An improved numerical analysis of the transient oil de-congealing process in a heat exchanger under low temperature conditions

In the present study, an improved heat exchanger model is proposed to efficiently analyze the cold oil removal process inside a fuel-cooled oil cooler. When exposed to low temperature condition, oil within a heat exchanger begins to congeal, preventing oil flow and causing loss of cooling. The conventional heat exchanger models, however, shows limits in reflecting the highly varying viscosity effects due to large temperature difference. To overcome this, the conventional porous media model was rewritten with the friction and Colburn j-factors that include the temperature dependent property variation. The property correction method by Shah and Sekulic [31] was added to enhance the prediction accuracy. Also, a relief valve model based on the porous media approximation is developed. The developed models were validated against the experimental data. Transient three-dimensional numerical simulations are carried out to analyze the effects of operating conditions on de-congealing phenomenon inside the FCOC.