Foam Inserts Research Articles

Improving a shell-tube latent heat thermal energy storage unit for building hot water demand using metal foam inserts at a constant pumping power

The phase transition heat transfer during the melting and solidification processes of phase change materials (PCMs) was modeled in a shell-tube thermal energy storage unit. For the first time, special attention was dedicated to the heat transfer enhancement on the heat transfer fluid (HTF) side by placing metal foam (MF) inserts in the HTF tube. The MF inserts on the HTF side were placed next to the fin bases to produce the maximum heat transfer enhancement. A two-temperature local thermal non-equilibrium model was applied to accurately model the transient heat transfer in the MF domains. To perform a fair heat transfer analysis and consider the hydrodynamic aspects of heat transfer, the pumping power for driving the HTF fluid was kept fixed. The finite element method with automatic time-step control was used to integrate the model equations. Results show that the insertion of the MF in the HTF tube enhances conduction heat transfer but reduces flow for a constant pump power. Using a small amount of MF provides a good flow rate and a convective heat transfer while using a large amount of MF provides good conduction heat transfer but a poor flow rate and convection. A moderate amount of MF inserts results in poor conduction and a poor flow rate, notably increasing the phase transition time. A 5 % MF insert could provide about a 13 % shorter solidification time compared to a 25 % MF insert. Thus, a well-designed and engineered MF insert configuration on the HTF side can reduce the phase transition time and improve the energy storage power.

A shell-tube latent heat thermal energy storage: Influence of metal foam inserts in both shell and tube sides

Enhancing heat transfer in latent heat thermal energy storage systems is of utmost importance to facilitate the efficient absorption and release of thermal energy. The primary objective of the current study is to investigate the influence of a metal foam layer on heat transfer enhancement in both the heat transfer fluid side and the shell side. The research explores the incorporation of a fixed 30 % foam layer, which can either extend along the tube wall or penetrate deeper into the shell, moving away from the heat transfer fluid tube. A local thermal non-equilibrium two-temperature heat equation model is utilized to mathematically model the interactions within the metal foam embedded in the heat transfer fluid tube and the phase change material domain. The governing equations are solved using the finite element method. The results indicate that adjustments to the inlet pressure and the metal foam shape parameter (FL) can significantly reduce the melting time, with a variation of approximately 40 %. Specifically, at a constant inlet pressure of 750 Pa, the energy storage power at a 90 % charging increases from 32.2 W (FL = 0.75) to 48.7 W (FL = 1.37). A modification of FL shape parameter increased the power output by 34 %.

Optimizing thermal performance in tube-in-tube heat exchangers with metal foam inserts: experimental and RSM analysis

ABSTRACT This study investigates tube-in-tube heat exchanger performance under steady-state conditions, examining co-current and counter-current flows. It explores various configurations, including metal foam enhancements, to optimize heat transfer efficiency and minimize pressure drop. Driven by the potential of metal foam to enhance heat transfer, the study aims to demonstrate significant improvements in thermal performance compared to conventional designs. Experimental methods involve testing four configurations with Nickel foam (10 PPI, 0.90 porosity) inserts, evaluating temperatures and pressure drops across flow rates of 25 to 50 LPH. Hot water at 65°C flows in the annulus, while normal water at 31°C flows in the outer annulus. Results show metal foam’s substantial enhancement in heat transfer, with counter-current metal foam configurations achieving up to 3.71 times greater efficiency than parallel flow setups. Moreover, comprehensive performance evaluation reveals that the counter-flow heat exchanger with metal foam is 2.03 times more efficient than the conventional co-current flow without metal foam. Conclusions highlight metal foam’s effectiveness in improving heat transfer performance and optimizing thermal systems through systematic parameter optimization using response surface methodology.

