Varying Aspect Ratio Research Articles

Large-eddy simulation of non-isothermal flow over an array of cylinders placed inside a converging channel

This work evaluates the flow and thermal characteristics of a gas-turbine blade trailing-edge. The study is carried out using large-eddy simulation (LES) for Reynolds number, Re=5900. In view of the realistic conditions, a converging channel with a staggered arrangement of fins with varying aspect ratio is considered for the higher pressure of the coolant and the larger temperature difference between the blade and the coolant. The present results are compared with the parallel channel case to identify the effects of converging flow passage of the channel on the flow and thermal characteristics. The computational setup and methodology are thoroughly validated using reference data from experiments as well as LES available in the literature. The results are analyzed in terms of Q-criterion, streamlines, vorticity and turbulent heat flux contours, and the Nusselt number profiles at several locations in the flow domain. The present results shows, unlike in the parallel channel case, a dominant spanwise component of velocity that helps in the formation of a strong vortex behind the first row itself, and the Nusselt number consistently increases from the first to the last row. The maximum gain and diffusion of turbulent heat flux occur within a recirculation zone and along the free-shear layer, respectively. The heat flux from the end-wall is extracted mainly by the spanwise velocity component, which is also responsible for its advection to the central region. Heat transfer is observed to be higher from fins compared to the end-walls, which underscores the importance of the active participation of fins in the analysis of heat transfer at the trailing-edge.

Rehabilitation of overload-damaged reinforced concrete columns using ultra-high-performance fiber-reinforced concrete

Abstract One of the problems experienced by reinforced concrete (RC) structures, whether a mistake at the design phase or a change in building use, is an overload. The goal of this study is to determine whether ultra-high-performance fiber-reinforced concrete (UHPFRC) is effective in repairing damaged concrete columns utilizing 30 mm thin concrete jacketing made of different steel fibers at various contents with varied aspect ratios (28, 37, and 45). Nine pieces of 500 mm long RC column specimens with a cross-sectional size of 150 mm × 150 mm were cast as part of the experimental program. By loading these columns with roughly 90% of their actual ultimate axial load capacities, damage was caused, and the columns were subsequently strengthened and rebuilt using UHPFRC jacketing materials. The results demonstrated that when steel fiber content increased, so did the mechanical qualities, such as compressive and tensile strengths. Rehab materials that contained 0.5% steel fiber recovered 138% of their maximum load-bearing capacities, while materials that contained 1.5% steel fiber recovered 164% of their original capacities, which were roughly 1.38–1.64 times that of the unjacketed reference column. Additionally, it was observed that employing steel fiber in UHPFRC contents in these approaches resulted in the ultimate displacement being improved from 2.91 to 5.53 mm at 1.5% of steel fiber content, which is an increase of almost double that of control specimens.

Finite element analysis of unreinforced masonry walls with different bond patterns

Masonry is the oldest building material, yet it is also the least understood due to the non-linear and composite nature of masonry, which consists of brick units, mortar, and unit-mortar contact. In this paper, the response of a two-dimensional masonry wall with a window opening subjected to an in-plane lateral pushover loading is simulated by varying the interface properties of brick such as crushing, elastic, cracking, and shear properties. The simplified micro-modeling technique with the Engineering Masonry model for bricks and linear stiffness properties for the interfaces in the bed and head joints is employed to investigate the geometric nonlinear behavior of the masonry wall. The pushover curves obtained from the numerical simulations indicate that there is a significant influence on the lateral load response of the wall due to elastic, crushing, and shear parameters while the cracking parameters have less impact on the ductile capacity of the structure. Moreover, the study is also extended to examine the effect of bond patterns such as English, Stretcher, Flemish, and Header bond with varied aspect ratios of 1,1.5 and 0.75. In all four bond patterns, it was observed that the walls with lower aspect ratios exhibited higher strength. Further, in comparison to the other bond patterns, walls with the Flemish bond pattern demonstrated higher strengths at both lower and higher aspect ratios.

