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ARTICLE:
M. Rantala
Tamglass Engineering Ltd. Oy, Tampere, Finland Reijo Karvinen
Tampere University of Technology, Korkeakoulunkatu 6 P.O. BOX 589,FI-33101 Tampere, Finland
ABSTRACT In glass tempering, the glass plate is first heated to 640°C and then cooled rapidly. In addition to radiation, forced convection is used to control the process. This paper reports experimental results and discoveries of a study of single round impinging jets, used in tempering furnaces. Long nozzle-to-surface distances and coarse nozzle-to-nozzle spacings are typical of these applications. Though axisymmetric impingement jet heat transfer has been widely investigated, no results exist on these kinds of impinging jets.
This paper presents measured local heat transfer results on the constant heat flux boundary condition for various-diameter, short sharp-edge nozzles under incompressible or choked flow. In measuring the local heat transfer coefficient, we ran an electric current through a thin steel plate to produce a constant heat flux boundary condition. The correlations reported in the literature for impinging jet heat transfer are not valid for our case, because our distance-diameter ratio was much greater than that in the literature. One interesting result was that if the momentums of impinging jets are the same, local heat transfer is equal.
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JET-22 pages
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