Heat transfer in a smooth scalene triangular duct with two rounded corners

doi:10.1016/0735-1933(85)90048-X

International Communications in Heat and Mass Transfer

Volume 12, Issue 3, May–June 1985, Pages 251-258

https://doi.org/10.1016/0735-1933(85)90048-X Get rights and content

Abstract

Measurements of average heat transfer coefficients in a scalene triangular duct having two rounded corners were made at locations of 55 and 100 hydraulic diameters from the sharp-edged inlet to the channel. Individual side average heat transfer coefficients were obtained. Although there are small differences between the three sets of data, heat transfer coefficients averaged over the entire test section are adequately represented by the Colburn equation for smooth circulat tubes, with no effect of location of the test section.

References (6)

D.A. Campbell et al.
Int. J. Heat Transfer
(1968)
W.H. Lowdermilk et al.
NACA RM E53J07
(1954)
E.R.G. Eckert et al.
ASME J. Heat Transfer
(1960)

There are more references available in the full text version of this article.

Cited by (14)

Machine learning approach for optimization and performance prediction of triangular duct solar air heater: A comprehensive review
2023, Solar Energy
This paper presents a comprehensive review of various kinds of distinct artificial roughness employed in rectangular and triangular duct solar air heaters to aid prospective researchers in finding a critical gap in the domain of solar air heaters. A Machine Learning (ML) model is developed using 72 distinct rib combinations compiled to 454 datasets and trained using an Artificial Neural Network (ANN) to predict the performance of ribbed triangular duct Solar Air Heater (SAH). The developed ML model predicts the data with an average deviation of <3%. Owing to reasonably accurate predictions, the same could be increased when more cases (geometric or operating parameters) are added to the databases by retraining the ANN. Further, a second law analysis of the rib configurations features collector efficiency and entropy generation variation with Re for various rib parameters. For the Re range of 4000 to 18000, optimum parameters such as rib height, pitch, chamfer angle, and inclinations are obtained for triangular duct SAH. This could help design engineers obtain the performance parameters of ribbed triangular duct SAH with other artificial roughness designs, possibly with a combination of different geometrical and operating parameters, without having to perform tests.
Heat transfer correlation for circular and non-circular ducts in the transition regime
2020, International Journal of Heat and Mass Transfer
A new model to predict the Nusselt number in the entry region of smooth non-circular ducts and channels is developed, for both uniform heat flux and uniform wall temperature boundary conditions. The model, valid for the laminar, transition, turbulent and fully turbulent regimes, is developed using the asymptotic results for both laminar and turbulent flow in circular and non-circular ducts. The proposed model is valid for fluids with Prandtl numbers between 0.7 and 78, Reynolds numbers in the range of 890 to 248,800, and a ratio of the length of the duct to the square root of the cross-section area in the range of 0.001 to 0.03. Comparisons are made with several existing databases for circular and non-circular ducts, showing that the proposed correlation has an overall root mean square error equal to 10.0%, which is smaller than the other literature correlations. This correlation is shown to provide good predictions against the entire database, for both boundary conditions. One of the major accomplishments of this work is the versatility of the proposed equation, where for calculating the Nusselt number on circular and most common noncircular ducts a unique equation is necessary.
Effect of apex angle variation on thermal and hydraulic performance of roughened triangular duct
2017, International Communications in Heat and Mass Transfer
Citation Excerpt :
This decreases the heat transfer coefficient value up to zero at the corners, in the case of sharp cornered triangular duct and value of heat transfer coefficient strongly depends on the corner angles [18–19]. The fluid interaction at the corners can be improved by modifying triangular duct which results in considerable augmentation of heat transfer rate [20–22]. Under the turbulent flow conditions, formation of laminar sublayer takes place over the hot surface which also decreases heat transfer rate between fluid and hot surface.
The experiments were performed to analyze the influence of apex angle on thermal and hydraulic characteristics of triangular duct for Reynolds number range from 2000 to 16,000. Four different triangular ducts of apex angle 30°, 60°, 90° and 110° were fabricated for the experimentation. The one side of the duct is roughened with dimple shaped roughness element. The both relative shortway length (s/e) and relative longway length (l/e) of dimple shaped roughened element was kept constant (i.e., 10) but relative roughness height (e/D) is varied from 0.016 to 0.038. Result shows that apex angle plays an important role in heat transfer. The experimental results are presented in a form of correlation for Nusselt number (Nu) and friction factor (f).
