CFD INVESTIGATION INTO THE FLOW FIELD IN A FOUR ROW STAGGERED PLATE FIN-AND-TUBE HEAT EXCHANGER EXPERIENCING GROSS FIN-SIDE FLOW MALDISTRIBUTION USING THE K-ω TURBULENCE MODEL

摘要

The flow field in a section of a four-row staggered plate fin-and-tube heat exchanger with gross inlet flow maldistribution has been investigated using CFD modelling. The commercial CFD code Fluent 6.3 has been used to carry out 3D unsteady flow modelling using the low Reynolds number variation of the standard k-ω turbulence model. A significant amount of flow dispersion is shown to occur upstream of the heat exchanger inlet resulting in a 37 % reduction in inlet velocity before the flow enters the heat exchanger. Flow dispersion as the fluid passes through the heat exchanger results in a further 28 % reduction in the average flow velocity. Significant sections of the heat exchanger experience angled flow resulting in a flow pattern commonly seen in inline tube arrangements. The lower friction factor of the inline flow regime results in a higher mass flux when compared to areas exhibiting the staggered flow regime. This variation results in off-centre velocity peaks entering and leaving the heat exchanger. On average the non-uniform flow cases resulted in a 29.4 % increase in pressure drop across the heat exchanger system when compared to uniform flow conditions. Average heat transfer coefficients for the non-uniform flow conditions showed a 20.3 % increase over uniform flow conditions of equal mass flow.