Influence of Al2O3–H2O nanofluid on performance of twisted minichannels

• Thermal-hydraulic performances of the TMC with nanofluid are studied.
• Different cross section configurations and structural parameters are considered.
• The best operating regime for the TMCs is at lower Reynolds numbers.
• Average enhancement factors provided by the nanofluid range from 1.04 to 1.25.
• Correlations are proposed for Nu number and f factor.

Laminar flow and heat transfer characteristics of Al2O3–H2O nanofluid in the twisted minichannel (TMC) with different structural parameters are studied using a 3D numerical scheme. Effects of the cross section configuration (elliptic, half circular, square, rectangular, and triangular), twist pitch to channel length ratio (P/L = 0.25, 0.50, and 1.0), nanoparticle volume fraction (φ = 0–4%), and Reynolds number (Re = 300–1500) are investigated. The obtained results show that all the tested TMCs have better heat transfer performance than the smooth circular minichannel, the average enhancement factors provided by the TMCs range from 1.04 to 1.51. It is also found that lower values of the P/L ratio result in higher heat transfer coefficients and pressure drops. Likewise, the best operating regime for the TMCs is at lower Reynolds numbers. The square TMC with the lowest P/L ratio of 0.25 offers the highest value of the heat transfer rate to pumping power ratio at the minimum studied Reynolds number of 300. For all the cases, the nanofluid flow presents higher values of the heat transfer coefficient and pressure drop compared to the base fluid; the nanofluid has better thermal-hydraulic performances than the base fluid when its volume fraction is 1%. Finally, correlations are developed for the TMCs with different cross section geometries in the range of the studied Reynolds number, i.e. 300–1500.

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