V-shaped Ribs Research Articles

Experimental assessment and modeling of solar air heater with V shape roughness on absorber plate

A roughness of the absorber plate can improve the efficiency of a solar air heater. To boost the efficiency of triangle solar air heaters, this research presents the results of a comparison study between with and without rib roughness on absorber plates. Both use black paint with graphene nanoparticles infused into it, coating an absorber plate. Both numerical and experimental methods have been used to examine the impact of surface roughness on friction factors and heat transport properties. ANSYS 14.5 software module and RNG turbulence, k-€ model is used to conduct a three-dimensional simulation and solve the governing equations in the turbulent situation. Based on experimental data, it has been established that smooth plates are more efficient in converting heat into useful work than rough ones, on average, by a factor of 4.82 and 4.46, respectively. The length of the duct in the solar air heater mitigates the temperature gradient seen in the simulation result. The roughness of V-shaped ribs has a far larger effect on the heat transfer and friction factor properties than do variations in relative roughness pitch (P/e) and Reynolds number (Re). Experimental observations supported by modeling and simulation confirms that triangular duct absorber surface roughness provides improved outcome.

Optimization of Nusselt number and friction coefficient for double pass solar heater with aluminum V-Ribs as roughness on GI material sheet using genetic algorithm

In this era, alternative energy fronts in areas such as solar energy are driven by needs. Due to the less efficient collector (solar based), various structures and techniques have been implemented to improve their efficiency. In this work, we formulated a genetic algorithm is applied to obtain an optimized set of operating parameters for a two-cycle solar collector with aluminum V-shaped ribs as an roughness material so that thermal performance can be optimized. Then obtained results using GA (Galvanized Iron) are compared against the experimental results. Thermal performance which is related to rate heat transfer which in turn is affected by different parameters and the range of these parameters which are considered in this work are; Reynolds number (Re) 800 to 12000, angle of attack (α) 25° to 80°, relative roughness spacing (p/e) 15 to 25 and relative roughness height (e/Dh) is 0.025 to 0.045. A set of optimized values of these parameters which affects heat transfer rate is thus obtained by genetic algorithm is then compared against the experimental ones. In the study of comparison, we get that the Nusselt number (Nu) is 1.08 times compared to the experimental one, and the friction factor (f) is 0.97 times compared to the experimental one.

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.

Effect of Different Arrangements of V-Shaped Ribs on the Performance of an Optically Enhanced Parabolic Trough Solar Collector

Abstract In this article, a V-shaped ribbed tube is utilized to improve the thermal performance of a parabolic trough collector (PTC). Six different rib arrangements are employed, and a detailed analysis is presented. In addition, the effect of adopting a secondary reflector (SR) on the temperature distribution around both a smooth and a ribbed parabolic trough receiver (PTR) tube is conducted. A computational fluid dynamics model is employed to study the heat transfer and fluid flow characteristics inside the tube. Results show that V-shaped ribs are an effective tool to stir up the flow and increase the velocity gradient of the fluid near the inner surface of the tube. This helps increase the convective heat transfer rate and reduce the tube’s maximum circumferential temperature. Moreover, results from the study show that the secondary reflector contributes to a further decrease in the tube surface temperature and hence improves the overall thermal efficiency of the collector. The combination of a V-shaped ribbed PTR tube and a secondary reflector is thus shown to be beneficial for the PTC system, especially at high Reynolds numbers.

Heat Transfer and Friction in a Rectangular Channel With Varying Numbers of Walls Roughened With 90-Deg Transverse or 45-Deg V-Shaped Ribs

Abstract An experimental investigation was performed to measure the regionally averaged heat transfer distributions and friction factors for fully developed turbulent flow in a rectangular channel with a width-to-height aspect ratio (AR = 3). Data for transverse 90-deg and 45-deg V-shaped, carbon steel ribs placed on one, two, or four sides of the channel were reported for a Reynolds number range (Re = 5,000–60,000). The pitch-to-rib height ratio (P/e) was set at 10 while the rib height-to-channel hydraulic diameter (e/Dh) is 0.041. This corresponds to a roughness Reynolds number range (e+=25−500). For both rib configurations, results show the highest thermal performance was achieved in the channels with four-ribbed wall followed by the two and one-ribbed wall channels, respectively. Using the law of the wall similarity, friction roughness functions (R) and heat transfer roughness functions (G) were developed based on four-sided friction and heat transfer data. Moreover, friction and heat transfer data of similar rib designs were obtained from literature and correlated to the corresponding friction and heat transfer roughness functions. Covering a wide range of roughness Reynolds numbers, more robust heat transfer and friction correlations were developed which can be used by designers to accurately predict both heat transfer and friction in ribbed channels with different numbers of ribbed walls. Using these correlations, one can predict the measured friction and heat transfer data of this study with maximum errors of 9% and 7%, respectively.

