# CFD Analysis of a Tubular Heat Exchanger for the Conditioning of Olive Paste
###### Abstract
These studies proved a significant improvement in the olive oil aromatic fraction and the relative EVOO quality. As well, they confirm the possibility of using a heat exchanger to rapidly increase the olive paste temperature before malaxation and the possibility of reducing the olive paste conditioning time. Research conducted by [19] by using the tube-in-tube heat exchanger between crusher and the malaxer machine on the industrial scale demonstrated that the malaxation time can be reduced to 10 min without any reduction in phenolic content (357.9 g/kg). When the malaxation time, after the flash heating treatment, was risen to 30 min, the phenol content was increased by 17% when the olives were milled with a disc crusher and 27% with a de-pitting machine. While the oil extraction yield is statistically equal to the traditional process yield when the heat exchanger was employed. A recent technology introduced in the mechanical extraction process of olive oil is reported in [20], where a cooling treatment of the olive paste (from 30 to 25 \({}^{\circ}\)C) before malaxation step was performed by using a tube-in-tube heat exchanger. The results showed that the cooling treatment leads to a significant improvement of phenolic compounds in the oils. In addition, by malaxing at 30 \({}^{\circ}\)C compared to 25 \({}^{\circ}\)C, for the same time, no difference in oil yield was found. An innovative heat exchanger was employed in a commercial olive oil extraction plant by [21], which is the mixing-coil heat exchanger, having a mixing-coil inside. The research demonstrated that the mixing-coil heat exchanger completed the malaxer, and malaxation time was reduced of about 50% compared to the time used in the traditional malaxing without heat exchanger. Similarly, the research reported by [22], which consists of a combination of industrial olive oil extraction plant with a spiral heat exchanger and other advanced technologies, demonstrated that using a heat exchanger in addition to the malaxer generates rapid heating of the olive paste and, therefore, reduced the conditioning time of about 20 min. In the tube-in-tube heat exchanger, the product to be heated/cooled flows in the inner cylinder, while the service fluid in the annular section between the two cylinders and the heat exchange between the heat transfer fluids occurs under transient state operation through a conductive element, which allows the management of the heat or cold demand in the heat exchanger. However, when the fluid passing through the exchanger is highly viscous or is a sticky fluid such as olive pastes the convective heat transfer mechanism generates critical conditions due to the limited heat transfer coefficients that can be achieved given the low Reynolds number values that generally characterize the fluid flow [23]. In the olive oil industry, olives have a variable inlet temperature during harvesting period and during the 24 h of processing. The olives in fact, before processing, stop in outdoor spaces of the mills; therefore, their inlet temperature is strongly dependent on the environmental one. This causes, for the same setting of the feed pump, a different flow rate of the pastes in the heat exchanger and, consequently, a different heat exchange effect. In addition, although the tube-in-tube heat exchanger is a well-known technology and used in many food industries, its application and behavior on olive pastes is not well known, despite the increasing use of this technology in industrial mills. To this purpose, mathematical modelling could represent a powerful tool for understanding the performance of a heat exchanger in heat transfer when some parameters change. As it is known, CFD analysis is essential to optimize the design of component without realizing expensive prototypes and experimental tests. CFD applications in food processing are manifold. In [4], the authors developed a 3D CFD simulation model for two different geometry configurations of the malaxer machine to evaluate the design parameter's influence on the flow and temperature fields.