V-shaped Ribs Research Articles

Effects of cross-sectional aspect ratio of V-shaped ribs and blockage ratio on heat transfer in a channel at a low Reynolds number

V-shaped ribs were investigated with the objective of enhancing heat transfer at the high-temperature side of a fin-plate type heat exchanger used in a railway vehicle compressor. The high-temperature side supplied with compressed air has a Reynolds number of approximately 4000, which is not sufficiently high to generate strong turbulence. When a 3D printer is used to fabricate a heat exchanger, the cross-sectional aspect ratio or blockage ratio of the ribs should be greater than the optimum value in order to attain a certain value of strength. In this study, a series of numerical analyses were conducted to investigate whether increasing the aspect ratio or the blockage ratio was more advantageous for achieving high heat transfer. Ribs with cross-sectional aspect ratios ranging from 0.3 to 5 were investigated. The investigated blocking ratios were 0.1 and 0.3. The results of computational fluid dynamics calculations were used to investigate the influences of flow separation–reattachment, secondary flow, and turbulence on heat transfer. The results demonstrated that the introduction of V-shaped ribs with a high blockage ratio into the channel at a low Reynolds number resulted in greater heat transfer enhancement compared with the effect of introducing ribs with a high cross-sectional aspect ratio.

Three-dimensional fluid topology optimization for heat transfer

In this work, an in house topology optimization (TO) solver is developed to optimize a conjugate heat transfer problem: realizing more complex and efficient coolant systems by minimizing pressure losses and maximizing the heat transfer. The TO method consists in an idealized sedimentation process in which a design variable, in this case impermeability, is iteratively updated across the domain. The optimal solution is the solidified region uniquely defined by the final distribution of impermeability. Due to the geometrical complexity of the optimal solutions obtained, this design method is not always suitable for classic manufacturing methods (molding, stamping....) On the contrary, it can be thought as an approach to better and fully exploit the flexibility offered by additive manufacturing (AM), still often used on old and less efficient design techniques. In the present article, the proposed method is developed using a Lagrangian optimization approach to minimize stagnation pressure dissipation while maximizing heat transfer between fluid and solid region. An impermeability dependent thermal conductivity is included and a smoother operator is adopted to bound thermal diffusivity gradients across solid and fluid. Simulations are performed on a straight squared duct domain. The variability of the results is shown on the basis of different weights of the objective functions. The solver builds automatically three-dimensional structures enhancing the heat transfer level between the walls and the flow through the generation of pairs of counter rotating vortices. This is consistent to solution proposed in literature like v-shaped ribs, even if the geometry generated is more complex and more efficient. It is possible to define the desired level of heat transfer and losses and obtain the closest optimal solution. It is the first time that a conjugate heat transfer optimization problem, with these constraints, has been tackled with this approach for three-dimensional geometries.

An experimental study on convective heat transfer performance of steam and air flow in V-shaped rib roughened channels

ABSTRACTAn experimental study on heat transfer characteristics of steam and air flows in a V-shaped ribbed channels was conducted. The effects of Reynolds numbers and rib angles on heat transfer of steam and air were obtained. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were 13.9%, 20.6%, 27.1%, and 27.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively. The correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air in V-shaped ribbed channels were developed.

Numerical Study on Heat Transfer Enhancement in a Rectangular Duct with V-Shaped Ribs

This research aims to study the numerical investigation of heat transfer and fluid flow characteristics of multiple cylinder v-rib with combined staggered rib in a rectangular duct. The conventional heat exchangers were usually used as flat plate rib shape leading to increase pressure drop from obstructive flow. Therefore, the inclined cylinder V-shaped rib was modified to use in this work. The cylinder shape rib increases pressure drop (less than flat plate rib) because of the rounded shape of cylinder v-rib creating the smooth flow of the fluid. The heat transfer and the pressure drop are represented in term of Nusselt number (Nu) Friction factor (f), respectively. The relation of Nu with f values was analysed to obtain the Thermal performance enhancement factor (TEF). The velocity vector and temperature contours were examined by the Computational Fluid Dynamics (CFD). The data was compared with the experimental result. The channel size was simulated at the rectangular duct height (H) of 30 mm and width (W) of 300 mm with rib-to channel-height ratios (e/H) at 0.1, 0.2, 0.3 and the angle of attack (α) at 30°. Air was used as the test fluid. Reynolds number (Re) was varied from 12,681 to 35,000 with constant heat flux on the bottom wall of the tested section. Simulation results represented the velocity vectors and temperature contours. It was found that the increasing of e/H leading to provide high co-rotating of the flow. The highest TEF (TEF = 2.05) was observed at 30(, e/H 0.3 and Re 12,618.

