Heat transfer data are reported for partially ionized argon flowing in a water-cooled circular tube, 1/2 in. in dia. Experiments were run with initial mixed-mean temperatures up to 21,000 deg R at Reynolds numbers from 140–527 based on equilibrium properties evaluated at the entrance mixed-mean temperature. Measured plasma flow Nusselt numbers computed on an enthalpy basis correlate well with low temperature, constant property results after the first 5–10 diameters of the tube entrance region; closer to the entrance, Nusselt numbers were about 30 percent higher than constant property entrance region predictions. The tendency of the data to approach the constant property solution rapidly was predicted by a laminar finite-difference analysis for plasma flow published earlier [1]. The analysis was modified for the present study to improve its accuracy. The finite-difference theory under predicts the heat transfer in the first few tube diameters; two possible reasons for this discrepancy are the poor resolution in the inlet enthalpy profiles near the tube wall and nonequilibrium between electrons and heavy particles in this region.

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