Heat Transfer Enhancement Devices Research Articles

Elliptical vibration chiseling: a novel process for texturing ultra-high-aspect-ratio microstructures on the metallic surface

Highlights Elliptical vibration chiseling is proposed based on a game-changing process principle for the high-efficient texturing of ultrahigh-aspect-ratio surface microstructures. Uniformed microstructures with an aspect ratio of 2–12 in the spacing scale of 1–10 μm have been successfully fabricated using elliptical vibration chiseling. The developed process model of elliptical vibration chiseling has been verified by the measured results of the microstructures’ geometric parameters. An inclined elliptical trajectory of tool vibration is more suitable for elliptical vibration chiseling than the standard elliptical trajectory. The deterministic process effects on the surface generation of microstructure in elliptical vibration chiseling have been demonstrated.

Flow and heat transfer of nanofluids in a cylindrical permeable wavy channel embedded in porous medium using Buongiorno’s model

This investigation deals with the flow of Al2O3–water nanofluid in a wavy porous channel embedded in porous rocks. Fluid exchange takes place uniformly between porous rocks and the wavy channel. In this analysis, cylindrical and parallel plate wavy porous channels are considered. Consequences of Brownian motion and thermophoresis on the flow inside a wavy porous channel are elucidated. The modeled equations are made dimensionless by using dimensionless quantities. Impacts of flow parameters on the velocity, temperature, Nusselt number and friction factor are depicted through graphs. The numerical results with respect to parallel plate wavy porous channel are validated by comparing with the published results. The effectiveness of the cylindrical wavy porous channel as a heat transfer enhancement device in comparison to the parallel plate wavy porous channel is confirmed in this study. Designing devices at microlevels and understanding the heat transfer enhancement mechanism in wavy channels using the nanoparticle addition are the major outcomes from the results of this numerical investigation. The heat and mass transfer rate enhancements in the wavy porous channels are due to the higher Brownian motion in the boundary layer region and accelerated thermophoresis through thermal and concentration boundary layer thicknesses.

Heat transfer improvement using additive manufacturing technologies: a review

To provide a comprehensive review of additive manufacturing use in heat transfer improvement and to carry out the economic feasibility of additive manufacturing compared to conventional manufacturing. Heat transfer improvement is particularly interesting for different industrial sectors due to its economic, practical, and environmental benefits. Three heat transfer improvement techniques are used: active, passive, and compound.According to numerous studies on heat transfer enhancement devices, most configurations with strong heat transfer performance are geometrically complex. Thus, those configurations cannot be easily manufactured using conventional manufacturing. With additive manufacturing, almost any configuration can be manufactured, with the added benefit that the produced parts’ surface characteristics can enhance heat transfer. It can, however, lead to a significant pressure drop increase that will reduce the overall performance. In the given article, a comparison of the capital cost of a 100 MW parabolic trough power plant has been carried out, considering two types of solar receivers; the first is manufactured using conventional methods, and the second uses additive manufacturing. The heat transfer of the new receiver configuration is investigated using computational fluid dynamics through ANYS Fluent.Although the cost of additive manufacturing machines and materials is high compared to conventional manufacturing, the outcome revealed that the gain in efficiency when using additive-manufactured receivers leads to a reduction in the number of receiver tubes and the number of solar collectors needed in the solar field It implies a considerable reduction of parabolic trough collector plant capital cost, which is 20.7%. It can, therefore, be concluded that, even if initial setup expenses are higher, additive manufacturing could be more cost-effective than traditional manufacturing.With the reduction of the parabolic trough collector plant capital cost, the levelized cost of electricity will eventually be reduced, which will play a role in increasing the use of solar thermal energy.No review studies discuss the manufacturing potential and cost-effectiveness potential of additive manufacturing when producing heat transfer improvement equipment, especially when producing long pieces. In addition, the paper uses a novel receiver configuration to investigate the economic aspect.

