The morphology of ice-structure in a planar nozzle subjected to forced internal convection flow

The present paper deals with the ice-formation in a planar nozzle with various convergence angles. Experiments have been carried out for different wall cooling parameters B in the range between 4 and 25 and for different flow rate Reynolds numbers in the range of 5,000 < Re _4h  < 50,000 for two different convergence angles of the nozzle. For all experiments with the larger convergence angle of the nozzle (2.5°), only smooth ice-layers could be observed. However, for the nozzle with the smaller convergence angle (1.25°), also wavy ice-layers could be detected. This interesting result is a justification for the hypothesis that the formation of wavy ice-layers is caused by flow laminarisation (due to the rapid growth in ice-layer thickness with increasing axial position from the inlet) and retransition to the fully turbulent state (after the acceleration falls below a certain critical value). Thus, this paper proves for the first time, that wavy ice-layers are suppressed by superimposed strong flow acceleration.