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This thesis describes work relating to the thermal management of hydrocarbon fluids issuing from (typically sub-sea) wells and passing through flow lines to a processing facility (typically an offshore platform). The hydrocarbon fluids must be kept at a temperature above that at which solids (typically waxes or hydrates) are formed. One way of achieving this “Thermal Management” is to place the flow lines inside a carrier pipe through which is also passed (in a separate pipe) a heating fluid (typically hot water). The design of such “bundle” systems is a significant challenge because of the complex combined natural convection and radiation heat transfer processes involved. In related work, Computational Fluid Dynamics (CFD) methods are being used to predict these complex processes and the principal objective of the work described in this thesis was to carry out new experiments to validate these predictions. Experiments were carried out on an industrial scale 5-Pipe Bundle covering the full range of bundle orientations from horizontal to vertical so as to be able to simulate horizontal and inclined flow lines and risers. The bundle chosen was 3 m long with a 30 inch (762 mm) internal diameter carrier pipe with 4 pipes mounted inside it. The four internal pipes were respectively a 14 inch (355.6 mm) outside diameter pipe, a 8 inch (219.1 mm) outside diameter pipe and two 4 inch (114.3 mm) outside diameter pipes. These 4 pipes represented the hydrocarbon product pipe, the test pipe and the heating flow and return pipes in a typical industrial bundle. A support mechanism on which the bundle can be rotated from 0 to 360° was designed and constructed. In the experiments, the surface temperatures of each pipe surface were kept constant but differences were imposed between the respective surfaces. Heat flow rates from or to each pipe surface in the bundle were measured using a calorimetric method and the results were compared with those predicted using the ANSYS CFD code. Good agreement was obtained between the heat flows measured and those calculated from the code. This thesis also describes an analytical and numerical work on natural convection heat transfer inside a vertical pipe taking into account the effect of solids formation by freezing of the fluid at the wall.

Ce travail concerne la mesure et la caractérisation du transfert thermique à la paroi externe d’un faisceau de tube de refroidissement inséré dans des colonnes à bulles type « slurry ». La valeur du coefficient de transfert de chaleur est estimée à partir des équations de la chaleur. Une colonne de 0,15 m de diamètre et de 4 m de haut, équipée de deux tubes en U (3 cm de diamètre externe), a été utilisée pour mettre au point la métrologie nécessaire. L’eau a servi de fluide de refroidissement. Le mélange diphasique air-huile Syltherm XLT®, puis le mélange triphasique air-huile Syltherm XLT®-microbilles d’alumine poreuses (dS ~ 80 μm), ont servi de fluides modèles. L’incertitude de nos mesures a été estimée à environ 8 %. En système diphasique, les variations du coefficient de transfert de chaleur avec la vitesse superficielle du gaz ont pu être corrélées par une loi semblable à celle de Deckwer (1980). Cependant, la valeur de la constante de corrélation semble dépendre de l’orientation du faisceau de tubes par rapport à l’axe de la colonne. Un tel comportement n’a jamais été rapporté dans la littérature. L’écart du faisceau à un faisceau idéal (i.e. parfaitement droit et symétrique) peut être un paramètre crucial pour le transfert de chaleur. En système triphasique, la valeur du coefficient ne varie pas de façon significative jusqu’à une concentration massique d’environ 18,8 %, avant de diminuer d’environ 10 % pour une concentration massique de 21,3 %. Ce résultat est surprenant. Les variations rapportées dans la littérature sont en effet souvent contradictoires, mais toujours continues dans la gamme de concentrations testée. La métrologie mise au point a été implantée dans une colonne de 1 m de diamètre et de 5 m de haut, équipée de 24 tubes en U (6 cm de diamètre externe). Celle-ci est jugée représentative d’un réacteur pour le procédé Fischer-Tropsch. Les premiers résultats indiquent que la caractérisation thermique de l’installation sera plus délicate que pour la petite colonne / This work investigates the measure and characterisation of heat transfer in slurry bubble column reactors equipped with a bundle of cooling tubes. The value of the shell-tube heat transfer coefficient is estimated at thermal steady-state regime using heat transfer equations. A 15 cm in diameter, 4 m high bubble column, equipped with a two U-tubes (3 cm O.D.) bundle has been used to assess the metrology selected. The cooling fluid was water. Air-Syltherm XLT® heat transfer fluid and air-Syltherm XLT® heat transfer fluid-porous alumina particles (dS ~ 80 μm) were successively used as shell fluids. The uncertainty of our measures has been estimated to be around 8 %. The variations of the shell-tube heat transfer coefficient with superficial gas velocity can be modelled using the well-known correlation by Deckwer (1980). However, a smaller constant value than indicated by Deckwer et al. (1980) was obtained and it was found to be dependent upon the orientation of the tube bundle relatively to the column axis. This has never been reported in the literature and implies that any difference relatively to the ideal tube bundle – perfectly straight and symmetric – might be critical for heat transfer. Addition of solid particles has little effect on heat transfer for solid concentrations below 18.8 %w/w. A further increase up to 21.3 %w/w induced a 10 % decrease of the value of the shell-tube heat transfer coefficient. This was surprising, as existing literature results display continuous variations of the heat transfer coefficient values in the range of solid concentrations tested, even though trends of variation could be opposite. The assessed metrology was implemented into a 1 m in diameter, 5 m high bubble column equipped with a 24 U-tubes (6 cm O.D.) bundle. This pilot plant was considered to be large enough to mock up a slurry bubble column reactor for the Fischer-Tropsch process. First results indicate that thermal characterisation will be more complex than for the smaller diameter column