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IntroductionExtended surfaces (or fins) play a major role in the design of heat exchange devices within different fields of application, aimed at providing a heat transfer enhancement effect through an increase in the total exchange area. Although fins of uniform longitudinal profile are more commonly employed, owing to the obvious advantages in manufacturing and installation, extended surfaces of variable profiles are also of great practical interest, in connection with optimized designs towards the minimization of the fin weight and consequent reduction on the fin material utilization (Kern and Kraus, 1972;Snider and Kraus, 1983).

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The oil and gas industry needs accurate flow measurement since it is required by law, and so, considered as a field of legal metrology. Nevertheless, curves and other commonly found obstacles may affect the quality of flow measurements, due to disturbances to the flow, such as swirl and asymmetries in the velocity profile. Single-path ultrasonic flow meters are often used to measure the flow rate in flare gas installations, even though they are sensitive to such disturbances. The present paper uses numerical tools to obtain disturbed flow fields downstream from single-and double-elbow pipe installations, aiming to investigate the effects of the mounting angle on disturbed ultrasonic flow measurements, taking into consideration the contributions of all velocity components. Several transducer mounting angles from 0° to 180° are assessed varying the Reynolds numbers (based on the pipe diameter D) from 10 4 to 2 × 10 6 and axial positions up to 80D downstream from the curve. Results indicate that the correction factors for installation effects are mostly greater than in the guidelines and regulations, which suggests that, in real situations, the flow rate is being underestimated. Moreover, badly located measuring installations may be upgraded just by changing the mounting angle of the ultrasonic transducers.

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