Enhancing heat transfer in internal flows is a critical aspect in the design of high-performance heat exchangers, cooling channels, and energy conversion systems. Conventional smooth channels often exhibit limited heat transfer due to the development of laminar boundary layers and insufficient fluid mixing, particularly at moderate Reynolds numbers. To overcome these limitations, a variety of surface modifications and turbulence-promoting devices have been proposed, including ribs, dimples, protrusions, and vortex generators. Among these, discrete ribs have received considerable attention because of their ability to locally disrupt the boundary layer, generate secondary flows and vortices, and enhance convective heat transfer without excessively increasing pressure drop.

Liu and Wang [1] proposed a semi-attached rib design in 2011, in which the ribs were perforated at the corners to allow partial fluid passage. Numerical simulations using Fluent 6.3 over Re = 10^4–2.5×10^4 demonstrated that semi-attached ribs could substantially improve local heat transfer and flow performance. Notably, semi-attached ribs with a 45° attack angle outperformed fully attached and detached ribs in overall thermal efficiency while eliminating low-heat-transfer regions.

Experimental studies by Tanda [2] in the same year investigated forced-convection heat transfer in rectangular channels with 45°-inclined rib turbulators. The effects of rib spacing and rib pitch-to-height ratios on thermal performance were systematically examined using Liquid Crystal Thermography (LCT), showing that optimal configurations can significantly enhance heat transfer for both single- and double-rib wall channels.

Chang et al. [3] introduced a novel Heat Transfer Enhancement (HTE) technique using deep V-shaped ribs. They experimentally investigated the heat transfer performance and pressure drop in a rectangular channel with these surfaces for both forward and backward flows over a Reynolds number range of 1,000–30,000. The HTE ratio, compared with smooth-wall conditions, showed significant improvement, particularly in laminar flow, with values ranging from 9.5 to 13.6 for forward flow. Moreover, the reduction in HTE with increasing Reynolds number in turbulent flow, which is a common limitation for many HTE devices, was mitigated by the combined HTE surfaces. Empirical correlations were also developed to support design applications.

Yemnisi et al. [4] performed an experimental analysis of airflow over successive rectangular ribs with varying heights and spacings. Their findings indicated that increased rib height enhanced turbulence, flow separation, and reattachment, leading to higher heat transfer rates than in smooth channels, with enhancements up to 113% in laminar flow and 50% in turbulent flow at the highest rib heights.

The numerical study by Yungseri et al. [5] on inclined discrete ribs demonstrated that rib attack angles significantly influenced turbulent flow behavior and heat transfer rates. At high Reynolds numbers, attack angles of 60° and 120° provided the highest thermal performance, while at low Reynolds numbers, the effect of rib inclination was minimal.

Shen et al. [6] numerically studied U-shaped channels with discrete ribs, showing increased Nusselt numbers and friction factors. The combined presence of protrusions and dimples was found to optimize heat transfer performance while minimally impacting pressure drop. Similarly, Parsaeimehr et al. [7] investigated turbulent nanofluid (water/Al2O3) flow in rectangular channels with inclined ribs. Their results revealed that the rib attack angle, Reynolds number, and nanoparticle volume fraction all played key roles in enhancing convective heat transfer, with maximum enhancement occurring at a 60° attack angle.

Further studies in 2018 by Wang et al. [8] and Srinivasan et al. [9] emphasized the effects of rib geometry, spacing, and arrangement on both heat transfer and friction loss in rectangular channels. These studies collectively confirmed that discrete ribs can significantly improve thermal performance across a wide range of operating conditions.

Recent investigations by Liu et al. [10] and Shen et al. [6] focused on perforated and slotted ribs, highlighting the benefits of secondary flows induced by holes and slots in improving heat transfer efficiency while maintaining acceptable pressure drops. Experimental and numerical analyses demonstrated that perforated ribs can reduce recirculation zones behind ribs and provide more uniform heat transfer distributions, making them particularly promising for internal cooling applications such as turbine blade channels and high-performance electronics cooling.

Finally, Sivakumar et al. [11] examined rectangular divergent channels with square ribs and varying rib heights. They observed that moderate rib heights can significantly increase heat transfer while causing only minor increases in pressure drop, underscoring the potential for geometric optimization in practical applications. Despite extensive studies on ribbed channels, several gaps remain. Most prior research focused on fully attached, detached, or semi-attached ribs under steady-state turbulent flows. In contrast, systematic investigations of the effects of discrete rib geometry, spacing, and orientation in conjunction with emerging fluids, such as nanofluids, remain limited. Moreover, the combined effects of rib inclination, perforation, and high-Reynolds-number turbulent flows on local and overall thermal performance are not yet fully understood. Addressing these gaps is crucial for designing advanced heat transfer surfaces in energy-intensive engineering applications.

