Abstract
Vortex generation and flow disruption in heat exchanger passages by means of surface modification is a widely used passive heat transfer augmentation technique. The present paper contains the results of numerical and experimental studies of the hydraulic resistance and heat transfer in the rectangle duct with oval-trench- and oval-arc-shaped dimples applied to the heat transfer surface. For the turbulent flow in the duct (Pr = 0.71, Red = 3200–9 × 104—for heat transfer determination and Red = 500–104—for the friction factor measurements), rational geometrical parameters of the oval-trench dimple were determined: relative elongation of dimple l/b = 5.57–6.78 and relative depth l/b = 5.57–6.78, while the value of the attack angle to the mean flow was fixed φ = (45–60)°. The comparison of the experimental and numerical modeling for the flow in the narrow duct over the surface with a single- and multi-row dimple arrangement has revealed a good agreement. It was found that the average heat transfer coefficient magnitudes in such ducts could be increased 1.5–2.5 times by means of single and multi-row dimple application on the heat transfer surface. The heat transfer augmentation for the surfaces with the oval-arched dimples was found to be 10% greater than the one for the oval-trench dimples. The corresponding friction factor augmentation was found to be 125–300% in comparison to the smooth surface duct. The obtained experimental data were used for the data generalization. Derived generalized equation allows for predicting the friction factor and heat transfer coefficient values for the flow over the single-row oval-trench simple arrangement. The maximal deviation of the experimental data from the proposed equations was found to be 20%. The application of the artificial neural networks for predicting the hydraulic resistance and heat transfer augmentation in such ducts was presented.
Highlights
Application of symmetric and asymmetric spherical shaped dimples on heat transfer surfaces is a method for heat transfer augmentation extensively investigated over the last decades [1,2,3,4,5,6,7,8]
Intensive vortex generation in the flow over such dimpled surfaces accompanied by the intensive generation of turbulence in the boundary layer and flow detachment significantly affects the aerodynamic characteristics of the flow as well as the heat and mass transfer near the wall
Such optimal dimple geometrical parameters have to ensure heat transfer augmentation with the this challenging issue by the researchers will be decisive for heat-exchange equipment production relatively low friction factor growth, in comparison to the flow over the smooth surface
Summary
Application of symmetric and asymmetric spherical shaped dimples on heat transfer surfaces is a method for heat transfer augmentation extensively investigated over the last decades [1,2,3,4,5,6,7,8]. Energies 2020, 13, x FOR PEER REVIEW Such optimal dimple geometrical parameters have to ensure heat transfer augmentation with the relatively low friction factor growth, in comparison to the flow over the smooth surface. Such optimal dimple geometrical parameters have to ensure heat transfer augmentation with the this challenging issue by the researchers will be decisive for heat-exchange equipment production relatively low friction factor growth, in comparison to the flow over the smooth surface. A fairly full overview of the experimental investigations on fluid this challenging issue by the researchers will be decisive for heat-exchange equipment production for flow and heat transfer in the ducts with dimpled surfaces for various technical applications is manufacturers and customers. A fairly full overview of the experimental investigations on fluid flow presented in [1]. The comprehensive review on the topic is presented in monographs [9,10]
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