Project and Objectives

The aim is to simulate a water/air heat exchanger in which hot water enters the coil of the finned heat exchanger and is cooled by the external airflow generated by a fan, whose impeller geometry is known, as well as the geometry of the channels and fins.

Approach to the analysis

The geometry characterized by detailed and widely distributed shapes (fins) would generate a mesh with a very high number of cells, significantly increasing the computational load and resulting in long processing times, without necessarily producing more reliable results. The solution adopted in these cases is to replace the fins with a porous medium instead.

A porous medium is nothing more than a permeable solid (in red in the image above) that must be characterized by a curve for pressure losses and thermal properties in order to accurately reflect heat exchange behavior. After generating the porous medium, we then need to develop these characteristic curves through a dedicated preliminary study, isolating a small section of the finned structure and simulating the flow for various values of flow rate and temperature.

At this point, our ‘streamlined’ model is ready for an initial steady-state analysis, performed to determine if the heat exchanger’s dimensions are sufficient to meet the intended target. By simply imposing boundary conditions regarding the hot water flow rate, outlet pressure, and fan speed, the following results were obtained:

It is possible to observe how the fluid field is accelerated consistently with the CAD geometry of the fan and the speed assigned to the rotating region, as well as the buoyancy effects of the hot air due to gravity. This ensures thermal exchange boundary conditions that are much closer to reality than what is typically achieved, where, at best, the manually set assumption could be a radial or even uniform distribution of velocities across the passage area.

After validating the geometry, one can proceed with a time-dependent analysis using a rotating mesh, delving deeper into the interaction between the blades and the fluid. This approach allows the observation of dynamic pressure phenomena, shock waves, and similar effects.

Conclusion

Thanks to our engineering services, it is therefore possible to oversee all phases of the design of a heat exchanger and its accessory components that enable its operation.