonstrated one of the most effective techniques in improving heat transfer rates by increasing surface area and disrupting fluid flow with the disadvantages of significantly increasing the pumping power losses. In the early stages, researchers typically designed fins intuitively based on their background and understanding of physics. Thereafter, due to the advances in computer technology and numerical simulations, the possibility of designing optimal fins increased with the help of several optimization algorithms. Fin size/shape optimization has been developed for years; however, it cannot considerably changes the mandated configuration or arrangement provided by designers. Different from the aforementioned optimization techniques, the topology optimization (TO) operates on the design domain’s topology by optimizing the material (solid or fluid) distribution spatially. Actually, it holds the maximum number of design variables in optimization and thus theoretically the most performance. In the current work, a novel design of fins with a convergent-divergent distribution is acquired by applying the density-based TO on a 2D counter flow PHE. The optimization objective is to maximize the exchanged heat between cold and hot fluids while the pressure loss is controlled using the inlet velocity. Inspiring from the topological features, a convergent-divergent fin arrangement is self-designed using rectangular fin shape. For comparison purpose, a PHE with conventional design of fins is introduced having the same solid fraction, boundary conditions and dimensions of the optimized PHE. Thereafter, a CFD analysis is carried out on the three PHEs with optimized, self-designed and conventional fins to evaluate and compare their performance. For the same pumping power, the heat transfer rate of the PHEs with optimized and self-designed fins is higher than the PHE with conventional fins with an intensification up to 25% and 10% respectively. To confirm the superiority of the optimized and self-designed fins over the conventional one, the synergy field number that represents the synergy angle between the velocity and temperature gradient vectors is utilized to test and compare the convective heat transfer performance. The results show an advantage of both optimized and self-designed fins over the conventional design with an improvement up to 42% and 15% respectively.

Work In Progress