Rib Arrangements Research Articles

Ontogeny and variability in ribbing of Late Valanginian lamellaptychi (Ammonitina)

Late Valanginian (Early Cretaceous) lamellaptychi of the genus Mortilletilamellaptychus were collected from seven ammonite-controlled sections in south-eastern France demonstrate distinct changes in ribbing during growth. Simpler juvenile ribbing, which is essentially uniform for all of the specimens studied, differs distinctly from the complicated arrangement of the adult ribs. Changes in ribbing morphology were observed in the five species studied, two of which were identified as new (i.e. Mortilletilamellaptychus heterocostatus sp. nov. and M. bicostatus sp. nov.).

Effects of rib arrangements on the flow pattern and heat transfer in an internally ribbed heat exchanger tube

A numerical simulation was carried out to investigate the effects of rib arrangements on the flow pattern and heat transfer in an internally ribbed heat exchanger tube. Details of the flow structures in the tube with parallel type ribs (P-type ribs) and V shape type ribs (V-type ribs) were presented and analyzed, respectively. The results reveal that rib arrangements have perceptible effects upon the flow pattern and heat transfer in the ribbed tube. The average Nusselt number and friction factor in the V-type ribbed tubes were about 57–76% and 86–94% higher than those in the P-type ribbed tube, respectively. The performance evaluation criterion (PEC) based on the same pumping power in the V-type ribbed tube varied from 1.32 to 1.74, which were about 27–41% higher than that in the P-type ribbed tube. To further understand the effects of rib arrangements on the heat transfer in the ribbed tube and reveal the essence of heat transfer enhancement, an analysis was also carried out from the point view of entransy dissipation extremum principle. The results demonstrate that the longitudinal swirl flow with multiple vortices induced in the V-type ribbed tube was a more effective flow pattern for heat transfer, compared to the longitudinal swirl flow with single vortex generated in the P-type ribbed tube.

CFD investigation on particle deposition in aligned and staggered ribbed duct air flows

This study investigated the effects of surface rib arrangements on particle deposition in two-dimensional ribbed duct air flows by CFD method. The turbulent duct air flows were simulated by Reynolds stress model (RSM) with UDF correction, and the particle motions were solved by discrete particle model (DPM). The surface ribs were arranged in aligned or staggered layouts. The air velocity profiles for both smooth and ribbed duct flows as well as the particle deposition velocity for smooth duct cases were all in good agreement with the relative literature data. The simulation results showed that the surface ribs with aligned arrangement have better performance on small particle deposition enhancement, compared with staggered surface ribs. Nevertheless, the large particle deposition rates are not enhanced obviously by both kinds of surface ribs. Considering the flow drag increase, the maximum particle deposition enhancement can reach 425 times for particles with 1 µm diameter. Finally, the mechanisms of particle deposition enhancement by aligned and staggered surface ribs were analyzed and discussed from the views of rib interception, deposition area increase, turbulent eddy capture and the flow passage width. Surface ribs with aligned arrangement are recommended to be applied in particle removal and air clean devices.

Shaping frequency response of a vibrating plate for passive and active control applications by simultaneous optimization of arrangement of additional masses and ribs. Part II: Optimization

It was shown in Part I that an ability to shape frequency response of a vibrating plate according to precisely defined demands has a very high practical potential. It can be used to improve acoustic radiation of the plate for required frequencies or enhance acoustic isolation of noise barriers and device casings. It can be used for both passive and active control. The proposed method is based on mounting several additional ribs and masses (passive and/or active) to the plate surface at locations followed from an optimisation process. In Part I a relevant model of such structure, as a function of arrangement of the additional elements was derived and validated. The model allows calculating natural frequencies and mode-shapes of the whole structure. The aim of this companion paper, Part II, is to present the second stage of the method. This is an optimization process that results in arrangement of the elements guaranteeing desired plate frequency response, and enhancement of controllability and observability measures. For that purpose appropriate cost functions, and constraints followed from technological feasibility are defined. Then, a memetic algorithm is employed to obtain a numerical solution with parameters of the arrangement. The optimization results are initially presented for simple cases to validate the method. Then, more complex scenarios are analysed with very special demands concerning the frequency response to present the full potential of the method. Subsequently, a laboratory experiment is presented and discussed. Finally, other areas of applications of the proposed method are shown and conclusions for future research are drawn.

