Magnetic Resonance Imaging of Water Freezing in Packed Beds Cooled from Below

Abstract

Full-field quantitative visualization of freezing interfaces requires the introduction of high resolution noninvasive methods. Magnetic Resonance Imaging (MRI) is a versatile tool for mapping the distribution of liquids (primarily water) in three-dimensional space, and is the only practical solution in systems that are strongly refracting or opaque to visible light. MRI is employed to visualize freezing in water-saturated packed beds consisting of spherical beads cooled from below. Imaging of the stagnant interstitial water is accomplished by exploiting the strong contrast in MRI signal between interstitial ice and liquid water. Our implementation of MRI allows fully three-dimensional reconstruction of the solidification front and adequate time resolution to quantify the freezing of the pore water. The wall effect, as expressed by the ratio of bed to bead diameter, is examined with respect to the shape and propagation rate of the freezing interface. MRI can.be effective only in media that do not affect the imposed magnetic fields. In heat transfer applications, extra provisions in terms of design and choice of materials of the test section are np.~essary to accommodate the special environment of the MRI scanner.Air Conditioning and Refrigeration Center Project 5