Procedure for hydraulic oil heat exchanger performance improvement through integrated CFD analysis

Present and future constraints on the layout of hydraulic circuits onboard mobile machinery will require more and more compact components with improved efficiency. The need to use IC engines complying with new standards on emissions will introduce new components into the engine hood, like Exhaust Gas Recirculation (EGR), Selective Catalytic Reduction (SCR), Dust Particulate Filter (DPF) and more, reducing the space available for components where traditionally the ratio between dimension and performance was not considered a 'hard boundary' to the design space. One of the components of the hydraulic circuit affected by the general tendency to an increase of the operating temperatures due to the new-generation engines introduction is the heat exchanger. The need to design properly tailored, efficient and compact heat exchangers is therefore one of the first priority targets in machine design. Accurate and reliable estimate of the performance at the design stage is a priority as well. This paper shows how the concurrent use of Computational Fluid Dynamics (CFD) and numerical approximations allow the performance prediction with a good correlation with the experimental results. The approach is applied to a cross-flow heat exchanger and is aimed at developing a software tool able to predict the global performance, yet being easily applicable to a wider range of cases. The approach used and described in this paper can be easily extended to a product set, variable in both dimension and technical characteristics. The key feature is to split the exchanger into sub-domains having homogeneous boundary conditions on either side, hot and cold, in order to estimate their performance in terms of WHTC (Wall Heat Transfer Coefficient) and pressure drop. This step applies a detailed CFD analysis. Results obtained are used as building blocks in a dedicated software tool developed at IMAMOTER-C.N.R. which sums-up the results to full scale. This approach features a reliable, yet flexible, evaluation of the exchanger performance under different environmental conditions and dimensions. The results obtained by the numerical analysis have been compared with experimental tests, showing the good degree of approximation achieved.