Rib Height Research Articles

Scaling Heat Transfer and Pressure Losses of Novel Additively Manufactured Rib Designs

Abstract Rib turbulators are a key cooling feature that enables increased heat transfer on the interior of gas turbine components. As metal additive manufacturing becomes available for developing turbine parts, it is becoming increasingly important to understand how the surface roughness intrinsic to this manufacturing method impacts the performance of rib turbulators. To explore what impact roughness has on rib turbulator performance, several relevant scale test coupons were manufactured on two different additive machines out of IN718. Additionally, several coupons were built at large scales to effectively reduce the relative roughness size impacts and determine scale effects. A range of different wavy broken rib designs, varying both rib wavelength and orientation within a channel were evaluated. Coupon geometry and surface roughness were characterized using both computed tomography scans and optical profilometry. Variations between the print methods were found to have limited impact on the surface roughness, but significant impact on the accuracy to meet the design intent with rib heights varying by 30%. Following characterization, coupons were flow tested and it was found that the ribs that more regularly disturbed the flow as a function of their geometry most significantly enhanced heat transfer and pressure drop. The performance index of the broken wavy ribs was similar to other advanced rib designs, such as broken or V shaped ribs, but augmentations to heat transfer and pressure drop were generally lower. The rib performance was compared as a function of relative roughness, and it was found that increases in relative roughness resulted in increased friction factor and heat transfer, especially at higher Reynolds numbers.

Energy, Exergy, environmental and economic based experimental investigation of solar air heater using a novel arc rib geometry

To enhance the thermal efficacy of solar air heaters, the most efficient method is to disturb the viscous layer by roughening the surface using the artificial rib. In this research, a discrete apex-down arc-shape rib geometry on a roughened plate is used to examine the energy-exergo and economic- environmental based performance of solar air heater. By changing the Reynolds number from 3000 to 14,000 and maintaining a gap width to rib height ratio of 4, a relative height rib ratio of 0.045, and a pitch to rib height ratio of 10, the effects of arc rib angles of 30, 45, and 60 degrees are studied. The environmental exergy loss was determined to be substantial, between 70 % and 80 %. Maximum system to air exergy loss occurs at Reynolds number of 3000 with 5.64 W. At a temperature parameter of 0.0377 m2K/W, both the thermal and exergetic efficiencies are at their highest, at 77.60 % and 3.81 %, respectively. In comparison to a plate having a plain surface, the suggested apex-down discrete arc rib performs better based on energy payback time, usable yearly energy, and enviro-economic criteria. Finally, at rib angle of 30°, the conditions that optimize the heat transfer and energy payback time, energy cost, exergo-economic, and enviro-economic characteristic of the current artificially roughened geometry of solar air heater.

Numerical investigation of different transverse Rib shapes on thermal convection in a channel filled with nanofluid

With the growing interest in energy optimization, corrugated surfaces are arguably an excellent choice, finding applications in areas as diverse as heat exchangers, automobiles, building energy efficiency, and chemical reactors. However, due to the poor thermal properties of conventional fluids, heat transfer is limited. The introduction of nanoparticles into fluids is a promising solution to improve their thermal performance. This paper does a detailed numerical analysis of how different factors affect the forced convection heat transfer in a two-dimensional ribed channel. The shape of the ribs is one of the factors that are looked at, along with some new parameters like e/H, which is the ratio of rib height to channel height, and L2/P, which is the test section to the pitch between the ribs. The aim is to determine the optimum geometry that maximizes the Nusselt number while minimizing the pressure drop. The study also examines the effects of nanoparticle type and concentration on heat transfer and fluid flow characteristics. To this end, the continuity, momentum, and energy equations were solved with the finite volume method using the SIMPLE scheme with the k-ε turbulence model at different Reynolds numbers ranging from 4000 – 14,000. The results indicate that triangular ribs with ratios e/H = 0.15 and L2/P = 4 increase the Nusselt number by 63.3 % while reducing the pressure drop by 22 % compared with the other cases. The improvement in heat transfer in the water-SiO2 case was the greatest compared with the other nanofluids tested. Particle size fraction and Reynolds number increased the Nusselt number in ribbed channels by 20.7 % compared with water.