Failure analysis of CFRP/Al single lap adhesive joint with enhancing porous metal foam insert

Cohesive failure is one of the main causes of adhesive bonding failure. The enhanced method and mechanism for adhesive signify a critical research issue for better adhesive joint design. This study proposes using a porous metal foam insert adhesive to enhance the carbon fiber reinforced polymer/aluminum single lap joint. In particular, stress distribution and failure locations of joints with and without insert were compared by simulation modeling. The insert of the Cu-foam, Fe-foam, and Ni-foam, compared to no insert, increased the shear strength of the bonded joint by 32.23 %, 36.66 %, and 66.82 %, respectively. Compared to no insert, the crack propagation of the joint with a metal foam insert was changed from the cross-section of the adhesive layer to the plane of the foam insert. The highest strength of the adhesive joint with the Ni-foam insert was further analyzed to determine fatigue behavior compared with pure adhesive joint under different stress levels. Compared to no insert, the fatigue life increased highly, and the crack path was prolonged.

Enhancing thermal-hydraulic performance in heat exchangers with metal foam inserts: a comprehensive experimental investigation

ABSTRACT This research investigates the use of metal foam inserts to enhance the thermal-hydraulic performance of double-tube heat exchangers, relevant for energy-efficient systems such as solar flat plate collectors. Motivated by the need for improved heat transfer efficiency, this study hypothesizes that metal foam integration can significantly boost performance. Through systematic experimental study, the impact of metal foam inserts on heat transfer and pressure drop characteristics is comprehensively evaluated across various configurations, spanning horizontal and vertical orientations. Experimental evaluations were conducted on four configurations, including both conventional and metal foam-integrated heat exchangers in horizontal and vertical orientations, using water as the working fluid and Nickel metal foam with 0.9 porosity and 10 PPI in the annular space. The findings highlight significant enhancements in heat transfer performance with metal foam integration across both horizontal and vertical heat exchanger configurations compared to conventional counterparts, particularly showcasing superior effectiveness and efficiency in the horizontal configuration. Results show that metal foam integration substantially enhances heat transfer, with horizontal configurations exhibiting a 14.56% higher heat transfer coefficient than vertical ones. Additionally, the comprehensive performance index improved by 1.17 times, indicating a better balance between heat transfer enhancement and pressure loss. These findings were validated against established correlations from the literature, confirming the superior effectiveness of horizontal metal foam heat exchangers.

Heat transfer analysis of subcooled flow boiling in copper foam helical coiled heat exchanger – A pore-scale numerical study

High performance thermal energy systems are crucial in fulfilling the growing demand of thermal energy. Consequently, numerous heat transfer enhancements have been proposed. Some of the promising methods are boiling flow heat transfer, helical coiled tube and metal foam insert. Although the performance of each strategy has been extensively studied, based on our literature review, the effectiveness of combining these strategies has not been investigated. This missing information may impede further development of efficient heat transfer systems. This study is therefore performed to investigate subcooled flow boiling heat transfer in helical tube with copper foam insert. A high-resolution three-dimensional pore scale model that considers the shape, porosity and pore density of the metal foam is developed and validated against the published experimental results. Using the model, the effect of inlet temperature, mass flux, wall heat flux, porosity, pore density and half-filled metal foam are studied. The results suggest that operating parameters have mild effects on the heat transfer performance. In contrast, porosity and pore density show significant influence in heat transfer coefficient and pressure drop. It has also been found that total heat transfer surface area and base area are better in characterizing heat transfer in pore-scale level than porosity and pore density at pore-scale level. Moreover, implementing metal foam at outer half of the tube is observed to offer slightly better heat transfer than implementing it at the inner side by around 4.8%. Overall, this study indicates that helical metal foam tubes offer the best performance at mass flux of 200 kg/m2∙s with performance index of 0.72, while straight tubes with 0.90 porosity has the highest performance index of 0.66. Empirical correlations to relate dimensionless parameters to the Nusselt number and friction factor is generated. Finally, the model developed in this study can serve to provide guidelines for the upcoming studies in boiling in metal foam structure and assist in designing metal foam heat exchangers.

