Faculteit Engineering Technology
Afdeling Thermal Engineering
Master opleiding Mechanical Engineering
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Heat exchanger shape optimization using adjoint method in Ansys Fluent
Domestic heaters based on combustion of natural gas are often used in the Netherlands for heating households. A heat exchanger is used to extract energy from the flue gases and heat up water. One of the most common designs in these domestic heaters is a pin-fin heat exchanger. In this thesis the shape of these pins is optimized, such that the heat transfer is improved while the pressure drop is decreased.
To optimize the shape of the pin, Computational Fluid Dynamics (CFD) analysis can be used to aid the engineer in which shapes lead to a better design. This optimization procedure is very labor intensive and many design iterations are needed. Another way of improving the geometry is by using the adjoint method. With this method sensitivity calculations for certain design variables can be performed on the results of the CFD computations. Based on these sensitivity calculations the shapes can be improved. This adjoint method is used in this thesis to optimize the shape such that both a lower pressure drop and a higher heat transfer is obtained.
Starting with converged CFD results, suitable adjoint solution methods and adjoint controls are determined. With the computed sensitivity fields for heat transfer and pressure drop, several objective combinations have been used to optimize the pin shapes. In the most extreme cases, e.g. the cases where one of the objectives is of main importance, a heat transfer increase of 8% is achieved while the pressure drop is slightly improved as well (-4%). When the objective combination is chosen such that the pressure drop is more important than the heat transfer, a pressure drop decrease of 48% is obtained while the heat transfer is almost maintained (-2%).
More balanced objective combinations lead to an improvement of 13.7% and 5.2% or 6.1% and 6.3% for pressure drop and heat transfer respectively. Similar results can be obtained for all three initial pin-fin geometries. Therefore it can be concluded that the adjoint method can be applied effectively to optimized the shape of the pins of a pin-fin heat exchanger, in such a way that both pressure drop and heat transfer improve.
|Prof.dr.ir. T.H. van der Meer
M.C. Vidya MSc.
Dr.ir. N.A. Beishuizen
Dr.ir. E.T.A. van der Weide