Simultaneous Measurement of Temperature and Size of Droplets in the Micrometer Range

A new optical instrument for simultaneous measurements of temperature and size of periodically generated droplets is described. With this instrument, basic phenomena such as droplet evaporation or combustion can be studied. The droplets, which are produced with a vibrating orifice droplet generator, can be injected into different environments to study, for example, evaporation in a rarefied media or combustion in a hot environment. To determine evaporation or burning rates, the size and the velocity of the droplets have to be measured for different lifetimes. The droplet size is determined from the interference pattern of the light scattered in the forward direction. The intensity distribution is recorded with a CCD-array. From the fringe spacing of the interference pattern the droplet diameter can be determined with an accuracy of 2%. Droplet velocities have been measured by a conventional LDV-technique. In the present paper the droplet temperature is determined from the angular position of the rainbow, which is measured with a CCD-array. The rainbow-angle is a function only of the refractive index. From the temperature dependence of the refractive index one obtains the temperature. Some typical experimental results are discussed.