Continuous turbulent liquid-liquid emulsification using open-cell solid foams: Experimental investigation and modelling

The study investigates the efficiency of liquid-liquid emulsification using three types of open-cell solid foams. Initially, the pressure drop profiles revealed the non-negligible impact of the inertial term at a low viscosity of the continuous phase, with profiles becoming more linear at higher viscosities. The Darcy-Forchheimer model effectively predicted pressure drops with a maximum mean relative error of 14%. Emulsification performance (seen as a decrease in the droplet size) was then evaluated by varying dispersed phase viscosity, superficial fluid flow velocity and foam insert packing length, comparing results with structured static mixers (SMX+). The droplet size of the dispersed phase rapidly decreased within the first foam inserts before stabilizing at a length of 175 mm. Under the same superficial velocity, the mean droplet diameter is correlated to the foam's mean pore size. SMX+ mixers exhibited emulsification capability comparable to solid foam with the largest pores, while medium and small pore foams produced smaller droplets. Finally, the Middleman's correlation with viscosity correction accurately predicted mean droplet size at equilibrium and across various scenarios.

The Effect of Uneven Metal Foam Distribution on Solar Compound Parabolic Trough Collector Receiver Thermal Performance

Solar energy is a key player among other renewable energies that reduce greenhouse gases and replace conventional fuel, i.e., to solve global warming and fossil fuel descending issues. However, the thermal solar systems’ performance should be enhanced to cope with intermittent solar radiation. Metal foam can be used as an enhancer in solar collectors’ receivers. However, metal foams are associated with pressure drop. To benefit from the metal foam as a thermal enhancer and overcome the pressure drop issue, the present study numerically and experimentally investigates a novel Compound Parabolic Solar Collector (CPC) receiver with innovative uneven metal foam inserts of varying thickness. Two pores per inch (PPI) Cu-foam inserts, PPI10 and PPI20, were tested. These inserts were strategically placed at three different positions along the receiver, with thicknesses of 3 cm, 2 cm, and 1 cm starting from the inlet side. In the experimental part, three tubular receivers were tested, empty, i.e., without metal foam, inserted with Cu-foam of PPI10, and inserted with Cu-foam of PPI20. The experiments were conducted from 09:00 AM to 04:00 PM. The investigation involved water volume flow rates from 0.2 to 0.6 l/min. The numerical part included solving the governing equations, i.e., mass, momentum, and energy conservation, simulating conditions similar to the experiments. The Brinckman model described the fluid flow through the metal foam. The thermal performance of the CPC system was evaluated using the Nusselt number (Nu), thermal efficiency, water bulk temperature, and water outlet-inlet temperature difference. Inserting Cu-foam of PPI20 resulted in the hourly maximum Nu and thermal efficiency compared to the empty and PPI10 cases. Experimentally, the hourly maximum Nu was 8.9, 8.4, and 7.9 for PPI20, PPI10, and empty receivers, respectively, at 0.6 l/min. The average thermal efficiency was 88.3, 85, and 81.9 for PPI20, PPI10, and empty receivers, respectively, at 0.6 l/min. As for the outlet-inlet water temperature difference, the highest values were at 0.2 l/min. Again, PPI20 recorded the best results, i.e., 23.3 K, 21.5 K, and 20.2 K for PPI20, PPI10, and empty cases, respectively.

BEARING CAPACITY, DEFORMITY AND CRACK RESISTANCE OF DAMAGED BEAMS REINFORCED WITH FIBER CONCRETE

The results of experimental studies of the load-bearing capacity, deformability and crack resistance of damaged beams reinforced with fiber concrete in the compressed and stretched zone are presented. Test samples are made of concrete and fiber concrete. The amount of steel fiber in fiber concrete is 2% of the volume of the product. Preliminary tests were carried out on prisms and cubes. During the manufacture of beam samples, before concreting, a foam insert was installed in the area of planned damage, the shape and dimensions of which corresponded to the damage. After the concrete set to 70% grade strength, the liner was pulled out, and the resulting cavity was filled with a 2% mixture of fiber concrete. Tests of material samples showed that the introduction of steel fiber into the composition of concrete in the amount of 2% by volume increases the compressive strength limit by 15.3%. The initial modulus of elasticity of fiber concrete of the specified mixture is 38.0% higher than that of ordinary concrete of this composition. Conducted experimental studies of damaged beams showed that a beam whose cross-section is 40% damaged in the middle-compressed zone, and the shape of the damage is close to rectangular, has a load-bearing capacity of 92.0 kN, or 93.9% of the load-bearing capacity of an undamaged beam. Cracking started at the 4th loading stage, when the load value was 26.0kN, i.e. 28.3% of the bearing capacity of the damaged beam. The maximum final crack opening width was 0.6 mm. A beam whose section is 40% damaged in the mid-stretch zone has a load-bearing capacity of 92.4 kN, or 93.2% of the load-bearing capacity of an undamaged beam. Cracking started at the 5th loading stage, when the load was 32.5kN, i.e. 35.2% of the bearing capacity of the damaged beam. The maximum final crack opening width was 0.8 mm. It is claimed that the strengthening of a beam with 40% damage in the compressed or stretched zone in the manner considered in the paper is effective, as it allows achieving its load-bearing capacity, which is more than 93% of the load-bearing capacity of an undamaged beam.

