AN INSTRUMENT FOR THE HEAT-FLUX MEASUREMENT FROM A CONTOUR OF A SURFACE WITH UNIFORM TEMPERATURE

An instrument for the measurement of the heat flux distribution along an internal or external contour of a surface with a uniform temperature is described. The main element in this instrument is an electrically heated narrow nickel/chromium ribbon which is mounted flush with, but thermally and electrically insulated from, walls on all sides. The walls are separately heated and are made of a highly conducting material (e.g., aluminum) to ensure a uniform temperature. Differential thermocouples are used to measure the temperature difference between the walls and Ni/Cr ribbon at various positions along the ribbon. The ribbon power is adjusted until the differential temperature is nulled at a particular position on the ribbon. Since conduction along the ribbon is small, the electrical power divided by the sensor area is a direct measure of the surface heat flux at the nulled position. This makes it possible to measure the local time-average heat flux at various positions along a contour of a surface inside a circular duct. The time constant in this application was 13 s. An uncertainty analysis shows that this instrument has an uncertainty of +/- 3.84% for a convective heat flux on the order of 900 W/m2.