Shaping frequency response of a vibrating plate for passive and active control applications by simultaneous optimization of arrangement of additional masses and ribs. Part I: Modeling

An ability to shape frequency response of a vibrating plate according to precisely defined demands has a very high practical potential. It can be applied to improve acoustic radiation of the plate for required frequencies or enhance acoustic isolation of noise barriers and device casings by using both passive and active control. The proposed method is based on mounting severaladditional ribs and masses (passive and/or active) to the plate surface at locations followed from an optimization process. This paper, Part I, concerns derivation of a mathematical model of the plate with attached elements in the function of their shape and placement. The model is validated by means of simulations and laboratory experiments, and compared with models known from the literature. This paper is followed by a companion paper, Part II, where the optimization process is described. It includes arrangement of passive elements as well as actuators and sensors to improve controllability and observability measures, if active control is concerned.

Multiphysics Simulation of the Bromine Cathode: Cell Architecture and Electrode Optimization

A central aim of flow battery research is to increase and improve the power density of the flow battery electrodes, thereby allowing smaller, more compact and less expensive equipment. This can be achieved by enhancing the catalytic activity of the cell, [1] or altering the redox couple the battery employs. [2, 3] One relatively overlooked option is to improve the electrode structure and layout of the battery itself. Because they are single-phase flow systems, interdigitated flow fields can be used without concern for flow maldistribution due to channel blockages. This work describes a broad set of parametric studies on the structural characteristics of the electrode required to accommodate the interdigitated flow field configuration. The model was implemented in COMSOL and accounted for convective Darcy flow through the porous electrode, ionic conduction within the pore space, diffusion from the bulk to the fiber surface, and electrochemical kinetics. The model was based on the hydrogen-bromine chemistry, specifically focusing on the bromine cathode half-cell. Constant pressure driven reactive flow through a fibrous electrode was applied for all cases, and the resulting performance was assessed as a function of engineering design parameters such as electrode thickness, length, porosity, fiber diameter, and fiber alignment. Adjusting these parameters lead to significant changes in permeability, species velocity, residence time, Reynold number, Sherwood number, and reactive surface area, which were all accounted for in the model. The attached figure shows a typical set of results for the effect of different fiber diameters at one specific porosity on the overall operation of the cell. The left panel shows overall polarization curves (top) and power curves (bottom), while the right panel demonstrates the effect of porosity and fiber diameter on the maximum obtainable power density for the cell. Preliminary models have shown that modifying the cell architecture can almost double the power density of the cell while the changes induced by tuning electrode characteristics can have similar effects. It was also found that the optimal set of electrode parameters depends on the specifics of the flow field rib and channel arrangement. Further modelling should reinforce what has previously been observed but will also allow for the determination of the optimal conditions to construct and operate the cell under. The information learned from this model will lead to the development of optimized electrode characteristics and cell architectures for flow battery applications. 1. Wu, T., et al., Hydrothermal ammoniated treatment of PAN-graphite felt for vanadium redox flow battery. Journal of Solid State Electrochemistry, 2012. 16(2): p. 579-585. 2. Huskinson, B.B.B., A metal-free organic-inorganic aqueous flow battery. Nature, 2014. 505(7482): p. 195-198. 3. Skyllas-Kazacos, M., et al., Recent advances with UNSW vanadium-based redox flow batteries. International Journal of Energy Research, 2010. 34(2): p. 182-189. Figure 1

Effects of rib spacing and height on particle deposition in ribbed duct air flows

