IR Thermography measurement of convective heat transfer coefficients with periodic excitation by Joule effect applied to the estimation of compact heat exchanger efficiency

International audience; A new methodology has been developed to characterize the loss of efficiency of heat exchangers due to a maldistribution of the two-phase flow. The approach consists to measure the distribution of the local heat transfer coefficients with a non-intrusive and fast measurement method, based on a periodic excitation by Joule effect and infrared thermography measurement. An analytical model of the heat transfer is used to deduce heat transfer coefficients from the amplitude of the outside tube temperature fluctuations amplitude and heat flux measurement. This method, initially developed for a cylindrical tube, has been also applied on various tube shapes, including microchannel flat tubes. As an example, the method is used to evaluate the heterogeneity of distribution of an air-water mixture in a compact heat exchanger composed of seven multiport flat tubes. The distribution of heat transfer coefficients was studied for a vertical downward header and horizontal channels and for mass flux from 29 kg.m-2.s-1 to 116 kg.m-2.s-1 and for quality from 0.10 to 0.70. Results are presented and discussed.