A phase-based method for measuring local convective heat transfer coefficients

Abstract

This paper presents an experimental technique that exploits the phase-shift between wall and fluid temperatures to measure local convective heat transfer coefficients. The phase-based method is described theoretically, analysed numerically and validated experimentally. In comparison to an established transient technique, it is shown that using phase-shift, rather than amplitude, reduces a heat transfer coefficient measurement's sensitivity to noise by a factor between 10 and 50. This robustness to noise reduces the heating power requirements for an experiment and enables high spatial resolution measurements. Phase-based methods have been demonstrated previously for calculating bulk heat transfer coefficients, or for local heat transfer coefficients on thin walls with radiative heating applied from the opposite side of the wall. These methods often require numerical reconstruction of the phase-shift with measured temperatures applied as a boundary condition. The phase-based method presented in this paper measures local heat transfer coefficients on thick walls by applying a periodic temperature change to the fluid flowing over the wall. Considering the heat equation for a 1D, semi-infinite solid results in a novel relation between phase-shift and heat transfer coefficient, allowing local heat transfer coefficients to be calculated without a numerical solution.