CFD Simulation of Heat Transfer Characteristics in a Rectangular Duct with Trapezoidal Turbulence Promoters

The heat transfer rate from the hot surface to the coolant flow increases by placing the ribs on the surface of the coolant flow passage. The effect of turbulence promoters with different angle of attack and with a fixed tapered angle on the heat transfer characteristics in a rectangular stationary duct is considered for this study. Here turbulence promoters increase the heat transfer in the duct. The examination has been conducted on the rectangular smooth duct and rectangular duct with inverted V-shaped ribs of a different angle of attack. The rib angle attack of 45º, 60º, 90º and tapered angle 20º (fixed) on the top surface of the rib are considered. The rib blockage ratio and pitch ratio are 0.0553 and 10 respectively. The heat transfer characteristics are compared with Reynolds number of 6000. The heat transfer and computational flow analysis are conducted by k-epsilon turbulence model in ANSYS FLUENT. The tapered angled cross-sectional inverted V-shaped ribs of 60º shown high average heat transfer coefficients among the 45º, 60º and 90º smooth duct.

Nusselt number and friction characteristics of solar air heater roughened with novel twisted V-shaped staggered ribs using liquid crystal thermography

The objective of this study is to investigate the Nusselt number and friction characteristics of rectangular channel solar air heater (SAH) ducts roughened with staggered V-shaped ribs using the liquid crystal thermography technique. Experimentation is performed for Reynolds numbers ranges from 3000 to 21000, relative roughness pitch (P/e) of 7–11, relative roughness length (S/e) of 6.15–10.26, relative staggered distance (d/e) between 2 and 6, and fixed angle of attack (α) and relative twist length (y/e). The change in temperature of the roughened absorber surface that produced the RGB (red, green, blue) colour pattern is acquired by a charge-coupled device and converted into (Hue, Saturation, and Intensity) HSI using MATLAB. For all the varied parameters, results are discussed in terms of Nusselt number, friction factor, thermal enhancement factor, and visualization of fluid flows. Results show that the maximum augmentation ratio in Nusselt number and friction factor is 3.43 and 2.57 times more than that of a smooth duct, respectively. Among the varied roughness parameter, a maximum TEP value of 2.69 is noticed with P/e of 9, d/e of 4, and S/e of 6.15. It is concluded that inclusion of staggered twisted V-shaped ribs helps in enhancing heat transfer with the least amount of friction penalty.

Heat Transfer Augmentation of a Solar Air Heater Using a Twisted V-Shaped Staggered Rib Over the Absorber Plate

Abstract An effort is made to study the performance of a solar air heater having the absorber surface roughened by providing staggered, twisted, and V-shaped ribs roughness. The liquid crystal thermography technique is applied to get the Nu distribution over the surface. Experimentation is done for Reynolds number ranges from 3000 to 21,000, relative roughness to pitch ratio (P/e) from 7–11 and relative staggered distance (d/e) of 2–6, for the fixed angle of attack (α), relative twist length (y/e), and relative roughness length (S/e). It is found that the maximum Nusselt number and friction factor augmentation are 3.43 and 2.57 times than that of the smooth duct. The maximum thermo-hydraulic performance (THP) value obtained is 2.69 for the P/e of 9 and d/e of 4. It can be inferred that staggered twisted V-shaped rib roughness helps to get the enhanced Nu with minimum friction penalty.

Flow and heat transfer performance of the channel with different shaped ribs cooled by mist/steam two-phase flow

The flow and heat transfer performance of mist/steam coolant in a straight channel with 45°/60°/75°V-shaped ribs, 45°/60°/75°/90°paralleled ribs and a smooth channel under different working conditions are studied. Based on vortex analysis, for mist/steam coolant, the regions where the Mainstream Secondary Flow Vortexes and the Longitudinal Secondary Flow Vortexes exist simultaneously can achieve better cooling performance. Among all mentioned rib structures, the 45°V-shaped ribbed passage achieves the best cooling enhancement, its sidewall average Nu number ratio is 33.8%–74.0% higher than the 90°paralleled ribbed channel. Although the heat transfer non-uniformity of the channel with 45°V-shaped ribs is not the lowest, it has lower heat transfer non-uniformity than the highest 45°paralleled ribbed channel. For mist/steam coolant, increasing inlet Re number, the sidewalls average Nu number ratio gradually decreases, but their heat transfer non-uniformity increases. As wall heat flux increases, the secondary flow vortexes in the channel does not change but both average Nu number ratio and the heat transfer non-uniformity clearly decreases. Raising mist/steam will not change the secondary flow vortexes structure. Instead, it will obviously increase the average Nu number ratio and heat transfer unevenness. Enlarging the mist diameter decreases the heat transfer performance of the sidewall, but also makes the sidewall heat transfer become less even.

