hitzdrahtanemometrie (KGHDA)

abstract

Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At very low free-stream velocities (u ≤ 0.1 m/s), hot-wire measure- ments are significantly influenced by buoyant convection. Below a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (μg) conditions are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis and the direction of the free stream are all per- pendicular to each other. The microgravity experiments were carried out in the Drop-Tower Bremen in which the residual acceleration is less than 10(-5) g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0 ≤ u ≤ 0.35 m/s corresponding to a Reynolds number range Re < 0.1 in standard air. This range includes pure free convection for Re → 0 and forced-convection-dominated heat transfer for Re = 0.1. At intermediate Reynolds numbers both transport mechanisms must be considered.

• C. Henselowsky, H. C. Kuhlmann, and H. J. Rath: Investigation of the influence of free convection on the heat transfer of cylinders with different aspect ratios. Microgravity Sci. Technol. XIII/3, 43-51 (2002)

experiment year: 2000
number of drops: 57