Rapid measurement of dispersion and velocity in freezing drops using magnetic resonance methods

Magnetic resonance (MR) methods are used to provide both rapid real-time dispersion and spatially resolved velocity measurements within suspended drops undergoing freezing. Two-mm-diameter drops composed of water, sucrose solution, oil-in-water emulsion or oil-in-sucrose-solution emulsion drops are thus studied. Dispersion measurements have been shown to give valuable insights into the transport processes and solidification behaviour of the freezing drops. It was possible to detect drop nucleation/recalescence, rupture and solution freeze concentration. Limited convection of unfrozen material, due to crystal growth, was detected. The spatial distribution of the velocity within freezing drops revealed the rotation of the water drops but not of drops composed of the other materials studied. Rapid increases in velocity were observed following nucleation, which were dampened down during subsequent heat-transfer-governed droplet freezing.

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