Minimization of exergy losses in a trapezoidal duct with turbulator, roughness and beveled corners
2016, Applied Thermal Engineering
Citation Excerpt :
This negative effect of non-circular ducts motivates the researchers to improve the thermal performance of such ducts by different techniques. Using of round corners [1–3], creating roughness [4–5], using of porous material [6–9], using of vortex generators [10–12], etc. are new techniques to enhance the heat transfer properties. Among these technologies, vortex generators are devices, which can increase the heat transfer rate with no significant effect on the pressure drop.
This research is focused on the study of force convective heat and exergy transfers characteristics of flow through a trapezoidal duct with turbulator. Two vortex generators are located in the duct to enhance the heat transfer rate. The numerical simulations are done for the Reynolds numbers in the range of 400 < Re < 1600. The conservation of mass, momentum, and energy equations are solved numerically by applying a finite volume approach. The results are presented for the friction factor, Nusselt number, and entropy generations (Friction, thermal and total entropy generations). Finally, the attention is focused on the minimization of exergy losses by using two techniques. These techniques were use of beveled corners and surface roughness for the duct. It was found that the total entropy generation decreases by installing the vortex generators inside the duct. These reductions are 24.9%, 24.4%, 25.8%, and 26.6% for Re = 400, 800, 1200, and 1600, respectively. Moreover, the total entropy generation decreases by using beveled corners for duct. These reductions in the total entropy rates are in the vicinity of 10.4%, 9.15%, 8.54%, and 8.1% for Re = 400, 800, 1200, and 1600, respectively.
Thermal and fluid dynamic characteristics of flow through triangular cross-sectional duct: A review
2016, Renewable and Sustainable Energy Reviews
Citation Excerpt :
The results were generalized in the form of correlations and friction factor estimated using correlation has close match with Von-Karman-Nikuradse line. The average heat transfer coefficient for each side of scalene triangular duct with rounded corners was experimentally estimated by Obot [95]. The maximum and minimum Nusselt number was observed for shortest and longest side respectively.
Duct geometry is one of the important factors which influence the heat transfer in laminar and turbulent flow conditions. Along with heat transfer, pumping power required for fluid flow through a duct is also an important concern in industries. In most of the industrial applications, the flow is turbulent in nature. Many studies were carried out to understand laminar and turbulent heat transfer through non-circular (such as triangular, rectangular, trapezoidal, hexagonal, elliptic and sinusoidal etc.) cross-sectional ducts. This paper presents the review of various studies which were carried out on triangular duct. Only natural and forced convective heat transfer using Newtonian fluids studies, based on experimental and numerical are considered in this article. For the improvement of heat transfer in triangular duct, different shaped artificial roughness were also used by mainly researchers and the results were presented by generating correlations for both heat transfer and friction factor. It can be concluded that the optimum heat transfer takes place under axially uniform wall heat flux with peripheral uniform wall temperature boundary conditions as compared to all other boundary conditions. The heat transfer can also be enhanced by rounding of corners but it also increases the pumping power which is directly linked with the operating cost.
Pressure drop for rib-roughened scalene triangular duct having two rounded corners
1987, International Communications in Heat and Mass Transfer
An experimental investigation of friction in a scalene triangular passage having two and three rib-roughened sides was made. The parametric study included variations of pitch-to-height and height-to-hydraulic diameter ratio over the ranges 4–20 and 0.065–0.149, respectively. The Reynolds number was varied between 2,000 and 30,000. Generalized correlations of the data are provided. With three roughened sides, the analysis indicates that good estimates of friction factor can be obtained using existing friction relations for cylindrical or plane geometry.

View all citing articles on Scopus

View full text

Heat transfer in a smooth scalene triangular duct with two rounded corners

Abstract

Int. J. Heat Transfer

NACA RM E53J07

ASME J. Heat Transfer