Thermal performance of flat plate solar water collector using air bubble injection

Abstract

The effect of injecting small bubble air into the water stream flowing in two spiral arrangement copper tube of 15 m length, 0.012 m diameter, and number of coils were 11 has been investigated. The inner surface of the solar collector was also painted with a matte black paint with a mixture of a nanomaterial (thermal dye with 5% of TiN). The performance of the solar collector was examined experimentally in Babylon-Iraq, longitude (44.4 E) and latitude (32.4 N) under the best experimental conditions of the province during the months of the beginning of the year. Venturi device was used to enter the air inside the tubes to mix with the water and then flow together inside the tube of the solar water collector. The experiment included the work of two parts, the first part was the flow of water only at four different levels (1,1.5,2,2.5) L/min. and the second part was the flow of water in addition to the injection of air bubbles, which was also done at different levels. Results show that the decrease in the mass flow rate leads to an increase in the outgoing temperature and thus an increase in the difference in the inlet and outlet temperature and in the cases of the incoming and outgoing systems. The maximum temperature difference in the closed system was 36.1 °C for water and air bubble flow rate of 1 L/min and 0.3 L/min., respectively. The maximum temperature difference in the opened system was 12.5 °C for the water and air bubble flow rate of 1 L/min and 0.3 L/min, respectively. The injection of 0.3 L/min. of air bubble through the water stream in the closed system led to increase the temperature difference, while in the opened system seems to have no effect.