On the thermal performance of a shell and double coil heat exchanger: Numerical analysis of the geometrical characteristics impacts

Using a double coil instead of a simple coil in a shell-and-coil heat exchanger results in more extraordinary heat transmission because of more space occupation. This work involves the numerical evaluation of heat transfer and fluid flow in a shell and double coil heat exchanger, utilizing a commercial CFD code based on the finite volume approach. The employed heat transfer fluids are pure water and Water/MgO-TiO2 hybrid nanofluid. The volume concentration of utilized hybrid nanofluid is φ1 = φ2 = 0.3. The fluid flow regime inside the shell and coil is laminar, considering the range of Reynolds number Re = 500–2,000. This work is divided into two parts. The first section investigates how the location of the hot stream (coil side) inlet and outlet affects the heat exchanger's thermal performance, comparing different types of heat transfer fluid. The second part examines how the double coil's exterior helix diameter affects it. The outcomes revealed that the supreme thermal performance belongs to the model where the hot stream enters the exterior coil, and Water/MgO-TiO2 is the working fluid. This model exhibits more significant thermal performance than the model, with pure water as the hot stream entering the exterior coil by approximately 158.62 % at Re = 500. Moreover, at Re = 2,000, this model shows better thermal performance by around 51.72 % compared to the model with pure water. In light of the obtained outcomes from the second section of this work, the model with the external helix diameter of D1 = 240 mm illustrates the maximum thermal performance at Re = 500. Growth of the external helix diameter by about 33.34 % leads to augmentations in thermal performance by about 35.94 % and 42.86 % at Re = 500 and Re = 2,000, respectively.