Selection of turbulence promoters for retrofit applications through thermohydraulic performance mapping

Many new heat transfer enhancement devices have been reported in the open literature in the past decades exhibiting innovative geometries and better thermal and hydraulic performance. For a practical application in tubular heat exchangers, the selection of the best inserts out of the many different geometries available can be a cumbersome task. This work shows an approach to reduce the complexity of the search by graphically displaying the relative increase of heat load and pressure drop by means of performance mapping plots. The analysis includes the use of Nusselt and friction correlations and their application at different Reynolds numbers and different fluid viscosities. Out of the different geometries available, a group of 51 are compared in terms of the effect on heat duty and pressure drop. The approach is extended to analyse the exchanger irreversibility. For different operating conditions and fluid types, it is shown that the perforated twisted tape is the best performing insert. This insert produces an increase in heat transfer rate between 4% and 7.3% and an increment in pressure drop between 2 and 3.43 times that of the base case.

Numerical Analysis and Parametric Optimization of a Static Wavy Flag for Heat Transfer Enhancement

This work investigates the effect of different parameters of a static wavy flag vortex generator on the heat transfer in a rectangular channel using Computational Fluid Dynamics (CFD) analysis. This work encompasses optimizing several parameters of a flag such as flag height from the surface, position in the channel, number of triangular shapes in a flag, and rectangular surface area of the flag. Post analysis results exhibit encouraging results with average Nusselt number in flag height (FH) optimization exceeding that in no flag condition by 41.84%, 47.79%, 54.68% for Re 8236, 12354, and 18344, respectively whereas further position optimization of FH optimized flag exceeds average Nusselt number in no flag condition by 46.86%, 70.68% and 87.26% for the corresponding Re. With significantly less practical application of flags for heat transfer enhancement in industry, this work aims to establish flags as an effective heat transfer enhancement device and demonstrate that with the right optimized parameters, a significant increase of heat transfer in the channel can be achieved.

Numerical simulation on fluid flow and heat transfer characteristics in inward sinusoidal rib enhanced tube heat exchangers for waste heat recovery: Comparisons and parametric studies

Waste heat recovery is of great importance in industrial applications, in which heat transfer enhancement technologies play important roles. Aiming to employing heat transfer merits from longitudinal vortexes for potential waste heat recovery applications, inward sinusoidal rib tubes (SRTs) were employed as heat transfer enhancement devices, and computational fluid dynamics on tubular turbulent heat transfer and flow characteristics of the SRTs were conducted. Comparisons of thermal-hydraulic performances for a SRT with some typical enhanced heat transfer tubes and parametric studies of the SRTs involving flow structures and heat transfer mechanisms were performed. The main findings obtained from this research showed that at the similar conditions the SRT yielded higher Nusselt number (Nu), friction factor (f) and overall thermal performance evaluation criterion (PEC) than the other typical enhanced tubes. It was obtained that thermal convection in the SRTs was enhanced by the combined flow structures from transverse vortexes and longitudinal swirl flows. The results in the case studies proved that increasing rib height ratio, and decreasing pitch length ratio and rib width ratio facilitated enhancement of both Nu and f. In terms of the rib number, the SRT with the rib number of 3 gave the largest Nu, while the SRTs at the rib numbers of 2 and 3 had comparable f and they had larger flow resistance than others. In addition, the highest PEC of about 1.73 was achieved by the SRT with a pitch length ratio of 0.804, a rib height ratio of 0.065, a rib width ratio of 0.217 and a rib number of 3 at a Reynolds number of 5000.

A review of acoustic aspect in synthetic jet

The synthetic jet actuators are promising heat transfer enhancement devices. They are used in active cooling systems and the future may replace classic fan systems. Although the flow and the heat transfer parameters are very important, these devices must be quiet enough to be used in offices and other spaces. In this paper, the acoustic investigations of the synthetic jet are compiled and discussed. The impact of actuators design on generated noise and the possible ways to noise decreasing are presented. In the end, the list of gaps and challenges are presented for laying down the foundation for future research.

