A Local Heat Flux Measurement Technique for Inclined Heat Exchanger Tubes

This article presents the design, fabrication, and calibration of thermocouple pairs for local heat flux measurement. The intended application of the thermocouple pairs is on the tubes of phase-change heat exchangers experiencing heat fluxes on the order of 10⁵ W/m². Particular advantages of this technique are that it is accurate even for thin-wall tubes, there are no restrictions on the tube inclination, and it is economical.

A thermocouple pair consists of a sheathed thermocouple which measures the tube outer surface temperature and a novel plug-type thermocouple which measures the tube inner surface temperature without interrupting the heat transfer phenomena. A calibration was performed by imposing a series of known heat fluxes on a condenser tube that had been outfitted with a number of thermocouple pairs and measuring the temperature difference between the thermocouples. The maximum uncertainty associated with the calibration constants was ±9.5%. This tube was then used as the condenser tube of a double-pipe heat exchanger to obtain local heat flux data that had previously been unattainable around a horizontal tube.

Keywords:

• in-tube condensation
• local heat flux measurement

The authors gratefully acknowledge financial support of this project by the US Department of Energy, Nuclear Engineering Education Research (NEER) project, award No. DE-FE07-02ID14341.