Rectangular Ribs Research Articles

The effect of external helical ribs tube on the heat transfer and pressure drop performance for multi - tube heat exchanger

The pressure drop and heat transfer characteristic for cross flow of turbulent air over helical rectangular ribs tubes heat exchanger were studied experimentally and numerically. The study includes the design and manufacturing of four models of multi-tube heat exchangers. Each model has three tubes in a line arrangement. Experiments were performed for Reynolds number range from (7200–31400) using different rib pitch to diameter ratios (P/D = 1.3, 1.5 and 1.8) with different ribs pitch angles. The height to diameter ratio of rib (h/D = 0.05) and width to diameter ratio is (w/D = 2) were fixed. The water flows with different rates inside the tubes with a range of (2, 3, 4, 5, 6 and 7) L/min. Three values for the inlet water temperatures to test tube were used. In the present numerical part, commercial software ANSYS Fluent 16.2 was employed to determine the heat transfer coefficient and pressure drop for the different models of cross flow heat exchangers. The results declared that the average Nusselt number and Pressure drop of the corrugated model has a relatively high different from that of the smooth models. In addition, the experimental and numerical were compared and gave a good agreement between them.

Computational fluid dynamics and laminar heat transfer of water/Cu nanofluid in ribbed microchannel with a two-phase approach

PurposeThis study aims to numerically investigate the heat transfer and laminar forced and two-phase flow of Water/Cu nanofluid in a rectangular microchannel with oblique ribs with angle of attacks equal to 0-45°. This simulation was conducted in the range of Reynolds numbers of 5-120 in volume fractions of 0, 2 and 4 per cent of solid nanoparticles in three-dimensional space.Design/methodology/approachThis study investigates the effect of the changes of angle of attack of rectangular rib on heat transfer and hydrodynamics of two-phase flow. This study was done in three-dimensional space and simulation was done with finite volume method. SIMPLEC algorithm and second-order discretization of equations were used to increase the accuracy of results. The usage of nanofluid, application of rips with different angles of attacks and using the two-phase mixture method is the distinction of this paper compared with other studies.FindingsThe results of this research revealed that the changing angle of attack of ribs is an effective factor in heat transfer enhancement. On the other hand, the existence of rib on the internal surfaces of a microchannel increases friction coefficient. By increasing the volume fraction of nanoparticles, due to the augmentation of fluid density and viscosity, the pressure drop increases significantly. For all of the angle of attacks studied in this paper, the maximum rate of performance evaluation criterion has been obtained in Reynolds number of 30 and the minimum amount of performance evaluation criterion was been obtained in Reynolds numbers of 5 and 120.Originality/valueMany studies have been done in the field of heat transfer in ribbed microchannel. In this paper, the laminar flow in the ribbed microchannel Water/Cu nanofluid in a rectangular microchannel by using two-phase mixture method is numerically investigated with different volume fractions (0-4 per cent), Reynolds numbers (5-120) and angle of attacks of rectangular rib in the indented microchannel (0-45°).

Experimental investigation and thermal analysis of solar air heater having rectangular rib roughness on the absorber plate

This study presents experimental investigation and thermal analysis of solar air heater having rectangular roughness on the absorber plate. The solar air heater used for the experiment was locally fabricated. The maximum intensity of solar radiation, ambient and solar air heater temperature were 827.87 W/m2, 33.77 and 112.0 °C respectively during the day time period of 9:00–18:00 h operation. The calculated thermal efficiency value ranged between 14.0 to 56.5%. The simulated minimum and maximum temperature of the solar air heater were 21 and 127 °C respectively, which were in reasonable agreement with experiment result of 20 and 112 °C. Thus, the solar air heater was considered capable of handling processes such as drying of various agricultural products, water heating etc. with temperature control mechanism.

Верификация моделей для турбулентных тепловых потоков при обтекании прямоугольного выступа на пластине

Верификация моделей для турбулентных тепловых потоков при обтекании прямоугольного выступа на пластине

Исследование влияния стреловидности несущих поверхностей и законцовок на аэродинамические характеристики перспективного беспилотного летательного аппарата

