Experimental assessment of a direct-contact heat exchanger bubbling hot water in a cooler liquid gallium bath

摘要

A direct-contact compact heat exchanger to enhance cooling of hot water, has been manufactured and tested experimentally. Hereby hot water is dispersed into a cooler liquid gallium bath in the form of small water bubbles emanating from 48 holes with 3 mm diameter each, drilled on four horizontal bubbles distribution tubes. Heat transfer limitations posed by gallium's low specific heat have been circumvented by imbedding cooling water tubes within the gallium. Thereby it was possible to maintain gallium at almost 30 °C during water bubbling; slightly above gallium's freezing point. Temperature reduction by about 23 °C was possible for hot water flow with initial temperature of about 60 °C and flow rate of 11.3 g/s when bubbled through such gallium bath that has temperature of about 30 °C and thickness of about only 18 mm. To realize such temperature drop for water using equivalent shell-tube heat exchangers of conventional kinds with 3 mm diameter tubing, a tube length in the range of 70 to 80 cm would be required. Theoretical considerations and empirical correlations dedicated to solid sphere calculations have been used to predict motion and heat transfer events for water bubbles moving through isothermal gallium bath. The computations were extended to include the experimental temperature conditions tested. Computations agree very well with experimental results.