A study of heat and mass transfer characteristics of jet impingement

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Kapasi, S.F., 1994. A study of heat and mass transfer characteristics of jet impingement. PhD, Nottingham Trent University.

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Abstract

Experimental and numerical mass/heat transfer data for a semi-confined axisymmetric jet impingement for laminar and turbulent flow and a range of nozzle to plate spacings has been completed. The experimental mass transfer results have been correlated into useful design equations with quoted uncertainties, thus making a valuable contribution to extending existing data.

The experimental programme involved measurement of mass transfer coefficients due to a laminar 4.93 mm diameter jet impinging on a flat surface. The test mass transferring surface was a silicon rubber swollen with ethyl salicylate. Deformations caused by convection on the polymeric surface was measured using holographic interferometry. The tests were conducted for Reynolds numbers of 500 < Re < 2000 with corresponding nozzle to plate spacings of 2 < z/d < 12. Tlie same geometric configuration was investigated for turbulent flow ranging 3000 < Re < 60000 with the same nozzle to plate spacings.

PHOENICS was adapted to produce numerical predictions initially for the semi-confined axisymmetric laminar impinging jet for 100 < Re < 2000 with nozzle to plate separation of 2 < z/d < 12. Further predictions using the same technique for turbulent flow have been made using a standard k - e model for jet flow rate range of 3000 < Re < 60000 with the same spacings.

The experimental laminar wall jet Sherwood numbers are shown to compare well with analytical and predicted results. The turbulent wall jet results also show good agreement with predicted values and available data. However errors in the mass transfer coefficients are exacerbated by the uncertainties in the physical properties of materials used in the experimental method. The confidence interval of the derived correlation equations are estimated to be ± 30 per cent. Although the effect of nozzle to plate separations on the wall jet mass transfer is shown to be insignificant within the investigated range, semi-confinement lowers the mass transfer rates by suppressing entrainment and turbulence. The wall jet heat transfer coefficients are independent of the inlet jet velocity profiles. The consequences of the flow patterns due to the semi-confinement boundary on the heat transfer coefficients are discussed.

An experimental jet impingement rig was designed for ease of replication and associated computer software for data analysis is described. Recent developments in computer hardware, processing speeds and optical equipment can be used for automatic analysis of this technique so that it can be used more easily.

Experimental measurements of the diffusion coefficients of the swelling agent into air have never before been obtained at the working temperature are estimated to have an uncertainty of ± 50 per cent. The refractive index and swelling properties of the silicon rubber agree well with published data and have been correlated into usable equations for convenience. The vapour pressure data of the swelling agent used has an uncertainty of 15 per cent which contributes to an uncertainty level in the mass transfer calculations to about 5 per cent.

Item Type:

Thesis

Creators:

Kapasi, S.F.

Date:

1994

ISBN:

9781369325461

Identifiers: