Ribbed Channel Research Articles

Flow and heat transfer in rotating smooth and ribbed multi-channel double-wall structure with multiple-jet impingement cooling

In this study, the heat transfer of multiple-jet impingement in rotating smooth and ribbed multichannel double-wall cooling structure with film extraction are investigated. The dimensionless jet-to-target spacing is 1, and the dimensionless jet-to-jet spacing is 3.55. In ribbed channel, the rib height is 1 mm and rib spacing is 8 mm. The experimental jet Reynolds number ranges from 2000 to 8000, and the maximum jet rotation number is 0.22. The test section contains five impingement channels. The local average convective heat transfer coefficient is measured by the “copper plate method”. The SST k-ω model is used to study the effect of rotation on the flow in channels. The results show that the heat transfer gap between high and low radius is more evident with an increase of the Roj. This is because the rotation effect increases and decreases the mass flow rate at high and low radius, respectively. Moreover, rotation can strengthen the impingement effect of the trailing side (TS) while weakening the effect of the leading side (LS) when the Roj is less than 0.06, Which causes differences in the heat transfer between the LS and TS of the impingement channel. Furthermore, affected by the ribs, the average heat transfer of ribbed target surface is improved. The area of high heat transfer region generated by impingement decreases, and an inverted butterfly-shaped high heat transfer region is generated near the film hole. Finally, the rib weakens the effect of rotation on the flow of target surface to some extent.

Large Eddy Simulation of Flow and Heat Transfer in a Ribbed Channel for the Internal Cooling Passage of a Gas Turbine Blade: A Review

Herein, 50 articles published over the past 20 years on using large eddy simulation (LES) for the internal cooling passage of a gas turbine, especially the mid-chord ribbed channel, are reviewed for the first time. First, the numerical challenges of performing LES on a ribbed channel and experimental verification are summarized. Next, LES data and the major engineering findings that are difficult to obtain experimentally or using Reynolds-averaged Navier–Stokes simulation (RANS) are covered, and heat transfer on and inside the rib, and the effects of rotation and buoyancy are discussed. Next, recent LES studies related to the shape of the ribbed channel are reviewed, and finally, the contribution of using LES for research on the internal cooling of gas turbines in the future, including those with ribbed channels, is anticipated.

Effect of the number of ribbed walls on the thermal performance in rectangular channels with 45-deg parallel or criss-cross ribs

Regionally averaged heat transfer distributions and friction characteristics are experimentally investigated for fully developed, turbulent flow in a rectangular channel with a width-to-height aspect ratio (AR=3). 45-deg angled rib turbulators are placed on one, two, and four sides of the channel in parallel and criss-cross configurations with a pitch-to-height ratio(P/e=10) and a rib blockage ratio(eDh=4.1%). For a roughness Reynolds number range(e+=25−500), results show that increasing the number of ribbed walls improves the overall channel heat transfer for the 45-deg parallel ribs. Results reveal that four-sided ribbed channels provided the greatest thermal performance followed by the two-sided and one-sided ribbed channels, respectively, for both angled rib designs. On the basis of the law of wall similarity, friction and heat transfer roughness functions are derived using the four-sided data reported in this work. Furthmore, friction factors and heat transfer coefficients of similar angled rib designs were obtained from open literature and similarly correlated to derive more robust friction and heat transfer correlations over the roughness Reynolds number range. Thermal designers can use these proposed correlations to predict friction and heat transfer in rectangular cooling channels (AR=1-5) with various numbers of ribbed walls. The measured friction factor and heat transfer coefficient of this study can be predicted using these semi-empirical correlations with maximum errors of 9% and 7%, respectively.

Numerical and experimental study of the influence of extended surfaces in rectangular channel subjected to constant heat flux

ABSTRACT The current paper reports the impact of variation of ribs’ pitch distance in the case of laminar flow and forced convection heat transfer upon flow characteristics in a rectangular channel experimentally and numerically. The thermal behavior of the ribbed channel with water as a working fluid was measured experimentally and compared to numerical simulations performed using Galerkin finite element method under the same operating and boundary conditions. Numerical analysis has been extended to investigate the entire ribbed channel with the presence of nano-particles in the base fluid to predict the performance of the heat transfer process with interaction with extended geometries. The analysis was done keeping heat flux constant at the bottom boundary condition. The impacts of the rib pitch-to-height ratio (p/e = 2.5, 3.125, 3.75, 4.375, and 5), nano-particle volume concentration (0% ≤ φ ≤ 4%), also Reynolds numbers (427.44 to 1282. 9), were all examined in the present study. The results show a good coincidence between the numerical and experimental study with a maximum deviation was nearly 3%. The main findings show that when the nano-fluid volume fraction increases from 0% to 4%, the average Nusselt number for all aspect ratios increases too. Meanwhile, the average skin friction decreases as the Reynolds number increase for different values of AR. Furthermore, the results revealed that the water – aluminum oxide nano-fluid with the concentration φ = 0.04 aid to improve the coefficient of heat transfer by 5% higher than the case of φ = 0.02, and up to 9.4% compared to pure water (φ = 0) due to an increase in viscosity. Finally, the current work shows that these extended surfaces with the use of nano-fluids can remarkably improve heat transfer properties with barely increased friction, making them suitable candidates for the development of efficient heat exchanger devices.

Flow and heat transfer for the mist/steam two-phase flow in the U-shaped channel with column-row-ribs and solid ribs

The comparison of flow field and heat transfer characteristics for the new mist/steam working fluid inside the U-shaped internal cooling channel of the gas turbine blades roughed with new V-45 deg. Column-Row-Ribs and V-45 deg. solid ribs are conducted under the limited working conditions in this work. First, the secondary flow vortex and droplets distribution in channels with different turbulators were analyzed. Then, qualitative heat transfer comparison of these two different ribbed channels was conducted. Furthermore, the quantitative analysis of heat transfer enhancement and heat transfer uniformity was presented under the condition of different mist/steam mass ratio (mist/steam) and droplets diameter (D0). Through the analysis, it is seen that the Mainstream Secondary Flow Vortexes in U-shaped channel roughed with 45° V-shaped Column-Row-Ribs has the similar structure as the channel with 45° V-shaped solid ribs. The droplets have a more even distribution in U-shaped channel roughed with 45° V-shaped Column-Row-Ribs than channel with 45° V-shaped solid ribs. And the new Column-Row-Ribs will help to solve the problem that the droplets deposit at the windward side of the solid ribbed channel, which benefits to promote the heat transfer evenness of the heated wall. The results proved that the U-shaped channel with 45° V-shaped Column-Row-Ribs cooled with the mist-steam coolant has better heat transfer characteristics than the 45° V-shaped solid ribs. For the U-shaped channel, there exists a best droplet diameter which can achieve the highest heat transfer enhancement.

Enhanced heat transfer of supercritical n-decane in cooling channels with triangular ribs for regenerative cooling

• A continuous ribbed channel is designed to enhance the cooling capacity. • The channel can provide up to 2.04 times superior heat transfer performance. • The insertion of ribs enhances the uniformity of buoyancy distribution. • The triangular rib channel improves axial temperature uniformity. • The mechanism of generating vortices in the slot is analysed. Regenerative cooling is regarded as an effective method for managing the heat of scramjet combustors, and the design of cooling channels is critical for removing more heat from the engine. A continuous triangular rib channel was proposed. The effects of rib position, height, and pitch on the heat transfer performance were investigated using Fluent 18.0. The SST k –ω turbulence model was used to study the thermal behaviour of supercritical n-decane in channels and showed good agreement with the experimental data. Results show that the insertion of triangular ribs at the bottom and top can reduce the bottom wall temperature by 243.8 K in the studied case. The triangular rib channel can provide up to 2.04 times superior heat transfer performance. The continuous triangular ribs significantly reduced axial temperature inhomogeneity. Local streamlines were studied to demonstrate the influence of rib parameters on the flow and heat transfer processes. A local heat transfer enhancement occurs when the rib has a large inclination. For the studied conditions, the generation of vortices was carefully evaluated, and it was found that the generation of vortices in the slot was related to the value of h / p .

