EXPERIMENTAL STUDY OF BUBBLE BEHAVIOUR IN SUBCOOLED FLOW BOILING OF WATER AT LOW PRESSURE

摘要

High-speed photographic techniques were used to investigate the behaviour of vapour bubbles during subcooled boiling of water. Pressures ranged from 1 to 3 bar, subcooling between 10 and 30 K, and mass flow rates from 0.02 to 0.2 kg/s. The experiments were performed on a vertical, upward flowing, annular test section with an inner electrically heated surface. Heat fluxes ranged from 0.2 to 1 MW/m{sup}2. It was found that bubble departure diameters decrease with increasing pressures. Such changes will affect typical bubble behaviour and hence, the heat transfer mechanism. Particular attention is given to; bubble shapes in the growing and condensing regions; bubble detachment diameters; lifetimes and their variations with subcooling, heat flux, flow rate and pressure.