Measurement of the thermal conductivity of fluids using laser spot lock-in thermography

• Published in: Measurement : journal of the International Measurement Confederation 2020-07, Vol.158, p.107740, Article 107740
• Main Authors: Bedoya, A., Colom, M., Mendioroz, A., Salazar, A., Marín, E.
• Format: Article
• Language: English
• Subjects: Contact resistance; Fluids; Heat conductivity; Heat transfer; Infrared analysis; Infrared cameras; Infrared imaging; Infrared lasers; Interfacial layer; Laser spot lock-in infrared thermography; Temperature; Temperature distribution; Thermal conductivity; Thermal contact resistance; Thermal resistance; Thermography
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2020.107740

[Display omitted] •A method is presented for thermal conductivity measurements in fluids.•The fluid fills a narrow gap between two solids.•Interfacial thermal resistance is measured by laser spot lock-in thermography.•Thermal conductivity is recovered from linear curve of gap thickness versus thermal resistance. In this work, we propose a new method to retrieve the thermal conductivity of fluids, kf, using laser spot lock-in infrared thermography. The measurement cell consists in two paralepidid blocks separated by a narrow gap of variable and known width, L. This gap can be filled with a gas or a liquid, producing a thermal contact resistance, Rth, which quantifies the thermal barrier to heat propagation. By focusing the laser spot close to the interface between the two solids, this thermal contact resistance can be obtained by fitting the temperature field recorded by the infrared camera to its analytical expression. Using the well-known relationship Rth = L/kf, the thermal conductivity of the fluid is obtained from a simple linear relation. Measurements performed in test samples show a good agreement between determined thermal conductivities and literature reported values, demonstrating the validity of the method.