article · Case Studies in Thermal Engineering
Numerical modelling evaluates how different expansion angles influence heat transfer and pressure drop in a microtube sudden expansion using copper and water nanofluids. Simulating Reynolds numbers from 10 to 100 across expansion angles of 30, 45, 60, and 90 degrees shows that increasing nanoparticle concentration and flow rate enhances the heat transfer coefficient. A 45-degree expansion angle delivers the best thermal performance, yielding the highest heat transfer coefficient when combined with a four percent nanofluid concentration at a Reynolds number of 100. This configuration outperforms a standard 90-degree expansion using pure water by over 43 percent. However, the 45-degree geometry causes the highest pressure drop due to wall vortices, whereas a 30-degree angle results in the lowest pressure drop due to smoother streamlines influenced by the Coanda effect.
Miniaturised electronic devices generate substantial heat that standard cooling channels struggle to dissipate efficiently. By optimising the physical angle of microtube expansions and combining them with heat-absorbing nanofluids, cooling systems can remove significantly more heat. Understanding the trade-offs between heat dissipation and pressure losses allows engineers to design more effective thermal management solutions for compact modern electronics.
The findings are relevant to developers of electronic cooling systems, microfluidic thermal devices, and compact heat exchangers. Because the study relies entirely on numerical finite volume simulations rather than experimental hardware testing, the work sits at an early stage of development. Moving towards commercialisation will require physical fabrication and experimental validation of the microtube geometries to assess real-world durability and pumping power requirements under continuous operating conditions.
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The present study has been numerically surveyed the effect of different expansion angles on the heat transfer and pressure drop characteristics of a sudden expansion in a microtube. For this purpose, Cu/water nanofluids flowing with Reynolds numbers (Re) of 10, 25, 50, and 100 through expansion angles of 30°, 45°, 60°, and 90° were modeled. Governing equations were solved by the finite volume method (FVM). The findings indicated that the heat transfer coefficient (HTC) could enhance by nanoparticles concentration and Re augmentation. Also, It was revealed that HTC of a sudden expansion with an angle of 45° has optimum hydrodynamic performance; then, sudden expansions of 30°, 90°, and 60° are followed. The highest HTC was achieved for a microtube containing 4 vol% nanofluids at Re = 100 with a 45° expansion angle, 43.63% higher than conventional expansion angle (90°) working with distilled water at Re = 10. By comparing HTC at various angles, it can be found that there is a 14.57% further HTC by changing the expansion angle from α = 90° with α = 45°. Furthermore, the pressure drop investigation showed that the expansion angle with α = 30° has the lowest pressure drop. In contrast, α = 45° produced the highest pressure drop because of giant vortices created along the tube wall. The velocity streamlines and contours explained the reason for a lower pressure drop of α = 30°, 45°, and 60° which was regular streamlines along the tube wall due to the Coanda effect.
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DOI: 10.1016/j.csite.2021.101637
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