Experimental and numerical simulation of heat transfer inside a concentric heat exchanger

The present study concerns an experimental and numerical investigation of heat transfer occurring in a concentric tube heat exchanger. Experimental measurements were conducted using a test bench located at the process engineering laboratory at the university of Ghardaia. Two modes of fluid flow in the exchanger were considered, namely: co-current and counter-current for different boundary conditions. On the other hand, the three dimensional flow is mathematically described by the Navier-Stokes equations, and by energy equation. The flow is assumed to be incompressible and single phase. The governing equations are discretized using finite volumes schemes and the solver is the commercial CFD software ANSYS 2019 R1. The velocity components are calculated at a staggered grid while the scalar variables are calculated at the main grid (not staggered). For coupling of mass and momentum equations, SIMPLE algorithm is used. The Green-Gauss cell-based scheme is used for gradient discretization. Second-order upwind central differencing is used for flow terms. For a fixed volumetric flow rate of cold water (350 l/h), and according to the variable volumetric flow rate of hot water, six (06) selected cases are studied. The obtained numerical and experimental results were in good agreement. The relative error does not exceed 4% for all studied cases. This work has led to a better understanding of the operating principle and the phenomenon of heat transfer in concentric tube exchangers. It has been demonstrated also that the effectiveness is increased by about 13% for the counter-current mode compared to the co-current mode. The counter-current configuration maintains a more consistent temperature gradient along the length of the heat exchanger.