Case Studies in Thermal Engineering (Aug 2022)
Numerical investigation of the thermal-hydraulic characteristics of turbulent flow in conical tubes with dimples
Abstract
Innovative designs of heat exchangers are crucial to increase the heat transfer effectiveness for the purpose of compactness, energy savings, and emission reductions, among others. In this paper, the thermal-hydraulic performance of turbulent flow inside dimpled and conical tubes under a constant heat flux of 40 kW/m2 is numerically investigated using Ansys-Fluent. The proposed novel design and the associated performance analysis were not covered before in the specialized research works of the related literature. Different geometrical and operational parameters (tube diameter ratio/flow modes) are varied to generate key performance indices for the dimpled and conical configurations compared to the traditional smooth heat exchanger case. The model was well-validated against both cases of dimpled and smooth tube configurations. Thermal-hydraulic performance parameters, mainly Nusselt number and friction factor, and performance evaluation criteria (PEC) are investigated for different diameter ratios (DR) of various conical tube heat exchangers of smooth and dimpled surfaces within a range of Reynolds number from 3000 to 40,000. The results for conical tubes with dimples showed considerable enhancements in heat transfer and the overall thermal-hydraulic performance compared to traditional smooth geometrical configurations. The study showed that convergent tube with dimples (DR = 1.5) presents the maximum value of PEC with 29.54% enhancement compared to the smooth geometry with DR = 1. The average-values of PEC over the whole studied range of Re with 8.03% enhancement compared to the smooth geometry at DR = 1, of all studied cases. In addition, convergent tube with dimples (DR = 1.5) presents a maximum percentage of the increase in Nusselt number ratio Nur (2.72 at Re = 3000) with 121.4% enhancement compared to the corresponding smooth one. Hence, it can be considered as a promising technique in terms of energy-saving, especially at low values of Reynolds number. It can also be deduced that the newly proposed design of convergent tube HEX with dimples has positive energy efficiency operational characteristics and environmental impacts in terms of potential CO2 reductions.