Research on improving heat transfer performance by using wavy ribs with different cross sections

Based on the change of the cross section in blade internal cooling channel rib caused by the service wear, starting from the widely used rectangular cross section, the most likely isosceles trapezoid and rectangular-semicircular cross section are considered, and the extreme design of the cross section (isosceles triangle) and the tentative exploration (spindle) are carried out. In this paper, the numerical calculation of SST k-ω turbulence model and the experimental research method of TSP measurement are used to thoroughly investigate the impact mechanisms of five different wavy rib cross-sections on the flow and heat transfer in turbine blade ribbed channels. The results show that different rib cross-sections alter the flow and heat transfer in channel by modifying flow allocation in height and width directions. The inclined sidewalls of the wavy ribs accumulate most of cooling air near the rib, which is the ultimate cause of the significant cooling effect. Under small rib radius and small rib angle, the heat transfer advantages of isosceles triangle and isosceles trapezoid cross-section wavy ribs are more obvious, which are increased by 14.88 % and 20.66 % respectively, but their friction factor is also 1.2 ∼ 2.0 times that of rectangular cross-section. The heat transfer of the large rib height on the isosceles triangular and isosceles trapezoidal cross-section wavy ribs is increased by 73.29 % and 185.31 %. Changes in Reynolds number have minimal impact on the friction factor, but significantly impact the overall heat transfer.

Preparation of Aluminum-Based Superhydrophobic Surfaces for Fog Collection by Bioinspired Sarracenia Microstructures.

Freshwater shortage is a growing problem. Inspired by the Sarracenia trichome fog-trapping and ultrafast water-transport structure, a series of hierarchical textured surfaces with high-low ribs with different wettabilities was prepared based on laser processing combined with dip modification. Through fog-collection performance tests, it was found that the samples with superhydrophobicity and low adhesion had the best fog-collection effect. In addition, it was observed that the fog-collection process of different microstructured samples was significantly different, and it was analysed that the fog-collection process was composed of two aspects: directional condensation and directional transport of droplets, which were affected by the low ribs number and rib height ratio. A design parameter was given to create the Sarracenia trichome-like structure to achieve a fast water transport mode. This study provides a good reference for the development and preparation of fog-collection surfaces.

Optimizing heat transfer in solar air heater ducts through staggered arrangement of discrete V‐ribs

AbstractThis research paper details an experimental study on airflow dynamics in a solar air heater. The heater's design incorporates unique, discrete V‐shaped ribs with staggered elements to enhance thermal performance. The study investigates the influence of various roughness parameters on flow characteristics. These parameters include a relative coarseness pitch (P/e) ratio of 12, a rib inclination angle (α) of 60°, a relative coarseness height (e/Dh) of 0.043, and a staggered element arrangement with a positioning ratio (p′/P) of 0.65. Additionally, the investigation includes scenarios with three gaps (Ng) between elements and a gap‐to‐rib width (g/e) ratio of 4. The research focuses on how changes to the Reynolds number, ranging from 3000 to 14,000, and alterations to the ratio of staggered element positioning to rib height (r/e), from 2 to 5, impact the flow dynamics. The outcomes indicate a significant boost in heat transfer performance, with the Nusselt number rising to 3.76 compared with a conventional smooth duct. The highest thermal efficiency recorded was 86%, at an r/e ratio of 3.5. These results underscore the potential of using discrete V‐ribs with staggered elements in rectangular ducts to improve heat transfer efficiency.

