The objective of this paper is to use fiber optic sensors embedded in a tube wall to measure local convective heat transfer coefficients of a single-phase fluid. By using Rayleigh backscatter and an interferometer technique, mechanical changes in a fiber sensor that are proportional to temperature can be detected. This allows the location and magnitude of the temperature along the fiber to be measured. Using these fibers, we can measure axial profiles of the wall temperature in a heated tube with an internal fluid. By using multiple sensors spaced circumferentially around the tube, we can then generate axial and circumferential temperature maps of the tube wall. When combined with a known uniformly applied heat flux, these measurements can be used to determine the local heat transfer coefficients for single-, two-phase, and supercritical flows.

In this study we consider a horizontal tube with internal diameter of 4.57 mm and heated length of 0.4 m. Using the fibers, wall temperature is measured every 0.7 mm in the streamwise direction at eight evenly spaced axial locations with an uncertainty of 2 °C. Co-located, calibrated thermocouples will verify the fiber temperature readings. Electric heaters provide a heat flux up to 20 W/cm². Using this setup, heat transfer coefficients in the developing and fully developed region are obtained for water in laminar flow regimes and compared with established convective heat transfer correlations and models. The measured heat transfer coefficients in agreement with what is expected. In future work, this test section will be used to study nearcritical carbon dioxide convective heat transfer in both steady and transient conditions.