Thermal and hydraulic numerical study for a novel multi tubes in tube helically coiled heat exchangers: Effects of operating/geometric parameters

Compactness with high performance heat exchangers are main challenges in a lot of engineering applications. Thus, this research reports CFD simulation of a novel MTTHC (multi tubes in tube helically coiled) heat exchanger using ANSYS-FLUENT 14.5. The aim of the work is to investigate the thermal and hydraulic performance of the MTTHC for turbulent flow. The effects of the operating and geometrical parameters of the coil on the cold/hot water Nusselt numbers, heat transfer coefficients, pumping power, effectiveness, and thermal-hydraulic index are studied and presented. The results show that, the largest heat transfer coefficient is found at N = 3 and β = 0° & 90°, and the pumping power (P) rises with ≅20 times if N changed from 1 to 5 at any β. Moreover, the effectiveness of the coil (ε) has the largest values at β = 0° & 90° and N=3, and it enhances with 8.5%, 9% and 7% if N increased from 1 to 3 at β = 0°, 45° and 90°, respectively. In addition, thermal-hydraulic index (ξ) improves with 5%, 8% and 6% if N increased from 1, to 3 at β = 0°, 45° and 90°, respectively. Finally, Numerical correlations for P, ε and ξ are correlated and presented within reasonable errors.