Fatigue performance of innovative open-rib orthotropic steel deck for super-long suspension bridge

This paper presents experimental and numerical studies on the fatigue performance of an innovative orthotropic steel deck (OSD) with open-ribs, apple-shaped cut-outs, and additional transverse ribs, which is employed by the Zhangjinggao Yangtze River Bridge. This bridge is set to become the world's longest suspension bridge upon completion. A full-scale section of the OSD was fabricated and subjected to fatigue loading with a total cycle of 12.3 million times. The interested cracking-prone fatigue details include rib-to-deck and rib-to-crossbeam welded joints, along with the apple-shaped cut-outs of the crossbeam. Experimental results indicated that fatigue cracks initiated separately beneath the deck plate, on the flange of the rib, and at the rib-to-crossbeam welded joint, with equivalent stress amplitudes of 159 MPa, 148 MPa, and 99 MPa at 2 million cycles, respectively. In addition, detailed finite element model of the OSD was developed using ABAQUS and validated against the experimental results. The effects of the geometry dimensions and structural details of the bridge deck, longitudinal ribs, crossbeams and transverse ribs that influence the fatigue performance of this OSD were analyzed and discussed. Parametric analyses revealed that increasing the thickness of the deck plate, the thickness or the height of the longitudinal rib, and the number of transverse ribs can effectively reduce the stress amplitudes at corresponding fatigue details, which therefore improves their fatigue performance. This study provides useful references for the fatigue evaluation and design of OSDs with open-ribs and apple-shaped cut-outs.

Numerical study on dynamic response of a novel ribbed thin-walled UHPC box-type utility tunnel under gas explosion

At present, RC utility tunnels are widely used in urban utility tunnels. As a typical confined space, the complex load effect generated by the internal gas explosion of the gas tank of utility tunnel may lead to local damage or overall destruction of the structure of RC utility tunnel. Therefore, it is an important topic to improve the anti-explosion capability of the utility tunnel and ensure the normal operation of the utility tunnel after gas explosion. UHPC structure is considered to have excellent anti-explosion performance, so a ribbed thin-walled UHPC utility tunnel structure was proposed, which improved the overall stiffness and anti-explosion performance of the UHPC utility tunnel through the ribbed section. In view of the shortcomings of fluid-solid coupling method in gas simulation, Computational Fluid Dynamics (CFD) was used to calculate the overpressure distribution after gas explosion in UHPC utility tunnel. The accuracy of UHPC constitutive model and prestress simulation method was verified by testing results from the gas explosion on unbonded prestressed UHPC slab. The gas explosion damage mechanism of ribbed thin-walled UHPC utility tunnel, UHPC-NC combined utility tunnel and RC utility tunnel were comparatively analyzed. And the pre-fabricated stiffener height, UHPC slab thickness and UHPC strength were investigated on the anti-explosion performance of ribbed thin-walled UHPC utility tunnel against gas explosion. It is found that the UHPC strength needs to be enhanced dramatically to improve the blast resistance. The anti-explosion capability of utility tunnel can be effectively increased by increasing the rib height or increasing the thickness of the UHPC utility tunnel structure, and the damage pattern of the utility tunnel can also be changed from flexure-shear failure to bending failure. The results of the study can provide a reference for the damage analysis and anti-explosion design of ribbed thin-walled UHPC utility tunnels.

Research on the Design of a MIMO Management System for Lithium-Ion Batteries Based on Radiation–Conductivity–Convection Coupled Thermal Analysis

In this study, the heat transfer model of a radiation–conduction–convection coupled lithium-ion battery pack is established through theoretical analysis. The temperature distribution and flow field distribution inside the battery pack are obtained by simulation using ANSYS Fluent software 2022 R1, and the reasonableness of the simulation model is verified with an experiment. This study also analyzes in detail the improvement effect of adding heat dissipation ribs, applying heat dissipation coatings, and adjusting the fan speed on the heat dissipation performance of the system. Under the same heat sink rib height conditions, the relationship between its thickness and total heat dissipation and thermal efficiency is studied in depth, and the temperature distribution of the cell under different rib thicknesses is obtained. At the same time, the emissivity of the heat sink coating under different coating thicknesses was measured by infrared thermography, and the relevant design values were determined through simulation experiments. Finally, based on the experimental test results of fan performance, a corresponding control strategy is proposed to construct an efficient and high-performance multiple-input multiple-output (MIMO) battery thermal management system. The experimental results show that optimizing the structure of the forced air cooling system through the above measures can ensure that the Li-ion battery operates within the efficient operating temperature range, thus extending its cycle life, improving its stability, and reducing the risk of thermal runaway. Meanwhile, the problem of excessive temperature difference between different modules is improved, and the output capacity of the energy storage system is increased.

