V-shaped Ribs Research Articles

Numerical and experimental investigation of different rib roughness in a solar air heater

A numerical study is aimed at comparing dissimilar types of repeated-rib roughness: arc-shape with gap and V-shape with gap on the absorber plate of the solar air heater having similar shape and size working under identical boundary conditions. Relative gap width (g/e) of 1, relative roughness height of 0.04, the relative roughness pitch of 10, p/P = 0.65, d/W = 0.69, No. of gaps = 1, attack angle α = 600 of the rib, heat flux 1000 W/m2, etc. are kept constant and variation in range of Reynolds number is 3000–15000. Numerical simulations are conducted with the help of ANSYS CFD tool, and results have been validated with the experimental studies. The V-shape ribs have maximum frictional loss penalty of 4.05 and Nusselt number enhancement of 3.4 at Re 3000. The arc-shape ribs have maximum frictional loss penalty of 3.94 and Nusselt number enhancement of 2.4 for Re 15000. The maximum THPP for the V-shape ribs and arc shape ribs are 2.21 and 1.5 respectively at Re 3000.

A comprehensive thermal-hydraulic assessment of solar flat-plate air heaters

This paper evaluates the thermal-hydraulic performance of flat-plate solar air heaters having roughened ducts using different turbulence generators. About 220 roughened ducts have been selected from the literature based on the availability of experimental f-factor and Nusselt number data. In particular, roughness elements are rectangular/square ribs, arc/wavy ribs, V-shaped ribs, wedge-shaped ribs, protrusions, and metal mesh. To assess the performance of different solar air heaters, collector efficiency (as a function of useful energy and pumping power) and entropy generation are estimated. The optimal duct is chosen based on the maximum collector efficiency and the minimum entropy generation and hence, is suggested to be a benchmark. The results show that the Reynolds number range of 10000 –16000 is recommended to be used for operating solar air heaters to get the optimal performance. The solar duct GKS3 is found to have the optimal performance when Re < 11000, and the duct GK23 has the optimal performance for 11000 < Re < 16000. These two solar air heaters (GKS3 and GK23) are recommended to be benchmarks for comparing and assessing the performance of all flat-plate solar air heaters. For Re > 16000, the solar collector GB5 is found to have optimal performance.

Employing V-shaped ribs and nanofluid as two passive methods to improve second law characteristics of flow within a square channel: A two-phase approach

This research attempts to investigate the effects of simultaneous utilization of V-shaped ribs and nanofluid as two heat transfer enhancement approaches inside a square channel on the second law attributes. For this purpose, the comprehensive entropy generation and exergy destruction analyses are carried out with the aid of the two-phase mixture technique for the copper–water nanofluid flow through the channel enhanced with the 45° V-shaped ribs. Firstly, a comparison is made between attack angles of 45° and 60°, which unveils the superiority of 45° because it shows lower entropy generation. The Cu nanoparticles are utilized as the main nanoparticles. Furthermore, the nanofluids containing the Ag nanoparticles are also simulated at two volume fractions of 0.01 and 0.03 to make comparison between different nanoparticle materials. The impacts of rib configuration including the rib pitch and its height are assessed using three rib pitches and three rib heights. The total entropy generation and total exergy destruction decrease as the volume fraction increases, such that an around 31.85% reduction occurs in the total entropy generation and total exergy destruction when the volume fraction increases by 0.03 for the case of rib height of 5 mm and rib pitch of 100 mm. Thereby, the second law efficiency rises by 15.64% in the same condition. Additionally, the installed 45° V-shaped ribs remarkably contribute to the total irreversibility reduction by means of creating four recirculation flows and powerful swirl flows. The results indicate that utilizing both larger rib height and smaller rib pitch (at the same time) exhibits lower exergy destruction and enhances the second law efficiency.