A Study on Thermal Performance of Palladium as Material for Passive Heat Transfer Enhancement Devices in Thermal and Electronics Systems

In this work, the thermal behavior of fin made of palladium material under the influences of thermal radiation and internal heat generation is investigated. The thermal model for the extended surface made of palladium as the fin material is first developed and solved numerically using finite difference method. The influences of the thermal model parameters on the heat transfer behaviour of the extended surface are investigated. The results show that the rate of heat transfer through the fin and the thermal efficiency of the fin increase as the thermal conductivity of the fin material increases. This shows that fin is more efficient and effective for a larger value of thermal conductivity. However, the thermal conductivity of the fin with palladium material is low and constant at the value of approximately 75 W/mK in a wider temperature range of -100℃ and 227℃ . Also, it is shown that the thermal efficiencies of potential materials (except for stainless steel and brass) for fins decrease as the fin temperatures increase. This is because the thermal conductivities of most of the materials used for fins decreases as temperature increases.However, keeping other fin properties and the external conditions constant, the thermal efficiency of the palladium is constant as the temperature of the fin increases within the temperature range of -100℃ and 227℃. And outside the given range of temperature, the thermal conductivity of the material increases which increases the efficiency of the fin. The study will assist in the selection of proper material for the fin and in the design of passive heat enhancement devices under different applications and conditions.

CFD analysis for thermal performance augmentation of solar air heater using deflector ribs

This paper presents the effect of deflector ribs on the thermal performance of flat plate solar air heater using Computational Fluid Dynamics (CFD) methodology. The analysis is carried out using two-dimensional computational domain for the Reynolds number range of 6000-18000. RNG k-є turbulence model is used to capture the turbulence characteristics of the flow. The deflector rib has a cross-section of isosceles triangle and is placed transversely with respect to the flow. The distance between consecutive ribs is varied as 40mm, 80mm, 160mm and 320mm while the air gap height is varied as 2mm, 3mm, 5mm and 10mm. The numerical model is validated against the well-known correlation of Dittus-Boelter for smooth duct. The simulation results reveal that the presence of deflector ribs provide augmented heat transfer through flow acceleration and enhanced turbulence levels. With reference to smooth duct, the maximum achieved heat transfer improvement is about 1.39 times for the inter-rib distance of 40mm and an air gap height of 3mm while the maximum fiction factor achieved was about 3.82 times for pitch value of 40mm and air gap height of 3mm. The highest thermal enhancement factor is achieved for the pitch value of 320mm and an air gap height of 3mm at Re=6000. The air gap height value of 10mm exhibits thermal enhancement factor values lesser than 1.0 and hence is not recommended for use as heat transfer enhancement device for the entire Reynolds number range used in the analysis. The pitch value of 320 mm exhibits thermal enhancement factor greater than 1.0 for almost all the Reynolds number range used in the analysis and varies between 0.93 and 1.07.

Influence of perforated triple twisted tape on thermal performance characteristics of a tube heat exchanger

One of the challenging tasks in the development of heat exchangers is to select an appropriate geometry that will consume minimum energy. This could be achieved by designing a suitable enhancing device which will boost the thermal performance characteristics of heat exchangers. Twisted tape swirl generator, a heat transfer enhancement device equipped in a tube heat exchanger would induce turbulence and superimposed vortex motion causing a reduction in the hydrodynamic or thermal boundary layer thickness which results in the improvement of convective heat transfer. In this study, a new design of perforated triple twisted tape (PTTT) insert was applied as a swirl flow device with four different porosities (Rp) of 1.2, 4.6, 10.4 and 18.6% to enhance the convective heat transfer of a tube heat exchanger. The effects of porosity (Rp) of PTTT swirl generators on heat transfer, fluid friction and thermal performance characteristics of a tube heat exchanger were experimentally investigated. The experiments were conducted under constant heat flux condition using air as the working fluid in turbulent flow regime for variation in Reynolds number (Re) from 7250 to 49,800. The Nusselt number of the tube installed with PTTT inserts for porosity ranging from 1.2 to 18.6% was found to be 88–320% higher, whereas, the friction factor was achieved to be 112–355% higher in comparison to the plain tube. The highest heat transfer result of 320% was obtained at a porosity of 4.6% with PTTT insert compared to the smooth tube. Despite the significant enhancement in heat transfer, the friction factor was obtained to be 355% higher in comparison to the plain tube at a porosity of 4.6% with PTTT insert. The experimental results demonstrated that Nusselt number, friction factor, and thermal enhancement efficiency (TEE) were increased with decreasing the porosity of the tape inserts except for 1.2%. The heat transfer performance was evaluated based on constant blower power and the values were found to be 1.13–1.5 relative to the plain tube. The maximum TEE of 1.5 was achieved using PTTT insert with a porosity of 4.6%. Based on the experimental data, the empirical correlations of heat transfer, friction factor and TEE were developed in terms of Rp, Re and Prandtl number (Pr) to predict the heat transfer, friction factor and TEE. The optimal design of PTTTs based on the evaluation of thermal performance with suitable porosity could be an excellent heat transfer enhancement device for many industrial applications.

