Thermal characterisation of triple tube heat exchangers by parameter estimation approach

A parameter estimation approach was applied to characterise the heat transfer inside a triple tube heat exchanger (TTHE) designed for the food industry. This type of heat transfer device represents a promising technology for the always increasing challenge of reducing the consumption of energy and raw materials. Especially, it provides a suitable solution for the heat treatment of highly viscous fluids; making the product flowing into the intermediate pipe, this kind of heat exchanger permits heat transfer both through the internal and the external surfaces, reducing the device size compared to traditional double tube heat exchangers. Moreover, this configuration reduces the problems related to product stratification, avoiding the risk of having part of the product burned and part not heated enough. However, the thermal design of these apparatuses is critical. Although they present a widespread industrial application, it is difficult to find correlations for their thermal behaviour. This study fills this gap by proposing an effective methodology for deriving a proper heat transfer correlation. Among the different methodologies that can be adopted to assess the performance of the TTHEs, the parameter estimation procedure represents a promising tool since it has been successfully applied in many disciplines of engineering. Following this approach, this study enables the successful and robust estimation of the heat transfer correlation for the product side Nusselt number starting from the temperature measurements at the inlet and outlet sections of the three tubes. The procedure was validated by adopting both synthetic and experimental data acquired from a TTHE for treating highly viscous fluid foods.