Wavy Leading Edge (WLE) Influence on a Rectangular Wing Using an Unsteady Analysis Approach

A rectangular wing with Wavy Leading Edge (WLE) effect was investigated experimentally and numerically. This research was carried out with the NACA 0018 profile. The morphology of humpback whale flippers, which are blunt and rounded in a specific pattern, inspired the design of the WLE. The rectangular wing was explored in pitching motion with a reduced frequency of k = 0.25 and varied aspect ratios. Multiple aspect ratios (AR) of the rectangular wing have been evaluated to determine the best wing aspect ratio, notably 3.9, 5.1, and 7.9. Only at AR 3.9 and 5.1 does the WLE perform efficiently in both upstroke and downstroke motion. WLE has a sinusoidal function shape. The improvement of lift force was stronger during upstroke motion than during downstroke motion. The stall is minimized during the pitching motion of the WLE wing, according to the numerical simulation. This result could be applied to fin stabilizers or wind turbines.

Effect of marginal variation of aspect ratio and frequency with kinematic asymmetry on flow field around flapping rigid wing in hover

Phase-locked two dimensional particle image velocimetry (PIV) measurements are used to capture flow field around rigid flat plate wings undergoing main flapping motion (hover) with water as fluid medium in quiescent condition. Experiments are conducted using asymmetric upper-lower stroke single degree of freedom main flapping motion. Two different aspect ratio (AR) 1.5 and 1.0 rectangular wings at 1.5 Hz and 2.0 Hz flapping frequency and chord based Reynolds number of the order of 104 are studied. To achieve the desired aspect ratio, wing span is varied while wing chord remains fixed. Flow features for downstroke and upstroke are comparable for all four cases investigated. This includes vortex shedding from wingtip during wing stroke, vorticity intensification caused due to vortex stretching which occurs more dominantly for AR = 1.0, occurrence of KH instability in shear layer formed due to wing sweep and added mass effect due to the flow dragged by flapping wing. Vortex filamentation and fragmentation phenomena are observed during downstroke and upstroke respectively due to faster downstroke and slower upstroke. Rossby number, which is the ratio of inertial to Coriolis force is significant for rotational flapping wing. With increase in Rossby number there is a reduction in the spanwise flow over wing which influences strength of wingtip vortex at beginning of a stroke. It is found that spanwise flow for AR = 1.5 is stronger than AR = 1.0 and consequently the strength of wingtip vortex is higher for higher aspect ratio. However, peak vorticity is higher for AR = 1.0 due to vortex stretching effect which is expected to be more dominant at lower AR due to three dimensional effects. Effect of marginal variation in wing aspect ratio, flapping frequency with kinematic asymmetry are studied using velocity field, vorticity (ωz) contours, λ2 criterion, peak vorticity variation and its spatial distribution as well as kinetic energy variation of the flow field. Kinetic energy distribution and its connection with wake capture is explored.

Numerical Analysis of Infill Plate Performance on Steel Plate Shear Wall (SPSW)

Steel Plate Shear Wall (SPSW) is one of the systems that can be used to minimize the effect of earthquakes on buildings. The main energy-absorbing element of the steel plate shear wall system is on the thin steel plate that are located on the center of the steel frame. This thin steel plate is called infill plates. This infill plate will later experience buckling and form a series of tension field action. This paper will prove that the infill plates in the steel plate shear wall system provides significant strength contribution in resisting lateral loads.The analysis was carried out by comparing the strength provided by steel plate shear wall system and simple beam-column steel frame system (without infill plate) with some aspect ratio variation (width per height). The material used for the infill plates was low yield strength (LYS) steel plate of 1.30 mm thick, while the column (vertical boundary element) used WF 400.200.8.12, and the beam (horizontal boundary element) used WF 350.175.7.11. The loading used a monotonic pushover loading of 2% drift (68.8 mm) for each specimen.The analysis result proved that the steel plate shear wall system (frame with infill plates) had significant strength advantage compared to the plateless frame system. The aspect ratio (L/h) on infill plates were also affects the strength of the entire system, where the greater the aspect ratio, the greater the strength. The strength value of the SPSW specimen at 2% drift loading on aspect ratio L/h = 1.00, 1.50, 2.00, 2.50 respectively was 614.95 kN, 634.88 kN, 646.69 kN, and 688.03 kN. Meanwhile, the strength increment percentage between steel plate shear wall systems compared to plateless frame systems in each aspect ratio was 21.67%, 32.39%, 42.48%, and 54.20%.

