Authors : Hameed K. Hamzah, Riyadh S. Al-Turaihi and Anwer A. Abass
Abstract: In the present research, heat transfer augmentation in shell and helical coiled tube heat exchanger with air bubble injection and Al2O3 nanofluid for turbulent flow has been studied. The thermal performance of helical coiled tube heat exchangers has been enhanced with the use of two techniques. The first is represented by air bubble injection in shell side with cold water to enhance the heat transfer rate outside helical coiled tube heat exchanger by creating turbulence in the flowing fluid and the second is represented by adding nanopartical to hot water to produce nanofluid with three volume concentrations (0.1, 0.2 and 0.3%) to increase the heat transfer rate inside the coil. In this research, a new model is designed to mix the air with the water. It ensures that there are small bubbles of water inside the shell and with specific distances to ensure that the excitation is inside the shell. This design was done laboratory and applied and the results were good by examining the number of bubbles and the distance between them by digital camera. The variations of Number of Thermal Units (NTU), exergy loss, dimensionless exergyand effectiveness due to the air bubbles injection with different air flow and fluid flow rate rates are evaluated. The results obtained for all concentrations at different air and nanofluid flow rate were compared with the case when air bubbles were not injected. The outcomes revealed that the heat transfer characteristics enhanced with nanoparticles volumetric concentrations and the air bubble injection. Besides this, water based Al2O3 nanofluid with 0.3% of Al2O3 nanoparticles gave more enhancement than Al2O3 nanofluid with 0.1% of Al2O3 nanoparticles as the enhancement in the heat transfer characteristics is directly proportional to the volumetric concentration of nanoparticles in the base fluid. Dependent on air injection condition and Reynolds number, air bubbles increased the amount of Nusselt number about 14-50%. Air bubble injection increased the effectiveness of heat exchanger about 2.5-47.5%.
Hameed K. Hamzah, Riyadh S. Al-Turaihi and Anwer A. Abass, 2018. An Experimental Investigation of Heat Transfer Augmentation of Water-Al2O3 Nanofluid Worked Inshell and Helical Coiled Tube Heat Exchanger with Air Bubble Injection Technique. Journal of Engineering and Applied Sciences, 13: 11135-11148.