Increase factor for forced convection at small heating elements

摘要

The convective heat transfer at small flush mounted elements is important for microelectronics and thermal sensing applications. The maximum heat transfer appears at the upstream area of the heating element with a length l*. The heat transfer coefficient h* averaged along the length l* of the heating element is larger than the heat transfer coefficient h at the same position of a uniformly heated part like e. g. a flat plate or cylinder. An increase factor K = h*/h is introduced for the characterization of this relation. The present study compares K values derived from boundary layer calculations, heat transfer measurements, calibrations of thermal wall shear stress sensors and from numerical calculations for l* = 0.01 to 4 mm. The increase factor K is dependent on the flow length l*, the heat transfer coefficient h and the thermal insulation.