Separated flows are widespread in many areas of science and technology, such as space technology, aviation, gas turbines, etc., which has a significant effect on the processes of hydrodynamics and heat transfer in them. The separation of the flow and its reattachment can serve as a powerful means of enhancing heat and mass transfer processes, and its organization is quite simple and reliable in terms of technology. This paper presents the results of the experimental study on hydrodynamics and heat transfer in the separation zone in front and behind a single rectangular perforated rib located on a flat plate heated by the law of qw = const. Experimental measurements were carried out using the Pitot-Prandtl tube and Dantec Dynamics hot-wire anemometry system, which allows us to obtain new characteristics of the turbulent boundary layer, both mean and oscillatory ones. We analyzed the influence of the perforation ratio of the rib and the location of the holes in the rib on the heat transfer efficiency. It was established that the stagnant and recirculation zones in front and behind the perforated rib were shifted and became smaller or disappeared. Findings of research show that jet flows, impinging on the heat transfer surface from the perforation holes, provide more efficient heat transfer behind the perforated rib, compared to that behind the solid rib.

A comprehensive study on heat transfer enhancement in microchannel heat sink with secondary channel

Microchannel heat sinks are used to remove high heat flux generated by electronic components. Microchannel heat sink has gained huge attention from former researchers due to its capability to enhance the heat transfer performance. However, the conventional design such as microchannel heat sink with rectangular channel becomes inadequate to remove very high heat flux due to thermal boundary layer thickness. In this paper, the effectiveness of secondary channel that implemented to the novel design which constructed by cavities and ribs are studied numerically for Reynolds number (Re) ranging from 100 to 450. The performance of proposed design (TC-RR-SC) is investigated by using a comparative analysis with related geometry such as microchannel with rectangular rib (CR-RR), microchannel with triangular cavity (TC) and microchannel with rectangular rib and triangular cavity (TC-RR). The result shows that TC-RR-SC design has an extraordinary overall performance compared to other designs due to combined effect of thermal boundary layer re-development and flow mixing in main channel. Besides that, the design shows the less flow and heat transfer irreversibility that contributed to thermal performance from the view of the second law of thermodynamics.

Comparative study on heat transfer enhancement of nanofluids flow in ribs tube using CFD simulation

AbstractThis study presents, a numerical investigation of two‐dimensional turbulent nanofluids flow in different ribs tube configurations on heat transfer, friction, and thermal performance coefficients using ANSYS‐FLUENT software version‐16. Governing equations of mass, momentum, and energy have been solved by means of a finite volume method (FVM). Four types of nanoparticles namely; Al2O3, CuO, SiO2, and ZnO with volume fraction range (1%‐4%) and different size of nanoparticles (dp = 30 nm, 40 nm, 50 nm, and 60 nm) with various Reynolds number (10 000‐30 000) in a constant heat flux tube with rectangular, triangular, and trapezoidal ribs were conducted for simulation. The results exhibit that Nusselt number for all cases enhanced with Reynolds number and nanofluid volume fraction increases. Likewise, the results also reveal that SiO2 with volume fractions of 4% and diameters of nanoparticles of 30 nm in triangular ribs offered the highest Nusselt number at Reynolds number of Re = 30 000. In addition, the higher value of thermal performance factor was obtained at Reynolds number of Re = 10 000.

Numerical study of heat transfer enhancement using vortex generator for thermal management of lithium ion battery

A numerical study of two types of vortex generator (VG) have been conducted to enhance heat transfer of cooling in the battery thermal management system. The thermal behaviour and cooling effects have been investigated to evaluate the heat transfer performance of two types of VG. Air flow model coupled with a pouch cell model is carried out in this study. The results show that both types of vortex generators can enhance heat transfer before VGs, but only delta winglet VG can still enhance local heat transfer after it due to more vortices generated that can mix cold and hot air flow between the top and bottom thermal layers completely. It is found that the heat transfer enhancement is due to bulk fluid mixing, boundary-layer modification and flow destabilization by VGs. The maximum temperature of pouch cell is also numerically investigated by a validated battery model. The result shows that the maximum temperature of a pouch cell can be decreased by both delta winglet and rectangular rib. For the discharging rate at 5C, it can be decreased by 10% and the local Nusselt number can be increased by 38% compared to the baseline scenario without any VGs.

