امير بابائي

In recent years, the existence of a balance between the heat transfer rate and pressure drop due to performance improvement is one of the most important issues in the design of heat transfer systems and the attention of researchers. The use of nanofluids and porous media are common methods for increasing heat transfer. However, these methods also exacerbate pressure drop in addition to increasing heat transfer. Hydrophobic surfaces with cavity areas cause a slip boundary condition on the surface and so diminishes pressure drop whereas expanding heat transfer. In this way, the present study provides a 3D numerical research on the hydro-thermal performance of water-Al2O3/CuO nanofluids and water/Al2O3-CuO hybrid nanofluid inside a U-bend tube incorporating a porous medium with both hydrophilic and hydrophobic surfaces. To a broad variety of governing parameters, the assessments were done. Applying a finite volume approach, simulations were performed in the laminar flow regime. Furthermore, a single-phase flow is adopted to simulate the nanofluid flow. Taking into consideration the equation of the Darcy-Brinkman-Forchheimer, to simulate the flow of fluids in the porous media. Moreover, the U-bend pipe's walls have steady and uniform heat flux as thermal boundary conditions. For various Darcy and Dean numbers, the average Nusselt number, volume fraction (0% to 5%), and performance eva‎luation criteria (PEC) were eva‎luated. The current study's outcomes were matched to the experimental data and the verity of the simulations is confirmed, owing to the theoretical and experimental results being in good accord. Considering the outcomes, a completely hydrophobic wall has a better hydro-thermal performance than a completely hydrophilic one and other hydrophilicity and hydrophobicity combinations. As well, improvement in heat transfer efficiency is considerably influenced by the Darcy number (10-4-10-1) and the augmentation of the porous thickness ratio. For example, applying porous medium with rp = 0.6 in the wall with a Darcy number of 0.1 increases the Nusselt number and pressure drop by 1285% and 1084%, respectively. In addition, in the case of adding copper oxide nano particles with a volume fraction of 5% in the base fluid and without applying the porous medium, the Nusselt number and pressure drop increase by 17.9% and 18.7%, respectively. Also, in the same configuration of the porous medium, adding copper oxide nanofluid with a volume fraction of 5% in the base fluid. It increases the Nusselt number and pressure drop by 5.4% and 25.7%, respectively. Additionally, average Nusselt number and pressure losses for all types of nanofluids show an incremental schema with augmenting volume fraction, while PEC exhibits a reducing pattern. While in the case of not applying porosity in the U-shaped tube for all nanofluids, the average Nusselt number, pressure drop and (PEC) show an increasing pattern with increasing volume fraction. Besides this, structures with permeable porous media or ones with Da = 0.1 and rp = 0.6 present the highest PEC.

سطح آبگريز , نانوسيال , محيط متخلخل , بررسي عددي , معيار ارزيابي عملكرد

Hydrophobic surface , Nanofluid , Porous media , Numerical investigation , Performance eva‎luation criterion (PEC)

amir babaei

hamid saffari