Exploring the feasibility of next-generation CO2-based adsorption cooling systems using different adsorbent reactor configurations

The present investigation expounds on the effects of the reactor geometry, cycle time and heating/cooling fluid temperatures on the performance of a 4-bed CO2 adsorption cooling system. Cylindrical adsorbent reactors of varying aspect ratios (AR) with an optimum number of internal longitudinal fins and non-finned reactors are compared. The study confirms the substantial effect of reactor configuration on the system COP, specific cooling effect (SCE) and power, energy interactions during various processes and the total cycle time (TCT), which the equilibrium or lumped system analysis fails to predict. An increment of 98 % and 189 % in system COP and SCE is attained by varying the aspect ratio of the reactor with fins under subcritical operations. In continuation, a reduction of 41 % in TCT is observed. The study confirms the optimum adsorption/desorption time for which the COP and SCE are maximum, especially for higher AR reactors. It is noteworthy that proper selection of reactor aspect ratio results in a better system COP, even at lower heating fluid temperatures. During the transcritical operations, an increment of 23 % in COP and 6 % in SCE is achieved for a gas cooler exit temperature of 35 °C. Moreover, the reactor configuration also affects the optimum gas cooler pressure for the transcritical cycle, like the gas cooler exit temperature. One of the crucial observations is that, for a given combination of reactor configuration, heating/cooling fluid temperatures, and operating pressures, there exists a minimum cycle time below which a cyclic steady-state condition is impossible to achieve. During the subcritical and transcritical operations, a maximum COP of 0.1 and 0.052 is achieved for the proposed adsorption chiller configuration, respectively.

Effects of aspect ratio and initial pressure on asymmetric flame and flame instability of premixed CO/air

Syngas is a promising alternative energy carrier with low carbon and pollutants emissions, and CO is the main component. The combustion characteristics of stoichiometric CO/air mixtures with varied initial pressure (0.5–1.5 atm) and aspect ratio (12–40) were examined through experiments in a rectangular closed duct. This experiment simulated the transport and storage conditions of CO to study its combustion characteristics at different aspect ratios and initial pressures. The flame images and overpressure dynamics were captured by high-speed camera and pressure sensor, respectively. Experiment results proved that the increase in aspect ratio had an important effect on flame shape evolution. The tilted flame for low aspect ratios was affected by buoyancy, while flames with high aspect ratios were influenced by competing buoyancy and intrinsic instability. The results showed that the flame morphology and dynamics were enhanced with increasing aspect ratio and initial pressure. The intrinsic instability of premixed CO/air combustion was investigated, and the formation mechanism of tilted flame and twisted flame were comprehensively analyzed. Qualitative distinctions were made between symmetric and asymmetric flame morphology regimes.

Probability-weighted ensemble support vector machine for intelligent recognition of moving wear debris from joint implant

Friction-induced wear debris from joint implants are effective resources in investigating artificial joint wear and cellular immune response mechanisms. To improve the accuracy of wear debris analysis, an intelligent recognition method is developed for wear debris measurement under motion conditions. In this method, the multi-view image sequence of moving wear debris is captured to acquire the variations of aspect ratio, area, and roundness features. Then multiple SVM models are integrated to identify wear debris types based on weighted probability to improve the accuracy. The proposed method can achieve a classification accuracy of 90.51%, which is better than HIVE-COTE2.0, MultiRocket, and other time series classification algorithms. This method can be applied to monitor wear status of artificial joint articulating surfaces.

Numerical analysis of H-Darrieus vertical axis wind turbines with varying aspect ratios for exhaust energy extractions

In this paper, a three-dimensional numerical study has been conducted by solving the unsteady Reynolds Averaged Navier Stokes equations with shear stress transport (SST) k-omega turbulence model to investigate the power production efficiency of a three-bladed H-Darrieus vertical axis wind turbines (HDWT) using S-1046 airfoil under accelerated wind conditions of the cooling tower exhaust system. Aiming to extract the waste energy from the exhaust air, four HDWTs having different aspect ratios were tested by varying the turbine diameter; and the moment and power coefficient values were calculated at tip speed ratios (TSR) in the range of 1.5–3.5. The results showed that the HDWT with a smaller aspect ratio (AR) of 0.44 gives a better power coefficient of 0.294 at TSR 2.5 as compared to other testing conditions. Further, a detailed flow field analysis around the HDWT for different ARs and TSRs has been provided in this paper to discuss the turbine's performance. Finally, a comparative study with the free-stream flow condition showed that HDWT provides 58.5% lower performance than the flow in the exhaust system at lower AR, indicating a positive guided flow effect on the turbine performance under exhaust flow systems.

