Numerical investigation of the effect of inlet flow distortions on forced draught air-cooled heat exchanger performance

Abstract

Forced draught air-cooled heat exchangers (ACHEs) are often arranged into banks consisting of multiple rows of fan-heat exchanger combinations. Fans on the outer edge of the banks are subject to severe cross-flow conditions as the air is swept past en route to fans located deeper within the banks. The cross-flow conditions give rise to increased inlet flow losses. The current investigation seeks to develop a better understanding of the nature of these increased inlet flow losses through the numerical resolution of flow fields associated with systems comprising a single and two banks of ACHEs. For installations comprising two banks of ACHEs it is found that the inlet flow losses of the periphery fan are dominated by flow separation occurring around the inlet lip of the fan inlet section. These flow losses can be reduced by the installation of a walkway at the edge of the fan platform or by the removal of the periphery fan inlet section. For a system comprising of a single bank of ACHEs it is found that the numerical models used accurately reflect the experimentally determined differences in inlet flow losses experienced by systems using either bell-mouth, conical or cylindrical fan inlet sections.