Experimentally Study the Effects of Fins Height and Space Ratio (H\\S) to the Fin thermal performance by Natural Convections

Heat transfer enhancement devices are widely used in various industrial, transportation, or domestic applications such as thermal power plants, means of transport, heating and air conditioning systems, electronic equipments and space vehicles. In all these applications, improvements in the efficiency of heat exchangers can lead to substantial cost, space and materials savings. The research work summarized in this articles presents an experimental investigation on the effect of fin space (S) on the fin performance using rectangular plate type fins. The steady-state natural convection heat transfer from vertical rectangular fins extending perpendicularly from horizontal square base was investigated experimentally at high range of temperatures from 50 to 150 C°. The effects of fin space parameter, fin height-space (H\\S) ratio and base-to-ambient temperature difference on the heat transfer performance of fin arrays were observed and the environmental condition were determined.. Five fin height-space ratios settings 1.31,1.43,1.67,1.85 and 2.27 with constant fin surface area were employed under free convection heat transfer conditions. The heat transfer area was kept the same. The performance of the fin expressed in terms of fin efficiency, effectiveness and thermal resistance as a function of the ambient temperature and fin space parameters has been study in this work. The dimensionless parameter Biot no. on the locally variable environmental condition is examined for different fin spaces and fin height-space (H\\S) ratio to the fin heat transfer rate. Also, the effect of environmental condition is study at the same (H\\S) ratio. Experimental results show that the effect of Height-Space ratio (H\\S) on fin performance is more significant.. The maximum increase in convection heat transfer coefficient value obtained is about 19 percent. The increase in heat transfer coefficient value is also manifested by a corresponding decrease in the fin base temperature. Also, it is concluded from the experimental results that the performance of heat transfer rate increase with increasing the height- space ratio (H\\S) and decreasing the fin space in respect of heat transfer coefficient, thermal resistance, overall efficiency and effectiveness.

Exergy transfer characteristics analysis of turbulent heat transfer enhancement in surfactant solution

This paper presents an exergy transfer analysis for turbulent drag reducing surfactant solution flow with and without heat transfer enhancement devices which employ static or dynamic mixers. Heat transfer and pressure drop measurements were performed at an inlet temperature of 297.7–298.2 K in pipe flow with a concentric tube heat exchanger. The environmental temperature in the analysis was set to be 288.2 K in assumption of a cooling system. The experimental range of the Reynolds number was 1.0×104 to 4.2×104. Adding surfactant to a water flow decreases the exergy transfer Nusselt number, Nue, owing to the heat transfer reduction and increases the exergy transfer efficiency, ηeff, by a maximum of 9.3% at high Reynolds numbers at moderate fluid transport distance owing to the drag reduction. Also the secondary flow caused by the enhancement devices increases Nue. The proposed flow performance curve which provides ηeff for an arbitrary Nue shows that ηeff in viscoelastic fluid flow compared to Newtonian fluid flow is small independently of the fluid transport distance, and that the installation of heat transfer enhancement devices has a positive effect on energy-saving in certain ranges of Reynolds numbers and fluid transport distances.

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel.

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Wall-mounted perforated cubes in a boundary layer: Local heat transfer enhancement and control