Determination of fiber orientation model parameters for injection molding simulations via automated metamodel optimization

Injection molded short fiber reinforced components reveal a sound light weight potential with moderate costs and thus are widely used in many demanding engineering applications. The accurate determination of the fiber orientation (FO) is essential for predicting the overall mechanical behavior of discontinuous (short or long, with varying aspect ratio) fiber reinforced composites. The simulation of the FO requires a proper modeling of the hydrodynamics, the closure transformation of the FO tensor and optionally the application of specific correction functions. The determination of parameters for the fiber orientation models commonly used in injection molding simulations is a challenging task because they cannot be determined directly in experiments. Hence, a novel way is shown in our paper to derive these parameters faster, more efficiently and accurately by the usage of an automated metamodel optimization. For this, injection molding simulations were performed iteratively by an optimization program until a minimal deviation error of the simulated parameters was reached. The optimization was performed based on proper computed tomography FO data of selected regions of interest. The new approach was tested for a rotationally symmetric Venturi tube geometry made from short glass fiber reinforced polyamide (PA-GF). The fiber orientation distribution models chosen were the iARD-RPR equation with 3 parameters and the novel anisotropic IISO equation with 5 parameters. It was shown that the optimization method is feasible for the calibration of fiber orientation models. Furthermore, the IISO equation with its 2 additional parameters allowed a more accurate prediction of the fiber orientation distribution, especially of the core layer of the injection molded part.

3D CFD Study of Scour in Combined Wave–Current Flows around Rectangular Piles with Varying Aspect Ratios

This study utilizes three-dimensional simulations to investigate scour in combined wave–current flows around rectangular piles with various aspect ratios. The simulation model solves the Reynolds-averaged Navier–Stokes (RANS) equations using the k–ω turbulence model, and couples the Exner equation to compute bed elevation changes. The model also employs the level-set approach to realistically capture the free surface, and couples a hydrodynamic module with a morphological module to simulate the scour process. The morphological module employs a modified critical bed shear stress formula on a sloping bed and a sand-slide algorithm for erosion and deposition calculations in the sediment bed. To validate the numerical model, simulations are conducted in a truncated numerical wave tank with the Dirichlet boundary condition and active wave absorption method. After validation, the numerical model is used to investigate the effect of aspect ratio and the Keulegan–Carpenter (KC) number on scour depth in a combined wave–current environment. The study finds that the normalized scour depth is highest for a rectangular pile with an aspect ratio of 2:1 and lowest for an aspect ratio of 1:2. The maximum normalized scour depth (S/D) for aspect ratios of 2:1 are 0.151, 0.218, and 0.323 for KC numbers 3.9, 5.75, and 10, respectively, whereas the minimum normalized scour depth (S/D) for aspect ratios of 1:2 are 0.132, 0.172, and 0.279. Additionally, the research demonstrates that the normalized scour depth increases with an increase in the KC number for a fixed wave–current parameter (Ucw).

Schlieren imaging investigation of flow fields in synthetic jets generated by different orifice geometries with varying aspect ratios

Schlieren imaging investigation of flow fields in synthetic jets generated by different orifice geometries with varying aspect ratios

Experimental study on the combined effects of patch density and elongation on wake structure behind a rectangular porous patch

This paper presents an experimental study on how both variable solid volume fractions and aspect ratios (length/width) of a centre-channel rectangular porous patch under aligned configuration of rigid and emergent stems impact the flow behaviour and wake structure. This study forms an essential extension to the existing fundamentals and knowledge on this topic. Through rigorous experimental tests by velocity measurement and dye visualization, the aspect ratio, rarely addressed before, is confirmed to play a critical role. Vortex street, unable to be triggered under a low solid volume fraction, however, can be generated by elongating the patch (increasing the aspect ratio). The key reason is that patch elongation promotes the generation of the wake vortex street by producing a relatively high transverse velocity gradient in the wake region. Meanwhile, Kelvin–Helmholtz vortex streets are triggered along the two patch lateral edges, re-increasing the in-patch velocity and imposing contributions to the wake vortex streets generation. By scaling the characteristic velocity (at the wake vortex initiation position and patch trailing edge) and solid volume fraction with the patch aspect ratio, three non-dimensional threshold maps can be established to express the combined effects of the solid volume fraction and aspect ratio on the initiation of the wake vortex street. They could be alternatively used for theoretical analysis and implementation on wake formation and structure subject to parameter availability.