BEARING CAPACITY, DEFORMABILITY AND CRACK RESISTANCE OF A DAMAGED BEAM REINFORCED WITH FIBER CONCRETE IN THE COMPRESSED ZONE

The paper presents the results of the study of the load-bearing capacity, deformability and crack resistance of a damaged beam reinforced with fiber concrete in the compressed zone. A beam with 40% damage is considered. The research was conducted in two stages. At the first stage, tests of prisms and cubes made of concrete and fiber concrete were carried out, which showed that the introduction of steel fiber into the composition of concrete in the amount of 2% by volume increases the compressive strength by 15.3%. The initial modulus of elasticity of fiber concrete of the specified mixture is 38.0% higher than that of ordinary concrete of this composition. According to the results of experimental studies of prisms, a diagram of concrete deformation, the nature of changes in relative linear deformations of fiber concrete, as well as graphs showing a comparison of the nature of deformation of concrete and fiber concrete were constructed. At the second stage, the beam sample was tested on a specially designed stand. Before concreting, a foam insert was installed in the zone of planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete set to 70% strength, the liner was removed, and the formed cavity was filled with a 2% fiber concrete mixture. A beam with 40% cross-sectional damage in the mid-compression zone and a near-rectangular damage shape was found to have a load-bearing capacity of 92.0 kN, or 93.9% of the load-bearing capacity of an undamaged beam. Cracking started at the 4th loading stage, when the load value was 26.0kN, i.e. 28.3% of the bearing capacity of the damaged beam. At the same time, 5 cracks formed in the area of pure bending. At the fifth stage, two more cracks appeared. At the 8th and 9th loading stages, 4 more cracks formed. A total of 12 cracks were formed. The maximum final crack opening width was 0.6 mm. Thus, the strengthening of a beam with 40% damage in the compressed zone by the method considered in the work allows you to achieve its bearing capacity, which is 93.9% of the bearing capacity of an intact beam.

EXPERIMENTAL STUDIES ON THE STRENGTHENING OF A BEAM DAMAGED IN THE TENSILE ZONE

The paper presents the results of a study of the bearing capacity of a beam damaged during hostilities, which was reinforced with steel-reinforced concrete. Consider a beam with 40% damage in the stretched zone. Before concreting, a foam insert was installed in the zone of planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete set to 70% strength, the liner was removed, and the formed cavity was filled with a 2% fiber concrete mixture. This is one of the options for beam strengthening in a complex program of testing damaged beams, which involves the study of a series of beams with different types of damage, the damage zone (tension and compression) and its dimensions, geometry and method of strengthening. For testing, the authors developed a special stand. The plane-transverse load bending of the beam under study is created with the help of a hydraulic jack and a metal I-beam with a traverse, which transmits two equally concentrated forces to the beam. The generated load is controlled by a model dynamometer of the Tokar system and a ring dynamometer, which acts as a support. Experimental studies have established that a beam whose cross-section is 40% damaged in the middle stretched zone, and the shape of the damage is close to rectangular, has a bearing capacity of 91.0 kN, which is 92.38% of the bearing capacity of an intact beam (98.5 kN ). Cracking started at the 5th loading stage, when the load value was 32.5kN, i.e. 35.7% of the bearing capacity of the damaged beam. At the same time, 4 cracks were formed. At the sixth stage, three more cracks appeared. At stages 9-12 of loading, 9 more cracks formed. The maximum final crack opening width was 1.1 mm. At the same time, 6 cracks formed in the zone of clean bending. During the entire testing process, the fiber concrete liner worked with the beam as a single unit. It can be argued that the strengthening of a beam with 40% damage in the stretched zone in the manner considered in the paper allows to achieve its bearing capacity, which is 92.38% of the bearing capacity of an undamaged beam.