Numerical Study of Turbulent Heat transfer enhancement in square-duct flow through of inline V-shaped discrete ribs

Numerical Study of Turbulent Heat transfer enhancement in square-duct flow through of inline V-shaped discrete ribs

Performance investigation of a solar thermal collector provided with air jets impingement on multi V-shaped protrusion ribs absorber plate

In the present work, the heat transfer through a solar thermal collector (STC) provided with jet air impingement on the absorbent plate fitted with multi V-shaped protrusion ribs is investigated experimentally. The investigation is carried out for geometric parameters such as Relative width ratio (WPR/WAPR), Relative protrusion rib height (hPR/dPR), Relative pitch ratio (PPR/hPR), Angle of attack (αPR) respectively. The values of the streamwise pitch ratio (XSW/dh) = 0.40, spanwise pitch ratio (YSW/dh) = 0.85 and jet diameter ratio (dj/dh) = 0.064 are kept constant. The overall performance of STC is effectively evaluated by varying Reynolds number (Re) in the range 2500–35,000. The results obtained from the experiments shows that the impingement jets flow on multi V-shaped protrusion ribs absorber plate accelerated the heat transfer through the solar collector channel. The optimal augmentation is obtained at WPR/WAPR= 5, hPR/dPR= 0.9, PPR/hPR = 8 and αPR = 65° respectively. Thermal-hydraulic performance parameter ( ηPR) has also been investigated and the maximum value of 3.44 is obtained for the range of parameters studied.

Enhancement of Mist Flow Cooling by Using V-Shaped Broken Ribs

Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45°, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1–3.1 W/cm2 and 3.4–9.4 W/cm2 for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow.

A two-phase simulation for analyzing thermohydraulic performance of Cu–water nanofluid within a square channel enhanced with 90° V-shaped ribs

A numerical investigation is conducted by implementing a two-phase model based on the mixture theory with the aim of assessing the attributes associated with the thermohydraulic performance of the Cu–water nanofluid through a square channel equipped by the 90° V-shaped ribs. The ribs are attached on the top and bottom walls of the channel with different rib heights and rib pitches. It is observed that the average heat transfer coefficient significantly enhances with the volume fraction increment such that it enhances around 22.7% with increasing the volume fraction from 1 to 2% at rib pitch of 100 mm and rib height of 2.5 mm. The presence of the ribs considerably intensifies the flow mixing and disrupts the thermal boundary layer by means of generating the four counter-rotating vortices. In addition, employing the ribs with greater heights as well as smaller pitches augments the heat transfer coefficient as well as Nusselt number, such that the Nusselt number increases about 28.3% when the rib height increases from 2.5 to 7.5 mm in the condition in which the rib pitch is 50 mm. The Figure of Merit (FoM), which shows the fraction of the convective heat transfer coefficient ratio to the pumping power ratio for the case of using the nanofluid compared to the water, is much higher than 1, which demonstrates the benefit of employing the nanofluid rather than the water. Furthermore, increasing the volume fraction results in a greater FoM, which manifests the greater merit of using the nanofluid at higher concentrations.

Experimental Study on the Influence of the Streamwise Position of Film Hole Extraction in Internal Ribbed Cooling Channels of Turbine Blades

The concurrent use of film cooling and internal cooling plays an important role to maintain the life of turbine blades and increase thermal efficiency. Several studies were published on the interaction of these cooling strategies but these are mainly investigations on how internal cooling influences film cooling. The present study contributes to an improved understanding on how the cooling extraction through film cooling holes is influencing internal flow structures and therefore internal cooling. The flow field in an internal cooling channel is investigated by measuring the velocity distribution with 2D-PIV. Heat transfer measurements are performed using the thermochromic liquid crystal technique. The test stand models a rectangular cooling channel (AR=2:1), which is equipped with parallel ribs of four different geometries (90° ribs, 60° ribs, 60°-V-shaped ribs and 60°-Λ-shaped ribs). Bleed holes are placed in the rib segments and are positioned at three positions in streamwise direction. The suction ratio is varied between 0 and 6 and the cooling channel Reynolds number is 30.000.