Optimization of metal foam pellet shape in packed beds for improved radial heat transfer using particle-resolved computational fluid dynamics

Process intensification in tubular reforming reactors has always been a topic of interest, particularly for improving the radial heat transfer. The innovation of open-cell metallic foam pellets is the latest in this category, as they bear unique transport properties. This work presents the optimization of metal foam pellet shapes for improved radial heat transport, using a virtual design platform based on a modified version of particle-resolved computational fluid dynamics. To optimize the pellet geometry, different configurations such as pellet with inner holes, external grooves, and varied aspect ratios, as well as different foam morphologies (cell size ϕ and porosity ε) are considered, and the influence of each pellet configuration on flow and energy transport in a randomly packed bed setup has been investigated. Based on the desirable properties of the packed bed, such as low pressure drop, high heat transfer coefficient, increased surface area, and high catalyst inventory, the overall performance of the investigated pellet shapes is analyzed. The foam ring with the aspect ratio of 2.5 and ϕ = 0.45 mm, ε = 0.82 has been identified as optimal under the investigated operating conditions 250 < ReP < 2250, which is confirmed by pressure drop and heat transfer experiments.

The impact of neighborhood layout heterogeneity on carbon emissions in high-density urban areas: A case study of new development areas in Hong Kong

Under the climate change context, there is a universal appeal for a paradigm shift towards environmentally sensitive urban design. Previous studies focused on density parameters, while ignoring the rational layout of buildings in the neighborhood, especially the layout heterogeneity, which would cause different environmental performance outcomes under the intricate and dynamic interdependence among buildings. This study systematically explores the impact of five neighborhood layout heterogeneity indicators, including the coefficient of variation of building height, footprint area, volume, footprint aspect ratio, and surface-to-volume ratio, on carbon emissions, with consideration of several scenarios regarding different renewable energy application ratios. Totally 384 neighborhood cases are modeled under the same planning conditions in a new development area in Hong Kong and examined with the same simulation assumptions so as to exclude the impact of non-design related factors. The joint influences of different neighborhood layout indicators are examined by multiple linear regression analysis. The statistical results confirm the significant impacts of heterogeneity of building density and shape on neighborhood carbon emissions. It is found that the heterogeneity of building height would impede carbon reduction efforts due to higher mutual shading on rooftops and thus less solar harvesting, while the carbon reduction by building façade solar energy collection could be improved by the heterogeneity of building shape, including the variation of aspect ratio and surface-to-volume ratio. When considering both energy consumption and renewable energy collection, the heterogeneity of building height can lead to less net carbon emissions while that of building shape results in more net carbon emissions. Notably, the heterogeneity of neighborhood layout design would lead to the opposite result in carbon reduction efforts regarding solar energy collection and building energy consumption, which leaves a trade-off in decision-making when designing low-carbon neighborhoods.

Laser-induced periodic surface structuring for secondary electron yield reduction of copper: dependence on ambient gas and wavelength

One of the main limitations for future high-performance accelerators operating with positively charged particles is the formation of an electron-cloud inside the beam vacuum chamber, giving rise to instabilities. The Secondary Electron Yield (SEY) of the beam-facing surfaces gives a measure of the mechanism which drives this phenomenon. The laser-induced periodic structure formation on Cu surfaces has been demonstrated as a promising process to reduce SEY. In view of applications in beam chambers, we studied the laser process influence on SEY for 515 and 1030 nm wavelength femtosecond pulses on copper in different ambiences (air, nitrogen, vacuum). Depending on used process conditions, the surface composition differs, structures with varying aspect ratio are formed, i.e., periodic ripples and large-scale channels. Treatment in air at 515 nm is the most efficient for the formation of deeper structures allowing SEY maximum reduction first down to 1.6–1.7 and then below unity upon electron irradiation, thereby totally suppressing electron-cloud. Increasing the laser fluence, SEY will further reduce due to surface roughness enhancement via nanoparticle redeposition. This study reveals the fundamental role of LIPSS treatments to enable surface treatment in large-scale accelerator installations, where particle-free components are desired, and paves the way to potential future applications.