In this study, the influences of rib spacing and height on particle deposition in ribbed duct air flows were numerically investigated. The turbulent air flow was resolved using the Reynolds stresses model (RSM) with turbulent fluctuation correction, while the particle phase was tracked by the discrete particle model (DPM). The ratios of rib spacing to rib height p/e were 2, 4, 6, 8 and 10 while the ratios of rib height to duct diameter e/D were 0.05, 0.1 and 0.2. The air flow velocity profiles for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct obtained in the simulation agree well with previous related study data. It is found that particle deposition velocity is significantly enhanced by the surface ribs for several orders of magnitude, especially for small particles (τp+<1). Particle deposition enhancement increases with the decreasing rib spacing, while no significant difference is found for different rib heights. The mechanisms of particle deposition enhancement were analyzed and discussed in relation to different rib spacings and heights. Moreover, an efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. The maximum efficiency ratio can reach about 1000 for small particles (τp+<1) and about 100 for large particles (τp+>1) when p/e = 2 and e/D = 0.1. Therefore, a reasonable arrangement of surface ribs is an efficient and effective choice for enhancing particle deposition, and could be adopted in air filtration devices.

Effects of rib size and arrangement on forced convective heat transfer in a solar air heater channel

The article presents an experimental investigation on turbulent heat transfer and friction loss behaviors of airflow through a constant heat-fluxed solar air heater channel fitted with rib turbulators. The experiment was conducted for the airflow rate in terms of Reynolds numbers based on the hydraulic diameter of the channel in a range of 5000–24,000. In the present work, a comparative study between square and thin ribs (90°-rib) with three rib arrangements, namely, one ribbed wall (or single rib), in-line and staggered ribs on two opposite walls was first introduced. The study shows a significant effect of the presence of the ribs on the heat transfer rate and friction loss over the smooth wall channel. The comparison made at a single rib pitch and height also revealed that the thin rib performs better than the corresponding square one. Among the three arrangements, the in-line rib array provides higher heat transfer and friction loss than the staggered and the single one. However, the staggered thin rib provides the highest thermal performance. With this reason, only the staggered thin ribs at four different relative heights (BR = 0.1, 0.2, 0.3 and 0.4) and three relative pitches (PR = 0.5, 0.75 and 1.33) are investigated further. It is found that the staggered rib at BR = 0.4 and PR = 0.5 yields the highest heat transfer and friction factor but the maximum thermal performance is at BR = 0.2 and PR = 0.75.

Experimental investigation of heat transfer and flow using V and broken V ribs within gas turbine blade cooling passage

Gas turbines are extensively used for aircraft propulsion, land-based power generation, and various industrial applications. With an increase in turbine rotor inlet temperatures, developments in innovative gas turbine cooling technology enhance the efficiency and power output; these advancements of turbine cooling have allowed engine designs to exceed normal material temperature limits. For internal cooling design, techniques for heat extraction from the surfaces exposed to hot stream of gas are based on an increase in the heat transfer areas and on the promotion of turbulence of the cooling flow. In this study, an improvement in performance is obtained by casting repeated continuous V- and broken V-shaped ribs on one side of the two pass square channels into the core of the blade. A detailed experimental investigation is done for two pass square channels with a 180° turn. Detailed heat transfer distribution occurring in the ribbed passage is reported for a steady state experiment. Four different combinations of 60° V- and broken 60° V-ribs in a channel are considered. A series of thermocouples are used to obtain the temperature on the channel surface and local heat transfer coefficients are obtained for Reynolds numbers 16,000, 56,000 and 85,000 within the turbulent flow regime. Area averaged data are calculated in order to compare the overall performance of the tested ribbed surface and to evaluate the degree of heat transfer enhancement induced by the rib. Flow within the channels is characterized by heat transfer enhancing ribs, bends, rotation and buoyancy effects. A series of experimental measurements is performed to predict the overall performance of the channel. This paper presents an attempt to collect information about the Nusselt number, the pressure drop and the overall performance of the eight different ribbed ducts at the specified Reynolds number. The main contribution of this study is to evaluate the best combination of rib arrangements throughout the two pass cooling channels. After a series of experiments, it can be concluded that the distribution of peaks in heat transfer in the case of inlet V and outlet inverted V is high. The overall performances for broken ribs are higher compared with the continuous ribs in two-pass cooling channels.

CFD analysis to study effect of circular vortex generator placed in inlet section to investigate heat transfer aspects of solar air heater.

