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Comparison of heat transfer distributions on a flat plate impinged by under-expanded jets from a convergent nozzle and a circular orifice

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Abstract

Experiments are carried out for a circular orifice and a nozzle for the same contraction ratio to explore the heat transfer characteristics. The pressure ratios covered in this study are 2.36, 3.04, 3.72, 4.4 and 5.08 for jet to plate distances (z/d) of 2, 4, 6 and 8. The presence of vena contracta and absence of the stagnation bubble in the orifice flow are confirmed from the surface pressure distributions. It is found that higher Nusselt number for the orifice than the nozzle are due to different shock structures and shear layer dynamics. Peak Nusselt number is found as high as 84 % than that for the nozzle. In the wall jet region, the heat transfer rates for the orifice and nozzle are almost of the same order, thus producing steeper temperature gradients under similar operating conditions. The average heat transfer rates are almost 25 % higher for the orifice than that of the nozzle. The recovery factors are in general higher in case of orifice than the nozzle. However, this has not resulted in decreasing the heat transfer rates due to shear layer dynamics.

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Abbreviations

A :

Surface area of the target plate (m2)

C p :

Specific heat at constant pressure of the air (kJ/kg K)

C d :

Coefficient of discharge of orifice/nozzle

d :

Throat diameter of the nozzle (m)

h :

Heat transfer coefficient (W/m2 K)

I :

Current (Amperes)

k :

Thermal conductivity of the air (W/m K)

M :

Design Mach number at the nozzle exit plane

NPR :

Nozzle pressure ratio (P o /P ∞ )

Nu :

Nusselt number (hd/k)

P :

Surface pressure at a given radial location (Pa)

P o :

Total pressure at the inlet of the nozzle (Pa)

P ∞ :

Ambient pressure (Pa)

P exit :

Pressure at the exit of the nozzle (Pa)

q conv :

Net heat flux convected to the impinging jet (W/m2)

q joule :

Imposed Ohmic heat flux (VI/A) (W/m2)

q loss :

Total heat flux loss from impingement plate (W/m2)

q rad(f) :

Radiation heat loss from the front surface of impingement plate (W/m2)

q rad(b) :

Radiation heat loss from the back surface of impingement plate (W/m2)

q nat :

Heat loss by natural convection from the back surface of impingement plate (W/m2)

r :

Radial distance from the stagnation point (m)

R :

Recovery factor

Re :

Reynolds number (ρ \( \bar{V} \) d/μ)

T r :

Temperature of the target plate at a given radial location (°C)

T aw :

Adiabatic temperature of the target plate at a given radial location (°C)

T s :

Jet static temperature (°C)

T d :

Jet dynamic temperature (°C)

T 0 :

Jet total temperature (°C)

V :

Voltage (V)

\( \bar{V} \) :

Average velocity at the exit of the nozzle/orifice (m/s)

z :

Nozzle to plate spacing (m)

β :

Constriction ratio (diameter of the throat/diameter of the pipe)

ρ :

Density of the air corresponding to supply pressure (kg/m3)

μ :

Dynamic viscosity of the air (Pa s)

γ :

Specific heat ratio of the air

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Authors and Affiliations

  1. R & D E (E), DRDO, Pune, 411015, India

    M. D. Limaye

  2. Department of Mechanical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India

    R. P. Vedula & S. V. Prabhu

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  1. M. D. Limaye
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  2. R. P. Vedula
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  3. S. V. Prabhu
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Correspondence to S. V. Prabhu.

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Limaye, M.D., Vedula, R.P. & Prabhu, S.V. Comparison of heat transfer distributions on a flat plate impinged by under-expanded jets from a convergent nozzle and a circular orifice. Heat Mass Transfer 49, 309–326 (2013). https://doi.org/10.1007/s00231-012-1089-4

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  • DOI: https://doi.org/10.1007/s00231-012-1089-4

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