Numerical investigation of fluid flow and heat characteristics of a roughened solar air heater with novel V-shaped ribs

Solar air heaters convert clean solar energy into useable heat and thus have a wide range of applications. Computational fluid dynamics (CFD) can aid in the design and development of solar air heaters with optimized thermal efficiency. A detailed numerical study was conducted to investigate the fluid flow and heat transfer characteristics of a roughened solar air heater with novel V-shaped ribs having staggered elements. Three-dimensional steady-state numerical simulations were performed using the k− ε Re-Normalisation Group (RNG) turbulence model, and results were found to be in excellent agreement with experimental data. The effect of rib spacing was studied through varying the rib pitch to rib height ratio P: e = 6–14, for Reynolds numbers (Re) in the range of 4000–14 000. A significant enhancement in the rib-roughened solar air heater's thermal performance was observed. It was also established that an increment in P: e from 6 to 10 increases the Nusselt number (Nu) for all Re values investigated. About 72.6% Nu enhancement was predicted for P: e = 10 at Re = 12 000. It was further observed that an increment in P: e from 10 to 14 decreases the Nu for all values of Re considered.

Numerical investigation of pentagonal V-shape ribs to enhance heat transfer in hydrogen rocket engine cooling channels

Keeping the combustion chamber walls at a sufficiently low temperature ensures liquid rocket engines' safe and reliable operation. The most promising method to achieve that is the heat transfer enhancement techniques which optimize the heat transfer coefficient and increase the thermo-hydraulic performance. The present work is concerned with numerical studies on the effect of the pentagonal V-shape ribs to enhance the heat transfer coefficient of the rocket engine's cooling channels. Numerical simulations for various chamfering angels of the pentagonal V-shape rib are performed by the (SST,k−ω) turbulent model. The simulation findings show that the overall performance of the ribbed channel improved inversely with the pentagonal chamfering angle. Compared with a conventional channel, the average Nusselt Number and thermal-hydraulic performance of the ribbed channel enhanced up to 66.6% and 52% respectively, and the 5° pentagonal V-shape rib has higher thermal-hydraulic performance with a slight high the pressure loss penalty.

Economic analysis of artificially roughened solar air heater with v-shaped ribs

Due to the minimal transfer of heat from absorber plate to moving air in the duct, solar air heaters have low performance. One of the procedures to augment the heat transfer by substantial amount is by utilizing artificial roughness, by which the performance can be improved considerably. In this study, an economic investigation of solar air heater embedded with artificial roughness is accomplished numerically employing v-shaped roughness, with the objective of optimising life cycle solar savings. The non-dimensional parameters of roughness, namely, angle of attack (α), roughness pitch (p/e) and roughness height (e/Dh) are examined by varying temperature rise over the solar air heater (∆T) and solar radiations (I) for different economic parameters values i.e., cost of collector, cost of roughness elements, and cost of conventional fuel.

Streamwise evolution of turbulent flow and heat transfer over channel surfaces with V ribs and V-rib-dimple compound turbulators

Scale-Adaptive Simulations (SAS) were carried out to investigate streamwise evolution of turbulent flow and heat transfer over channel surfaces with V ribs and V-rib-dimple compound turbulators. The compound turbulators periodically consist of 45° V-shaped ribs and spherical dimples of varied sizes placed on the channel wall between the V-ribs. Three sets of dimple sizes are investigated with the same depth-printed diameter ratio of hd/d = 0.2. The aspect ratio of the rectangular channel is W/H = 4, and the rib pitch-to-height ratio is P/e = 10. The greatest global heat transfer enhancement and overall thermal performance is achieved by the V-rib-dimple case with the printed dimple diameter-rib pitch ratio of d/P = 0.167. Obvious streamwise development characteristics of the turbulent flow structure and heat transfer enhancement are observed in the V-rib and V-rib-dimple channels, and the key findings are as follows. (1) For the V-rib-dimple cases, the global heat transfer enhancement by the presence of dimples significantly depends on the channel length. In terms of heat transfer, the V-rib-dimple cases outperform the V-rib case when L/Dh > 5.1 and gain more improvement at larger L/Dh. (2) There is an obvious streamwise evolution of the heat transfer in the V-rib and V-rib-dimple channels. The regional Nusselt number ratios first increase to reach the peak value, then decrease, and finally settle at the fully developed value. Introducing dimples can expand the range of increasing regional heat transfer by over 45%, yielding up to 23.2% higher regional heat transfer for the V-rib-dimple cases in the fully developed region. (3) The near-wall advective transport dominants the local heat transfer for the V-rib case, but it is gradually attenuated as the boundary layer grows thicker, causing the local heat transfer to decrease downstream of the channel. While for the V-rib-dimple cases, the presence of dimples greatly enhances the near-wall turbulent transport, helping keep the high local heat transfer downstream. (4) The presence of dimples between V-ribs reduces the shear stress magnitude on the sidewall, especially in upstream regions, which can result in the lower total flow friction for short channels.

