HEAT TRANSFER EXPERIMENTS IN CHANNEL FLOWS OF HIGH-TEMPERATURE GASES
Experimental results are presented for the local heat transfer of laminar or turbulent flows of air in the presence of a longitudinal electric arc. Bulk flow tem-peratures up to 6,000 Ðš were used in a 0.4 5 m long channel of 0.03 m diam, with the arc current of 1,000 A and air mass flow rates 0.06 kg/s. The part of radiation heat-flux varied from 0.5 to 1.0 of the total. A transverse stream of air was introduced to supply turbulence to the air flow and partially to the arc flow at x/d = 5, as indicated by an increase of its voltage gradient. Radiation heat fluxes were measured with the help of calorimeters, and a simple relation to the arc current was derived. A comparison to the results of other authors'was performed for arc current up to 10,000 A. A deviation of the results for Nu-based convective heat transfer was observed, as compared to those for moderate temperature ranges, and was attributed to the uncertainty of temperature profiles and reference temperatures under the action of an electric arc. By making use of Stanton number, thermophysical parameters were excluded from the interpretation and a relation derived, coincided within the experimental error with an earlier one for turbulent high-temperature or medium-temperature gas flows in water-cooled channels with no radiation. Convective heat transfer was found practically independent on either radiative heat flux up to 5·105 or bulk-wall temperature ratio up to 15.