Heat transfer and flow characteristics of U-shaped cooling channels with novel wavy ribs under stationary and rotating conditions

Wavy rib is a kind of novel turbulator that can effectively improve the ribbed wall heat transfer of cooling channel and produce acceptable friction loss. Meanwhile, it has the advantage of simple structure. In this paper, the effects of wavy ribs on the heat transfer distributions of ribbed walls, side walls, and top wall are numerically studied in stationary and rotating U-shaped channels. The flow characteristics of cooling air are also analyzed. Taking the 45° V-shaped ribs as the reference scheme, the high-performance wavy ribs that have better heat transfer performance on ribbed wall and induce the same friction loss are selected. The channel aspect ratio is 1, with the height of 12.7 mm. The investigated Reynolds number is 25,000, and the rotation number is 0, 0.2, 0.3 and 0.4. Rib height (e-3e), rib round radius (0–5 mm), and rib angle (20–55°) are the three major geometrical parameters of wavy rib. The results show that, the diversion effect of wavy ribs on cooling air is the reason of friction loss suppression. On the one hand, the wavy ribs confine the fluid disturbance on side walls, leading to the heat transfer reduction. On the other hand, the impingement of cooling air on the channel top wall is strengthened, which improves the wall heat transfer. In stationary and rotating conditions, the high-performance wavy ribs increase the heat flux on heated surface corresponding to the ribbed wall by 5–21% and 4–24% respectively, and weaken the effect of Coriolis force on the heat transfer of the first pass. With the increase of rotation number, the friction penalty and heat transfer of leading side ribbed wall decrease, while the heat transfer of trailing side ribbed wall slightly increases, showing that those high-performance wavy ribs have a good versatility at multiple rotation numbers.

Numerical predictions on heat transfer and flow characteristics in a straight channel with different geometric parameters wavy ribs

A wavy rib is presented and its influences on the performance of a non-rotating straight channel are studied numerically. For each geometric parameter of wavy rib, the target surfaces are determined and the corresponding performance parameters are evaluated, to explore how wavy ribs affect channel heat transfer, especially the ribbed wall. Rib height (he = e − 3e), rib round radius (r = 0–5 mm), and rib angle (α = 20–55°) are the three key geometric parameters to study. The investigated Reynolds number is 25,000 and the channel aspect ratio is 1:1. The results indicate that three geometric parameters affect the channel performance by altering the diversion and obstruction of wavy ribs on cooling air. Among them, rib height is a dominant geometric parameter that determines the heat transfer improvement, while rib round radius and rib angle are mainly employed to reduce the friction loss. High rib height and large rib round radius, which can significantly increase heat transfer area and effectively decrease friction loss, respectively, are the basic features of high-performance wavy ribs. Meanwhile, the wavy ribs after optimal design perform better than 45° V-shaped ribs in heat transfer enhancement at the same friction penalty.

