Purpose

Thermal energy storage systems use thermal energy to elevate the temperature of a storage substance, enabling the release of energy during a discharge cycle. The storage or retrieval of energy occurs through the heating or cooling of either a liquid or a solid, without undergoing a phase change, within a sensible heat storage system. In a sensible packed bed thermal energy storage system, the structure comprises porous media that form the packed solid material, while fluid occupies the voids. Thus, a cavity, partially filled with a fluid layer and partially with a saturated porous layer, has become important in the investigation of natural convection heat transfer, carrying significant relevance within thermal energy storage systems. Motivated by these insights, the current investigation delves into the convection heat transfer driven by buoyancy and entropy generation within a partially porous cavity that is differentially heated, vertically layered and filled with a hybrid nanofluid.

Design/methodology/approach

The investigation encompasses two distinct scenarios. In the first instance, the porous layer is positioned next to the heated wall, while the opposite region consists of a fluid layer. In the second case, the layers switch places, with the fluid layer adjacent to the heated wall. The system of equations for fluid and porous media, along with appropriate initial and boundary conditions, is addressed using the finite difference method. The Tiwari–Das model is used in this investigation, and the viscosity and thermal conductivity are determined using correlations specific to spherical nanoparticles.

Findings

Comprehensive numerical simulations have been performed, considering controlling factors such as the Darcy number, nanoparticle volume fraction, Rayleigh number, bottom slit position and Hartmann number. The visual representation of the numerical findings includes streamlines, isotherms and entropy lines, as well as plots illustrating average entropy generation and the average Nusselt number. These representations aim to provide insight into the influence of these parameters across a spectrum of scenarios.

Originality/value

The computational outcomes indicate that with an increase in the Darcy number, the addition of 2.5% magnetite nanoparticles to the GO nanofluid results in an enhanced heat transfer rate, showing increases of 0.567% in Case 1 and 3.894% in Case 2. Compared with Case 2, Case 1 exhibits a 59.90% enhancement in heat transfer within the enclosure. Positioning the porous layer next to the partially cooled wall significantly boosts the average total entropy production, showing a substantial increase of 11.36% at an elevated Rayleigh number value. Positioning the hot slit near the bottom wall leads to a reduction in total entropy generation by 33.20% compared to its placement at the center and by 33.32% in comparison to its proximity to the top wall.

中文翻译：

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倾斜磁场下部分填充非达西多孔介质的储能外壳中水磁 GO-Fe3O4/H2O 混合纳米流体的浮力驱动传热和熵分析

 目的

热能存储系统利用热能来升高存储物质的温度，从而能够在放电循环期间释放能量。能量的存储或回收是通过在显热存储系统内加热或冷却液体或固体而发生的，而不发生相变。在显热填充床热能存储系统中，结构包括形成填充固体材料的多孔介质，而流体占据空隙。因此，部分填充流体层、部分填充饱和多孔层的空腔在自然对流换热研究中变得很重要，在热能存储系统中具有重要意义。受这些见解的启发，当前的研究深入研究了部分多孔腔内由浮力和熵产生驱动的对流换热，该腔体被差异加热、垂直分层并填充混合纳米流体。

设计/方法论/途径

调查涵盖两种不同的场景。在第一种情况下，多孔层位于加热壁旁边，而相对的区域由流体层组成。在第二种情况下，各层交换位置，流体层靠近加热的壁。使用有限差分法求解流体和多孔介质的方程组以及适当的初始条件和边界条件。本研究中使用 Tiwari-Das 模型，并使用球形纳米颗粒特有的相关性来确定粘度和导热率。

 发现

考虑了达西数、纳米颗粒体积分数、瑞利数、底部狭缝位置和哈特曼数等控制因素，进行了全面的数值模拟。数值结果的视觉表示包括流线、等温线和熵线，以及说明平均熵生成和平均努塞尔数的图。这些表示旨在深入了解这些参数在各种场景中的影响。

 原创性/价值

计算结果表明，随着达西数的增加，在GO纳米流体中添加2.5%的磁铁矿纳米粒子会导致传热率增强，案例1增加了0.567%，案例2增加了3.894%。如图 2 所示，案例 1 的外壳内传热增强了 59.90%。将多孔层放置在部分冷却的壁旁边可以显着提高平均总熵产生，在瑞利数值提高时显示出 11.36% 的大幅增加。将热缝放置在靠近底壁的地方，与放置在中心处相比，总熵产生减少了 33.20%，与靠近顶壁的位置相比，总熵产生减少了 33.32%。