In a flow tube instrument modeled after a structurally simple and easy-to-use bubble viscometer, bubble ascent and liquid flow were examined to evaluate the physically defined viscosity of non-Newtonian liquid foods. For Newtonian and non-Newtonian test liquids, a dimensionless expression between the friction coefficient and Reynolds number, which was derived through analysis as an annular flow of liquid around bubble, indicated that the flow in the instrument was laminar. Prediction organized based on the empirical relation was advanced for evaluation of the non-Newtonian viscosity. The flow tube instrument was expected to be applicable to the conditions in drinking and eating, from a viewpoint of the characteristic shear rate ranging from 10 to 100 s−1.

To develop a structurally simple and easy-to-use viscometer for liquid foods, flow measurements and analyses were done in a flow channel instrument. Newtonian and non-Newtonian test liquids respectively employed in the experiments show viscosity and viscoelasticity. Changes of the modified friction coefficient during the flow processes characterized viscous flow in the instrument. The elasticity was found to be dominant in the early process, reducing the flow as a function of the relative magnitude of liquid viscoelasticity.

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