The Numerical Simulation for the Heat Transfer Enhancement Experiments of the HCCB-TBM First Wall

The first wall (FW) of helium gas-cooled ceramic breeder test blanket module for ITER need bears the loads like high-power density heat flux from plasma, nuclear heat from neutron deposition on the structure, and the transient high heat loads like plasma disruption. To enhance the helium gas cooling efficiency and security in FW, heat transfer enhancement technology should be used to improve and optimize the design scheme of helium flow channel for meeting the functional requirements of FW. Based on this objective, the filling–evacuating high-pressure helium-cooled loop (HPHCL) was built to test and prove the heat transfer enhancement schemes of helium gas cooling FW. In this paper, the design scheme of the filling–evacuating HPHCL was presented, and the key issues of engineering manufacture and the test cases are calculated and analyzed. Numerical simulation results are compared to acquire optimizational heat transfer enhancement schemes like placing transversal ribs and V-shaped ribs in the flow channel of front wall of FW. The helium gas turbulence intensity and the heat transfer area are improved through optimizing the distance and angle between V-shaped ribs and other coefficients to enhance heat transfer. The calculation results are used as reference for the verification experiments, which the 8–10-MPa high pressure helium gas will be selected as coolant.

리브가 있는 확대 사각 채널에서 국부 열전달

The local heat transfer of developed turbulent flows in the stationary ribbed divergent rectangular channels has been experimentally checked out. The rectangular divergent channels with the outlet hydraulic diameter(Dho) to inlet hydraulic diameter(Dhi) ratio of 1.49 have one-sided ribbed wall or two-sided ribbed walls, at which the ribbed walls with the flow attack angle of 60o are manufactured with a fixed rib height(e)=10 mm and the ratio of rib spacing(P) to rib height(e)=10. The measurements of heat transfer for V-shaped continuous ribs(case A), parallel broken ribs(case B), and V-shaped broken ribs(case C) have been conducted within the range of Re from 22,000 to 72,000.BR The comparison indicates that among the three different rib arrangements of case A, case B, and case C with two ribbed walls, the case A has the greatest Nusselt number, at which case A and case C produce 158% and 122 higher than case B at Re of 54,000.

Thermal performance of angled, V-shaped and leaning-V-shaped ribs in a rotating rectangular channel with 45° orientation

PurposeThe fluid flow in a rotating channel is obviously different from that in a stationary channel due to the existence of Coriolis force, which, in turn, enhances the heat transfer on the trailing side and reduces the heat transfer on the leading side. The purpose of this paper is to study various rib configurations combined with channel orientation on heat transfer and frictional loss in a rotating channel.Design/methodology/approachIn the present study, the k-ω SST model was used as the turbulence model. The fluid flow direction in the channel is radially outward. The angle between the rotation axis and leading side is 45°. The channel aspect ratio (W/H) is 2, the blockage ratio (e/Dn ) is 0.1 and the pitch ratio (P/e) is 10. The Reynolds number is fixed at 10,000 and the rotation number varies from 0 to 0.7. Angled ribs, reversed angled ribs, standard V-shaped ribs and outer-leaning V-shaped ribs, are examined.FindingsIt is found that the reversed angled rib configuration and the outer-leaning V-shaped rib configuration display better heat transfer performance than the V-shaped ribs in rotating condition, which is in contrast to stationary condition. At the leading side, the reversed angled rib and the outer-leaning V-shaped rib show better performance in recovering the heat transfer recession due to the negative effects of the Coriolis force.Research limitations/implicationsIn the present study, the fluid is incompressible with constant thermophysical properties and the flow is steady.Practical implicationsThe results of this study will be helpful in design of ribbed channels internal cooling for turbine blade.Originality/valueThe results imply that the rib configuration combined with channel orientation significantly impacts the heat transfer performance in a rotating channel. The reversed angled rib and the outer-leaning V-shaped rib show better heat transfer performance than standard V-shaped ribs, especially at high Rotating numbers, which is in contrast to stationary condition. The outer-leaning V-shaped rib has a relatively good heat transfer uniformity along the widthwise direction.

