Experimental study to investigate the influence of air bubble injection on solar water collector performance.

In this paper, the effect of injecting micro bubbles of air into a flowing water stream in copper tube of 8-meter length with a wavy design and a diameter of 0.0125 meter has been studied. The solar collector's inner surface moreover, coated with matte black paint that includes thermal die and 5% of TiN (Titanium Nitrate) nanoparticles to enhance the ability of solar radiation absorption. The solar collector's performance was evaluated. The experimental rig was designed and built in Karbala-Iraq, latitude (32.6160 oN) and longitude (44.0249 oE) within the first four months of the year. The air was introduced into the tubes through a venturi device, which mixed with the water and then flowed together inside the solar water collecting tube. The first section of the experiment involved only four various levels of water flow (0.5, 1, 1.5, 2) L/min, while the second section involved a water flow with injection of air bubbles at three different levels (0.25, 0.35) L/min. The result showed that as the rate of mass flow is reduced, the outgoing temperature rises, resulting in a rise the difference in temperature between the entrance and the output temperatures in both the incoming and departing systems. The largest temperature difference was 6.6 oC for opened system and 9.1 oC for closed system. But the small flow rate showed that the collector efficiency is decrease. Also, the results shows that the best efficiency for opened system at 1 liter per minute and 2 liter per minute for closed system. The average efficiency in the closed system was (65.57 %) at water and air bubble flow rate of 2 L/min and 0.35 L/min, respectively. The average efficiency of the opened system was (39.27 %) for water and air bubble flow rate of 1 L/min and 0.25 L/min, respectively. [ABSTRACT FROM AUTHOR]