This invention relates to a device for measuring the physical properties of liquids and in particular to a device for measuring physical properties of liquids using the interference of light waves.
It is well known in the art to use fiber optic systems for temperature measurement and monitoring of liquids. For example, these systems are commonly used when monitoring the temperature of flammable liquids because non-electrical sensing devices eliminate a source of explosion hazard associated with electrical temperature monitoring systems.
The thermal conductivities of liquids are often measured because the thermal conductivities of liquids are required for various heat transfer analyses. These conductivities are commonly obtained with a transient hot-wire apparatus. In this technique a thin platinum wire, serving as both a heating element and a thermometer, is heated resistively with a current pulse of about one second duration. The thermal conductivity of the surrounding medium is determined from the temperature change of the wire as a function of time. In this type of analysis an approximate solution of the heat conduction equation is used, where the slope of the change in temperature versus the natural log of time curve is inversely proportional to the thermal conductivity of the medium. In applying this method, a number of corrections are necessary due to the finite diameter and finite thermal conductivity of the platinum wire. Additionally, a correction for the temperature dependence of the fluid properties is necessary. With these corrections incorporated into the analysis, the technique allows for thermal conductivity determinations with an accuracy of 0.2%.
Another method for measuring temperature using an optical fiber is disclosed in Langeac U.S. Pat. No. 4,563,639. In the apparatus of Langeac, a probe is formed by winding an optical fiber in a generally solenoid shape. U.S. Pat. No. 4,621,929, issued to Phillips and entitled "Fibre Optic Thermal Anemometer," teaches a device for measuring the heat transfer coefficient of a sample.