Thermal performance improvement in water nanofluid/GNP–SDBS in novel design of double-layer microchannel heat sink with sinusoidal cavities and rectangular ribs

In this numerical study, laminar flow of water nanofluid/GNP–SDBS (graphene nanoplatelet–sodium dodecylbenzene sulfonate) for 0–0.1% solid nanoparticles mass fraction was investigated for Reynolds numbers of 50–1000 in 3D space via finite volume method. In the newly proposed microchannel design, the cooling fluid is moving in countercurrent in the upper and lower layers of the microchannels, and there are cavities and sinusoidal routes on the solid walls of the microchannel, and the presence of rectangular ribs on the flow centerline along the fluid path enhances mixing for cooling fluid and creates better heat transfer for warm surfaces. The results of this study show that this special design of the microchannel can have a substantial increase in Nusselt number and heat transfer so that in the considered geometry by adding solid nanoparticles mass fraction it is possible to increase average Nusselt number for each Reynolds number by approximately 20%. Also, the mixing of the fluid because of formation of secondary flows has a strong effect on making the temperature distribution uniform in the cooling fluid and solid bed (wall) of the microchannel, especially in the lower layer. The upper layer of the microchannel always has a lower temperature due to indirect contact with heat flux compared with the lower layer. In this study, by increasing Reynolds number and mass fraction of solid nanoparticles the Nusselt number is increased and heat resistance of the lower wall of the microchannel is reduced. Based on the investigation of flow field and heat transfer, the use of the proposed design of the microchannel is recommended for Reynolds number less than 300.

Heat transfer performance evaluation in circular tubes via internal repeated ribs with entropy and exergy analysis

In the present study, heat transfer enhancement in circular tubes via internal repeated ring-type ribs is, numerically, investigated and validated with experimental data obtained by Huang et al. (2015). Thermal evaluation is also done for tubes with rectangular, trapezoidal and triangular ribs. Furthermore, entropy and exergy analysis are performed on all the tested tubes. Air is used as the working fluid at (3.6 × 103 ≤ Re ≤ 1.65 × 104). The rib-depth to tube-inner diameter ratio (e/d) and the rib-pitch to tube-inner diameter ratio (p/d) in the tubes ribs configurations are considered. The performance evaluation criterion (PEC) is employed to estimate the optimum case that gives high thermal hydraulic efficiency (THE). It is found that the best (THE) accompanying with lower entropy and higher exergy are achieved for the tube with ring-type ribs compared to other shapes. The flow phenomena, temperature and pressure contours are illustrated with a consistent evaluation.

Turbulent forced convection flow inside inward‐outward rib corrugated tubes with different rib‐shapes

AbstractThe thermal and hydrodynamic behaviors of forced convection turbulent flow inside the corrugated tube are investigated numerically. The ribs of corrugated tube are distributed in inward‐outward arrangement simultaneously and alternately (referred as IOCT). Three roughness shapes of the corrugated tube are examined; rectangular, semicircular, and trapezoidal ribs. The computational model is validated through comparison with the predicted results with correlated and experimental ones of related works. The performance of IOCT is compared thermally and hydrodynamically with that of the inward‐rib corrugated tube (ICT), outward‐rib corrugated tube (OCT) and smooth tubes. The results reveal that the heat is exchanged effectively by employing IOCT than utilizing OCT but with extra pumping power losses. At the maximum Re, it is found that the heat transfer of IOCT is 17.7% higher than that of OCT, and utilizing IOCT instead of ICT results in a reduction of friction factor by about 27.2%. Also, IOCT exhibits a lower friction factor and pressure drop penalty than that imposed by ICT. Also, roughness shapes have an insignificant effect on the thermal and hydrodynamic performances of IOCT for the same rib geometrical parameters. Furthermore, the influence of variation pitch‐to‐diameter ratio is also examined for various rib shapes of IOCT.

Influence of microstructure geometry on pool boiling at superhydrophobic surfaces

Periodically patterned superhydrophobic surfaces with rectangular rib and circular post arrays were utilized as heat transfer surfaces in a boiling apparatus with the water pool undergoing saturated pool boiling. The surface microstructures were geometrically defined by cavity fraction (the ratio of projected cavity area to surface area), pitch (the center to center distance between microfeatures), and feature height. Surface heat flux and surface superheat, the difference between the heated surface and the pool saturation temperature, were measured for each surface. Ten different micropatterned surfaces with post or rib geometries were considered with cavity fraction varying from 0.5 to 0.98, pitch varying from 8 to 40 μm, and microfeature height at 4 μm or 15 μm. The surface heat flux was measured across a range of surface superheats spanning 2–38 K. It is demonstrated for the first time that the transition from nucleate boiling to film boiling on rib patterned surfaces depends strongly on the cavity fraction. Increasing the microstructure height from 4 μm to 15 μm modestly increases the transition temperature. Nucleate boiling is more suppressed on post patterned surfaces than on rib patterned surfaces. Further, the rib structured surfaces exhibit a sudden transition from nucleate to film boiling while the post structured surfaces exhibit a gradual transition, with the vapor film growing slowly across the surface. Once stable film boiling is reached, the surface microstructure negligibly influences the heat flux for all surfaces.

