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首页> 外文期刊>International Journal of Heat and Mass Transfer >Irreversibility analysis of thermally driven flow of a water-based suspension with dispersed nano-sized capsules of phase change material
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Irreversibility analysis of thermally driven flow of a water-based suspension with dispersed nano-sized capsules of phase change material

机译：用分散的相变材料分散纳米粒度的水基悬浮液的热驱动流动的不可逆转分析

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A precise understanding of the thermal behaviour and entropy generation of a suspension comprising nano-encapsulated phase change materials (NEPCM) is important for the thermal energy storage and heat transfer enhancement in various engineering applications. Studies to date, have improved the knowledge of the heat transfer of NCPCM. However, a suspension comprising NEPCM in the porous medium could enhance the overall heat transfer performance. Therefore, this study aims to investigate the thermal, hy-drodynamic and entropy generation behaviour of the NEPCM-suspensions in a porous medium. Conjugate natural convection heat transfer and entropy generation in a square cavity composed of a porous matrix (glass balls), occupied by a suspension comprising nano-encapsulated phase change materials, and two solid blocks is numerically investigated. Galerkin Finite Element Method is employed to solve the nonlinear coupled equations for the porous flow and heat transfer. The phase transition and the released/absorbed latent heat of the nano-capsules are attributed in a temperature-dependent heat capacity field. The thermal conductivity ratio (1 ≤ R_k ≤ 100), the Darcy number (10~(-5) ≤ Da ≤ 10~(-1)), the Stefan number (0.2 ≤ Ste ≤ 1), the porosity of porous medium (0.2 ≤ ε ≤ 0.9), the dimensionless fusion temperature (0.05 ≤ T_(fu) ≤ 0.95), the solid walls thickness (d_s = 0.1 and 0.3), and the volume fraction of the nano-capsules (0.0 ≤ Φ ≤ 5%) are considered for the numerical calculations. The numerical results illustrate that the rates of heat transfer and the average Bejan number are maximum and the generated entropy is minimum when the fusion temperature of the nano-capsules is T_(fu) = 0.5. Besides, adding the nano-sized particles of encapsulated phase change materials to the host fluid increases the heat transfer rate up to 45% (for the studied set of parameters) and also augments the average Bejan number. The total entropy generation elevates with the increment of the volume fraction of the nanoparticles, for low values of the Darcy number; however, a downward trend can be found for higher values of the Da. The combination of NEPCM-suspensions (with latent heat thermal energy storage) and a porous medium (with the extended surface area) provides an extensive capability for thermal enhancement and energy storage applications. In this regard, the findings of the current work demonstrate that the selection of the fusion temperature and Darcy number are two essential key parameters, which could change the trend of the results.
机译：精确了解包括纳米封装相变材料（Nepcm）的悬浮液的热行为和熵产生对于各种工程应用中的热能存储和热传递增强是重要的。迄今为止的研究，改善了NCPCM的传热的知识。然而，在多孔培养基中包含Nepcm的悬浮液可以增强整体传热性能。因此，本研究旨在研究多孔介质中NEPCM悬浮液的热性，HY-DOTY动力学和熵生成行为。用包括纳米封装的相变材料占据的多孔基质（玻璃球）组成的正方形腔中的共轭自然对流传热和熵产生，并且在数值上研究了两个固体嵌段。采用Galerkin有限元方法来解决多孔流量和热传递的非线性耦合方程。纳米胶囊的相转变和释放/吸收潜热归因于温度依赖性的热容器。导热率比（1≤r_k≤100），达西数（10〜（-5）≤Da≤10〜（-1）），斯特凡数（0.2≤STE≤1），多孔介质的孔隙率（ 0.2≤ε≤0.9），无量纲熔化温度（0.05≤T_（FU）≤0.95），固体壁厚（D_S = 0.1和0.3），纳米胶囊的体积分数（0.0≤φ≤5％ ）被认为是数值计算。数值结果说明了传热和平均Bejan数的速率最大，并且当纳米胶囊的熔化温度为T_（FU）= 0.5时，产生的熵最小。此外，将纳米尺寸的封装相变材料颗粒添加到宿主流体增加到45％的传热速率（用于研究的参数集），并且还增加了平均Bejan号码。总熵产生随着纳米颗粒的体积分数的增量而升高，对于达西数的低值;然而，可以找到向下趋势以获得更高的DA值。 Nepcm悬架（具有潜热热能存储器）和多孔介质（延伸表面区域）的组合为热增强和能量存储应用提供了广泛的能力。在这方面，目前工作的发现表明，融合温度和达西数的选择是两个基本关键参数，可以改变结果的趋势。

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