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.
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.