Magnetic Resonance and Magnetic Resonance Imaging Studies of Sprays
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Date
2022-02
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University of New Brunswick
Abstract
The process of spray atomization is ubiquitous in industry yet quite complex to analyze theoretically and study experimentally. Magnetic resonance imaging (MRI) is a non-invasive measurement technique successfully employed to study fluid features in flow systems. This thesis focuses on the use of MRI to study three areas of spray research: the flow inside the spray nozzle; the "near-nozzle" region; and the freezing spray accumulation on a cold surface.
The features of the spray strongly depend on internal nozzle flow. One of the areas of great interest is a measurement of flow inside the nozzles, where the flow has a high velocity (m/s) in a small channel structure (sub-mm). In motion-sensitized MRI, when displacement during the encoding time becomes greater than the pixel size, a velocity misregistration takes place. To address this issue, the encoding time must be reduced. We demonstrate how the reduction of the encoding time can be achieved by applying a Time-Of-Flight (TOF) approach.
Another interesting region of spray atomization is spray imaging in the "near-nozzle" region. Standard preparation schemes are difficult to employ due to sprays’ fast speeds (>10–20 m/s) and low density. In this thesis, the interval between the preparation and the readout stages was reduced by performing a Single Point Imaging (SPI) encoding [10] on the rising gradients. This also enabled the use of 90-degree flip angles to maximize the spray signal and saturate the stationary water signal.
The third area of research in this thesis is spray deposit. One important example of spray deposits is sea spray icing. It causes ice accretion on ships and offshore structures which leads to marine disasters. We show that a portable Magnetic Resonance (MR) instrument could be an efficient tool to evaluate the features of the sea spray spongy ice. A portable unilateral magnet permits to characterize the evolution of sea-ice brine inclusions in two types of ice: stationary seawater ice; and seawater spray ice. Using a unilateral MR device, features such as spray ice growth, brine content, and distribution can be examined.