Investigation of the Influence of Free Convection on the Heat Transfer of Cylinders with Different Aspect Ratios

The heat transfer from an electrically heated cylinder (wire) of finite length to the surrounding fluid can be divided into heat radiation, conduction and convection. A technical application of these cylinders with typical dimensions of 1-2 mm length and a few micrometers diameter is the Hot-Wire-Anemometry.This systematic study should clarify the influence of the convection to three dimensional heat transfer of cylinders. For this aim it is planned to investigate Reynolds numbers below Re = 1 (creeping flow). For this reason measurements should be done under 1g in the earth laboratory and also under microgravity (μg) conditions. Comparisons of these measurements under otherwise same conditions allows to distinguish between the pure convection heat transfer and the contributions due to conduction and other effects. For measarements under μg the Drop Tower Bremen can be used as research facility. Due to the fast response of convection to changes in the gravity conditions the Drop Tower is an ideal and cost efficient experimental tool. The experimental setup is build to operate at velocity range of 0-l m/s which includes the whole range of convection from pure free convection at 0 m/s over mixed convection up to pure forced convection at velocities above about 0.15 m/s. This velocity region corresponds to a range of the Reynolds number of Re = 0 - 0.18 for a cylinder of 5 μ m diameter at Tf= 140℃ in air at an ambient temperature of about 21℃.