HEAT TRANSFER ENHANCEMENT AND SCALE FORMATION: EXPERIMENTAL STUDIES IN FALLING FILM EVAPORATORS USING COPPER METAL FOAM

Abstract

Performance enhancement of horizontal tube falling film evaporators using thin metal foam was studied. A copper foam was brazed over the outer surface of a copper horizontal tube and used in the falling film evaporator of a desalination system. It was observed that the distillate production and heat transfer rate was enhanced by more than twice with the modified tube. Effect of feed rate, feed temperature, and subcooling on distillate production was studied for the copper foam-wrapped heat exchanger tube evaporator. A metal foam-wrapped heat exchanger tube was also used to study the effect of scale formation. The effects of temperature, flow rate, and seawater turbidity on scale formation was studied. Total scale deposit weight was observed after every 16 h of operation for a total run time of 128 h. It was observed that scale formation reduces with an increase in flow rate and increases with seawater temperature. It was also observed that scale formation is lower when the system is operated with seawater of low turbidity. The heat transfer enhancement surface promotes scale formation due to the increase in metal surface area in contact with seawater as in the copper foam-wrapped tube. Energy-dispersive X-ray spectroscopy and scanning electron microscopy were applied to investigate the mineralogy and microstructure of the deposits.