Thermal behaviors in heat exchanger channel with V-shaped ribs and grooves

An experimental work has been conducted to explore the influence of the combined V-rib and chamfered-V-groove vortex generator (VG) on flow and heat transfer behaviors in a heat exchanger channel having a constant heat-flux on the top wall. Firstly, the V-shaped ribs were mounted on the plain top-wall with a view to creating multiple vortex flows inside. The investigated geometrical parameters were three relative rib pitches (RP = P/H = 1.0, 1.5 and 2.0) and relative rib heights (called “blockage ratio”, RB = e/H = 0.3, 0.4 and 0.5) at a single attack angle (α = 45°). Secondly, the ribs were again placed on the chamfered-V-grooved top-wall having three relative groove-pitches (RP = 1.0, 1.5 and 2.0) like the rib case but at a fixed groove width and depth. Air as the test fluid flowed through the heat exchanger channel for Reynolds number (Re) ranging from 5300 to 23,000. Influences of the newly designed heat exchanger surface on the Nusselt number (Nu) and friction factor (f) have been examined and compared with the flat surface data at similar test conditions. The experimental result reveals that the combined rib-groove with small RP and large RB yields the heat transfer and friction loss higher than the one with large RP and small RB. Nevertheless, thermal enhancement factor (TEF) obtained at a constant pumping power shows that the combined rib-groove case with PR = 1.5 and RB = 0.4 provides the highest value around 1.907. To explore the influence of the rib thickness on thermal performance, the rib thickness size was reduced to be a very thin rib, called the “baffle”. The study points that at PR = 1.5, the baffle-groove with RB = 0.3, 0.4 and 0.5 provide, respectively, TEF around 2.12, 2.14 and 2.11, indicating that the baffle-groove performs better than the rib-groove around 13%.

Experimental Study of Heat Transfer and Pressure Loss in Channels with Miniature V Rib-Dimple Hybrid Structure

In order to increase the thermal efficiency, the gas turbines are designed to operate at higher temperature, which requires highly efficient cooling structures for turbine blades. The dimples and ribs are effective surface structures to enhance the convective heat transfer in the gas turbine blade internal cooling. In the present study, a novel hybrid cooling structure with miniature V-shaped ribs and dimples is presented, and the heat transfer and pressure loss characteristics are obtained experimentally. The heat transfer performance of the rib–dimple structures, which include three different rib height-to-hydraulic diameter ratios of 0.017, 0.029 and 0.044 and one dimple configuration with the dimple depth-to-diameter ratio of 0.2, are studied by using the transient liquid crystal thermography technique for turbulent flow in rectangular channels within the Reynolds number range from 10,000 to 60,000. It is found that the miniature V-shaped ribs arranged upstream the dimples can significantly improve the heat transfer performance of the dimples, resulting in a more uniform heat transfer distribution on the surface. The V rib-dimple hybrid structure in the channel shows much higher heat transfer enhancement than the counterparts with only the dimples in the channels.

Mallomonas gusakovii sp. nov. (Chrysophyceae, Synurales), a new species from Phu Quoc Island, Vietnam

Mallomonas gusakovii sp. nov. is described from Vietnam based on silica-scale morphology studied by means of transmission and scanning electron microscopy. This species belongs to section Quadratae and is characterized by large and broad scales of three types with an internal reticulation, V-shaped rib and a forward projecting wing. Different types of the V-shaped rib in taxa from section Quadratae are discussed. Scales of Mallomonas gusakovii were found only in two sites in Phu Quoc Island, Southern Vietnam.

Numerical investigation on the flow and heat transfer characteristics in a rectangular channel with V-shaped slit ribs

Described in this paper is a numerical investigation on the concept for improving thermal performance of channel cooling by placing the V-shaped slit ribs. Five different geometrical models are investigated, including the ribs with rectangular slits, V-shaped slits, anti-V-shaped slits, broken V-shaped slits and broken anti-V-shaped slits. The effect of slit shapes on the thermal performance of channel cooling are evaluated with the Reynolds numbers ranging from 10,000 to 25,000. Results obtained show that the channels with broken slits give the higher heat transfer performance due to the higher turbulence intensity. Correspondingly, the pressure losses in these cases are in the higher level. The thermal performance index, which comprehensively evaluates the thermal performance of channel cooling, shows the thermal performance in the channels with broken slits is in the highest level due to the increased heat transfer enhancement and limited increase of pressure loss penalty.

