CFD Investigation of Heat Transfer and Flow Patterns in Tube Side Laminar Flow and the Potential for Enhancement

Heating and cooling of process streams is a standard operation in many industries. This operation is often performed in heat exchangers where the heated or cooled fluid flows under laminar conditions inside the tubes. The mechanisms of heat transfer under those flow conditions are complex and poorly understood, since they can involve both forced and natural convection making accurate prediction for heat exchanger design a challenge. In this paper Computational Fluid Dynamics (CFD) techniques in conjunction with heat transfer measurements are employed in order to investigate laminar flow behaviour in heating and cooling cases. Heat transfer in the laminar flow regime is low by default but can be greatly increased by the use of passive heat transfer enhancement techniques such as tube inserts. Tube side enhancement in laminar flow is commonly used in heat exchanger design and leads to much smaller more efficient heat exchangers. CFD will also be used to investigate the heat transfer mechanism found in enhanced tubes. Devices investigated are wire matrix turbulators (hiTRAN), twisted tapes and coils. The results from the CFD simulations are compared with experimentally measured data. The CFD simulation results show good agreement with the experimental data. The Nusselt number was found to have increased by several times over the empty tube when using enhancement devices, with different improvement levels depending on the device used. The perceived mechanism for this increase was the greater movement of fluid evident from the CFD simulations.