Processing droplet temperature measurement data obtained with Rainbow Thermometry

The state of the art in Rainbow Thermometry is presented. Rainbow Thermometry is a technique for measuring size and temperature of transparent droplets. For data inversion a rainbow pattern is employed, which is formed by a single droplet or by constructive interference of laser light scattered by an ensemble of spherical droplets. In the first case, one speaks about Standard Rainbow Thermometry (SRT), investigated since 1988. In the second case, the technique is called Global Rainbow Thermometry (GRT). studied since 1999: here, the non-spherical droplets and liquid ligaments results in a uniform background and thus do not influence the interference pattern. formed by the spherical droplets, from which average size and temperature are derived. This is a large improvement with respect to Standard Rainbow Thermometry. which is strongly influenced by particle shape. Moreover, GRT is applicable for smaller droplets than the standard technique because the global pattern is not spoiled by a ripple structure. Data inversion schemes based on inflection points, minima and maxima are discussed for SRT and GRT. The standard technique is applied to a monodisperse burning droplet stream, where the problems with particle shape do not exist. Global Rainbow Thermometry is applied to a heated water spray, where the standard technique fails. For both applications the accuracy in the temperature measurement was a few degrees Celsius.