Abstract
This article is a review of recent studies on the effects of fluid particles upon NMR signals. Probability density of velocity of fluid particles in a circular pipe can be obtained from the first spin echo amplitude. Turbulent diffusion or Lagrangian correlation can be discussed by analyzing the second spin echo amplitude. This article has 6 sections. Section 1 summarizes the history of the study of this field. Section 2 explains the relation between NMR signals and velocity of fluid particles. In section 3, some formulas of spin echo amplitudes in laminar flow region are shown. Path integral method to analyze spin echo amplitudes in turbulent region is presented in section 4. Cumulant expansion method is presented in section 5. Observations of intermittent flow which appears in the transitional region from laminar to turbulent flow are reported in the last section.