CFD analysis of 2-dimensional artificially roughened solar air heater duct with additional circular vortex generator, inserted in inlet section is carried out. Circular transverse ribs on the absorber plate are placed as usual. The analysis is done to investigate the effect of inserting additional vortex generator on the heat transfer and flow friction characteristics inside the solar air heater duct. This investigation covers relative roughness pitch in the range of 10 ≤ P/e ≤ 25 and relevant Reynolds numbers in the range of 3800 ≤ Re ≤ 18000. Relative roughness height (e/D) is kept constant as 0.03 for analysis. The turbulence created due to additional circular vortex generator increases the heat transfer rate and at the same time there is also increase in friction factor values. For combined arrangement of ribs and vortex generator, maximum Nusselt number is found to be 2.05 times that of the smooth duct. The enhancement in Nusselt number with ribs and additional vortex generator is found to be 1.06 times that of duct using ribs alone. The maximum increase in friction factor with ribs and circular vortex generator is found to be 2.91 times that of the smooth duct. Friction factor in a combined arrangement is 1.114 times that in a duct with ribs alone on the absorber plate. The augmentation in Thermal Enhancement Factor (TEF) with vortex generator in inlet section is found to be 1.06 times more than with circular ribs alone on the absorber plate.

Turbulence and pressure drop behaviors around semicircular ribs in a rectangular channel

The article represents an experimental investigation on friction and turbulent flow characteristics of free airflow through a rectangular duct fitted with semicircular ribs of uniform height (e = 3.5 mm) on one principle wall. The aspect ratio of the rectangular duct was AR= 5 where the duct height (H) was 30 mm. Four different rib pitches (P) of 28 mm, 35 mm, 42 mm and 49 mm were examined with constant rib height to hydraulic diameter ratio (e/Dh = 0.07) and constant rib height to channel height ratio (e/H = 0.116). The experimental results show some significant effects of pressure drop as well as turbulent characteristics at various configurations among different numbers of rib arrangements varying Reynolds number in the range of 15000 to 30000. Experimental results have been compared with numerical analysis and it can be seen a good agreement. The result explains the phenomena elaborately between two periodic ribs and enables to optimize the rib pitch ratio in terms of turbulence kinetic energy for maximum heat transfer.

Thermal performance of turbulent flow in a solar air heater channel with rib-groove turbulators

The paper presents an experimental study on turbulent flow and heat transfer characteristics in a solar air heater channel fitted with combined wavy-rib and groove turbulators. The experiments are performed by controlling the airflow rate to obtain Reynolds numbers in the range of 4000 to 21,000. To produce recirculation flow in the tested channel having a constant heat-flux on the upper wall only, the triangular wavy ribs are placed repeatedly on the tested grooved channel walls. Three test cases of different rib-pitch to channel-height ratios (PR=P/H=0.5, 1 and 2) with a single rib-to-channel height ratio (BR=b/H=0.25) are introduced in the present work. The wavy ribs are placed with the attack angle of 45° relative to main flow direction. There are three types of rib arrangements, namely, rib-groove on the upper wall only, inline rib-groove, and staggered rib-inline groove on two principal walls. The experimental result reveals that the combined rib-groove on both the upper and lower walls of the test channel provides the highest heat transfer rate and friction factor in comparison with the smooth channel with/without ribs. However, the ribbed-grooved upper wall at PR=0.5 yields the highest thermal performance. The combined rib-groove turbulator is found to be considerably higher thermal performance than the groove alone.