Multi-scale ultrasonic imaging of sub-surface concrete defects

This paper introduces a new method for creating the ultrasonic image of concrete that utilizes both linear and nonlinear wave properties in a single measurement. Linear ultrasonic imaging relies on wave velocity. The resolution of linear ultrasonics for various inclusion sizes and inclusion-to-base material ratios is numerically and experimentally studied. The nonlinear ultrasonic testing (NLUT) image is based on the acoustic nonlinearity coefficient, calculated using inputs of the first and second harmonic amplitudes, wave number, and the distance between the transmitter and receiver. The ultrasonic waveform is decomposed into its harmonics using wavelet transform. Their wave velocities, wave numbers, and amplitudes are extracted to calculate the linear wave velocity and the acoustic nonlinearity coefficient. Four calibration samples with different inclusions are tested to evaluate the effectiveness of combining two imaging methods: pure concrete, concrete with small foam inserts simulating air inclusions, and two concrete samples with larger foam inclusions. The angle dependence of acoustic nonlinearity coefficient is shown. The results show that constructing both linear and nonlinear ultrasonic imaging is necessary when the defect’s properties are unknown.

BEARING CAPACITY OF A BEAM DAMAGED DURING COMBAT ACTIONS STRENGTHENED WITH THE USE OF FIBER CONCRETE

The paper presents the results of a study of the load-bearing capacity of a beam damaged during hostilities, which was reinforced with steel-reinforced concrete. A beam with 20 percent damage in the compression zone is considered. Before concreting, a foam insert was installed in the area of the planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete was set to 70% grade strength, the liner was pulled out, and the resulting cavity was filled with a 2% mixture of fiber concrete. This is one of the beam strengthening options in a comprehensive damaged beam testing program, which involves the study of a series of beams with different types of damage, varying damage zone (tensile and compression) and its magnitude, geometry and method of strengthening. The authors developed a special stand for testing. The load-bearing capacity of the damaged beam reinforced with fiber concrete was 80.6 kN, or 89.5% of the load-bearing capacity of the intact beam. Cracking started at the 4th load stage, when the load value was 16.1 kN, or 20% of the bearing capacity of the damaged beam. At the same time, 10 cracks formed in the zone of pure bending, the opening width of which did not exceed half the price of the microscope division, which is 0.005 mm. At the next eight stages of loading (up to 48.4kN), no new cracks were observed, and the width of the opening of all the ones that had previously formed doubled - it reached 0.01mm. At the 12th, 13th and 19th stages of loading, 4 more cracks appeared. The maximum final crack opening width was 1.2 mm. Up to a load of 68.5kN, which is 85% of the load-bearing capacity of the damaged beam, the reinforced concrete liner works with the beam almost as a unit, and then the compressed zone of concrete squeezes out the liner. It is claimed that the strengthening of a beam with 20% damage in the compressed zone in the manner considered in the work allows to achieve its bearing capacity, which is almost 90% of the bearing capacity of an undamaged beam.

Experimental investigation of the heat transport and pressure drop in open-cell polyurethane foams