Effects of continuous wavy ribs on heat transfer and cooling air flow in a square single-pass channel of turbine blade

A wavy rib with the simple structure is proposed for the internal cooling channel in turbine blade, in order to enhance heat transfer and reduce pressure loss. The heat transfer performance and flow characteristics of a single-pass, stationary channel with wavy ribs are studied by numerical method. The channel width is 12.7 mm, with an aspect ratio of 1. Four major geometric parameters of wavy rib, including rib height (he = e−3e), rib round radius (r = 0–5 mm), rib angle (α = 20–55°) and rib thickness (th = 0.5e−2e) are investigated in optimal design. Furthermore, the potential high-performance wavy ribs are explored as well. The investigated Reynolds number is 10,000–40,000. Meanwhile, the typical 45° V-shaped ribs which have high heat transfer improvement are selected as the reference scheme of wavy rib. Both the rib height (e) and rib width are 1.58 mm, and the rib pitch P/e is 10. From the results, flow behavior of cooling air is presented, then heat transfer performance and thermal performance of channel walls, including ribbed walls and side walls, are analyzed. The results show that the rib height, rib round radius and rib angle have great impact on heat transfer and flow of channel, while the influence of rib thickness is relatively small. Heat transfer performance and pressure penalty are positively correlated with rib height and rib angle, while negatively correlated with rib round radius. As a result, wavy ribs with high rib height and large rib round radius perform better in increasing heat transfer and decreasing pressure drop. The diversion effect of wavy ribs on cooling air is responsible for friction penalty reduction. Due to the advantages of saving space and reducing pressure loss, small rib angle is beneficial to improve the performance of wavy ribs as well. In comparison with 45° V-shaped ribs, high-performance wavy ribs induce that ribbed wall Nu/Nu0 and ribbed wall area improve by 7–37% and 28–52%, respectively, without friction loss increasing. It is indicated that the wavy rib appears to be an effective method of heat transfer improvement in internal cooling channels.

Computational fluid dynamics analysis of a V-rib with gap roughened solar air heater

A CFD analysis of a solar air heater has been carried out using V-shaped ribs as artificial roughness on the absorber plate. The relative roughness pitch, P/e = 6-12, Reynolds number of 3800-18000, relative roughness height, e/D = = 0.042, and angle of attack, ? = 30?-75?, have been selected as design variables of V-shaped rib for analysis. The ANSYS FLUENT 15.0 with renormalization group k-? turbulence model is selected for the analysis of computational domain of solar air heater. The enhancement of Nusselt number and friction factor with Reynolds number for different values of a relative roughness pitch are presented and discussed by CFD analysis. The effect of angle of attack and Reynolds number on enhancement of Nusselt number and friction factor is also presented. The optimum value of rib configuration based on constant pumping power requirement has been derived using thermohydraulic performance parameter and has been found maximum at angle of attack of 60? and P/e = 10.

Heat transfer and pressure drop measurements in channels roughened by variously shaped ribs on one wall

ABSTRACTHeat transfer and pressure drop measurements were conducted to study the thermal-hydraulics in a square, round-edged channel roughened by ribs (e/Dh = 0.0638, p/e = 10) on one wall at Reynolds numbers ranging from 5.0 × 104 to 2.5 × 105. Three variously shaped ribs were investigated: Transverse ribs with square cross sections, transverse ribs, and upstream directed 60° V-shaped ribs with round-edged rib front and rear surfaces. Friction factors, Nusselt number ratios, roughness functions, and the thermal performance were presented. The highest heat transfer and best thermal performance is reached by the upstream directed V-shaped ribs.

Detached eddy simulation of turbulent flow and heat transfer in cooling channels roughened by variously shaped ribs on one wall

Delayed Detached Eddy Simulations with the k-ω-SST turbulence model were conducted for 8.0 MPa pressurized helium-gas flow in cooling channels with rib arrays on one wall at a Reynolds number of Re = 1.05 × 105. Turbulent flow and heat transfer were determined for arrays of eight variously configured V-shaped and transverse ribs. The relative roughness was e/Dh = 0.0638 and 0.0652 and the rib pitch was p/e = 10. The results showed that for ribs not extended over the total channel width, form drag was reduced and flow stagnation regions with a low heat transfer at the rib corners on the sides disappeared, whereas heat transfer by forced convection increased. Compared to smooth channel flows, the Nusselt numbers were increased by a factor of 1.6–1.8 and 2.2–2.5 for the transverse and V-shaped ribs, respectively. The corresponding friction factors were enhanced by a factor of 2.4–2.9 and 2.8–3.7, respectively. Evaluation of the thermal performance of structured cooling channels in comparison with smooth cooling channels revealed that thermal performance was best for the upstream directed 60° V-shaped ribs. The results showed that secondary flow motion induced by a V-shaped rib configuration caused an outward convective fluid transport within the recirculation region behind the rib. Vortical structures associated with local heat transfer deterioration behind the rib could be eliminated by appropriate designs of rib cross sections. Both lateral convective fluid transport and the elimination of vortical structures deteriorating heat transfer were found to lead to a significant heat transfer enhancement in the leeward rib region for the V-shaped ribs with modified cross section.

