A SEMINAR ON

“HEAT TRANSFER OF JET IMPINGEMENT ”

Presented by; Shinde Sudhir MohanMM15M09

Savitribai Phule Pune UniversityDepartment of Technology

PuneMechanical & Material Science Engineering

INTRODUCTION It is method for removing a large amount of

heat from striking surface. The fluid exist the nozzles located a short

distance from the surface It is a method of achieving particularly high

heat transfer coefficients in many engineering applications.

like cooling of turbine blades, electronics components

APPLICATION

Internal cooling of turbine blade Cooling of laser weapons, microeletronics

components . Quenching and annealing of non ferros sheet

metal. cooling in grinding processes

LITERATURE REVIEW

PRINCIPLE OF IMPINGEMENT

NOMENCLATURE r/d =radial distance from the stagnation point, d = jet or nozzle diameter, m h = heat transfer coefficient, W/m2K. H = distance between orifice and impingement

plates, m q = heat flux, W/m2 Q = volumetric flow rate, m3/s r = radial distance from the stagnation point, m Re = Reynolds number, dimensionless T = temperature, K ε = emissivity, dimensionless μ = dynamic viscosity, kg/ms ρ = density, kg/m3

OBJECTIVE

To study :The effect of jet width to height

ratio and Reynolds number on the heat transfer characteristics of a laminar flow slot jet impinging on a constant heat flux wall

DESIGN CONSIDERATIONS

Jet type (round of slot) Nozzle to target surface spacing Location of exhaust ports Induced or imposed cross flow Surface motion Angle of impingement Nozzle design Temperature differences between the jet and

the impingement surface

NUMBER OF IMPINGEMENT NOZZLES

Most studies carried out with single nozzles

All industrial applications use array of nozzles where the air jets may interact with each other.

DISTANCE FROM NOZZLE TOIMPINGEMENT SURFACE

Maximum Nusselt number occurs at the stagnation point when the jet is at a distance of six to eight diameters away from the impingement surface. This is the end of the potential core.

A spatial variation in convective heat transfer coefficient occurs away from the stagnation point.

When the distance from nozzle to impingement surface is small (h/D<6), there is a secondary maximum of Nusselt number at a radial distance of 0.5 to 2 nozzle diameters due to the transition from laminar to turbulent boundary layer flow.

EXPERIMENTAL SET-UPa) air jet impinging

b) water jet impinging

Gas Flow Meter recorded the air flow rate in standard liters per minute

(SLPM)

positive displacement pump 0.75kW 2900rpm

JET IMPINGEMENT TEST SECTIONNozzles of 0.5mm, 1mm and 1.5mm diameterOrifice plates 5mm thickness

stainless steel foil of 25μm thickReynolds number Re from 1000 to

20000

jet to target spacing H from 0.5d to 6d

copper bus bar electrodes(50mm x 10mm x 10mm)

Temperature measurement a FLIR ThermaCAM™ A40 infrared camera

HEAT TRANSFER COEFFICIENT

heat flux, q Ts surface

temperature

REYNOLDS NUMBERQ = volumetric flow rate, m3/sρ = density, kg/m3μ = dynamic viscosity, kg/ms

RESULTS AND DISCUSSION

Air Jet

low Reynolds numbers, high heat transfer coefficients can be achieved by small diameter nozzles.

d = 0.5mm; H/d = 2, 4; Re = 1000, 5000

d = 0.5mm, 1mm, 1.5mm; H/d = 2; Re =5000;

d = 1.5mm, H/d = 1, 2, 4; Re = 20000

CONCLUSIONS

for jet diameters of 0.5mm to 1.5mm, Reynolds numbers of 1000 to 20000 and dimensionless jet-to-target spacings of 1 to 4 was investigated.

low jet-to-target spacings and high Reynolds numbers.

the area averaged heat transfer increases with decreasing jet diameter and this is attributed to the higher jet velocities involved when smaller nozzles are used.

The water jets also exhibit secondary peaks, however these have only been observed at a low Reynolds number of 10000 and a low H/d of 1

REFERENCES Babic, D., Murray, D. B., Torrance, A. A., Mist Jet Cooling of

Grinding Processes, Int. J. Mach. Tools Manufact. 45, pp. 1171-1177, 2005

Narumanchi, S. V. J., Amon, C. H., Murthy, J. Y., Influence of Pulsating Submerged Liquid Jets on Chip-Level Thermal Phenomena, Transactions of the ASME, Vol. 125, pp. 354-361, 2003.

Hollworth, B. R., Durbin, M., Impingement Cooling of Electronics, Journal of Heat Transfer, ASME, Vol. 114, pp. 607-613, 1992.

Fitzgerald, J. A., Garimella, S. V., Flow Field Effects on Heat Transfer in Confined Jet Impingement, Transactions of the ASME, Vol. 119, pp. 630-632, 1997.

Thank you!