EFFECT OF INJECTED AIR BUBBLES DIAMETER ON HEAT TRANSFER FROM A CONICAL COOLING COIL

This study represents enhancement of heat transfer for a conical coil heat exchanger. One of the effective methods for enhancing the heat transfer rate in heat exchangers using injection bubbles. A conical coil immersed inside a tank, where the conical coil is the evaporator of a vapor compression refrigeration system. Experimental investigation was carried out to test the effect of air bubble diameter injection on Nusselt number. The air bubbles were injected from the bottom of tank in different number (15 to 40) at flow rates of air varying from (5 to 15) L/min. The results proved significantly increase in diameter of bubbles injection at (0.5 and 1) mm leads to increasing in heat transfer rate from the tank and Nusselt number (Nu) because affected on boundary layer around the coil , But at (1.5) mm the characteristics of heat transfer were decreases because the big diameter leads to insulation around the coil. The results also showed that the air bubbles injection in water has an optimal flow rate value at ** L/min in. Also, the COP of the refrigeration system and the Nusselt umber increased by **% and ***%, respectively compared with no bubbles injection case.