Effect of V-shaped Ribs on Internal Cooling of Gas Turbine Blades

Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperature. The rotor inlet temperatures in most gas turbines are far higher than the melting point of the blade material. Hence the turbine blades need to be cooled. In this work, simulations were carried out with the leading edge of gas turbine blade being internally cooled by coolant passages with V-shaped ribs at angles of 30°, 45° or 60° and at three aspect ratios (1:1, 1:2 and 2:3). The trailing edge of the blade was cooled by cylindrical and triangular pin-fin perforations in staggered and inline arrangements. Numerical analyses were carried out for each configuration of the cooling passages. The best cooling passages for leading edge and trailing edge were deduced by comparing the results of these analyses. It was found that using V-shaped ribs and fins induces a swirling flow, which in turn increases the velocity gradient and hence produces an improvement in heat transfer. The results show that under real time flow conditions, the application of V-shaped ribs and pin-fin perforations is a very promising technique for improving blade life.

Experimental and numerical investigation of heat transfer inside two-pass rib roughened duct (AR = 1:2) under rotating and stationary conditions

Heat transfer enhancement inside ribbed channels for turbine blades is a critical phenomenon that impacts overall performance and life of the gas turbine. Present study investigates heat and fluid flow in a rectangular duct with heat transfer enhancement features, under rotating and stationary conditions. The heat transfer data obtained experimentally has been explained using numerical prediction of flow features. Detailed heat transfer coefficients have been measured on the walls of two-pass rectangular duct (AR=1:2) featuring V-shaped rib turbulators, using transient liquid crystal thermography (TLCT). The first pass and second pass featured nine V-shaped ribs each and the bend featured a 90° rib connecting the blade tip underside and the two-pass divider wall. The flow in the first pass was developing in nature. The rib-pitch to rib-height ratio (p/e) was 9.625 and the rib-height to channel hydraulic diameter (e/dh) was 0.125. The baseline case for the rib roughened duct was geometrically identical smooth duct (with no heat transfer enhancement features). Stationary experiments were carried out for Reynolds numbers ranging from 25000 to 75000. The rotation experiments were carried out at 400RPM (Ro=0.036) and 700RPM (Ro=0.063), at Reynolds number of 25000 (Ro=Ωdh/V,Re=Vdh/ν). Also, numerical simulations were performed for a similar test model under similar flow conditions, using realizable k-∊ turbulence model. Detailed discussion on rib induced secondary flows and rotational effects on heat transfer in smooth and rib roughened duct are presented in this paper using results obtained from detailed heat transfer measurements from experiments and fluid dynamics predictions from numerical simulations.

Large-eddy simulation of turbulent flow and structures in a square duct roughened with perpendicular and V-shaped ribs

In this paper, highly disturbed turbulent flows confined within a square duct with uniformly spaced V-shaped ribs mounted on one wall are investigated using large-eddy simulation (LES). Two V-shaped (60° and 45°) rib cases are studied in comparison with the perpendicular (90°) rib case. The LES results are validated against a set of water-channel measurement data newly acquired by the authors. The effects of different shaped ribs on turbulent flow are systematically studied in terms of the mean velocity field, turbulence statistics, and coherent structures. The results show that strong secondary flows in the pattern of a pair of large symmetrical streamwise-elongated vortices exist in all three rib cases. The impacts of rib geometry on turbulent coherent structures are investigated using vortex identifiers, temporal autocorrections, spatial two-point autocorrelations, and velocity spectra.