Foam-like materials have a large specific surface area and complex structure that promotes flow turbulence, which makes them useful for heat transfer. In the literature, heat transfer in metal foams (MF) with high thermal conductivity is mainly considered. In the present paper, an experimental study of the hydraulic and heat transfer characteristics of a rectangular channel filled with polyurethane foam (PUF) inserts with a thermal conductivity of 0.2 W⋅m−1⋅K−1 in the air flow was carried out. The open-cell PUF samples had 20 and 80 pores per inch (PPI), 0.97 and 0.98 porosity, 269 µm and 60 µm fiber diameter, respectively. The Reynolds number, based on the fiber diameter ranged from 0.04 to 50. From the results of hydraulic tests, friction coefficients were determined based on the fiber diameter and permeability. The Forchheimer coefficient was 0.198 and 0.318 for 20 and 80 PPI samples, respectively. The permeability was 1.889 10−7 ⋅m2 and 7.535 10−9 ⋅m2 for 20 and 80 PPI samples, respectively. The Nusselt number for both tested PUF samples was correlated with the Reynolds number based on the fiber diameter in a power law with the Reynolds number exponent and constant equal to 0.61 and 0.037 respectively. The intensity of heat transfer in the PUF samples was 7–12 times lower than that in MF. However, a significant heat transfer enhancement is still possible compared to the empty channel up to 7 times. The heat transfer performance of PUF was higher compared to the empty channel, but the thermal performance factor was lower than one. Nevertheless, in practical situations where the mass or cost of the heat exchanger is preferable, PUF can be considered as a heat transfer intensifier.

Eccentricity analysis of annular multi-tube storage unit with phase change material

Thermal energy storage (TES) with phase change materials (PCM) can improve energy efficiency by reducing energy availability and demand mismatch. However, despite the potential of this technology, the low thermal conductivity of PCM slows down the storage cycle and limits its commercialisation. The literature has proposed many solutions to improve heat transfer, such as fins, encapsulation, or metal foam inserts, which are too expensive and complicated. This study focuses on an inexpensive and practical solution, the eccentricity of shell and tube heat exchanger (STHE). Eccentricity's impact has been well established, but its effects on multi-tube cases have not yet been examined. This study investigates the eccentricities of four horizontal STHE with 1, 2, 3, and 4 tubes. The paper presents the ideal combinations of tube number and eccentricity for maximising TES efficiency and explores the underlying heat transfer and fluid mechanics phenomena. The enthalpy double porosities model accurately predicts the PCM melting and solidifying characteristics with varied eccentricities. Results reveal that the eccentric charge performance is better than the concentric tube(s) arrangement. The optimal eccentricity of the charging cycle depends on the tube number. The optimal eccentricities of the single and multi-tube systems are 6 and 10. The total melting time of optimal eccentricity for the four-tube, three-tube, two-tube, and single-tube is optimised by 63 %, 63 %, 60 % and 54 % compared to the concentric cases, respectively. The optimal eccentricity of the single-tube case has the shortest melting time, which increases linearly with the Rayleigh number. The concentric cases consistently exhibit the best performance and shortest solidification time as the Rayleigh number increases. The total solidification time of the single-tube case is reduced by 56 %, 52 % and 49 % compared to the four-tube, three-tube and two-tube, respectively. The multiphysical mechanisms of the charge and discharge cycles are discussed.

Multifunctional auxetic and honeycomb composites made of 3D woven carbon fibre preforms

Three dimensional (3D) woven composites started to find applications in various industrial sectors, mainly in aerospace and with a potential in automotive. 3D-woven fabrics can be architected to form complex and near-net-shape preforms ready for automated composites manufacturing. The 3D-woven honeycomb fabric is designed to include additional functionality into finished composites, such as positive and negative Poisson's ratios. In this study, complex honeycomb architectures were created using various weave designs to demonstrate the effects of auxetic behaviours when manufactured into a composite structure. A Staubli 3D-weaving system equipped with Jacquard UNIVAL 100 and creel of 3072 6 k carbon fibre tows were used to weave the designed honeycomb architecture. With the aid of hard polyester foam inserts, the 3D-woven fabrics were converted to honeycomb and auxetic preforms. These preforms were infused using epoxy resin to manufacture a set of honeycomb and auxetic composite structures. In comparison with the baseline honeycomb structure, it is proven that the developed auxetic composites exhibited negative Poisson’s ratio of − 2.86 and − 0.12 in the case of tensile and compression tests respectively.