Effect of Microfins on Thermal Performance of Microchannel Using CFD

In the present study, the fluid flow and heat transfer characteristic of microchannel heat sink with microfins are studied numerically at Reynold number ranging from 400 to 1200. The influence of microfins on the Nusselt number and pressure drop are investigated. Five different types of microfins namely cylindrical microfins (Case A), diverge cylindrical microfins (Case B), diverge cylindrical microfins with semi-circle rib (Case C), diverge cylindrical microfins with rectangular rib (Case D) and diverge cylindrical microfins with triangular rib (Case E) are designed. A comparative analysis of these five types of microfins with bare microchannel has been conducted. The result highlighted the extended microfins augmented the heat transfer characteristic by disrupt the thermal boundary layer. The overall thermal performances of microchannel heat sink with microfins are 1.1 – 1.47 times higher compared to bare microchannel.

Numerical investigation and performance analyses of rectangular mini channel with different types of ribs and their arrangements

An investigation of a three-dimensional rectangular minichannel with different types of longitudinal vortex generators, (rectangular and trapezoidal) which are considered as ribs along the channel, is carried out. Five different models with different angles of attack and height of ribs have been designed and studied numerically for analyzing the heat transfer and overall performance of the channel in single-phase laminar flow. The results indicate that the configurations with the attack angles of 60° have the best heat transfer performance. An augmentation for heat transfer performance improves with the increase of rib's height and the Reynolds number in the channel, however, flow resistance increases in return. Minichannels with both rectangular and trapezoidal ribs have better results for heat transfer and flow performance in comparison to a minichannel with rectangular ribs only. The model with all trapezoidal ribs leads to best overall performance due to its better flow performance, which is a crucial factor in the overall efficiency. The overall performance of the minichannel enhanced by 52.7% for the case “M3” in comparison with the smooth channel.

Parameterization investigation on the microchannel heat sink with slant rectangular ribs by numerical simulation

The slant rectangular ribs (SRRs) arranged in a microchannel can enhance heat transfer efficiency due to the flow disturbation, the interruption of boundary layer and increase of heat transfer area. In order to fully understand the mechanism of heat transfer enhancement, the flow and heat transfer in the microchannel with single- and double-row slant rectangular ribs are numerically simulated at Reynolds number ranging from 62.5 to 625. Numerical results show us that, great difference of flow pattern between microchannel heat sinks (MCHS) with single- and double-row slant rectangular ribs exists, and enormous influence of parameters of SRRs on heat transfer presents in various conditions. The flow disturbation of SRRs is the crucial factor to enhance heat transfer. Thereafter, the parameters such as attack angle, height, length, width and pitch of SRRs are evaluated by the average Nusselts number with identical pump power. Solid foundation for design of MCHS with SRRs can be provided.

Numerical Analysis of Deterministic Micro-Textures on the Performance of Hydrodynamic Journal Bearing

Now-a-days a lot of thrust is given on the research related to geometrical modifications of hydrodynamic lubricated bearing systems. Introducing deterministic micro-textures on the journal surface is considered to be one of the key approaches for improving the bearing performance. In this paper, bearing performance analysis is done without considering the effect of cavitation to study the effect of different triangular, circular and rectangular micro-textured grooves and ribs on the hydrodynamic journal surfaces using COMSOL Multiphysics software. Initially, the static performance analysis is carried out for hydrodynamic journal bearing system with smooth surface using thin fluid film analysis method and the results of the same are validated using analytical results. In the later part of the paper, the numerical analysis is carried out for different micro-textured journal surfaces. The simulation results of these studies shows that the value of maximum fluid pressure and frictional power loss are significantly affected by introduction of these deterministic micro-textures. Bearing with rectangular micro-textured ribs on the journal surface resulted in maximum pressure is development and frictional power losses as compared with other deterministic micro-textures. Similarly the rectangular micro-texture grooves gave minimum pressure development and frictional power losses as compared with other deterministic micro-textures.