A detailed review on various V-shaped ribs roughened solar air heater

Solar air heater (SAH) is a popular and economical device which collects the solar energy and is employed for space heating, drying of agricultural products, food items, and leather, seasoning of timber, etc. Attachment of artificial roughness on the absorber surface is an appropriate method to augment the heat transfer from the heated surface to the air flowing through SAH duct. Use of artificial roughness has been an area of great interest for researchers as far as the cooling of turbine blades, and combustion chambers are concerned. This technique is effective in enhancing the heat transfer in a micro-channel heating/cooling system. Present paper holistically furnishes concise information about various kinds of V-shaped roughness geometries used in SAHs for improving its performance covering experimental, analytical, numerical and computational fluid dynamics (CFD) approaches. In this paper, 124 research articles have been referred, which provide a detailed comprehensive and comparative study revealing the effect of various geometrical parameters and different V-shaped roughness patterns on the performance of SAH. This article also brings in the information about the correlation developed by researchers for heat transfer and friction factor. This comprehensive review will be quite useful for technical persons and researchers working in the area of SAH.

Heat Transfer and Turbulent Flow Structure in Channels With Miniature V-Shaped Rib-Dimple Hybrid Structures on One Wall

An experimental and numerical study has been conducted on heat transfer and turbulent flow structure in channels with novel hybrid structures with miniature V-shaped ribs and dimples on one wall. One miniature V-shaped rib was arranged immediately upstream each individual dimple to form the hybrid structure, which aims at inducing additional near-wall secondary flow interacting with the dimple vortex flow and further improving the heat transfer. Steady-state convective heat transfer experiments were done to obtain the heat transfer and pressure loss of the turbulent flow over the surfaces with the miniature V rib-dimples for the Reynolds numbers from 18,700 to 60,000. In addition, the turbulent flow structure in the V rib-dimpled channels has been predicted by carrying out numerical computations. The experimental results indicated that the overall heat transfer enhancement of the miniature V rib-dimpled channels can be increased by up to about 60.0% compared with the counterpart of the dimpled only channel, and by about 23.0% compared with the counterpart of the miniature V ribbed only channel. The miniature V ribs showed appreciable effects on the heat transfer and pressure loss characteristics for the turbulent flow over the V rib-dimpled surfaces. The numerical computations showed that the miniature V rib upstream each dimple produced strong near-wall downwashing secondary flow, which significantly changed the flow patterns and intensified the turbulent flow mixing inside and outside the dimple and above the surrounding wall. These unique near-wall flow characteristics generated a significant heat transfer improvement in both the magnitude and the uniformity.

Thermal-hydraulic study on rib and dimple structures for cooling the First Wall of DEMO

The thermal hydraulics of helium-gas cooled channels for the First Wall of DEMO structured by fully attached and semi-detached upward directed V-shaped ribs and spherical dimples in a staggered array were investigated. Large-Eddy-Simulations with the dynamic Smagorinsky sub-grid scale model were performed. The global and local heat transfer coefficient, pressure drop and cooling performance were analyzed. Compared to smooth channel flows, the global heat transfer coefficient was increased by a factor of 2.6–2.9 and the corresponding pressure drop was increased by a factor of 5.3–5.7 for the V-shaped ribs. Here, the semi-detached ribs provided the highest heat transfer and the best cooling performance. The dimpled structures increased the heat transfer by the factor of 1.1–1.4 without a significant pressure drop rise when compared to smooth channel flows, but regions of local heat transfer deterioration occur over each upstream dimple half.

Effect of V-shaped rib roughness on the performance of nanofluid-based direct absorption solar collectors

Solar heating systems, which used nanofluid-based direct absorption solar collectors, have been recently introduced as the more efficient solar thermal systems because of the volumetric absorption of solar radiation within the direct absorption solar collectors. In this paper, a new direct absorption solar collector is constructed with the V-shaped ribs on its bottom surface in order to study the outdoor thermal performance of the conventional and ribbed collector, experimentally. Using graphene oxide nanofluid as the working fluid, the energy and exergy efficiencies of the conventional and ribbed direct absorption solar collectors are obtained by varying the nanofluid volume fraction, flow rate and the rib geometry (forward and backward rib). Measuring the spectral transmittance of the nanofluid samples shows that the absorbed energy fraction (F) for collector channel depth of 1 cm is 50.9%, 59.82%, 64.5% and 65.3% for nanofluid samples of 125 ppm, 250 ppm, 500 ppm and 1000 ppm, respectively. In volumetric flow rate of 15 L h−1, the zero-loss efficiency for BR-DASC and FR-DASC is increased up to about 16.6% and 11.7%, compared to DASC. These values attain 21% and 13.4% when the volumetric flow rate increases from 15 to 45 L h−1. The optimum volume fraction of graphene oxide nanofluid is 500 ppm in conventional and forward-ribbed direct absorption solar collectors in terms of both energy and exergy efficiencies. The higher friction factors, as a result of ribs, lead to lower exergy efficiency of the ribbed direct absorption solar collector in comparison with the conventional one.