A passive convective heat transfer enhancement device based on perforated obstacles is proposed. The perforation crosses the obstacle from the flow-facing side to the rear side. In this configuration a jet is delivered from the obstacle perforation, thus changing the topology of the wake behind the obstacle. Measurements of the convective heat transfer over a flat plate equipped with perforated wall-mounted cubes are carried out using infrared thermography. Flow fields measurements are performed with Particle Image Velocimetry to address the effect of the perforation (and of the jet issuing from it) on the wake topology and on the heat transfer distribution. A modal analysis is carried out with Proper Orthogonal Decomposition to extract the coherent structures organization and the modifications induced by the perforation of the obstacle. When comparing the results of the perforated cubes with those of a solid cube, it can be observed that perforated obstacles offer a simple solution to obtain a localized increase of the convective heat transfer when the perforation crosses the obstacle creating a jet directed towards the wall. This is obtained at the expenses of a reduced space-averaged heat transfer rate due to a ’lift-up’ of the recirculation bubble past the obstacle, which postpones the flow reattachment and reduces the velocity of the reattaching flow. Nevertheless, in case of large perforation angles (thus jet issuing with larger angle with respect to the streamwise direction) this penalty is significantly reduced, providing a local gain in terms of heat transfer rate with almost the same overall heat transfer performances as a solid obstacle.

Flow and Heat Transfer Characteristics of Supercritical Hydrocarbon Fuel in Mini Channels With Dimples

An idea of using dimples as heat transfer enhancement device in a regenerative cooling passage is proposed to extend the cooling limits for liquid-propellant rocket and scramjet. Numerical studies have been conducted to investigate the flow and heat transfer characteristics of supercritical hydrocarbon fuel in a rectangular cooling channel with dimples applied to the bottom wall. The numerical model is validated through experimental data and accounts for real fuel properties at supercritical pressures. The study shows that the dimples can significantly enhance the convective heat transfer and reduce the heated wall temperature. The average heat transfer rate of the dimpled channel is 1.64 times higher than that of its smooth counterpart while the pressure drop in the dimpled channel is only 1.33 times higher than that of the smooth channel. Furthermore, the thermal stratification in a regenerative cooling channel is alleviated by using dimples. Although heat transfer deterioration of supercritical fluid flow in the trans-critical region cannot be eliminated in the dimpled channel, it can be postponed and greatly weakened. The strong variations of fuel properties are responsible for the local acceleration of fuel and variation of heat transfer performance along the cooling channel.

Thermal performance of rotating two-pass ribbed square channel with wavy sidewalls

Detailed Nusselt number (Nu) distributions over Leading Endwall (Le-E) and Trailing Endwall (Tr-E), Fanning friction coefficients (f) and thermal performance factors (TPF) of a radially rotating two-pass square channel enhanced by in-line 45° endwall ribs and wavy sidewalls were measured at the test conditions of 5000⩽Re⩽20,000, 0⩽Ro⩽0.3 and 0⩽Bu⩽0.053. No previous study has examined the thermal performances of a rotating ribbed two-pass channel with wavy sidewalls. A selection of heat transfer data illustrates the individual and interdependent effects of Re, Ro and Bu on local and region-averaged Le-E and Tr-E Nu. A set of Le-E and Tr-E heat transfer correlations that determines the rib-wise and regionally averaged Nu over the inlet and outlet ribbed endwalls, as well as over the smooth bend endwall is generated. Along with the f data detected from the ribbed endwalls and wavy sidewalls at isothermal conditions, the TPF values at various rotating conditions are evaluated. The heat transfer, pressure drop and TPF performances for the two-pass channel with present combined passive Heat Transfer Enhancement (HTE) device at rotating conditions are subsequently compared with those generated by the typical HTE devices deployed in the internal coolant channels of a gas turbine rotor blade. Acting by the combined Re, Ro and Bu effects, present region-averaged Nusselt numbers over the rotating Le-E (Tr-E) of the inlet-leg, sharp bend and outlet-leg are respectively raised to 3.20–5.80 (4.10–8.59), 4.26–10.48 (5.03–15.47) and 1.48–12.47 (4.64–8.24) times of the Dittus–Boelter reference levels. With the f coefficients increased to 9.61–25.7 times of the Blasius equation levels by present HTE measure and the 180° sharp bend, present TPF values obtained at the rotating test conditions fall in the range of 2.87–0.71, suggesting the favorable heat transfer effectiveness with cooling applications to gas turbine rotator blades.

