Purpose

This study aims to analyze the unsteady flow of hybrid Cu-Al₂O₃/water nanofluid over a permeable stretching/shrinking disc. The analysis of flow stability is also purposed because of the non-uniqueness of solutions.

Design/methodology/approach

The reduced differential equations (similarity) are solved numerically using the aid of bvp4c solver (Matlab). Two types of thermophysical correlations for hybrid nanofluid (Type 1 and 2) are adopted for the comparison results. Using correlation Type 1, the heat transfer and flow analysis including the profiles (velocity and temperature) are presented in the figures and tables with different values control parameters. Three sets of hybrid nanofluid are analyzed: Set 1 (1% Al₂O₃ + 1% Cu), Set 2 (0.5% Al₂O₃ + 1% Cu) and Set 3 (1% Al₂O₃ + 0.5% Cu).

Findings

The comparison of numerical values between present (Types 1 and 2 correlations) and previous (Type 2 correlations) results are in a good compliance with approximate percent relative error. The appearance of two solutions is noticed when the suction parameter is considered and the unsteady parameter is less than 0 (decelerating flow) for both stretching and shrinking disc while only one solution is possible for steady flow. The hybrid nanofluid in Set 1 can delay the separation of boundary layer but the hybrid nanofluid in Set 3 has the greatest heat transfer rate. Moreover, the inclusion of wall mass suction for stretching case can generate a significant increment of heat transfer rate approximately 90% for all fluids (water, single and hybrid nanofluids).

Originality/value

The present findings are novel and can be a reference point to other researchers to further analyze the heat transfer performance and stability of the working fluids.

中文翻译：

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混合纳米流体在可渗透拉伸/收缩盘上的不稳定轴对称流动和传热

目的

本研究的目的是分析混合Cu-Al ₂ O ₃ /水纳米流体在可渗透拉伸/收缩盘上的非稳态流动。由于解决方案的非唯一性，因此还旨在进行流动稳定性分析。

设计/方法/方法

简化的微分方程（相似性）借助bvp4c求解器（Matlab）进行数值求解。比较结果采用两种类型的混合纳米流体的热物理相关性（类型1和2）。使用类型1的相关性，在图形和表格中使用不同的值控制参数显示了包括轮廓（速度和温度）在内的传热和流动分析。分析了三组混合纳米流体：组1（1％Al ₂ O ₃  + 1％Cu），组2（0.5％Al ₂ O ₃  + 1％Cu）和组3（1％Al ₂ O ₃  + 0.5％）铜）。

发现

当前（类型1和2的相关性）和先前（类型2的相关性）结果之间的数值比较符合近似百分比相对误差。当考虑吸力参数并且对于拉伸和收缩盘片而言，非稳定参数小于0（减速流量）时，会出现两种解决方案，而对于稳定流量，则只有一种解决方案。组1中的杂化纳米流体可以延迟边界层的分离，但是组3中的杂化纳米流体具有最大的传热速率。此外，对于所有情况（水，单纳米和混合纳米流体），包括用于拉伸箱的壁质量抽吸装置在内，都可以显着提高传热率，大约为90％。

创意/价值

目前的发现是新颖的，可为其他研究人员进一步分析工作流体的传热性能和稳定性提供参考。