Performance enhancement of a novel serpentine channel cooled plate used for cooling of Li-ion battery module

One of the most significant challenges of battery thermal management system is manifested in maintaining optimal battery performance by keeping the overall battery temperature within a narrow temperature range. The present work aimed to study a novel design of ribbed serpentine channel cooled plate (SCCP) as an effective cooling module of Li-ion battery. The study included a numerical simulation of the effect of the rib orientation (90 ͦ, 75 ͦ, 60 ͦ, and 45 ͦ) and the rib shape (semi-circular, trapezoidal, and triangular) on the hydrothermal performance of SCCP. The study was conducted under laminar flow conditions for a Reynolds number range (200–1000) and battery cell discharge rate range (1C–2C). The numerical simulation results were validated against experimental measurements of the performance of a SCCP with semi-circular ribs that rotated by 90 ͦ. The validation showed a good agreement with a maximum deviation of 8% and 11% for the Nusselt number and the friction factor, respectively. The results of the study indicated that the ribs play a vital role in improving the heat transfer. It is found that the rib orientation was more effective than the rib shape in enhancing the hydrothermal performance improvement factor. In addition, the triangular rib with 45 ͦ orientation showed highest performance improvement factor compared with the other SCCP designs with a value of 1.3.

Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel: Reynolds Number Effect

Large eddy simulations were performed for the conjugate heat transfer in a ribbed channel with a geometry, that mimics the internal cooling passage of a gas turbine, using 566, 100, 10, and 1 as the solid and fluid thermal conductivity ratios (K*) and 30,000, 7000 (turbulent flow), and 1000 (laminar flow) as the Reynolds numbers. A fully coupled simulation was conducted using the immersed boundary method (IBM) and a dynamic sub-grid-scale (SGS) model. In pure convection, a decrease in the Reynolds number from 30,000 to 7000 increased the heat transfer on the channel wall by 5% but decreased that on the rib by 20%. When K* > 10, the Reynolds number effect is stronger in the rib than in the wall. In the laminar flow, the effect of conduction appears at a low K*, and the heat transfer promotion is poor in the typical ribbed channel geometry. In the turbulent flow, if K* ≥ 100, then a heat transfer promotion is expected in the ribbed channel even at a low Reynolds number. For K* < 10, the thermal performance in the turbulent flow is worse than that in the laminar flow, and thus, no rib effect is expected.

Two-phase simulation of the generated entropy for the nanofluid flow inside a ribbed passage for cooling of a PV cell

• Introduce a new ribbed channel configuration with nanofluid for PV cooling. • The triangular-shaped rib demonstrates better performance. • Using the nanofluid reduces the thermal entropy generation about 65.1% • The overall irreversibility descends with nanofluid by increasing Reynolds number. Current work deals with the generated entropy of alumina–water nanofluid in a ribbed passage to cool the photovoltaic (PV) cell. The two-phase mixture approach is employed to model the nanofluid within a ribbed channel with discrete V-form and staggered rib roughness. The nanofluid is analysed at a concentration of 1%, and the outcomes are compared to pure water. This study focuses on the influences of the cross-section shape of the ribs. Four different shapes of the rib cross-section, including circular, elliptical, square, and triangular-shaped, are investigated in this paper. The results indicated that using the nanofluid rather than water considerably reduces the thermally generated entropy such that the highest reduction in this parameter is about 65.1%. Employing the ribbed channel demonstrates smaller thermal entropy by generating six intense cross-flows. The highest reduction in the thermally generated entropy rate is around 72.9% when the triangular-shaped rib is used. Besides, the positive influence of the nanofluid is about 2.3 times higher when the ribbed channel is utilised. The triangular-shaped rib demonstrates better performance and considerably contributes to the lower thermal irreversibility. The overall irreversibility descends when the nanofluid is used and by an increase of Reynolds number.