Effects of Rib Shapes on the Entropy Generation in a Ribbed Duct

Ducts are often used in reactors and heat exchangers. Using rough surfaces in ducts is recognized as an effective technique to enhance heat transfer. In this research, an entropy generation analysis is carried out for turbulent flow inside a ribbed duct. Numerical simulations are performed to study the effects of rib shapes and flow Reynolds numbers on friction factor, Nusselt number, and different types of entropy generation containing the frictional and thermal ones. All simulations are performed for Reynolds number in the range of 20,000 to 60,000 and six rib shapes (rectangular, square, isosceles trapezoidal, rectangular trapezoidal, equilateral triangle, and nonequilateral triangle). A shear stress transport k-omega turbulence model is used for the numerical simulations. It was found that the ribs with no inclined surfaces such as square and rectangular shapes create more thermal irreversibility. Moreover, it was shown that among different rib shapes, the equilateral triangle rib has the highest frictional entropy generation over the entire range of the Reynolds number, whereas the rectangular rib has the lowest one.

The effect of rib shape on the behavior of laminar flow of oil/MWCNT nanofluid in a rectangular microchannel

In this research, the laminar and forced flow and heat transfer of oil/multi-walled carbon nanotubes nanofluid in a microchannel have been numerically investigated. The studied geometrics is a two-dimensional rectangular microchannel with the proportion of length to height of 150 (L/d = 150). The purpose of this research is to investigate the effect of using rectangular, oval, parabolic, triangular and trapezoidal rib shapes on behavior and heat transfer of nanofluid flow in the rectangular microchannel. This research has been simulated in Reynolds numbers of 1, 10, 50 and 100 and volume fractions of 0, 2 and 4% of nanoparticles by using finite volume method. The results of this research indicate that the existence of ribs enhances the friction factor and Nusselt number, significantly. Also, the shape of rib is one of the most important factors for determining the behavior and heat transfer of cooling fluid flows. Among the investigated rib shapes, the parabolic rib, comparing to the augmentation of friction factor, has the best proportion of Nusselt number enhancement.

Rib in Turbulent Boundary Layer

Experimental and theoretical investigations of the flow structure, with the flow over a variety of protrusions and depressions on the initially smooth surfaces are of considerable practical interest, since the there are constructive or random occurring depressions and cavities found on many different convective surfaces. With the flow over the depressions and protrusions, the boundary layer separation and its reattachment can lead to occurring specific phenomena, which have a significant impact on drag and heat transfer. These phenomena, which are encountered in the course of experimental studies and obtaining adequate mathematical models, are complicated and hard-to-understand.The paper presents experimental results of hydrodynamics and heat transfer in the separation zone before and after a single rectangular rib and a round corner rib with the height of approximately y+ = 100, which are placed on the flat plate that is heated according to the law of qw=const. Experimental studies were conducted using a Pitot-Prandtl microprobe and a hot-wire Dantec Dynamics anemometry system, which allowed us to obtain both the mean and the fluctuating characteristics of the turbulent boundary layer and determine the boundaries of the vortex and separation zones.It is shown that the structure of vertex zones before and after the rib has a strong dependence on the rib shape and size. New experimental data on the mean and fluctuating characteristics in the turbulent boundary layer with the flow over the rectangular ribs with and without round top corners are obtained. Also, the fluctuations of temperature and especially velocity in the boundary layer after the rib are significantly higher than in the layer on the flat plate. The changing characteristic of the friction and heat transfer coefficients indicates that the increase of the heat transfer coefficient exceeds the growth of the friction coefficient after the ribs with the size 30 < y+ < 100.

Turbulent flow and heat transfer of Water/Al2O3 nanofluid inside a rectangular ribbed channel

In present study, the turbulent flow and heat transfer of Water/Al2O3 nanofluid inside a rectangular channel have been numerically simulated. The main purpose of present study is investigating the effect of attack angle of inclined rectangular rib, Reynolds number and volume fraction of nanoparticles on heat transfer enhancement. For this reason, the turbulent flow of nanofluid has been simulated at Reynolds numbers ranging from 15000 to 30000 and volume fractions of nanoparticles from 0 to 4%. The changes attack angle of ribs have been investigated ranging from 0 to 180°. The results show that, the changes of attack angle of ribs, due to the changes of flow pattern and created vortexes inside the channel, have significant effect on fluid mixing. Also, the maximum rate of heat transfer enhancement accomplishes in attack angle of 60°. In Reynolds numbers of 15000, 20000 and 30000 and attack angle of 60°, comparing to the attack angle of 0°, the amount of Nusselt number enhances to 2.37, 1.96 and 2 times, respectively. Also, it can be concluded that, in high Reynolds numbers, by using ribs and nanofluid, the performance evaluation criterion improves.