An experimental study on channels formation during solidification of aqueous ammonium chloride

The formation of freckles during the unidirectional solidification of aqueous ammonium chloride inside a test cell cooled from the bottom was investigated experimentally with and without the vibration of the test cell. The effects of base temperature, initial concentration, inclination of the test cell, vibration amplitudes and vibration frequencies on the channel formation inside a test cell were investigated. Experiments were carried out for 15%, 25%, 30% and 32% NH4Cl concentrations, at base plate temperatures of −21, −26 and −38 °C, and at inclination of 0–30° from the vertical, and vibrated at several amplitudes of 2.54, 4.45 and 6.35 mm under vibration frequencies from 10 to 50 Hz.The experimental results show that channels are formed during the solidification for all concentrations except at the 15% concentration. The channels formed during solidification are observed to be more pronounced and lesser in number with increasing concentration. The channels formed decreases in number with decreasing base plate temperature. Channel suppression is influenced by the vibration amplitude, with the larger-amplitude vibration being more effective. The application of vibration to the test cell shows that the mushy zone thickness and the number of channels are reduced. Vibration at a lower frequency of 10 Hz does not suppress the formation of channels as good as vibration at a higher frequency of 50 Hz. The suppression effect of the inclination angle on the occurrence of channels is observed to be insignificant.