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Investigation of flow structure and heat transfer characteristics in an array of impinging slot jets

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Abstract

In this study, an experimental and numerical study is carried out to investigate flow field and heat transfer characteristics of unconfined and confined arrays of four turbulent slot air jets issuing from the lower surface and impinging normally on the upper surface. Pressure and temperature distributions on the surfaces were obtained for the nozzle-to-plate spacing (H/W) of 1–10 and for the Reynolds numbers in the range of 5000–15,000 at the jet-to-jet centerline spacing (S/W) of 9. The effects of jet confinement, Reynolds number and nozzle-to-plate spacing on the flow structure and heat transfer were investigated. Pressure distributions are obtained experimentally and numerically, while heat transfer distributions are computed numerically. It is observed that the surface pressure distributions on both impingement and confinement plates are independent from the Reynolds number, while they have been largely affected from the nozzle-to-plate spacing. Jet confinement causes a considerable difference at the flow field especially for small nozzle-to-plate spacings. Subatmospheric regions are not observed for unconfined jet. However three different types of subatmospheric pressure regions occur on both impingement and confinement plates for confined jet. Nusselt distributions on the impingement plate for both unconfined and confined jet configurations depend on the Reynolds number and nozzle-to-plate spacing. It is concluded that there is a strong correlation between subatmospheric regions and secondary peaks in Nusselt distributions. The numerical results obtained using the Realizable k-ε turbulence model is in good accordance with the experimental results for moderate values of nozzle-to-plate spacings.

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Abbreviations

C p :

Pressure coefficient (ΔP/(ρU 2o /2))

C :

Specific heat at constant pressure (J/kg K)

C 1 , C µ , C 2 , C 1ε , C 3ε :

Constants in the Realizable k-ε turbulence model

E :

Total energy (J)

G b :

Generation of turbulent kinetic energy due to buoyancy

G k :

Production of turbulent kinetic energy due to velocity gradients

h :

Convective heat transfer coefficient (W/m2K)

H :

Nozzle-to-plate spacing (m)

k :

Turbulent kinetic energy (m2/s2)

k a :

Thermal conductivity of air (W/m K)

L :

Length of slot nozzle (m)

Nu :

Nusselt number (h W/ka)

ΔP :

Difference between the surface pressure and the atmospheric pressure (N/m2)

p :

Pressure (N/m2)

q :

Convective heat flux (W/m2)

Re :

Slot nozzle Reynolds number (UoW/υ)

S :

Jet-to-jet centerline spacing (m)

S k , S ε :

Source terms

T :

Temperature (K)

T w :

Impingement wall temperature (K)

T j :

Jet exit temperature (K)

V o :

Nozzle exit velocity (m/s)

u, v, w :

Velocity components in x, y and z directions (m/s)

u τ :

Friction velocity (m/s)

W :

Slot nozzle width (m)

x :

Displacement on the plates along direction of slot width (m)

y :

Displacement along direction of jet axes (m)

z :

Displacement on the plates along direction of slot length (m)

y + :

Dimensionless distance (y+ = yuτ/υ)

υ :

Kinematic viscosity (m2/s)

ρ :

Density of air (kg/m3)

ε :

Turbulent dissipation rate (m2/s3)

(τ ij ) eff :

Deviatoric stress tensor

µ eff :

Effective viscosity (kg/ms)

µ :

Laminar viscosity (kg/ms)

µ t :

Turbulent viscosity

δ ij :

Kronecher delta function

σ k , σ ε :

Turbulent Prandtl numbers

Y M :

Fluctuation rates related to the overall dissipated turbulent thermal energy

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Authors and Affiliations

  1. Department of Mechanical Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey

    Yucel Ozmen & Gokhan Ipek

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  1. Yucel Ozmen
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  2. Gokhan Ipek
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Correspondence to Yucel Ozmen.

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Ozmen, Y., Ipek, G. Investigation of flow structure and heat transfer characteristics in an array of impinging slot jets. Heat Mass Transfer 52, 773–787 (2016). https://doi.org/10.1007/s00231-015-1598-z

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  • DOI: https://doi.org/10.1007/s00231-015-1598-z

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