Numerical Simulation (CFD) to Explore Optimal Vortex Generator Array Configurations in Air Cooled Condensers
air cooled condensers, vortex generator arrays, numerical simulation
Heat exchangers such as evaporators and condensers are a major component in applications of air conditioning, refrigeration and power conversion systems. Air-cooled condensers (ACC) used in power stations reject heat to the environment very similar to air conditioning systems. Rejection of heat to the ambient air is not very efficient and a more effectives design is sought in the fin component of the condenser. The current project proposes the use of vortex generator arrays in the plain fin of a flat tube heat exchanger to enhance heat transfer performance and increase system efficiency by achieving a breakthrough design. In the field of heat exchanger design, prior research has shown that vortex generators can be used for improving air side heat transfer. Elsherbini and Jacobi (2002) obtained 31% heat transfer enhancement with a pressure drop penalty of 10% for leading edge delta-wing VGs on a plain-fin-and-tube heat exchanger. Joarder and Jacobi (2005) assessed leading edge delta wings on flat-tube, louvered-fin compact heat exchanger and obtained an average heat transfer augmentation of 20% and a pressure drop of less than 7%. These results were obtained from full scale testing of VGs in prototype heat exchangers. It is anticipated that creating arrays of delta-wings will generate further enhancement of heat transfer while not increasing the pressure drop. In order to explore this further, a numerical simulation of such vortex generators deployed in different array configurations is proposed. Two challenges arise in designing such systems. The wings must be spaced far apart to avoid destructive interference but close enough to enhance as much surface area as possible. Another challenge is to test for various Reynolds numbers based on wing size to generate a vortex that can flow cleanly through the passage. The proposed work is focused on the deployment of such vortex generators in different array configurations in such a way that constructive interference of the vortices occurs. First, flow visualization experiments were performed in a water tunnel to guide the design and placement of delta winglets. Based on the conclusions from these experiments, different array deployments are being simulated numerically on commercial finite volume based CFD software (ANSYS Fluent). Different parameters such as angle of attack, number of delta winglets, their placement relative to each other and to the walls of the fin, etc. will be varied to determine the greatest enhancement effect and the results of heat transfer enhancement versus the pressure drop penalty will be reported in the final manuscript. Recommendations will be made on an optimal vortex generator configuration in order to maximize the heat transfer while not increasing the pressure drop significantly. REFERENCES  Elsherbini, A. and A.M. Jacobi, 2002, J. HVAC&R Res., 8:357-370.  Joarder, A., and A.M. Jacobi, 2005, Int. J. Heat Mass Trans., 48:1480.