Analysis of the Influence of the Heat-Absorbing Surface of an Air-Cooled Solar Collector on its Thermal and Mechanical Properties

Abstract This paper presents the analysis of existing forms of heat absorbing surfaces of air solar collectors, which gained the greatest popularity in the world. The obtained data allowed to conclude that there is a need for the development of solar collectors with air as a coolant with an improved form of heat absorber, which will reduce the operational and capital costs of solar systems and allow the efficient use of such structures in a moderate climate without additional mechanisms for the transfer of coolant. The use of computer simulation helped to compare the thermal characteristics of air-borne solar collectors of a different design. The substantiation of the expediency of installing as a heat absorber of flow turbulators in the form of a screw has been fulfilled, as well as the height of the air channel of the solar collector has been determined, in which the maximum heating of the transfer medium is observed. In addition, the loss of pressure in the air channel of the solar collector with flow turbulators was determined and the comparison of the obtained data with the values of pressure losses in the air collector of the matrix type and the air collector with V-shaped ribs was made.

Numerical heat transfer study of turbulent square-duct flow through inline V-shaped discrete ribs

Numerical heat transfer study of turbulent square-duct flow through inline V-shaped discrete ribs

Heat transfer and pressure loss of turbulent flow in channels with miniature structured ribs on one wall

This paper presents an experimental and numerical study of turbulent flow heat transfer and pressure loss in channels with structured miniature ribs on one wall with the aim to improve the internal cooling performance of gas turbine blades and combustor liners. Miniature transverse, angled, V-shaped and W-shaped ribs are investigated respectively in the study, and the aspect ratio of the channels is kept to be 6:1, and the rib pitch to height ratio is 10 and the rib height to mean hydraulic diameter ratio is 0.029. The experiments were carried out at the Reynolds numbers ranging from 10,000 to 60,000, and a low-Reynolds number k-ε turbulence model was also adopted to simulate the turbulent flow and heat transfer in the channels. Both experimental and numerical results have shown that the shapes of miniature ribs have appreciable influences on the heat transfer and pressure loss performance in the channels. The experiments showed that the W ribs have the highest heat transfer and pressure loss performance in the channel, and the angled ribs have the lowest heat transfer and pressure loss performance in the channel. The W-ribbed channel shows respectively the globally averaged Nusselt numbers and overall Nusselt numbers of 2.2–2.6 and 2.9–3.3 times those of a smooth channel, and the friction factors of 2.5–3.7 times those of the smooth channel, which are higher than those of the V-ribbed channel and the transverse-ribbed channel. The miniature structured ribs show appreciable higher thermal performance than the conventional sized ribs. Furthermore, the numerical simulations show different vortex flow structures near the wall induced by the structured miniature ribs on the wall, which are responsible for the high-performance heat transfer enhancement.

Numerical investigation of heat transfer enhancement in a solar air heater roughened by multiple V-shaped ribs

The heat transfer and flow characteristics of a multiple V-shaped rib roughened solar air heater were numerically investigated. Calculations were performed for different geometrical parameters of the channel and rib, focused on their detailed effects on the maximum heat transfer enhancement. The multiple V-shaped ribs greatly enhanced the heat transfer, and the maximum thermohydraulic performance factor was found to be 2.35 in the studied ranges. Increasing the spanwise rib number produces two opposing effects on the heat transfer performance, resulting in an optimal spanwise rib number giving the maximum thermohydraulic performance factor. The geometrical parameters of the rib and channel influence the optimal spanwise rib number by changing the affecting factors of the thermohydraulic performance factor. The optimal spanwise rib number decreased with an increase in the channel height, rib attack angle, and relative rib pitch, whereas it first increased and then remained constant with an increase in the relative rib height.