열전달 향상 장치에 따른 평판형 태양열 집열기의 압력강하 및 열전달 특성

Abstract : The surface roughness and heat transfer enhancement devices are known to increase the performance of a flat plate soar collector. This study includes the experiments on the effect of the several heat transfer enhancement devices inserted in duct to simulate the flat-plate solar collector. Experiment was basically at a constant heat flux on the upper duct wall. Inserted heat transfer enhancement devices are Chamfered rib 10°, Chamfered rib 20°, Rib & Groove and Rib & Dimple. Reynolds number is in the range of 2,300 to 22,000 which corresponds to turbulent regime. With the heat transfer enhancement devices, heat transfer would increase by the secondary flow and the increase of the heat transfer area. Pressure drop also increases with the insertion of the enhancement devices. Rib & Dimple model is the best in heat transfer enhancement, however, Chamfered rib 10° model is the lowest in the pressure drop. Considering the heat transfer enhancement simultaneously with low pressure drop increase, performance factor was the best for the Chamfered rib 10°.

Numerical study of hydrodynamic and heat transfer of nanofluid flow in microchannels containing micromixer

In this study heat transfer and fluid flow of Al2O3/water nanofluid in two dimensional parallel plate microchannel without and with micromixers have been investigated for nanoparticle volume fractions of ϕ=0,ϕ=4% and base fluid Reynolds numbers of Ref=5, 20, 50. One baffle on the bottom wall and another on the top wall work as a micromixer and heat transfer enhancement device. A single-phase finite difference FORTRAN code using Projection method has been written to solve governing equations with constant wall temperature boundary condition. The effect of various parameters such as nanoparticle volume fraction, base fluid Reynolds number, baffle distance, height and order of arrangement have been studied. Results showed that the presence of baffles and also increasing the Re number and nanoparticle volume fraction increase the local and averaged heat transfer and friction coefficients. Also, the effect of nanoparticle volume fraction on heat transfer coefficient is more than the friction coefficient in most of the cases. It was found that the main mechanism of enhancing heat transfer or mixing is the recirculation zones that are created behind the baffles. The size of these zones increases with Reynolds number and baffle height. The fluid pushing toward the wall by the opposed wall baffle and reattaching of separated flow are the locations of local maximum heat transfer and friction coefficients.

Thermal performances of enhanced smooth and spiky twisted tapes for laminar and turbulent tubular flows

This experimental study investigates the heat transfer properties over developing and developed flow regimes, the pressure drop coefficients and the thermal performance factors (TPF) of tubular flows with the continuous and spiky twist tapes enhanced by perforated, jagged and notched winglets. The axial distributions of Nusselt number (Nu) and the mean Fanning friction factors (f) of the tubular flows at Reynolds numbers (Re) ranging from 500 to 40000 are comparatively examined for five different types of twisted tapes with three twist ratios (y) of 1.875, 2.186 and 2.815 for each type of twisted tapes. Through this comparative study, the favorable types of twisted tapes which generate the higher degrees of HTE impacts over the developing and developed flow regimes are respectively identified. These newly devised twist tapes enrich the varieties of passive heat transfer enhancement (HTE) devices, especially for retrofit applications. A set of selective Nu and f results illustrates the thermal characteristics of the enhanced tubular flows by these twisted tapes. The HTE and TPF properties for all the present types of twisted tapes are subsequently compared with those reported for other types of twisted tapes in the literature. Among these comparative groups, the present V-notched spiky twisted tape generally offers the highest HTE impacts with favorable TPF performances. Empirical correlations that evaluate the averaged Nu over the developing and developed flow regimes; as well as and tube-wise averaged f for the enhanced tubular flows fitted with all the present types of twisted tapes are generated.

Heat transfer enhancement of natural convection with ribs

Natural convection heat transfer is found in many industrial applications such as nuclear technologies, electronic circuit board cooling, solar panel cooling and many other fields. When natural convection heat transfer coefficients are insufficient, passive heat transfer enhancement devices (called ribs/fins) are often used. In this paper, the effect of periodic patterns of protrusions (ribs) on the free-convection heat transfer of a vertical plate, with a uniform heat flux rate boundary condition, is experimentally investigated. The convective fluid is air. Two-dimensional, high resolution heat transfer measurements are performed by using infrared thermography and the heated thin foil technique. Experiments are performed on two types of ribs pattern topology: single or two staggered rows of ribs inclined at different angles and single or two-staggered rows of V-ribs.