Enhancement of airside thermal and flow performances of heat exchangers with louvered fins

The heat exchangers are used in air conditioners, heat pumps, marine, land and air vehicles, refrigeration systems, thermal and nuclear power plants, in short, they are used from industrial products to domestic products. Increasing the heat transfer capacity of a heat exchanger means that the volume of the heat exchanger and the material that is used will be reduced. Louvered fin heat exchangers are used in many applications due to their potential of high heat transfer enhancement ability. The ability of the louvered fin heat exchangers to be designed to provide the highest heat transfer enhancement with the lowest possible pressure drop is of great importance for achieving high thermal - flow performance. Louvered fin heat exchangers provide heat transfer enhancement based on two basic principles. The intermittent geometric structures break the boundary layer and slow the growth of boundary layer thickness. As the low boundary layer thickness also means high heat transfer coefficient, heat transfer is enhanced. Another principle is that the louvers direct the flow and the fluid flows between the fins. The flow path of the flow circulating between the different fins is extended, the cold - hot fluid mixture increases and thus the average heat transfer coefficient is increased throughout the heat exchanger. Due to the above mentioned abilities of the louvered fins, it is of great importance to design meticulously considering the geometric characteristics and flow conditions. There are three methods which are used to investigate the heat transfer and pressure drop characteristics of louvered fin heat exchangers: experiments with real - scale heat exchangers, experiments with scaled-up models and numerical studies with the CFD approach. Experimental studies with scaled-up models and CFD studies provide deep understanding of the relationship between flow structure and heat transfer. In the early studies on louvered fins, the researchers thought that louvered fins caused turbulence by creating a rough effect and thus caused heat transfer enhancement. In the following period, the actual heat transfer enhancement mechanism was understood by means of the flow visualization experiments performed with scaled - up models. In the scope of this thesis, the above mentioned three methods were used to investigate the flow, heat transfer and pressure drop characteristics of the louvered finned heat exchangers. CFD studies with Ansys FLUENT 16.2 software, flow visualization studies with PIV method, heat transfer and pressure drop characteristics with real scale heat exchangers in wind tunnel were performed. The CFD study combined the advantages of the other two methods, both heat transfer and pressure drop characteristics were obtained, as well as information about flow structure were obtained by visualization results. Heat transfer and pressure drop correlations are derived using CFD results.