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DOI: 10.1615/ICHMT.2008.CHT.590
page 16

Koorosh Mohammadi
Institute of Thermodynamics and Thermal Engineering, University of Stuttgart, Germany

Wolfgang Heidemann
Institute of Thermodynamics and Thermal Engineering, University of Stuttgart, Germany

Hans Mueller-Steinhagen
Institute for Technical Thermodynamics, German Aerospace Centre (DLR) Stuttgart - Cologne - Alméria/Spain


The effect of baffle orientation on the heat transfer and pressure drop of shell and tube heat exchangers in the domain of turbulent flow is investigated numerically using the commercial CFD code FLUENT. The segmentally baffled shell and tube heat exchangers considered follow the TEMA standards and consist of 76 and 660 plain tubes respectively, with fixed outside diameter and arranged in a triangular layout. Air, water and engine oil with Prandtl numbers in the range of 0.7 to 206 are used as shell-side fluids. For horizontally and vertically orientated baffles, simulations are performed using different flow velocities at the inlet nozzle. A shell-side gain factor suitable for the assessment of shell and tube heat exchangers is introduced as ratio of the shell side heat transfer coefficient to the shell-side pressure drop. To facilitate the decision between horizontal and vertical baffle orientation, a performance factor Φ is used as ratio of the gain factor for horizontally orientated baffles to the gain factor for vertical baffle orientation.
The simulation results show a significant influence of the baffle orientation on the shell-side pressure drop and heat transfer of shell and tube heat exchangers. In the shell and tube heat exchanger with leakage flows the vertical baffle orientation seems to be more advantageous than the horizontal orientation. The benefit of vertical baffle orientation on horizontal baffle orientation is more noticeable for gases. Contrariwise, the simulation results for shell and tube heat exchangers without leakages show the advantage of the horizontal baffle orientation over the vertical orientation, particularly in the inlet and outlet zone for all investigated shell-side fluids.
The comparison of calculation results with and without leakage flows presents different behaviour and underlines the importance of a consideration of tube-baffle leakage and bypass streams for the prediction of the performance factor of technical heat exchangers.

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