University of Twente Student Theses


Parameter study of a staggered pin-fin heat exchanger using openfoam

Alan, G.A.S. (2016) Parameter study of a staggered pin-fin heat exchanger using openfoam.

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Abstract:In this study a sensitivity analysis is performed with respect to heat transfer and pressure drop in a pin-fin heat exchanger of a domestic heater. A simplified model of the heat exchanger is simulated in which the pitch (in two directions), the diameter and the pin height are varied. The analysis is carried out by means of CFD simulations using OpenFOAM open source software. The present work shows a validation of OpenFOAM against FLUENT, where good agreement in terms of heat transfer is found. Additionally, a validation against data from literature (for heat transfer in tube banks) showed good agreement at high Reynolds numbers. Following this, an analysis is performed on the flow in a pin-fin heat exchanger. Scaling of the velocity profile based on mass conservation and the ideal gas law is presented. The entrance effect based on these results is found to be visible up to the fifth row of pins. Furthermore, the effect of adding more pin rows to the simulation is shown to increase pressure drop linearly. Subsequently, the sensitivity analysis is performed on the heat exchanger slice. Pressure drop and heat transfer performance are measured in terms of Pascal and thermal efficiency respectively. This is done in order to eliminate the influence of the high temperature differences and changing flue gas properties on the results. An ideal heat exchanger has high heat transfer and low pressure drop while having a small volume. To this end, both unscaled and volume-specific performance is considered. The sensitivity analysis shows that increasing the pin height leads to higher pressure drop and lower thermal efficiency. This is due to the lower driving temperature difference for heat transfer when the pins are higher. This observation is valid for all the diameters of the pins considered here. On the other hand, both the thermal efficiency and pressure drop are higher when a large diameter is used. However, when volume-specific scaling is used it appears that higher pins are better in terms of pressure drop. This shows that a different conclusion is found when volume-specific scaling is used. Likewise, the effect of changing the longitudinal pitch on the performance is shown. Constant pressure drop is seen at constant diameter while varying the longitudinal pitch. Simultaneously, heat transfer decreases, but despite this a smaller heat exchanger with the smaller longitudinal pitch is possible. This can be achieved by adding more pin rows to account for the lower thermal efficiency. Again, a large diameter gives both high heat transfer and pressure drop. Furthermore, a decrease of the transverse pitch is shown to lead to a higher pressure drop and higher thermal efficiency. This is due to the flue gas flowing less freely through the heat exchanger and therefore exchanging more heat and causing more pressure drop in the heat exchanger. The influence of a change in the boundary conditions is shown for the inlet velocity, the inlet temperature and the convection coefficient to the water channels. An increase of the inlet velocity resulted in a linear increase of heat transfer and a quadratic increase of pressure drop. The increase of the inlet temperature caused a linear increase of heat transfer and a linear decrease of pressure drop. Lastly, the influence of the convection coefficient to the water channels is small when compared to the effect of the other boundary conditions.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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