Heat fluxes distribution and uncertainty in low-Reynolds flow regimes inside a ribbed channel

Experimental studies on the local convective heat transfer enhancement induced by ribs in channels are generally carried out in steady state, by imposing a known heat flux on the ribbed surface and subsequently retrieving the convective heat flux by means of a local heat balance, i.e. by subtracting all the non-convective heat fluxes from the source term. Such heat fluxes are retrieved from temperature measurements by means of models, whose complexity can range from simple algebraic expressions to complex simulations. In this context, an experimental technique based on FEM simulations, a radiative model for semi-transparent enclosures, and a filtering technique to retrieve the heat fluxes across the plane of the heated surface has been developed and tested in a 1:10 AR channel, for Reynolds number ranging from 650 to 7500 and a flow of air. This paper presents a discussion on the heat flux distribution as a function of the Reynolds number for a streamwise-pointing chevron (V) rib configuration with 60° angle of attack, with P/e = 20, showing the increasing weight of non-convective heat dissipations as the Reynolds number decreases, and their effect on the uncertainty of the Nusselt number measurement.

Combined effects of bleed hole extraction and rotation on internal heat transfer in a ribbed two-pass channel

Serpentine passages arranged with ribs, are commonly used to guide the cooling air and remove heat transferred from hot gas. In this study, the effects of bleed hole extraction on internal heat transfer of ribbed channel are numerically studied in a rotating frame. Three positions of bleed hole are studied as rotation number ranges from 0 to 0.2. The flow structure and heat transfer features are depicted and evaluated through qualitative and quantitative analysis. Numerical results reveal that heat transfer distribution features are quite different for channel with bleed holes at different locations. The allocation of bleed hole extraction flowrate varies distinctively under rotating condition. Rotation is responsible for affecting the flow reattachment and corresponding secondary vortex structures, and consequently heat transfer features. Channels rotated in clockwise and counter-clockwise direction share opposite Coriolis force acting direction, thus effects of heat transfer augmentation are different. The effects of bleed hole position on local heat transfer are more pronounced on the endwall opposite to the endwall where the Coriolis force acts. Channel with bleed holes at upstream position shows the poorest heat transfer enhancement at inter-rib regions, with maximum reduction by 11.4% under stationary condition and 13.2% under rotating condition.

Measurements of Turbulent Transport in a Square Channel With One Ribbed Wall

Abstract The velocity field of the fully developed turbulent flow in a one-sided ribbed square channel (rib-height-to-channel-height ratio of k/h=0.0667 and rib-pitch-to-rib-height ratio of p/k=9) was measured at Reynolds numbers (based on the channel height h and the mean bulk velocity uB) of Reh=5.0×104 and 1.0×105 by means of laser Doppler anemometry (LDA). Triple velocity correlations differed slightly between both Reynolds numbers when normalized by the bulk velocity and the channel height, similarly to the first- and second-order statistical moments of the velocity. Their near-wall behavior reflected the crucial role of turbulent transport near the rib crest and within the separated shear layer. Sweep events occurred with the elongated flow structures of the flapping shear layer and gained in importance toward the channel bottom wall, while strong ejection events near the rib leading and trailing edges coincided with flow structures bursting away from the wall. Despite the predominant occurrence of sweep events close to the ribbed wall within the inter-rib spacing, ejection events contributed with higher intensity to the Reynolds shear stress. Ejection and sweep events and their underlying transport phenomena contributing to the Reynolds shear stress were almost Reynolds number-insensitive in the resolved flow range. The invariance to the Reynolds number can be of benefit for the use of scale-resolving simulation methods in the design process of rib structures for heat exchange applications.

Effects of a high Reynolds number and rotation on the leading-edge heat transfer of a ribbed cooling channel with a cross-section consisting of a semicircle and a rectangle

Owing to the recent increase in the demand for gas turbines with increased thrust, efficiency, and performances, the optimization of the heat transfer performance is necessary. In this study, the heat transfer performance in a combined-shaped cooling channel with angled ribs was investigated experimentally. The channel cross-section (Dh = 18.23 mm) was composed of a semicircle and a rectangle, which is appropriate for simulating a turbine blade leading-edge. The rib angle was 60° and staggered, and it was placed on the trailing and leading surfaces with a pitch-to-height ratio (P/e) of 10.0. The effects of the Reynolds number and rotation were studied. The Reynolds number varied from 18000 to 63000, and the rotation number ranged from 0 to 0.8. The results revealed that in the non-rotating ribbed channel, the Nu/Nu0 ratio along the streamwise direction first increased and then decreased slightly after a peak, followed by an increase. The Nu/Nu0 ratio reached a maximum of 6.4 in the rotating channel, and was greater than that in the non-rotating channel by a factor of 1.79. It was found that owing to the rib–rotation interaction, the Nu/Nus ratio exhibited different trends with an increase in Ro at different measurement points with small and large radii. The findings can serve as the basis for the development of high-performance gas turbines with increased thrust and efficiency.

