Shielded Hot-wire Viscosity Sensor On-line for a Flowing System Using a Shield of High Thermal Conductivity

Abstract

Application of a hot-wire viscosity sensor, which measures the intensity of the natural convection around a hot wire, have been limited to the stagnant systems. For the adaptation of the hot-wire viscosity sensor to flowing systems, the hot-wire viscosity sensor was protected from the effects of the flow by using a stainless steel shield. The shield was normally left open, and was closed only when the measurement was done. Although the hot-wire sensor response was influenced by the flow outside the shield through the high thermal conductivity of the shield material, this effect could be eliminated when the sensor was used at a sufficiently high flow rate outside the shield. The shielded hot-wire sensor responded well to changes in the viscosity of the test fluid in a wide range of viscosity. The effects of the size of the shield and the heat-flux applied on the sensor response were investigated. The shielded hot-wire viscosity sensor was used for the monitoring of the hydrolysis of starch by α-amylase.