EFFECT OF GAS FLOW DIRECTION ON PASSIVE SUBSEA COOLER EFFECTIVENESS

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 x 10(5) 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 x 10(5) 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 flowheat 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.