SINOPSIS

The goal of the study is to evaluate the thermohydraulic characteristics of a passive buoyancy-dominated heat exchanger aimed at subsea processing of natural gas produced. The 3D unsteady buoyancy-induced water flow through a staggered tube bank at the Grashof number of 3 × 10⁵ is simulated using the full Navier-Stokes equations with no turbulence model. Direct numerical simulation of the external draft flow is combined with the simultaneous unsteady Reynolds-averaged Navier-Stokes modeling of the internal natural gas flow in plain serpentine pipes at Re = 8 × 10⁵ and simulation of heat conduction through the massive steel pipe wall. The paper compares water flow and external heat transfer characteristics for two cross-flow cooler configurations with the downward and upward internal gas flow that correspond to the counterflow and the parallel-flow heat exchanger schemes. It was found that though there is a pronounced difference in the local characteristics of external heat transfer and water flow, in general the gas flow direction does not influence the cooler effectiveness; the total heat output values for both schemes considered are almost the same. The computational fluid dynamics data are in accordance with the effectiveness-number of transfer units method analysis performed using the water mass flow rate based on the volume-averaged draft velocity. The conclusion is that the cooler performance does not depend on the inlet and outlet collector location that gives some freedom in cooler design.