Effect of Opening on the Performance of Bamboo-Reinforced Concrete Wall Panels under One-Way In-Plane Action

This study focuses on the effect of opening on the performance of bamboo-reinforced concrete wall panels subjected to one-way in-plane action. The study evaluates the performance of six bamboo-reinforced concrete wall panels, of which three are solid wall panels and the remaining three specimens are having an opening at its center. All the prototype specimens were subjected to a uniformly distributed load that was applied at an eccentricity of 1/6 of its wall thickness. The specimens considered in this study had a constant slenderness ratio of 25, with varying aspect ratios and thinness ratios. The aspect ratio considered for the wall panels were 1, 1.20, and 1.52, and thinness ratios considered include 16.50, 20.75, and 25. The area of the opening provided was exactly 25% of the area of the specimen and was provided at the center of the specimen. The study reveals that the load-carrying capacity of a wall panel is dependent on its aspect ratio and thinness ratio. The ultimate load was found to decrease with an increase in aspect ratio, whereas it increased with increase in thinness ratio irrespective of the presence of the opening.

Bioprinting of structurally organized meniscal tissue within anisotropic melt electrowritten scaffolds.

The meniscus is characterised by an anisotropic collagen fibre network which is integral to its biomechanical functionality. The engineering of structurally organized meniscal grafts that mimic the anisotropy of the native tissue remains a significant challenge. In this study, inkjet bioprinting was used to deposit a cell-laden bioink into additively manufactured scaffolds of differing architectures to engineer fibrocartilage grafts with user defined collagen architectures. Polymeric scaffolds consisting of guiding fibre networks with varying aspect ratios (1:1; 1:4; 1:16) were produced using either fused deposition modelling (FDM) or melt electrowriting (MEW), resulting in scaffolds with different internal architectures and fibre diameters. Scaffold architecture was found to influence the spatial organization of the collagen network laid down by the jetted cells, with higher aspect ratios (1:4 and 1:16) supporting the formation of structurally anisotropic tissues. The MEW scaffolds supported the development of a fibrocartilaginous tissue with compressive mechanical properties similar to that of native meniscus, while the anisotropic tensile properties of these constructs could be tuned by altering the fibre network aspect ratio. This MEW framework was then used to generate scaffolds with spatially distinct fibre patterns, which in turn supported the development of heterogenous tissues consisting of isotropic and anisotropic collagen networks. Such bioprinted tissues could potentially form the basis of new treatment options for damaged and diseased meniscal tissue. STATEMENT OF SIGNIFICANCE: This study describes a multiple tool biofabrication strategy which enables the engineering of spatially organized fibrocartilage tissues. The architecture of MEW scaffolds can be tailored to not only modulate the directionality of the collagen fibres laid down by cells, but also to tune the anisotropic tensile mechanical properties of the resulting constructs, thereby enabling the engineering of biomimetic meniscal-like tissues. Furthermore, the inherent flexibility of MEW enables the development of zonally defined and potentially patient-specific implants.

Impact of vapour bubble movement on the process of two-phase heat transfer phenomena over hybrid elliptical tubes

The use of modified surface to improve the performance of two-phase heat exchanger in terms of pressure drop and heat transfer rate is one of the current need of industries. In light of this, the current analysis compares the diabatic two-phase heat transfer performance of hybrid elliptical tubes with that of traditional circular tubes at atmospheric pressure using distilled water as a quiescent test fluid. For the purpose of this investigation, a circular tube made of AISI 304 with a diameter of 25 mm and a heating length of 130 mm is used. In order to maintain the same surface area and heating length as a circular tube, the hybrid elliptical tubes are fabricated with varying aspect ratios of 1.17, 1.31, and 1.47. The heat flux varies between 14.87 and 94.82 kW/m2. For two orientation angles, i.e. 0ᵒ and 90ᵒ, the heat transfer performance of hybrid elliptical tubes are investigated. The analysis of results confirmed that both the tubes exhibit boiling characteristics. However, hybrid elliptical tubes outperform circular tubes in terms of heat transfer rate. It is also found that the hybrid elliptical tube with 0ᵒ orientation resulted in higher heat transfer coefficient about 20.61%, 36.74% and 20.69% than that of 90ᵒ orientation for aspect ratio of 1.17, 1.31 and 1.47 respectively. Regardless of orientation angle, the hybrid elliptical tube with aspect ratio of 1.31 demonstrated the highest heat transfer coefficient of all aspect ratios. Also, a non-dimensional correlation is developed which is found to predict the heat transfer coefficient of circular as we as hybrid elliptical tubes within an error band of ±12%.