INSTITUTE OF PHYSICS PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 12 (2001) 1–5 www.iop.org/Journals/mt PII: S0957-0233(01)18472-9 Low-cost viscometer based on energy dissipation in viscous liquids C Hashimoto 1 , G Cristobal, A Nicolas, P Panizza 2 , J Rouch and H Ushiki 1 Centre de Physique Mol´ eculaire Optique et Hertzienne, UMR 5798, Universit´ e Bordeaux I, 351, Cours de la Lib´ eration, Talence 33400, France E-mail: ppanizza@cribx1.u-bordeaux.fr Received 31 October 2000, accepted for publication 11 January 2001 Abstract We describe a new type of low-cost easy-to-use viscometer based on the temperature elevation in a liquid under shear flow. After calibration, this instrument can be used to measure the apparent steady state viscosity for both Newtonian and non-Newtonian liquids with no yield stress. We compute the rise in temperature due to viscous dissipation in a Couette cell and compare it to experimental results for different fluids. We show that the variation of the temperature with shear rate can be used to characterize the rheological behaviour of viscous fluids and to evaluate their viscosity in a large domain, from typically a few cP up to more than 10 P, with an accuracy of about ±5%. In contrast to simple viscometers, non-Newtonian fluids can be studied with this apparatus. We give experimental results for Newtonian and non-Newtonian liquids and show that they are very similar to those given in the literature by using much more sophisticated instruments. Keywords: fluid viscosity, Couette cell, viscous dissipation, viscometer, shear flow, rheology, fluid characterization 1. Introduction It is well known that simple viscometers like capillary tubes or falling-ball instruments give precise values of the viscosity of liquids, but in a quite restricted range for a given instrument. Furthermore they are unable to give information on non- Newtonian fluids. Indeed non-Newtonian regimes are usually connected to structural changes of the fluid microstructure under flow. The transient time to reach steady state under stress can be long, from a few minutes up to hours. Therefore capillary or falling-ball viscometers are unsuitable to study non-Newtonian fluids since the steady state under stress can never be obtained with these types of instrument. To gain information on non-Newtonian fluids, expensive rotating rheometers have to be used. In this paper we first evaluate the thermal elevation (in a stationary state) due to viscous dissipation of a liquid in a Couette cell. Even at moderate shear rates, we show that this temperature elevation can be significant 1 On leave from Tokyo University of Agriculture and Technology, 3-5-8, Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. 2 To whom correspondence should be addressed. and therefore quite easy to measure with a standard laboratory instrument. On this basis, we describe an easy-to-use low-cost instrumental set-up (about 1/15 of the cost of a commercial rheometer) which allows us to characterize the rheological behaviour of Newtonian or non-Newtonian fluids. Using this set-up we give experimental results both for Newtonian (water–glycerol solutions, micro-emulsion systems) and for non-Newtonian liquids like quaternary solutions made of brine, surfactant, dodecane and pentanol. After calibration, the value of the temperature, shear and time-dependent viscosity can be measured with an accuracy of about ±5% in a large domain, from few cP up to more than 10 P, for shear rates varying continuously from 0 up to 1000 s −1 . 2. Experimental set-up We used a home made set-up depicted in figure 1. It consists of a Couette cell made of two concentric cylinders of respective radii R 0 = 25 mm and R 1 = 26 mm, and of heights H = 60 mm. The inner cylinder is fixed while the outer one rotates at a given angular velocity, ω, by using a variable rotating 0957-0233/01/010001+05$30.00 © 2001 IOP Publishing Ltd Printed in the UK 1