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Heat transfer characteristics of single circular jet impinging on a flat surface with a protrusion

Abstract

An experimental investigation of heat transfer from a single circular jet impinging normally on a flat plate with a protrusion of depth 1, 2 and 3 mm was carried out. The temperature was measured over a Reynolds number range of 10,000 to 33,000 and nozzle exit-to-plate spacing ranged from 2 to 10 jet diameters. The average heat transfer characteristics were compared with the results from the literature, and the agreements were good. Further, numerical simulations were performed using ANSYS Fluent 18.1 to compare the results with those from experiments. The results showed that the increase of jet Reynolds number and relative depth of protrusion enhances the heat transfer on the impinging surfaces up to 16.69% compared to a flat surface. The maximum increase in the Nusselt number occurs at a spacing of 5 jet diameters (nearly at the end of Potential core zone) and Reynolds number 33000 for all cases. Further, the average percentage change of Nusselt number over the Reynolds number range decreased from 9.74% to 4.73% as protrusion depth increases from 0 to 3 mm due to flow separation. The study of the effect of heat input on the heat transfer enhancement was carried out by comparing Nusselt number for heat supply values of 60 W and 90 W. For higher heat input (90 W) and longer stand-off distance (Z/d = 10) it was observed that the effects of weak impingement flow field are counter acted by natural convection plume flow emanating from the heated surface. Hence, in such cases, impingement cooling is not effective.

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Abbreviations

A S :

Surface area of impingement plate [m2]

β :

Co-efficient of volume expansion [K−1]

d :

Diameter of jet nozzle [mm]

d or (∆T)Ref :

Temperature difference across laminar sublayer

D :

Diameter of protrusion [mm]

D h :

Hydraulic diameter of impinging surface [mm]

δ :

Depth of dome [mm]

d/D :

Diameter ratio

δ/D :

Protrusion relative depth

g :

Gravitational acceleration [m/s2]

Gr :

Grashof number

\( \overline{h} \) :

Average heat transfer coefficient [W/m2K]

K air :

Thermal conductivity of air [W/m K]

L c :

Characteristic length for horizontal surface [m]

M:

Mach number

\( {\overline{Nu}}_o \) :

Average Nusselt number based on diameter of nozzle

\( {\overline{Nu}}_p \) :

Average Nusselt number based on diameter of impinging plate

ϑ :

Kinematic viscosity of air [m2/s]

P :

Power supplied from DC Power source [W]

Pr :

Prandtl number

Q Cond :

Conduction heat losses [W]

Q Conv :

Convection heat transfer from impingement plate [W]

Q Rad :

Radiation heat losses [W]

Q Supply :

heat supplied from power source [W]

q" :

Heat flux in [W/m2]

Ra :

Rayleigh number

Re :

Reynolds number

R :

Radial distance from stagnation point [mm]

T a :

Temperature of atmospheric air [°C]

T f :

Air film temperature [°C]

\( \overline{T_S} \) :

Average surface temperature of the impingement surface [°C]

T R :

Local temperature at thermocouple points from 0 to R [°C]

ϑ :

Non-dimensional temperature

U C :

Centre line velocity [m/s]

y 1/2 :

Half jet width [mm]

y+, u+ :

Dimensionless law of the wall variables

Z:

Jet axial distance [mm]

\( \raisebox{1ex}{${y}_{1/2}$}\!\left/ \!\raisebox{-1ex}{$Z$}\right. \) :

Jet spread rate

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Correspondence to K Srinivasan.

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Nagesha, K., Srinivasan, K. & Sundararajan, T. Heat transfer characteristics of single circular jet impinging on a flat surface with a protrusion. Heat Mass Transfer 56, 1901–1920 (2020). https://doi.org/10.1007/s00231-020-02814-z

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