Performance estimation of Triangular Solar air heater roughened absorber surface: An experimental and simulation modeling

The roughness on the absorber surface can increase the performance of a triangular solar air heater. This paper reveals a comparative study of smooth and rough absorber surfaces with V ribs to improve triangular solar air heater performance. The absorber plate coated with graphene nanoparticles doped into the black paint in both cases. The investigation incorporated rib roughness parameter as P/e = 1.4 for the arrangement and investigated at different parameters of the solar intensity. The roughness effect on friction factor and heat transfer characteristics has been investigated numerically and experimentally. A three-dimensional simulation is conceded out using Ansys 14.5 software and k-ε, RNG turbulence model to solve the governing equation in turbulence case. Using MATLAB optimizable Gaussian process regression (GPR) analysis, create an energy and exergy efficiency analysis prediction model. The experimental results indicate an average 4.93% thermal efficiency increase, and average exergy efficiency increases by 4.41 % to compare smooth plates. The simulation result shows temperature variation inside the duct, which is reduced through the length of the solar air heater. Compared to Reynolds number changes and relative roughness pitch (P/e), V-shaped rib roughness significantly impacts friction factor and heat transfer characteristics. We conclude that better outcomes are obtained after investigating triangular duct designs absorber surface roughness patterns.

Heat transfer enhancement of hydrogen rocket engine chamber wall by using V-shape rib

The cooling capacity of regenerative cooling channels is still insufficient for the liquid rocket engine due to the high temperature of the combustion chamber and the little refrigerant mass flow. To improve the thermo-hydraulic performance of the combustion chamber wall, a V-shape rib is proposed, and its effect on heat transfer and pressure drop is investigated. Numerical models are built of a regenerative cooling channel with V-shape rib using CFD commercial software. Simulation results showed that V-shape ribs enhance convection heat transfer and improve thermo-hydraulic performance by 23 % compared to smooth cooling channels. Although the maximum temperature was reduced by 20.9 % , the flow resistance increased slightly. The overall heat transfer coefficient of the cooling channel with 30 ∘ V-shape rib is superior to that of the 60 ∘ and 45 ∘ V-shape ribs, and 30 ∘ V-shape rib with 10 m m pitch has the best cooling capacity. • A low temperature of the rocket engine chamber wall is essential to ensure safe operation. • Three V-shape ribs are investigated and compared with the smooth regenerative cooling channel. • 30° V-shape rib has a better thermo-hydraulic performance than the 60° and 45° V-shape ribs.

Case Studies on Enhanced Heat Transfer in a Square Duct with Modified V-Shaped Ribs (MVR): A CFD Analysis

This research presents structural improvement of V-shaped ribs for a tested square duct (TSD). The V-shaped ribs, which are inserted at the middle of the TSD (called type A), and the V-shaped ribs, which are placed on the opposite TSD walls (called type B), are modified to increase the structural stabilization. The effects of rib height to duct height, b / H = 0.05 – 0.30 ; V-shaped bar thickness to duct height, a / H = 0.025 and 0.050; and flow directions (V-Upstream and V-Downstream) are considered. The new design of the V-shaped ribs is called “modified V-shaped ribs or MVR.” The present problem is solved by the numerical method (commercial code). The flow and heat transfer features of the TSD are illustrated. The numerical result reveals that the MVR give both flow and heat transfer patterns similarly as the general V-shaped rib. The impinging flows, swirling flows, and disturbing thermal boundary layer, which lead to enhanced heat transfer, are observed. Over the investigated range, the enhanced heat transfer about 18.12 times above the smooth duct with the optimal thermal enhancement factor about 4.16 is detected.

