Bachelor's thesis Michael Sietmann

 

Efficiency enhancement of fan-heat-exchanger configurations with CFD

The combination of heat exchangers and fans has a widespread usage in HVAC technology. The finned tube heat exchanger is an important component of air-water heat pumps, recooling plants and forced air cooling devices for example. In case of air-water heat pumps the heat exchanger is used to extract heat from the ambient air and lead it to a refrigerant circulation. In forced air cooling devices the heat exchanger can be used for example for cooling a fluid circulation. Often, the heat exchangers are combined with a fan to increase heat exchange through forced convection. To make the exemplary mentioned devices more profitable, an increase of efficiency of finned tube heat exchangers is reasonable. Therefore, the finned tube heat exchanger in combination with a fan will be investigated in this thesis by CFD-Simulation. Because of different cross section of the rectangular heat exchanger and the round fan the flow will not be optimal. The main goal of this thesis is to show room for improvement for fan-heat exchanger-combinations through CFD-Simulation of the actual situation and to develop concepts for increasing the efficiency. For this, a case will be investigated, which allows a comparison of the efficiencies of the developed concepts. As an example of a fan-heat exchanger combination a dry cooler is used. Besides the concept for the dry cooler housing, studies of geometrical properties of the dry cooler will be conducted. Therefore the effect of a
radius on the outflow and on the inflow side of the heat exchanger and the vertical position of the heat exchanger inside the dry cooler on the stream and on the heat transfer will be analyzed. During the thesis the possibility of modelling finned tube heat exchanger as a porous media should be turned out. For the evaluation of the simulations the graphical results of the simulation, the pressure drop over the heat exchanger, data of flow velocity and an heat exchanger model, constructed with a User-Defined-Function, will be used. To validate the results of the simulation they will be compared to measurement data and reference data.