# An experimental study on the flow and heat transfer characteristics of an impinging jet

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## Abstract

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.

## Key Words

Impinging Jet Convection Liquid Crystal Image Processing## Nomenclature

*c*Specific heat

*D*Jet nozzle diameter

*H*Distance between the nozzle exit and the impingement plate

*h*Convective heat transfer coefficient,

*h=q*″/(*T*_{ w }−*T*_{ rec })*h′*Convective heat transfer coefficient,

*h*′=*q*″/(*T*_{ w }−*T*_{jmax})*k*Thermal conductivity

*l*_{n}Jet nozzle length

*n*Normal distance from the wall surface

- NTSC
National Television System Committee

*Nu*Nusselt number,

*Nu=hD/k**Nu′*Nusselt number,

*Nu′=h′D/k**q″*Heat flux,

*q″*=−*k*_{ f }∂*T*/∂*n*- γ
Radial coordinate

*Re*Reynolds number,

*Re*=ρ*U*_{jmax}*D*/μ- R35C1W
Chiral nematic liquid crystal starting to respond at about 35°C with an approximate bandwidth of 1°C

*T*Static temperature

*t*Time

*U*Mean velocity

*u*RMS value of the fluctuating velocity

*x*Axial coordinate

- α
Thermal diffusivity of air, α=

*k*/(ρ*c*_{ p })- β
Nondimensional time,\(\beta = h\sqrt t /\sqrt {\rho ck} \)

- δ
Difference

- θ
Normalized temperature, θ=(

*T*−*T*_{ i })/(*T*_{rec}−*T*_{ i })- θ′
Normalized temperature, θ′=(

*T*−*T*_{ i })/(*T*_{jmax}−*T*_{ i })- μ
Viscosity

- ρ
Density

## Subscripts

*b*Bulk mean

*i*Initial condition

*j*Jet exit condition

- max
Maximum value

*p*At constant pressure

- rec
Recovery condition

- ref
Reference value

*w*Wall condition

- ∞
Free stream value

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## References

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