Thermal performance augmentation by rib-arrays for helium-gas cooled First Wall applications

Rib-roughening the helium-gas cooling channels in the plasma facing components of DEMO (First Wall, limiters or the divertor) enhances heat transfer and reduces structural material temperatures. In the present study the applicability of six different surface-attached rib-arrays and of two different detached rib-arrays was examined for increasing the thermal performance within the helium-gas First Wall cooling concept. The rib-arrays consisted of transversally oriented or upstream directed 60° (with respect to the centerline) V-shaped ribs with different rib cross section (square, trapezoid, 2mm radius round-edged front- and rear-rib-surface). Turbulent flow and heat transfer for 8MPa pressurized helium-gas with a helium mass flow rate of 0.049kg/s were computed by the Detached-Eddy-Simulation approach. A constant heat flux density of 0.75MW/m2 and 0.08MW/m2 was applied at the plasma-facing and breeding-blanket-facing First Wall structural surface respectively. The results showed that structuring the thermally highly loaded cooling channel surface with rib-arrays of 60° V-shaped ribs provides an efficient heat transfer and increases the cooling performance of the First Wall. The corresponding heat transfer coefficient was in the range from 7.1 to 7.5kW/m2K and from 7.6 to 8.1kW/m2K for the attached and detached V-shaped ribs respectively. Compared to smooth channel flows, only 14–16% of the pumping power is required to obtain an equivalent heat transfer performance or, from another point of view, the heat transfer coefficient can be increased by 168–172% for a constant pumping power.

Thermohydraulic performance of solar air heater with staggered multiple V-shaped ribs on the absorber plate

Fluid flow and heat transfer in a solar air heater roughened with staggered multiple V-shaped ribs on the absorber plate were investigated numerically. Three dimensional simulations were performed for different rib geometries with varying stagger distance; rib height, pitch, and attack angle; and Reynolds number. Staggered multiple V-shaped ribs provide better heat transfer than the corresponding inline arrangement, with maximum enhancement 26% and 18% for average Nusselt number and thermohydraulic performance factor, respectively. Streamwise primary vortex with inter-rib subsidiary vortex is still the basic flow structure for the staggered ribs, similar to the inline case. The gap flow induces two competing effects on heat transfer, enhancing heat transfer efficiency maximally at the optimum stagger distance. Maximum thermohydraulic performance factor for the staggered ribs was 2.43 in the range of parameters studied.

Effect of ribbed and smooth coolant cross-flow channel on film cooling

The influence of ribbed and unribbed coolant cross-flow channel on film cooling was investigated with the coolant supply being either a plenum-coolant feed or a coolant cross-flow feed. Validation experiments were conducted with comparison to numerical results using different RANS turbulence models showed that the RNG k–ε turbulence model and the RSM model gave closer predictions to the experimental data than the other RANS models. The results indicate that at a low blowing ratio of M=0.5, the coolant supply channel structure has little effect on the film cooling. However, at a high blowing ratio of M=1.0, the adiabatic wall film cooling effectiveness is significantly lower with the plenum feed than with the cross-flow feed, especially for the cases with ribs. The film cooling with the plenum model is better at M=0.5 than at M=1.0. The film cooling with the cross-flow model is better at a blowing ratio of M=0.5 in the near hole region, while further downstream, it is better at M=1.0. The results also show that the coolant cross-flow channel with V-shaped ribs has the best adiabatic film cooling effectiveness.

Effect of various rib arrangements on heat transfer in a semicylinder channel with effusion flow

ABSTRACTThe flow and heat transfer characteristics of various rib configurations on a concave channel surface with effusion holes were investigated. A semicylindrical channel with three rows of effusion holes was used to simplify the blade leading edge and eight kinds of ribs were attached on the internal concave surface for comparison. Continuous and broken ribs were both applied at 90°, as were upstream-pointed V-shaped and downstream-pointed V-shaped ribs. The Reynolds-averaged Navier–Stokes equation was solved using commercial software. The result included the divided-area-averaged and local Nusselt number distribution; the overall average Nusselt number on the concave surface is also discussed.