Combined Experimental/Numerical Method Using Infrared Thermography and Finite Element Analysis for Estimation of Local Heat Transfer Distribution in an Internal Cooling System

In the present study a method for estimating local heat transfer distributions of internal cooling systems is described. Experimental data and finite element analysis are applied for this method. The investigations considered in this paper are based on experiments performed on a two-pass cooling channel connected by a 180 deg bend with internal rib arrangements. The solid walls of the cooling channels are made of a metallic material. During the experiment the temperature response of the outer surface induced by heated internal flow is recorded by infrared thermography. The internal heat transfer distribution is obtained using an optimization routine. For each loop of the optimization a transient thermal simulation of the solid body is performed applying the boundary and inlet conditions of the experiment. The temperature of the outer surface calculated by the finite element simulation is compared to the measured temperature recorded by infrared thermography. The difference of these temperature distributions is minimized by adapting the distribution of the internal heat transfer coefficients. The adaptation is conducted on single elements of the inner surface and will be presented in detail in the paper. This approach allows us to achieve a high resolution in heat transfer while minimizing the required iterations. The combination of experimental data and finite element analysis allows us to consider three-dimensional conduction effects in the solid and the streamwise fluid temperature development. Results are compared to literature data.

A numerical study of flow structure and heat transfer in a square channel with ribs combined downstream half-size or same-size ribs

The present study employs square cross-section ribbed channels with different arrangements of downstream half-size ribs to determine the most optimal configurations for augmenting heat transfer rates with minimized pressure drop penalties. The channel inlet Reynolds number ranges from 20,000 to 160,000. The influence of downstream ribs arrangement on the overall performance characteristics of ribbed duct is observed with six different cases. A case of an array of six big continuous ribs installed on one wall with a pitch ratio of P/e = 20, is first designed (Case A). Four cases are then designed with inserting half-size and same-size ribs downstream the big ribs (Case B, Case C, Case D and Case E, respectively). The last case has a different pitch ratio and half-size ribs in the middle of two neighbor big ribs (Case F). The details of turbulent flow structure temperature fields, local heat transfer, normalized heat transfer, and thermal performance factor were obtained using Computation Fluid Dynamics (CFD) with the v2f turbulence model and constant heat flux thermal boundary conditions applied to all surfaces. The overall performances of six ribbed channel are evaluated and compared. The results reveal that the usage of downstream ribs is a suitable way to decrease the pressure loss and improve the flow structure, while keeps comparable enhancement in heat transfer as expected. Compared with Case A, all other cases yield the lower friction factor except for Case B. Case D and Case F present the prominent effect of their thermal enhancement factor, suggesting that the two cases exhibit individual advantage when different performances are taken into account to augment the heat transfer of ribbed channels.

Heat Transfer Measurements in an Internal Cooling System Using a Transient Technique With Infrared Thermography

In this paper, a transient method for measuring heat transfer coefficients in internal cooling systems using infrared thermography is applied. The experiments are performed with a two-pass internal cooling channel connected by a 180 deg bend. The leading edge and the trailing edge consist of trapezoidal and nearly rectangular cross-sections, respectively, to achieve an engine-similar configuration. Within the channels, rib arrangements are considered for heat transfer enhancement. The test model is made of metallic material. During the experiment, the cooling channels are heated by the internal flow. The surface temperature response of the cooling channel walls is measured on the outer surface by infrared thermography. Additionally, fluid temperatures as well as fluid and solid properties are determined for the data analysis. The method for determining the distribution of internal heat transfer coefficients is based on a lumped capacitance approach, which considers lateral conduction in the cooling system walls as well as natural convection and radiation heat transfer on the outer surface. Because of time-dependent effects, a sensitivity analysis is performed to identify optimal time periods for data analysis. Results are compared with available literature data.

Numerical simulations of heat transfer distribution of a two-pass square channel with V-rib turbulator and bleed holes

The blade tip region in gas turbine encounters high thermal loads due to temperature difference and hence efforts for high durability and safe operations are essential. Improved and robust methods of cooling are required to downgrade heat transfer rate to turbine blades. The blade tip regions, which are exposed to high gas flow, suffers high local thermal load which are due to external tip leakage. Jet impingement, pin cooling etc. are techniques used for cooling blades. A more usual way is to use serpentine passage with 180-degree turn. In this study, numerical simulation of heat transfer distribution of a two-pass square channel with rib turbulators and bleed holes were done. Periodical rib turbulators and bleed holes were used in the channel. The ribs arrangement were 60 degree V rib, 60 degree inverted V ribs, combination of 60 degree V rib at inlet and 60 inverted V rib at outlet section and combination of Inverted V at inlet and V rib at the outlet. The results were numerically computed using Fluent with Reynolds number of 12,500 and 28,500. Turbulence models used for computations were k-ω-SST and RSM. Temperature based and shear stress based techniques were used for heat transfer distribution prediction. The results for 60 degree V rib, 60 degree inverted V ribs were compared with the experimental results for validation of the results obtained. Detailed distribution shows distinctive peaks in heat transfer around bleed holes and rib turbulator. Comparisons of the overall performance of the models with different orientation of rib turbulator are presented. It is found that due to the combination of 60 degree inverted V rib in inlet and 60 V rib in outlet with bleed holes provides better heat treatment. It is suggested that the use of rib turbulator with bleed holes provides suitable for augmenting blade cooling to achieve an optimal balance between thermal and mechanical design requirements.

