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Heat transfer characteristics from in-line arrays of free impinging jets

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Abstract

An experimental investigation of the convective heat transfer on a flat surface in a multiple-jet system is described. A thin metal sheet was heated electrically and cooled from one side. On the other black coated side the temperature field was measured using an IR camera. Varied parameters were the jet Reynolds number in the range from 1,400 to 41,400, the normalized distance nozzle to sheet H/d from 1 to 10, and the normalized nozzle spacing S/d from 2 to 10. A geometrical arrangement of nine nozzle in-line arrays was tested. The results show that the multiple-jet system enhances the local and average heat transfer in comparison with that of a single nozzle. A maximum of the heat transfer was found for the normalized spacing S/d = 6.0. The normalized distance H/d has nearly no effect on the heat transfer in the range 2 ≤ H/d ≤ 4. The maximum average Nusselt number was correlated as a function of the jet Reynolds number \( ({\text{Nu}}_{{{\text{av}}_{\max } }} = 0.104\,\text{Re}^{0.7} ). \)

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Abbreviations

A :

plate area (m2)

d :

inner nozzle diameter (m)

H :

distance from jet exit to impingement plate (m)

I :

direct current (Ampere)

k :

thermal conductivity of air (W m−1 K−1)

Nu:

local Nusselt number, α d/k

q k :

conduction heat flux (W m−2)

q l :

electrical power (W m−2)

q ε :

radiation heat flux (W m−2)

q α :

convection heat flux (W m−2)

Re:

jet Reynolds number (V d/v)

r :

radius (m)

S :

jet-to-jet spacing distance (m)

T ad :

adiabatic wall temperature (°C)

T o :

heated wall temperature (°C)

T j :

jet exit temperature (°C)

T ∞ :

ambient temperature (°C)

t :

metal sheet thickness (m)

V :

mean velocity at jet exit (m s−1)

W :

metal sheet width (m)

x :

streamwise coordinate (m)

y :

coordinate perpendicular to streamwise direction (m)

α :

convective heat transfer coefficient (W m−2 K−1)

ε :

emissivity (-)

ν :

kinematic viscosity (m2 s−1)

ρ el :

specific electrical resistance (Ω m)

σ :

Stefan–Boltzmann-constant (W m−2 K−4)

Av:

average value

c:

IR camera temperature

f:

free convective

lo:

local value

st:

stagnation point of center jet

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Authors and Affiliations

  1. Institute of Fluid Dynamics and Thermodynamics, Otto-von-Guericke-University Magdeburg, Universitaetsplatz 2, 39106, Magdeburg, Germany

    M. Attalla & E. Specht

  2. South Valley University-High Institute of Energy-Sahary, 81511, Aswan, Egypt

    M. Attalla

Authors
  1. M. Attalla
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  2. E. Specht
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Correspondence to E. Specht.

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Attalla, M., Specht, E. Heat transfer characteristics from in-line arrays of free impinging jets. Heat Mass Transfer 45, 537–543 (2009). https://doi.org/10.1007/s00231-008-0452-y

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  • DOI: https://doi.org/10.1007/s00231-008-0452-y

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