Experimental and numerical investigation on deck system of a 102 m simply supported prestressed UHPC box-girder highway bridge

To address two main challenges (excessive mid-span deflections and numerous cracks in the main girder) in long-span prestressed concrete (PC) box-girder bridges, this paper proposes a long-span simply-supported UHPC box-girder bridge. In comparison to conventional PC box-girder bridges with three-dimensional prestress, the proposed UHPC box-girder consists only one-dimensional (longitudinal) prestress, and the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin and are strengthened with dense diaphragms and stiffening ribs. The 4th Beijiang River Bridge adopts this type of bridge with a span of 102 m, which is the longest span simply supported prestressed UHPC box-girder highway bridge in the world. Considering the fact that the thickness of the top plate of the UHPC box-girder is relatively thin (only 20 cm) and the transverse prestress is removed from the top plate, thus, under the direct action of wheel loads, the risk of bridge deck cracking may correspondingly increase. To investigate the mechanical behavior of the deck system of UHPC box-girder bridges, a 1:2 scaled experimental specimen associated with the field bridge is tested. The mechanical behavior of the new deck system is investigated and discussed. It is found that because the support strength of the stiffening rib is significantly weaker than that of the web, the UHPC deck slab should still be regarded as a two-way slab rather than a one-way slab in the elastic stage. In addition, although the test load location is unfavorable to the UHPC deck slab and the first crack appears on the UHPC deck slab, this deck system finally suffers from bending failure of the transverse rib. Furthermore, finite element analysis is carried out to study the mechanical behavior of this new deck system. Parametric analysis considers some factors including the reinforcement ratio in the transverse rib, the height of the transverse rib, and the space between transverse ribs. The results provide a good reference for design and optimization in the new deck system of UHPC box-girder bridges.

Energy Efficient Downsizing of Ribbed Confinements for Heat Exchange Applications

Abstract Downsizing double-pipe heat exchangers is possible by deploying ribs on the two sides of the heat exchangers. The shape of these ribs, along with two key geometric variables – pitch and height, are crucial in the selection of energy-efficient rib configurations. This is because, the enhancement in heat transfer performance comes at the cost of increased pressure drop. Thus, the goal of this three-dimensional numerical investigation is to identify favourable rib shapes and explore the effect of truncation on triangular ribs, something which is missing from existing literature. Truncation is expected to greatly affect the performance of triangular ribs, either adversely or favorably. To explore this conclusively, an unbiased and exhaustive analysis is carried out by comparing the performance of confinements with modified and regular triangular ribs, keeping plain confinements as the baseline. Furthermore, the effects of two principal design variables – rib height and rib pitch are explored for each shape. Separate results are presented for the inner and outer confinements of the double-pipe heat exchangers (pipes and annuli) to allow for the extrapolation of results for a wide range of applications employing internal flows in pipes and annuli. A phenomenological model is developed to classify the thermo-hydraulic performance of each confinement and identify optimal geometrical configuration and identify best performing design(s). Once optimal rib pitch-height combinations are identified, performance at this optimal combination is evaluated at different Reynolds numbers, spanning from 10,000 to 30,000.