Flow pattern change in horizontal rectangular laterally ribbed ducts through alteration of the ribs thickness and pitch

Experiments were conducted on two-phase flow in laterally ribbed rectangular ducts. Air–water adiabatic flow at atmospheric pressure and room temperature was driven through a 3.6m long rectangular ribbed test section with cross-section of 100×50mm. To investigate the effect of rib thickness and pitch on flow pattern diagrams and transition boundaries, nine various rib arrangements were implemented with thicknesses of 2, 4 and 8mm and pitches of 50, 60, and 80mm. Unlike non-ribbed rectangular duct, lateral rib arrangement did not allow any stratified flow to occur. However wavy, plug and slug flows were parallel in both flow conditions, rib existence caused explicitly coarser pattern shapes. Increasing the rib thickness, while keeping the pitch constant, results in different flow patterns to occur as well as dramatic changes in boundaries positions and shapes. On the other hand, as pitch shifts up at a constant rib thickness, one can notice the duplication of almost identical flow patterns and their boundaries however, boundary values undergo tangible changes. Consistent attention was paid to conditions under which wavy pattern zone extends while intermittent flow zones were avoided. Studies concerned ribbed duct are of major applicable value to designing and enhancing heat transfer systems.

0419 ガスタービン翼の内部冷却流路リターン部における伝熱・流動改善手法に関する研究(OS4-6 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

The cooling technology for the high temperature gas turbine blade is the one of the most important issues for its development. In this research the method for the heat transfer enhancement and the loss reduction of the rib turbulator and the return passage in the gas turbine blade is investigated. The combination of inclination direction of the rib turbulator for the inlet and outlet straight duct is optimized by the experiment and CFD. Using the result of the former, the rib arrangement in the returnpassage is also optimized by the experiment and CFD.

1224 TURBULENT HEAT TRANSFER ON AN INTERNAL COOLING PATH WALL IN GAS TURBINE BLADES

This paper presents an integrated model of a computational modes and the experimental study on a gas turbine internal blade cooling problem. A sharp bent channel with several different rib arrangements were investigated and the flow and heat transfer behaviours are analysed in various aspects of turbulence characteristics.

An Experimental and Numerical Study of Heat Transfer From Arrays of Impinging Jets With Surface Ribs

A combined experimental and numerical investigation of the heat transfer characteristics within arrays of impinging jets with rib-roughened surfaces is presented. Two configurations are considered: One with an inline arrangement of jets and ribs oriented perpendicular to the direction of cross-flow and one with a staggered arrangement of jets and broken ribs aligned with the direction of cross-flow. For both cases, the jet Reynolds number is 35,000, the separation distance measures H/D = 3, the spent air is routed through one exit contributing to the maximum cross-flow condition, and the rib height and width is both 1 D. The experiments are carried out in perspex models using the transient liquid crystal method. Local jet temperatures are measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. In addition to the measurements, a numerical analysis using the commercial CFD software package ANSYSCFX is conducted. Heat transfer predictions are compared with those obtained from experiments with regards to local distributions as well as averaged quantities. A good overall agreement is found but discrepancies for local values need to be accepted. The present investigation also emphasizes that configurations including rib roughness elements should be compared based on the amount of transferred heat flux in order to account for the area enlarging effect. This allows a correct evaluation of the thermal performance.