Effect of Thermal Convection on Viscosity Measurement in Vibrational Viscometer

Ali Akpek,Nobuyuki Fujisawa,Chongho Youn,Toshiharu Kagawa,Atsushi Maeda

doi:10.4236/jfcmv.2014.21003

Abstract

This paper describes the experimental study of viscosity measurement error in the vibrational type viscometer, which measures viscous damping of the oscillating circular plate in a fluid in continuously increasing temperatures. The experiments are carried out to measure non-uniformity of the temperature field in the test cup of the vibrational viscometer in continuously increasing temperatures, while changing the viscosity of the target fluids. Experimental outcomes show that non-uniformity of the temperature grows in the cup and results in viscosity measurement error, when the viscosity of the fluid increases. In order to understand this phenomenon, velocity measurement by particle image velocimetry is conducted in the test cup for fluids of varying viscosity. The results indicate that mixing is enhanced in the low-viscosity fluid by the occurrence of unsteady thermal convection, while weaker convection appears in the high-viscosity fluid.

Highlights

The vibrational type viscometer is a newly developed viscometer featuring efficacious continuous viscosity measurement capability, low cost and ease of use in comparison with other types of viscometer [1,2,3,4,5,6,7]
The basic principle of the vibrational viscometer is that viscous damping of the oscillation amplitude of a circular plate in the target fluid is proportional to the product of the fluid viscosity and density, which are functions of the temperature of the fluid
It is interesting to see that Tb is closer to Tc for the lowviscosity fluid, while it stays in the mid of Tw and Tc for the high-viscosity fluid. This may indicate higher mixing of the low-viscosity fluid in the cup. This result indicates that the temperature error in the test cup is influenced by the viscosity of the target fluid

Summary

Introduction

The vibrational type viscometer is a newly developed viscometer featuring efficacious continuous viscosity measurement capability, low cost and ease of use in comparison with other types of viscometer [1,2,3,4,5,6,7]. There are few studies on viscosity error due to non-uniformity of the temperature field in the fluid [8]. The viscosity measurement in the vibrational viscometer requires knowledge of the thermal convection in a test cup, which is heated from the bottom and the sides of the rectangular cup. Heating from the bottom and sides of the cup causes thermal convection, which promotes mixing of the fluid inside, and results in a uniform temperature field [9,10,11,12,13]. The magnitude of the thermal convection is a key to understanding the temperature fields in the cup and the accuracy of the viscosity measurement in the vibrational viscometer

Objectives

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Results

Conclusion