The local transfer coefficients which result from the impingement of a row of circular jets on a plane surface were determined by means of the naphthalene sublimation technique in conjunction with an innovative data acquisition system. Spanwise average and surface average transfer coefficients were also deduced from the local measurements. The parameters that were varied included the jet Reynolds number, the spacing between adjacent jet orifices, and the separation distance between the jet orifices and the impingement surface. The local transfer coefficient distributions enable the identification of surface locations where the impinging jets provide effective heating (or cooling). At locations that are mid-way between adjacent jets, relatively high local transfer coefficients may exist owing to the collision of the spreading flows from adjacent impinged jets. The stagnation point transfer coefficient exhibits a maximum as a function of the orifice-to-impingement separation distance. Both the spanwise average and surface average transfer coefficients take on their largest values on the impingement line and diminish with increasing downstream distance.
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The localS herwoodn umberr esultse nablet hei dentification of surfacel ocationsw heret he impingingj ets providee ffectiveh eating( or cooling) and wherec old (or hot) spotsm ay develop.O wing to the collision of the wall jets from adjacenti mpingedj ets, the transfer coefficientas t positionsm id-wayb etweenth ej ets may take on relatively large values.T he effect of such collisions is accentuateda t high Reynolds numbers, smallj et orifices pacingsa, nd small orifice-to-impinge- ment separationsA. t sufficientlyl arge downstream distancest,h e spreadingo f the impingedj ets and the mixing of fluid from adjacentj ets producesa two-dimensionawl all jet flow. The stagnationp oint transferc oefficiente xhibitsa maximuma s a functiono f theZ /D separationd istance. The spanwisea veragetr ansferc oefficienttsa keo n their highestv alue at the impingementl ine and diminish with downstreamd . istanceA. t X/D = 4, the spanwise averagec oeffictenItS 35-507 ; of that on the impinge-mentl ine. The surfacea veragec oefficientsa re largest whent hea veraginga reai s confinedt o thei mpingement line and diminish as the averaginga reae ncompasses more and more of the downstreamp ortion of the impingemenpt late.F or a sectiono f the impingement plate which extendsf rom X/D = 0 to X/D = 12, the averagec oefficientis 30-50:; of that at the impinge-mentl ine. Acknowledgement-Trheese arcrhe porteidn this paper was supported, in part, by NSF GrantE NG75-03221.
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