FLOW BOILING OF A HIGHLY VISCOUS POLYMER SOLUTION
Flow boiling experiments with mixtures of poly dimethyl siloxanes and n-pentane are carried out in a vertical annular channel. The mixtures are fed to the test section with a subcooling of 30 − 65 K. The flow condition at the inlet can be characterized as creeping flow with Re-numbers as small as 0.01. Strong radial temperature gradients prevail throughout the entire evaporation process, indicating a laminar flow character even under boiling conditions.
Analysing the experiments, heat transfer to a homogeneous liquid phase, subcooled boiling, fully developed nucleate boiling, convective heat transfer to a two-phase flow and flash effects due to pressure loss can be distinguished.
Yet heat transfer can be described as a first approximation by a simple model which is based on laminar single phase heat transfer and incorporates an additional convective term reflecting the augmentation of convection through the gas phase.