Bond properties of GFRP bar embedded in marine concrete subjected to sustained loads

In this work, a total of 20 beam type concrete specimens were prepared to investigate bond behavior of glass fiber reinforced polymer (GFRP) bar embedded in marine concrete. The influence of sustained loads (load level: 0.25, 0.45 and 0.65 ultimate load (Pu)) and stirrup on bond properties was investigated. After sustained load period, flexural bond test was conducted to determine bond stress and slip. Test results indicate that bond strength of GFRP bars shows decreased trend with increasing sustained loading. Compared with specimen not subjected to sustained load, bond strength significantly decreased under 0.25, 0.45 and 0.65 Pu. Also, sustained load deteriorates the bond stiffness and bond toughness. What’ s more, differences in failure modes and bond strength of steel bar and GFRP bars in flexural bonding tests were analyzed and compared. All GFRP bar specimens subjected to sustained load exhibit bars pull-out failure. In contrast to steel bar, the influence of stirrups on GFRP bar-marine concrete bond strength is relatively limited (specimens with stirrups exhibited only 1.8 % increase over specimens without stirrups), due to GFRP bars lower rib heights and weaker mechanical interlocking with concrete. Characterization of different stages of bond-slip curves of GFRP bar beam specimen subjected to sustained loads was carried out and bond-slip curves of GFRP shows two peaks. According bond strength and slip test data, bond stress-slip mathematical relationship model between GFRP bar and marine concrete under sustained load has been fitted.

Numerical study of cooling performance and flow characteristics of film hole-broken rib composite structure with squealer tip

The gas turbine blade tip might face substantial heat loads because of leakage flow between the blades and the casing. For blade tip cooling, a composite cooling structure with film holes and broken ribs is first used on GE-E3 blade in this work. The flow and cooling characteristics of the innovative structure are studied by numerical simulation under various blowing ratio (BR) conditions. Meanwhile, the impact of modifying both the rib angle and the rib height on the adiabatic film cooling effectiveness (AFCE) at the tip of the squealer is analyzed. According to the results, adding rib structures to the squealer tip can effectively regulate the paths of cavity vortices and kidney-shaped vortex pairs (KVP) at the tip. As a result, the averaged AFCE at the blade tip is improved. The notch pressure-side broken rib structure has good aerothermal performance, and the highest AFCE at BRs of 0.50, 1.00, and 1.50 basically occur under the “R60-100 %” condition (R60 refers to the rib structure of 60°, and 100 % is the ratio of rib height to notch depth), and the corresponding AFCE are 27.71 %, 26.00 %, and 32.47 % higher than those of the no-rib case, respectively. The corresponding AFCE increased by 27.71 %, 26.52 %, and 32.47 %, respectively, compared to the no-rib condition. The highest AFCE at a BR of 1.50 occurs at “R75-70 %“, which is a 38.20 % increase in AFCE compared to the no rib case. The improvement in AFCE is due to the difference in the flow of the cooling jets, which are subject to cavity vortices at different BRs. The analysis shows that the addition of ribs disrupts the formation of KVPs and weakens the influence of the cavity vortex, thus reducing the low AFCE region at the lower end of the tip groove and increasing the AFCE. However, due to the blocking effect of the ribs, the pressure loss at the blade tip is elevated. The proposed blade tip cooling structure is expected to provide new ideas for the next generation of advanced gas turbine cooling designs.

Deep neural network model for predicting thermal-hydraulic performance of a solar air heater with artificial roughness: Sensitivity, generalization capacity, and computational efficiency

A novel coupled computational fluid dynamics-deep neural network approach is proposed to accurately predict the performance of an artificially roughened solar air heater. Computational fluid dynamics data sets are used to develop an optimized neural network model for the prediction of thermal-hydraulic performance factor. The optimized neural network model with softmax transfer function in hidden layers has an architecture of 3‐37‐37‐1 and it predicts the thermal-hydraulic performance factor of the artificially roughened solar air heater with maximum, mean, and minimum error of 2.54 %, 0.245 %, and 0.0009 %, respectively. The concept of Shapley values is adopted to evaluate the global sensitivity analysis of the optimized deep neural network model and it is found that rib height is the most influential design parameter for the artificially roughened solar air heater. The generalization capacity of the neural network model is evaluated by comparing its predictions with experimental data, demonstrating superior predictive performance over traditional computational fluid dynamics simulations. The optimized artificial neural network model achieves a computational time gain of approximately 100 % against computational fluid dynamics.