CFD based performance analysis of solar air heater provided with artificial roughness in the form of V – Shaped ribs

The current study comprises of computational fluid dynamics (CFD) analysis of solar air heater integrated with V-shaped ribs on the absorber plate with artificial roughness. The investigation of various fluid flow properties namely flow behaviour, temperature distribution and velocity distribution are performed using Renormalization group (RNG) k-ɛ turbulent model. The turbulence intensity of 5% is considered to investigate the mentioned fluid flow properties by considering the relative roughness height (e/D) range between 0.02 and 0.04, relative roughness pitch (P/e) as 10 and angle of attack (α) from 30° to 90°. The working parameters namely Reynolds number (Re) and intensity of solar radiations ranges from 2500 to 18,000 and 1000 W/m2 respectively. The direction and intensity of solar radiations are monitored by using Discrete Ordination (DO) model. The effective efficiency (ηeff) for different values of relative roughness height is analysed theoretically using the heat energy balance equation keeping relative roughness pitch as constant. The results indicated maximum effective efficiency as 74% for Reynolds number and relative roughness height values of 14,000 and 0.034 respectively.

Direct numerical simulation of turbulent duct flow with inclined or V-shaped ribs mounted on one wall

In this research, highly disturbed turbulent flow of distinct three-dimensional characteristics in a square duct with inclined or V-shaped ribs mounted on one wall is investigated using direct numerical simulation. The turbulence field is highly sensitive to not only the rib geometry but also the boundary layers developed over the side and top walls. In a cross-stream plane secondary flows appear as large longitudinal vortices in both inclined and V-shaped rib cases due to the confinement of four sidewalls of the square duct. However, owing to the difference in the pattern of cross-stream secondary flow motions, the flow physics is significantly different in these two ribbed duct cases. It is observed that the mean flow structures in the cross-stream directions are asymmetrical in the inclined rib case but symmetrical in the V-shaped rib case, causing substantial differences in the momentum transfer across the spanwise direction. The impacts of rib geometry on near-wall turbulence structures are investigated using vortex identifiers, joint probability density functions between the streamwise and vertical velocity fluctuations, statistical moments of different orders, spatial two-point autocorrelations and velocity spectra. It is found that near the leeward and windward rib faces, the mean inclination angle of turbulence structures in the V-shaped rib case is greater than that of the inclined rib case, which subsequently enhances momentum transport between the ribbed bottom wall and the smooth top wall.

Thermal–hydraulic analysis of a solar air heater fitted with a wire-roughened absorber plate

This study is to evaluate heat transmission and friction in a rectangular solar air heater with a V-shaped wire rib roughness on the absorber plate that operates in fully formed turbulent flow. Additionally, studies are performed to generate prediction equations for the average friction factor, Stanton number, and efficiency index. The Reynolds number [Formula: see text]–[Formula: see text], angle of attack [Formula: see text]20[Formula: see text]–90[Formula: see text]), relative roughness pitch [Formula: see text]–[Formula: see text], relative roughness height [Formula: see text]–[Formula: see text], and the aspect ratio [Formula: see text]–[Formula: see text] was varied. The efficiency index [Formula: see text] is commonly employed as a thermo-hydraulic performance metric. It is computed as [Formula: see text]. The wire roughness and airflow parameters [Formula: see text] are optimized to maximize heat transfer while retaining minimal friction losses. On the basis of resemblance criteria, average Stanton numbers, average Nusselt numbers, and even average friction factors are derived. The results are compared to those obtained with a smooth absorber duct under similar airflow circumstances in order to assess the increase in heat transfer coefficient and friction factor. The [Formula: see text], and [Formula: see text] have a significant influence on thermo–hydraulic performance, according to these studies. With [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], the optimal configuration geometry for wire roughness and solar air heater duct is identified.

Comparison of V-shaped rib and curve-angled ribs by computation heat transfer enhancement and pressure drop internally two-phase flow in two-pass channel

In the present study two shapes of ribs are used to improve the heat transfer coefficient. Ribs are constructed in two types viz a V–shaped rib and curve rib. The ribs are used to improve the heat transfer. Heat transfer and space reduction while maintaining the durability of the design and thus better cooling and thus avoiding thermal stress. Simulation numerical solution by CFD with ANSYS WORKBENCH R1 2021 with in established turbulence model standard K-ε was conducted. The experiment performed for two-phase flow of water (8 L/min) and for air (16.67 L/min) at constant rib temperature about 60 °C. The study results show that the enhancement percentage in curve rib is about 90.3% while in V-shaped rib is 88.27%. The results showed that the curve ribs was the optimum design.