NMR FLOW IMAGING OF PASTES IN STEADY-STATE FLOWS

The velocity profiles and volume concentrations of free water and the solids matrix of flowing pastes can be mutually determined independent ly via flow experiments in an NMR tomograph. This supplies direct proo f of the relative displacement of free water in flowing pastes. The tw o phases can be distinguished with the help of NMR by their different magnetic relaxation times (T2). It is possible to measure the wall-sli p of the two phases and, hence, to differentiate between the shear and slip shares of the total volumetric flow. When the evaluation of the flow experiments is based on a material law, the accompanying material functions can then be derived for pastes or suspensions from the velo city and concentration distributions. For example, as in the case of t he fully-developed steady-state pipe flow, without any additional assu mptions or corrections as is normally necessary for capillary rheometr y. Through the use of NMR, it is possible to correlate the rheological features of the material in question, its flow behaviour and its flow -induced structural changes.