INFLUENCE OF FREE-CONVECTION ON THE HEAT-TRANSFER FROM HOT-WIRE PROBES

The present paper is concerned with the experimental determination of the influence of free convection on the heat transfer from horizontal hot-wire probes in cross flow. Free convective flow can be minimized under microgravity conditions and its quantity can be determined by comparisons with terrestrial investigations. Using the developod experimental setups it is possible to investigate all three flow regimes, i.e. pure free, mixed, and pure forced convection (0 less-than-or-equal-to Re less-than-or-equal-to 0.1). It was found that the influence of free convection is limited to Reynolds number Re less-than-or-equal-to 0.0045, independent of the overheat ratio. Based on the findings of Collis and Williams [12], the influence of free convection can be neglected for Re > 0.58 . Gr1/3. The fluid properties are computed at the film temperature. Two correlations are established for the regime of pure forced convection. End losses to the supports were determined in a vacuum experiment, thus allowing comparison with theoretical investigations. The difference between the analytical computations and the measurement data in the range 0 less-than-or-equal-to Re less-than-or-equal-to 0.02 is caused by the three-dimensional heat transfer occuring in the experimental investigation.