Numerical investigation of the effect of oscillating injection nanofluid flow on forced convection heat transfer enhance
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Numerical investigation of the effect of oscillating injection nanofluid flow on forced convection heat transfer enhancement over a backward-facing step Hesam Moayedia Rasht, Iran Received: 26 August 2020 / Accepted: 13 November 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, the effect of the oscillating injection flow on laminar forced convection of nanofluid flow over a 2D backward-facing step was numerically investigated. The effects of Reynolds number, Strouhal number, and momentum flux ratio in terms of injection velocity, and injection position on the fluid flow and heat transfer were studied. The comparison of the results of the oscillating injection with different cases (with and without constant injection) indicates that using oscillating injection flow generates periodic oscillation in the flow and heat transfer characteristics, which can lead to heat transfer enhancement. Furthermore, the time-spatial average Nusselt number based on the Strouhal number exhibited a resonant-type behavior, and the best effect of flow oscillation on the heat transfer rate was achieved at St 0.1. The numerical results showed that the oscillating injection can provide a heat transfer enhancement of about 144% in X j H for Reynolds number of (Re 100) and momentum flux ratio of (J 4). Moreover, it was found that the maximum effectiveness parameter, as a sufficient and reliable criterion, at the Re 100 is equal to η 1.54.
Abbreviations a cP dP ER f hx H J K L Nu P q Re
Injection slit width (m) Specific heat coefficient (J kg K) Particle diameter (m) Expansion ratio Frequency of the oscillation (Hz) 2 Local heat transfer coefficient (W m K) Step size (m) Momentum flux ratio 2 Thermal conductivity (W m K) Length of the bottom wall downstream of step (m) Nusselt number Pressure (Pa) Heat flux (W m2 ) Reynolds number
a e-mail: [email protected] (corresponding author)
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924
St t T Tf TP u U v x Xj Xr y
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Eur. Phys. J. Plus
(2020) 135:924
Strouhal number Time (s) Temperature (K) Time scale based on flow parameter (s) Time period of oscillation (s) U-component of velocity vector (m/s) Velocity magnitude (m/s) Y-component of velocity vector (m/s) X coordinate (m) Injection position (m) Recirculation zone (m) Y coordinate (m
Greek symbols η ϕ κb μ ρ τ
Effectiveness parameter Nanoparticles volume fraction Boltzmann constant (m2 kg s2 K) Dynamic viscosity (N m/s) Density (kg/m3 ) Non-dimensional time scale
Subscripts in f Mean nf p
Local value at inlet Base fluid Time-spatial average Nanofluid Nanoparticle
1 Introduction The fluid flow separation phenomenon and its subsequent reattachment due to a sudden expansion occur in many practical engineering applications in various fields including HVAC systems, transportation, aerospace, nuclear energy, power plants, and petrochemical and food industries. A benchmark for this problem is the forced convection flow over a backward-facing
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