Based on previous experimental temperature profiles that were collected in a lab-scale foam filled tube (Bianchi2012,Bianchi2013), extensive simulations of conjugated heat transfer were performed to systematically investigate the role of different coupling scenarios between the support and the reactor wall, using a 3D scanned model geometry to validate the simulation results with experiments. Thanks to this detailed model analysis, a better understanding is possible on how the wall coupling in a structured catalytic reactor packed with metal foam supports influences the heat transfer. The coupling is of enormous importance for industrial applications, on heat removal in case of exothermic reaction and on the opposite for endothermic ones. In the current numerical investigations, carried out using the open source tool OpenFOAM, the focus is on the characterization of the contact area between the foam and the reactor wall. Starting from perfect contact between the two, the contact area was decreased by selecting randomly some boundary spots of the foam and considering them as adiabatic. In addition, the location of the selected structures could be restricted to regions near the inlet to investigate the influence of the strut location. Finally, all connections between the foam and the reactor wall were considered adiabatic as a limiting case with heat transfer only by convection. In correspondence to the experimental data collected previously, the study was carried out with different gases, nitrogen and helium, through a foam with different solid material, aluminium and FeCr alloy, in order to investigate the influence of the thermal conductivity on the temperature profile. The numerical setup used was comparable to the previous experimental setup, a stainless steel tube of 2.8 cm internal diameter filled with a cylindrical foam bed of 10 cm length. As a result of the numerical analysis we could identify that even if only a few struts have a direct contact with the tube wall and they can thus significantly enhance the heat transfer.
Sulla base di profili termici raccolti su un impianto di laboratorio costituito da un tubo riempito di schiuma metallica (Bianchi2012,Bianchi2013), sono state effettuate simulazioni con l'obiettivo di comprendere la relazione tra il supporto catalitico strutturato di schiuma metallica e lo scambio termico coniugato. Questo fenomeno ha un'importanza rilevante nell'applicazione industriale per ottimizzare lo scambio nei reattori, sia per l'asporto di calore nelle reazioni esotermiche, che il contrario in quelle endotermiche. Lo studio ha come obiettivo la caratterizzazione dell'area di contatto tra schiuma e parete del reattore, possibile grazie all'utilizzo del software OpenFOAM, impiegando come geometria il modello 3D della schiuma sperimentata per validare i risultati di simulazione e confrontarli con gli esperimenti precedenti. Partendo dal caso ideale di contatto perfetto tra schiuma metallica e parete del reattore, l'area di contatto tra i due è stata diminuita selezionando casualmente delle zone di collegamento e considerandole come adiabatiche. In aggiunta, la selezione delle strutture connesse con la parete è stata ristretta alla parte iniziale del tubo per studiare l'influenza della posizione sullo scambio termico. Infine, tutti i punti di connessione sono stati considerati adiabatici come caso limite, eliminando la componente conduttiva dello scambio termico data dalla connessione con la parete, e privilegiando lo scambio per convezione. In attinenza con gli esperimenti precedenti, sono stati inoltre studiati due differenti tipologie di gas in alimentazione, azoto ed elio, e di supporti solidi, alluminio e lega ferro-cromo, per valutare l'influenza delle proprietà termiche sul profilo di temperatura nel reattore. Per le simulazioni è stato utilizzato un setup simile allo sperimentale, un tubo di acciaio inossidabile con un diametro interno di 2.8 cm riempito con un letto cilindrico di schiuma metallica della lunghezza di 10 cm. Come risultato dell'analisi numerica si è ottenuto un'importante influenza della componente conduttiva, per cui anche poche zone di connessione tra schiuma e parete calda sono sufficienti allo scambio termico.
A simulation study of structured catalytic reactors packed with metal foam supports : the influence of wall coupling
RAZZA, SILVIA
2014/2015
Abstract
Based on previous experimental temperature profiles that were collected in a lab-scale foam filled tube (Bianchi2012,Bianchi2013), extensive simulations of conjugated heat transfer were performed to systematically investigate the role of different coupling scenarios between the support and the reactor wall, using a 3D scanned model geometry to validate the simulation results with experiments. Thanks to this detailed model analysis, a better understanding is possible on how the wall coupling in a structured catalytic reactor packed with metal foam supports influences the heat transfer. The coupling is of enormous importance for industrial applications, on heat removal in case of exothermic reaction and on the opposite for endothermic ones. In the current numerical investigations, carried out using the open source tool OpenFOAM, the focus is on the characterization of the contact area between the foam and the reactor wall. Starting from perfect contact between the two, the contact area was decreased by selecting randomly some boundary spots of the foam and considering them as adiabatic. In addition, the location of the selected structures could be restricted to regions near the inlet to investigate the influence of the strut location. Finally, all connections between the foam and the reactor wall were considered adiabatic as a limiting case with heat transfer only by convection. In correspondence to the experimental data collected previously, the study was carried out with different gases, nitrogen and helium, through a foam with different solid material, aluminium and FeCr alloy, in order to investigate the influence of the thermal conductivity on the temperature profile. The numerical setup used was comparable to the previous experimental setup, a stainless steel tube of 2.8 cm internal diameter filled with a cylindrical foam bed of 10 cm length. As a result of the numerical analysis we could identify that even if only a few struts have a direct contact with the tube wall and they can thus significantly enhance the heat transfer.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/112081