The Effect of Single-Sided Ribs on Heat Transfer and Pressure Drop Within a Trailing Edge Internal Channel of a Gas Turbine Blade

Abstract Convective cooling in a gas turbine blade internal trailing edge channel is often insufficient at the sharp trailing edge. This study examines convective heat transfer and pressure drop within a simplified nonrotating trailing edge channel. The internal passage has been modeled as a right triangular channel with a 9 deg angle sharp corner. A copper plate was heated from underneath via a uniform heat flux heater and examined via infrared thermography for two cases: smooth wall and single-sided ribbed wall. Nonuniformity in the heat flux due to conduction is corrected by a Reynolds-averaged Navier–Stokes (RANS) conjugate heat transfer calculation, which was validated by the mean velocity, friction factor, and temperature fields from experiments and large eddy simulation (LES). Nusselt number distributions illustrate that surface heat transfer is increased considerably with ribs and coupled with the vortices in the flow. Heat transfer at the sharp corner is increased by more than twofold due to ribs placed at the center of the channel due to secondary flow. The present single-sided ribbed channel utilizes secondary flow toward the corner and is presumed to have better thermal performance than a dual-sided ribbed channel. Thus, it is important to set the appropriate rib length within the channel.

Thermal Boundary Effect on the Heat Transfer Performance of a Ribbed Cooling Channel with Intersecting Ribs

Thermal Boundary Effect on the Heat Transfer Performance of a Ribbed Cooling Channel with Intersecting Ribs

Heat transfer enhancement by sinusoidal wavy tape insert in two-pass ribbed channels

The turbine inlet temperature is one of the most critical parameter that determines the thermal efficiency and thrust-weight ratio of the gas turbine. However, the higher gas turbine inlet temperature significantly increases the thermal stress on the blade, which necessitates effective cooling strategy to reduce the blade temperature. In this study, a united blade cooling strategy was developed by adopting a two-pass ribbed cooling channel with wavy tape for the reason that ribs are near-wall turbulence promoters while the wavy tape is core-region promoter with relatively lower pressure-drop penalty. Ribs and wavy tape may complement each other in the cooling channel. The synergistic effect of the combined near-wall and core-region heat transfer promoter was numerically studied for Reynolds numbers from 6000 to 30000. Two key geometrical factors, namely rib to wave crest phase shift and relative wave amplitude, have significant effect on the thermal performance. The results demonstrate that wavy tape with different phase shift configurations can eliminate the lower heat transfer areas and produce more uniform heat transfer. The 0? phase shift achieved best overall thermal performance, which provided 1.07-1.08 times the flat tape heat transfer enhancement with 1.09-1.11 times the pressure drop penalty. The better heat performance is due to the secondary flow induced by wavy tape, which enhances the fluid mixing between near-wall and core-region.

Entropy generation investigation of nanofluid flow in the ribbed rectangular channel under magnetic field

Entropy generation investigation of nanofluid flow in the ribbed rectangular channel under magnetic field

LDA measurements in a one-sided ribbed square channel at Reynolds numbers of 50,000 and 100,000

