Study on backward-facing step flow and heat transfer characteristics of hybrid nanofluids
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Study on backward‑facing step flow and heat transfer characteristics of hybrid nanofluids Cong Qi1 · Zi Ding1 · Jianglin Tu1 · Yuxing Wang1 · Yinjie Wang1 Received: 22 August 2020 / Accepted: 20 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract As high heat dissipation has increasingly become the primary factor restricting the capability of electronic elements, and the high temperature of the equipment operation will affect its reliability. In this study, a backward-facing step (BFS) model to explore the flow and heat transfer characteristics of water and 5% mass fraction of Cu/Ni-water hybrid nanofluids has established. This paper focused on the influence of the number of step layers and the step expansion ratio (ER) on the flow and heat transfer characteristics of hybrid nanofluids. The increase in the number of steps will increase the Nu of the downstream wall of the steps and bring the peak position of Nu forward. The heat exchange effect of the hybrid nanofluids is better than that of water. The increase in flow velocity has the greatest influence on Nu of the lower wall of the step, followed by the increase in the step expansion ratio and the increase in the number of steps. Keywords Hybrid nanofluids · Backward-facing step · Heat transfer characteristic · Flow characteristic List of symbols cp Specific heat of nanofluids, J kg−1 K−1 cpbf Specific heat of base fluid, J kg−1 K−1 cpnf Specific heat of the nanofluid mixture, J kg−1 K−1 cpp Specific heat of nanoparticle, J kg−1 K−1 fx Unit mass force in the x direction fy Unit mass force in the y direction h Convective heat transfer coefficient, W m−2 K−1 kf Thermal conductivity of base fluid, W m−1 K−1 knf Specific heat capacity of the nanofluid mixture, J kg−1 K−1) kp Thermal conductivity of nanoparticles, W m−1 K−1) Nu Nusselt number * Cong Qi [email protected] Zi Ding [email protected] Jianglin Tu [email protected] Yuxing Wang [email protected] Yinjie Wang [email protected] 1
School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, China
P Pressure drop, Pa t Flow time, s Tw Average temperature of wall, K u Velocity of nanofluids in the x direction, m s−1 uin Inlet flow velocity of the nanofluid mixture, m s−1 v Velocity of nanofluids in the y direction, m s−1 Greek symbols λ Thermal conductivity of copper, W m−1 K−1 μ Dynamic viscosity of nanofluid, Pa s ρ Density of nanofluids, kg m−3 ρbf Density of base fluid, kg m−3 ρnf Density of the nanofluid mixture, kg m−3 ρp Density of nanoparticle, kg m−3 τw Shear stress of the lower wall, Pa φ Nanoparticle volume fraction, % Subscripts bf Base fluid nf Nanofluids P Identical pump work w Wall
Introduction With the development of science and technology, the performance of electronic components and chips is getting stronger, but the corresponding power consumption is also
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increasing. High power consumption brings high heat dissipation, and the high temperature genera
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