Experimental study on bending forming of AZ31 magnesium alloy equal curvature panel

Abstract The process parameters of bending forming for magnesium alloy panel are determined, and magnesium alloy panel bending tools are developed. The experimental research is completed, and several specifications of magnesium alloy panels are processed successfully, without cracks, rib buckling, or rib shoulder collapse defects. During the bending process of the magnesium alloy panel, the press height and rib height ratio have a significant effect on the microstructure of the panel. With the increase of press height and rib height ratio, the grain size decreases. The microstructure and properties of the magnesium alloy panel are improved and grains are refined. When the rib height ratio is 7/2 and press height is 7 mm, the minimum grain size at the rib of the panel is 15.6 µm and the minimum grain size at the skin surface is 17.2 µm.

Bond performance between ribbed BFRP bar and seawater sea-sand concrete: Influences of rib geometry

To solve the corrosion problems of steel bars in reinforced seawater sea-sand concrete (SSC) structures, fibre reinforced polymer (FRP) bars are promising alternatives. The bond between FRP bars and SSC determines the capacity and serviceability limit states of structures composed by them. The rib geometry of FRP bars is one of the most important factors influencing their bond performances with concrete. However, it has not received sufficient attentions on existing studies and standards. Therefore, this study investigated the bond performance between SSC and ribbed basalt FRP bars with different rib geometry through pull-out tests on 36 specimens. It is found that the bond strength declined with the increase of rib width and dent width, while the increase of rib height improved the bond strength. The ultimate and residual slip were strongly correlated with the rib spacing. Finally, a bond strength model that can well predict the experimental results was proposed.

Analyzing the impact of sinusoidal wavy rib geometric parameters on turbine blade thermal and fluid dynamics

The wavy rib is a spoiler structure designed to improve flow and heat transfer within turbine blade cooling channels, offering valuable insights for efficient cooling design in aerospace applications. This study employs a blend of experimental validation and detailed numerical simulations to investigate how rib height, amplitude, and discontinuity size collectively impact heat transfer enhancement and flow resistance in wavy ribs. By integrating TSP temperature field measurements with SST k-ω numerical calculations across 8 rib heights, 7 amplitudes, and 9 discontinuities at Reynolds numbers ranging from 10000 to 40000, the research reveals intricate relationships between these parameters. Studies have shown that there is a strong interaction between amplitude and rib height, as well as amplitude and discontinuity. Under small amplitude, Nu/Nu0 increases monotonously with the increase of rib height, but increases first and then decreases under large amplitude. When the discontinuity is small, the dimensionless Nusselt number (Nu/Nu0) of the ribbed wall increases first and then decreases with the increase of rib height, while it increases monotonously when the discontinuity is large. In contrast, the interaction between amplitude and discontinuity is weak. The ribbed wall with the greatest heat transfer improvement has Nu/Nu0 nearly 80 % higher than the reference wavy rib scheme, but it also has the highest corresponding pressure loss. The best overall thermal performance is 20 % higher than the reference structure, and the ribbed wall Nu/Nu0 is also increased by 24 %. The change of Reynolds number at the inlet of the channel has little effect on the wall Nu/Nu0 and pressure loss of the wavy rib channel.