Laser Doppler anemometry (LDA) measurements in the fully developed turbulent flow through a one-sided rib-roughened square channel with a rib-height-to-channel-height ratio of k/H = 0.0667 and a rib-pitch-to-rib-height ratio of p/k = 9 were carried out at Reynolds numbers (based on the channel height H and the mean bulk velocity u_B) of {Re}_H = 5.0 cdot 10^4 and 1.0 cdot 10^5. Mean velocities, Reynolds normal, and shear stresses were determined. The first- and second-order statistical moments of the velocity differed slightly between both Reynolds numbers when normalized by the bulk velocity and the channel height. Deviations were attributed to a minor elongation increase in the large recirculation region behind the rib with increasing Reynolds numbers. The crucial role of turbulent diffusion was reflected in the non-coincidence of the maximum primary mean shear and the Reynolds normal stress as well as outward drifts of the Reynolds stress peaks along the rib crest. Turbulent diffusion contributed significantly to the turbulence kinetic energy (TKE) budget near the rib crest and within the separated shear layer, while mean convection made a remarkable contribution only at the rib leading edge. The detailed first- and second-order moments provide a basis for the validation of computational methods and turbulence models.Graphic abstract

Thermal analysis of interaction between buoyancy induced flow under parallel rotation and rib induced vortices: Experimental and numerical study

This paper performing both experimental and numerical approaches underlines the aiding and opposing effects of secondary vortices resulting from parallel mode rotation on convective heat transfer coefficient in a rectangular channel in smooth and rib roughened channels. The Nusselt number is obtained by measuring the wall and fluid temperature at the Reynolds number ranging from 5118 to 10,677 and 0.07<Δρ/ρ<0.42. In addition, the Nusselt number is investigated in ribbed channels with one wall being perpendicularly ribbed at pitch ratio (P/e) and blockage ratio (e/Dh) equal to 15 and 0.088, respectively. Numerical simulations also allow to consider the effects of rotational induced secondary flows caused by centrifugal and the Coriolis forces in high rotation numbers (0<Ro<0.56) and Buoyancy numbers (0<Buo<1). The numerical results with non Boussinesq approximation for density variation show good agreement with experimental results, while it is revealed that the Nusselt number is underestimated if Boussinesq approximation is used. As the Reynolds number increases, the larger Buoyancy number is required to affect the Nusselt number. That is, under certain conditions which is expressed in terms of GrΩα/Re the rotational buoyancy effects may be negligible and the Nusselt number is equal to stationary case. However, in rib roughened channels the rotational buoyancy causes the reattachment point to occur closer to upstream rib while physical presence of ribs reduce the enhancing effects of rotation. Thus, for practical use in rotating cooling systems such as turbo-generators or electrical machinery, rib roughened channels are not recommended.

Numerical analysis and optimization on flow and heat transfer performance of a steam-cooled ribbed channel

It aims to enhance the heat transfer performance and reduce the pressure loss of the steam-cooled ribbed channels in the gas turbine blades. Numerical calculations were performed to analyze the flow and heat transfer characteristics in the steam-cooled ribbed channel for different inlet Reynolds number (10,000 ≦ Re ≦ 90,000), rib angle (30° ≦ α ≦ 90°), rib height ratio (0.05 ≦ e/D ≦ 0.15) and rib pitch ratio (0.5 ≦ P/D ≦ 1.5). The flow and heat transfer analysis, response surface analysis, significance analysis and parameter optimization were performed by using the Response Surface Methodology. The results show that the variations of Re, α, e/D and P/D change the size, shape and swirling strength of the secondary flows in different extent, leading to the change of flow and heat transfer characteristics in the steam-cooled ribbed channel. Increasing Re and e/D, and decreasing P/D at the low-medium level of e/D obviously enhance the Nu/Nu0; Decreasing Re and e/D, and increasing P/D result in a reduction in the f/f0. An increment in α first increases and then decreases both the Nu/Nu0 and f/f0. Among the four influence parameters Re, α, e/D and P/D, Re is the most significant parameter affecting the Nu/Nu0, followed by e/D, α and P/D; e/D has the most significant influence on the f/f0, followed by α, Re and P/D. The multi-objective optimization for lower pressure drop and higher heat transfer is achieved at Re of 90,000, α of 41.5152, e/D of 0.1157 and P/D of 0.9747. Compared with the reference channel, the optimized channel has a 86.19% enhancement in heat transfer coefficient and a 38.32% improvement in comprehensive thermal coefficient, at the same Reynolds number (Re = 90,000).