In this study, a comprehensive numerical investigation is conducted to examine the effects of discrete ribs on flow structure and heat transfer in a rectangular channel. The influence of rib height, spacing, attack angle, and arrangement is systematically analyzed under both laminar and turbulent flow conditions. The outcomes aim to provide insights for the optimal design of ribbed surfaces in high-performance cooling and heat transfer systems.

This study focuses on turbulent convective heat transfer and flow behavior within a rectangular cavity with ribbed surfaces. The cavity is considered a simplified model of internal cooling passages commonly used in heat exchangers, turbine blade channels, and electronic cooling systems. The working fluid is air, entering the cavity at a uniform inlet velocity U0 and temperature T0.

Three rib geometries are investigated: triangular, square, and circular ribs. The ribs are mounted on one of the cavity walls to disturb the boundary layer and promote secondary flows, thereby enhancing convective heat transfer. The number of ribs (N) is also varied to examine its effect on both local and overall heat transfer rates.

The thermal boundary condition is a uniform heat flux applied to the ribbed wall, representing a constant heat source. The remaining walls are assumed adiabatic unless otherwise specified. The inlet is treated as a uniform-velocity, uniform-temperature boundary, and the outlet is assumed to be a pressure outlet, allowing fully developed flow.

The computational domain and rib configurations are schematically shown in Figs. 1-3. Fig.1 illustrates the rectangular cavity with triangular ribs, Fig. 2 shows the cavity with square ribs, and Fig. 3 depicts the cavity with circular ribs. These schematics highlight the geometric parameters, including rib height, width, and spacing, which are systematically varied to analyze their impact on the flow and heat transfer performance. The geometric and operating parameters illustrated in Figs 1-3 are summarized in Table 1. These parameters define the physical dimensions of the computational domain as well as the inlet flow and thermal boundary conditions employed in the present simulations. All parameters are kept constant unless otherwise stated to isolate the effects of rib geometry, rib spacing, and rib number on the flow field and heat transfer characteristics.

A grid independence study is performed by refining the computational Mesh using the Mesh Coeff parameter. The average heat transfer coefficient is monitored as the primary convergence indicator.

As shown in Table 2, mesh refinement beyond Mesh Coeff = 0.1 results in variations of less than 1% in the predicted heat transfer coefficient. Therefore, this mesh resolution is adopted for all simulations.

The numerical model is validated using the classical benchmark of turbulent air flow over a smooth flat plate. The predicted heat transfer coefficient is compared with well-established Nusselt number correlations for turbulent forced convection. The reference correlations are adopted from Bejan and Kraus [12] and Lienhard [13], which are widely used in high-impact heat transfer studies. The numerical results show very good agreement with the correlation-based predictions, confirming the accuracy of the present numerical

The simulations were performed for a rectangular channel of length L = m and height b = 0.25 m, with air entering at a temperature of T0 = 293 K and a velocity of U0 = 0.1 m/s under turbulent conditions. Eight different configurations were considered, varying the rib shape, size, and spacing. The geometrical parameters for each case are summarized in Table 4.

In this study, a detailed numerical analysis was performed to investigate the effects of discrete ribs on turbulent flow behavior and convective heat transfer in a rectangular channel. The influence of rib geometry, number of ribs, rib height, and base length was systematically examined using a finite element framework coupled with the k–ω SST turbulence model.

The results revealed that the presence of discrete ribs significantly alters the flow structure by inducing flow separation, recirculation regions, and secondary vortices, thereby effectively disrupting the thermal boundary layer and enhancing convective heat transfer. Increasing the number of ribs led to stronger turbulence generation and higher Nusselt numbers; however, this enhancement was accompanied by increased pressure losses along the channel. Rib height was found to strongly affect vortex intensity and heat transfer performance, with taller ribs intensifying flow disturbances but not always resulting in proportional HTE due to excessive pressure penalties.

Among the investigated geometries, rectangular ribs exhibited the highest heat transfer performance, owing to their ability to generate strong, sustained vortical structures downstream of each rib. In contrast, shorter ribs produced weaker flow disturbances but offered a more favorable balance between HTE and pressure drop. The distribution of the Nusselt number clearly correlated with vortex formation and reattachment zones, confirming the dominant role of flow dynamics in thermal enhancement mechanisms.

Overall, the present results highlight that an optimal rib configuration can significantly improve thermal performance while maintaining acceptable pressure losses. The findings of this study provide practical design guidelines for the development of advanced ribbed cooling channels in heat exchangers, turbine blade cooling systems, and electronic thermal management applications. Future work may extend the present analysis to three-dimensional configurations, transient flow conditions, and advanced working fluids such as nanofluids to further enhance thermal performance.

The authors declare no conflict of interest.

All data are included in the text.

This research received no specific grant from funding agencies in the public, commercial, or not-for-profit sectors.