Determination of application boundaries to Giulotto method to during measuring of longitudinal relaxation time in nuclear magnetic flowmeters-relaxometers

Abstract

The method of nuclear magnetic resonance, which is currently the most common in research and control of parameters of condensed matter, and the nuclear magnetic flowmeters-relaxometers that implement this method are described. The features of determining the times of longitudinal and transverse relaxation in nuclear magnetic flowmeters-relaxometers under different flow regimes of the medium in the process of monitoring its parameters have been established. The advantages of using a modulation technique for recording nuclear magnetic signals in flowmeters-relaxometers in comparison with other registration methods are noted. Using various approximations by the Giulotto method from the Bloch equations, a relation was obtained to determine the longitudinal relaxation time from the results of two measurements of the amplitudes of the nuclear magnetic resonance signal or resonant frequencies at different modulation frequencies. It has been experimentally proven that this relationship has a number of restrictions on its application for flowing liquid. These limitations are associated both with the technique of recording nuclear magnetic resonance signals and with the ability to generate such signals at different modulation frequencies of a constant magnetic field, the amplitudes of which differ from each other beyond the measurement error. The reasons that led to this discrepancy in the ratio for determining the time of longitudinal relaxation have been established. The limits of applicability of the obtained relation are found and it is experimentally proven that within these limits this relation can be used for reliable measurements of relaxation constants. Using experimental data, the relationship for determining the longitudinal relaxation time was studied. It has been proven that in a number of cases it is impossible to determine the desired value using the indicated relationship, although nuclear magnetic resonance signals of the current medium are recorded, and the medium has relaxation times. The results obtained make it possible to eliminate errors when using the nuclear magnetic resonance method to study flowing media and solve a number of complex problems in the energy, oil, chemical and pharmaceutical industries.