Evaluation of discharging performance of molten salt/ceramic foam composite phase change material in a shell-and-tube latent heat thermal energy storage unit

Molten salts are widely used energy storage media in integrated solar power systems, however, due to their high corrosivity and the extreme high-temperature environment, many current methods of heat transfer enhancement do not apply. Herein, we proposed to use ceramic foam to enhance the discharging performance of molten salt to efficiently supply heat for power generation. The ceramic foam was prepared and its corrosion resistance was confirmed experimentally. The discharging performance in a shell-and-tube latent heat thermal energy storage unit was numerically studied. It is found that compared to the configuration without enhancement, the solidification time of the ceramic foam-enhanced unit is shortened by up to 52.0%. The unit with the upper foam insert shows better discharging performance than the one with the lower foam insert. Different foam filling height is also considered and results indicate that the thermal energy release rate always increases with the foam filling height and that of the fully foam-inserted unit is 118.1% higher than that of the none foam-inserted unit. For the first time, the discharging performance of ceramic foam-enhanced molten salt is quantitatively evaluated. This study provides guidance on designing thermal energy storage sub-system with excellent heat supply performance for solar power generation.

Place smart, load hard - structural reinforcement of the trailing edge regions of a wind turbine blade strengthening the buckling resistance

Local buckling is one of the key driving forces of trailing edge failure in composite wind turbine blades. This study demonstrated a significant stiffness increase by adding a minor amount of foam material to the trailing edge region of a wind turbine blade. The proposed ‘place smart, load hard’ concept is based on the understanding of the local buckling in the critical trailing edge regions and to place additional foam there, where the blade is prone to buckle. The effective placing of foam inserts is numerically demonstrated for different load scenarios and its superiority compared to an experimentally validated blade model without foam inserts. The proposed strengthening method can be used for both building new blades and retrofitting old blades with local buckling issues in the trailing edge regions.

Review of analytical studies of melting rate enhancement with fin and/or foam inserts

Phase change materials (PCMs) are extensively used in thermal energy storage (TES) applications but most of them own poor thermal conductivities. Melting of a PCM can be thermally enhanced by means of inserting high-conducting fin and/or foam structures, nevertheless, relevant design guideline for a PCM system with these thermal enhancers is yet absent partly because our interpretation of such systems is limited to particular experiments or simulations that usually valid only over a certain (and narrow) range of parameter values. In order to develop such guideline for practicing engineers, one must gain a comprehensive understanding of melting characteristics under different conditions. Hence, this review concerns only on theoretical works of melting with/without fin and foam structures. Isothermal melting without inserts inside a rectangular box under lateral, basal and inclined heating conditions will be firstly reviewed, afterwards, heat transport dimensions of melting in horizontal cylinder and sphere are clarified. Of a PCM system fin structures can be classified into straight and non-straight fins, whereas the former can be further subdivided into “short” lumped fins and “long” semi-infinite fins. Comparatively, only a few works of non-straight fins and porous foams are perceived due mainly to their irregular and complicated structures. Furthermore, different criteria for evaluating the performance of melting rate enhancement are summarized. Accordingly, the research gaps of theoretical works are remarked and several recommendations are introduced.

Simulating the acoustic response of cavities to improve microphone array measurements in closed test section wind tunnels.

Cavities placed along wind tunnel walls can attenuate the turbulent boundary layer (TBL) fluctuations as they propagate into the cavity. Placing microphones within the cavities can thus improve the signal-to-noise ratio of acoustic data. However, standing waves form within these cavities distorting the acoustic measurements. This work uses a finite element (FE) solver to evaluate how cavity geometry (depth, diameter, and wall angle) and wall material (hard-walled and melamine foam) affect the amplitude and eigenfrequency of standing waves when excited by an incident acoustic plane wave. Good agreement between predicted and measured acoustic transfer functions is shown. Compared to cylindrical cavities, countersunk and conical cavities improve the overall response, i.e., reducing the quality factor quantifying the resonance and damping characteristics. Stainless steel coverings also reduce the quality factor. A finding is that the shape of the external foam holder rather than the cavity shape drives the standing wave characteristics for the melamine foam cavities. The optimization problem of minimizing the acoustic response while also attenuating the TBL is thus decoupled by using the melamine foam. Consequently, these considerations can be addressed independently by optimizing the outer cavity shape for acoustics and the melamine foam insert for TBL attenuation.