Flow And Heat Transfer Characteristics On A

Confined Slot Jet Impinging On A Constant Heat Flux

Surface

ByDahiru Umar Lawal

Abba Abdulhamid Abubakar

Outline

• Introduction• Literature Review• Problem Description & Methodology• Results and Discussion• Conclusion

Introduction• Impinging jets are jets of fluid on an impingement surface

that needs to be cooled/heated or dried.

• Impinging jets have received considerable attention due to

their inherent characteristics of high rates of heat transfer.

Applications…Impinging jets are widely applied in many industrial and engineering

applications. These includes:

Internal cooling of turbine blades

Cooling of laser weapons, fusion blankets, microelectronic

components and neutron beam system

Quenching and annealing of non-ferrous sheet metals

Tempering of glass, drying of textiles, wood, film materials and

paper

Freezing of tissues in cryosurgery

Literature reviewAuthor Reynolds Number Jet inlet

geometry

work

Sparrow et al. [1] 150 - 950 slot Derived the mass transfer correlation for the impinging

slot jet flows

Vadiraj et al. [2] 12000 - 28000 circle Study the effect of jet-to-plate spacing and Reynolds

number on the local heat transfer distribution to normally

impinging submerged circular air jet on a smooth and flat

surface

Chiriac et al. [3] 250-750 slot Investigate unsteady two-dimensional fluid flow and heat

transfer in a confined impinging slot jet using the

FAHTSO finite element codes

Fitzgerald et al. [4] 8500 - 23 000 circle Investigated the flow field of an axisymmetric, confined,

submerged, turbulent jet impinging normally on a flat

plate

Morris et al.[5] 8500 to 13 000 circle Investigate the local heat transfer coefficient distribution

on a square heat source due to a normally impinging,

axisymmetric, confined, and submerged turbulent liquid

jet

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

Problem Description

• A two-dimensional jet with uniform jet velocity enters from a nozzle of width W into a channel with height H and length L.

• CASE 1: Re = 500 and H/W = 2 to 5 for L=25 cm

• CASE2: H/W=3 and Re= 200, 300, 400 and 500 for L=25cm

• CASE3: H/W=5 and Re= 200, 300, 400,500,600 and 750 for L=50 cm

Problem Description…• Air is used as the cooling fluid in all cases, and standard

properties of air at 300K were used.• Governing Equations: flow assumed as 2-D, unsteady,

incompressible, and laminar, viscous dissipation effects neglected

∇.𝑢 = 0 1

𝜕𝑢

𝜕𝑡+ 𝑢 .∇u = −

1

ρ ∇p + 𝜈∇2u 2

𝜕𝑇

𝜕𝑡+ 𝑢 .∇T = α∇2T 3

Problem Description…

• Boundary Conditions:Top plate:

Left and Right walls, 𝜈 = 0, u = 0 and 𝜕𝑇

𝜕𝑦= 0

Jet inlet, 𝜈 = 𝑉𝑗 , u = 0 and 𝑇 = 300 K

Bottom plate:

Bottom Wall, 𝜈 = 0, u = 0 and 𝑞 = 1000 W/m2

Left and Right Outlet:

𝜕u

𝜕𝑥= 0,

𝜕u

𝜕𝑦= 0,

𝜕𝑇

𝜕𝑥= 0, 𝑎𝑛𝑑 p = 𝑃𝑎𝑡𝑚

Modeling

Numerical Implementation in Fluent using Finite Volume Technique

Both Steady & Unsteady analysis was carried out

Mesh and Time independent tests were also carried.

Computation is carried out for the entire domain as asymmetry is expected for the unsteady regime

PROPERTIES OF AIR AT 300K and 101325Pa

Density 1.225kg/m3

Specific Heat Capacity

at constant pressure

1006.43J/kg-k

Thermal conductivity 0.0242w/m-k

Viscosity 0.000017894kg/ms

Results & DiscussionVelocity Contour Plot for H/W= 2, 3, 4 and 5 and Re= 500

Results & Discussions….Cp & Nu for H/W= 2, 3, 4 and 5 and Re= 500

Results & Discussions….

Velocity Contour for Re= 200-750 and H/W=5

Results & Discussions….

Temperature Contour for Re= 200-750 and H/W=5

Results & Discussions….

Wall Pressure Coefficients for H/W=5 and Re=200-750

Results & Discussions….

Wall Pressure Coefficients for H/W=5, Re=750, and Time=0-6 Seconds

Results & Discussions….Stagnation Nusselt Number for H/W=5 and Re=200- 750

Validation

Conclusion• Cp varies with the H/W ratio, and peak values are

noticed in the stagnation region.• Heat transfer rate is higher for higher H/W ratio.• Heat transfer rate increases with increasing Reynolds

number.• If the Reynolds number is greater than the critical

Reynolds number, the flow and the thermal fields become time dependent and asymmetric.

References1. E.M. Sparrow, T.C. Wong, Impingement transfer coefficients due to initially laminar slot jets,

Int. J. Heat Mass Transfer 18 (1975) 597–605.

2. Vadiraj, K., & Prabhu, S. V. Experimental study and theoretical analysis of local heat transfer distribution between smooth flat surface and impinging air jet from circular straight pipe nozzle. Heat and Mass Transfer 51(2008). 4480-4495.

3. Chiriac V.A., Ortega A., “A numerical study of the unsteady flow and heat transfer in a transitional confined jet impinging on isothermal surface”, International Journal of Heat & Mass Transfer, 45(2002) 1237-1248

4. J.A. Fitzgerald, S.V. Garimella, Flow field effects on heat transfer in confined jet impingement, Trans. ASME, J. Heat Transfer 119 (1997) 630–635.

5. G. Morris, S.V. Garimella, Prediction of jet impingement heat transfer using a hybrid wall treatment with different turbulent Prandtl number functions, Trans. ASME, J. Heat Transfer 118 (1996) 562–569.

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