Microscale temperature measurement at an evaporating liquid meniscus

A microscale temperature measurement technique was used to investigate the heat transfer at an evaporating liquid meniscus. This evaporation process is the core element of capillary-driven heat transfer devices (e.g. heat pipes) and is also very important for nucleate boiling. Motivated by the well-known importance of the microscale interline region for the overall heat transfer performance of these processes, an experiment has been designed to investigate the microscale heat transfer phenomena and the wetting characteristics. The experimental setup includes a single capillary slot created by two parallel flat plates. One of the plates consists of plexiglas covered with a thin metallic foil that is electrically heated. The backside of the foil is covered with temperature sensitive liquid crystals. The color play of the crystals is recorded with a CCD camera in conjunction with a microscope. This enables the two-dimensional measurement of the temperature distribution underneath the evaporating meniscus with a theoretical spatial resolution of less than 1 mum. Simultaneously, the shape of the meniscus including the apparent contact angle between fluid and wall can be determined by backlight profiling. An uncertainty analysis for the liquid crystal calibration implies the feasibility of the technique for microscale application. Measurements at an evaporating meniscus show the local cooling due to the microscopic effects at the interline. (C) 2002 Published by Elsevier Science Inc.