Experimental Investigation of Natural Convection Heat Transfer in Bundle Pipeline

Abstract

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.