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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

EXPERIMENTAL INVESTIGATION OF FLUID CONVECTION NEAR AN EVAPORATINGWATER MENISCUS IN A HORIZONTAL CAPILLARY

Tapan Kumar Pradhan
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP-208016

Pradipta Kumar Panigrahi
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP-208016

Abstract

We have experimentally investigated the fluid convection near an evaporating water meniscus. The meniscus is located at the end of a horizontal glass square capillary. The velocity measurement near the water meniscus has been performed using micro-PIV technique. The flow pattern near the evaporating water meniscus depends on the channel size. Square capillaries of 500 μm and 1000 μm size have been used. The flow of water near the meniscus is unidirectional towards the evaporating meniscus for smaller capillary size. Evaporation from the meniscus causes flow of water from the inner bulk fluid towards the meniscus to replenish the water loss at the evaporating meniscus. When capillary height increases, the thermal buoyancy effect caused by the evaporative cooling near the meniscus becomes significant. Hence, one circulating flow pattern is observed in vertical plane near the evaporating meniscus caused by thermal buoyancy force for large capillary size. This behavior is contrary to the evaporation from volatile liquid like ethanol/methanol which causes two circulating loops due to Marangoni convection near the meniscus as reported in earlier studies. In case of evaporating water meniscus, no such Marangoni convection is observed near the meniscus. Absence of Marangoni convection in water meniscus may be due to the presence of contaminants which suppresses the surface tension gradient flow. The flow observed near the water meniscus is due to the combined effect of replenishment of water flow towards the meniscus and the buoyancy driven flow due to temperature gradient caused by evaporative cooling.

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