An experimental study on flow boiling heat transfer in porous-ribbed micro-channels

Experiments were carried out to investigate flow boiling heat transfer characteristics in a micro-channel heat sink with porous ribs at three rib-heights (i.e. Hrib = 200 μm, 400 μm, and 600 μm), three mass fluxes (i. e. 200 kg/m2s, 300 kg/m2s, and 400 kg/m2s), and a range of wall heat fluxes (30–1300 kW/m2). The heat transfer coefficients and temperature uniformity in porous-ribbed micro-channels under different conditions were analyzed and compared to the smooth micro-channels (i.e. smooth flat surface and smooth-ribbed surfaces). The flow regimes in both porous and smooth micro-channels were visualized under typical flow boiling conditions. The results showed that micro-channels with higher rib heights experience an earlier transition to the critical heat flux (CHF) region due to the narrower flow path. Compared to the smooth micro-channel, the configuration of porous coating significantly enhances the heat transfer in the micro-channel without ribs or with lower rib height (Hrib = 200 μm) due to the strong hydrophilicity, good liquid storage, and rewetting ability on porous surfaces. At G = 400 kg/m2s, the porous-flat surface achieves a 67.9 % enhancement of heat transfer coefficient in the micro-channel compared to the smooth-flat micro-channel. However, with a higher rib height (Hrib = 400 μm and 600 μm), the thermal resistance is increased which hinders the heat conduction along the rib-height direction. A significant superheat is observed at the bottom of porous surface, thereby deteriorating the heat transfer performance in the porous ribbed micro-channel.

Experimental investigation of effect of different configurations of semi-circular or half-round ribs on heat transfer enhancement in a rectangular duct

This research study investigated the impact of various configurations of semi-circular or half-round ribs on the thermal performance and frictional factor characteristics of a rectangular duct. During this research study, the ribs were provided on the inner surface of the test section’s bottom wall. Six distinct configurations of semi-circular ribs varying from continuous to hybrid arrangement were used. The range of Reynolds number was varied from 13,500 to 34,800; while the ratio of rib pitch to rib height (P/e ratio) was kept constant at 8. The ratio of the height of rib to hydraulic diameter of duct (also known as blockage ratio) was kept at 0.114. The results of experimental investigation showed that the Nusselt number ratio obtained was ranging from 1.36 to 2.74, while the friction factor ratio ranges from 1.70 to 4.51. The overall enhancement ratio for all configurations obtained was in the range of 1.06–1.80 times to that of plain duct. Among all rib configurations, the hybrid rib configuration showed superior ratio of Nusselt number and intermediate increase in ratio of friction factor as compared to all the other rib configurations. Hybrid rib configuration showed overall enhancement ratio values ranging from 1.45 to 1.80 times as compared to that of plain duct (duct without ribs) within the specified range of Reynolds number. The results of study showed that the hybrid configuration of semi-circular ribs exhibited superior overall thermal enhancement as compared to that of remaining tested rib configurations.

Shear performance of small-rib-height perfobond strip connector groups embedded in UHPC: Experimental investigations and design recommendations

Employing ultra-high-performance concrete (UHPC) with perfobond strip connector (PBL) groups for strengthening steel columns has emerged as a promising solution for the rehabilitation of steel structures. To reduce the cross-sectional area of strengthened members, PBL groups with small rib heights are adopted in thin UHPC layers. However, there are few studies focusing on the shear behaviours of small-rib-height PBL (SRHPBL) groups embedded in UHPC. Therefore, 20 push-out tests were conducted with the variables of SRHPBLs arrangements. The experimental results demonstrated the grouped effect of SRHPBLs embedded in UHPC: (1) the overall shear capacity of twin-rib SRHPBL groups were about 1.67 times higher than that of their single-rib counterparts; (2) the overall shear capacity of SRHPBL groups decreased as the rib spacing of SRHPBLs increased; (3) the overall shear capacity of both the single- and twin-rib SRHPBL groups increased with the row numbers of SRHPBLs, whereas the average shear capacity of an individual SRHPBL increased gradually as the row numbers of SRHPBLs decreased; and (4) the row spacing of SRHPBLs slightly affected the shear performance of single- and twin-rib SRHPBL groups. Finally, theoretical models were developed to predict the shear capacity of SRHPBL groups encased in UHPC.