Porous Absorber Research Articles

Thermo-mechanical solar receiver design and validation for a micro gas-turbine based solar dish system

This work presents the comprehensive development of a solar receiver for the integration into a micro gas-turbine solar dish system. Special focus is placed on the thermo-mechanical design to ensure the structural integrity of all receiver components for a wide range of operating conditions. For the development, a 3-dimensional coupled multi-physics model is established and is validated using experimental data. Contrary to previous studies, the temperature of the irradiated front surface of the absorber is included in the comprehensive validation process which results in a high level of confidence in the receiver design.Finally, a full-scale solar receiver for the integration into the OMSoP solar dish system is designed and its performance determined for a wide operating range to define its safe operating envelope using the validated model. It is shown that the receiver is capable of operating at 803°C with an efficiency of 82.1% and a pressure drop of 0.3% at the nominal operating point, while at the same time functioning effectively for a wide range of off-design conditions without compromising its structural integrity. At the nominal operating point, the maximum comparison stress of the porous absorber is 5.6 MPa compared to a permissible limit of 7.4 MPa.

Accelerated C2H2/CO2 Separation by a Se-Functionalized Porous Coordination Polymer with Low Binding Energy.

High-quality pure acetylene (C2H2) is a kind of crucial starting material for various value-added products. However, selective capture of C2H2 from the main impurity of CO2 via porous absorbents is a great challenge, as they possess extremely similar kinetic diameters and boiling points, as well as the explosive and reactive properties of C2H2. Herein, we report a porous coordination polymer (PCP), (NTU-55), which assembled from the coordination between a Cu dimer and a newly designed ligand with a nonmetal selenium (Se) site. Static single-component adsorption and dynamic breakthrough experiments reveal that desolvated NTU-55 can completely adsorb C2H2 from the C2H2/CO2 mixture (1/4, v/v) at 298 K, along with higher C2H2 capacity and much lower binding energy. The origin of this separation, as comprehensively revealed by density functional theory (DFT) calculations, is derived from the interaction discriminatory of C2H2 and CO2 toward accessible Se and Cu adsorption sites. To the best of our knowledge, this is the first time to find the positive effect of nonmetal Se sites for selective C2H2 capture.

Combustion behavior of rotary solid porous burners (RSPB)

The combustion behavior of rotary solid porous burners (RSPB), i.e., temperature (T), exhaust gas (CO and NOx) and combustion efficiency (nc) were investigated. The stainless wire-mesh type of porous media was selected as porous absorber with porosity of 0.82, thickness of 4.2 mm. The rice husk was used as the fuel with the humidity around 12-14%. The experiment showed that the T tends to increase following the rotating velocity (ro) rising around 0.5-1 rpm. When a ro increased to 1.5 rpm, a T had tendency decreasingly. Because, a ro was too high resulting in the fuel in combustion chamber were ejected quickly then the reaction time reduced not enough to burn fuel, leading to incomplete combustion. The air flow rate (Qa) of 40 m3/h and the fuel load input rate (Qf) of 2.3 kg/h, gave the highest of T due to the system become complete combustion. Corresponding to the level of CO, the least level was obtained at ro = 1 rpm, Qf = 2.3 kg/h and Qa = 40 m3/h. The qc yielded highest with 93.7% at the same condition. The NOx in this research was considered as low, not more than 40 ppm in all experimental conditions.

Sound Scattering Properties of Surfaces with Diffusers

This article compares the values of the normal scattering coefficient measured in a model experiment for two types of diffusers placed on a rigid surface. Wooden diffusers of cubic and pyramidal shapes were tested in a scale model of a room with dimensions of 0.7x0.4x0.4 m. Sound decay curves were measured at frequencies of 4kHz and 8kHz. Two large walls were covered with a porous absorber, on the third, in certain combinations, the investigated diffusers with a characteristic size of 3.5 cm were placed, the number of which varied from 0 to 29. The idea of the applied method is that the sound decay curve in a room with a non-diffuse sound field depends significantly from the scattering properties of surfaces. The decay curve was measured with different numbers of the diffusers on the test wall, which made it possible to determine the influence of the shape of the diffusers and their number on the value of the normal scattering coefficient. According to the results of the measurements a high scattering ability of cubic elements was revealed in comparison with pyramidal ones.

Porous CoNi nanoalloy@N-doped carbon nanotube composite clusters with ultra-strong microwave absorption at a low filler loading

This paper reports porous microwave absorber with ultra-strong absorption (−64.5 dB) at low filler loadings (10 wt%) which is fabricated via a simle and green method.

Gypsum-based sound absorber produced by 3D printing technology

The paper presents an alternative gypsum-based porous cellular sound absorber manufactured using 3D printing technology. The effects of cell structure and porosity on sound absorption coefficient have been experimentally investigated for the designed gypsum-based porous metamaterials. In addition to this, the numerical acoustic analyses were also performed to predict sound absorption behaviour of the produced gypsum-based porous metamaterials. Furthermore, the numerical flow analyses were also carried out to gain insight into the basic parameters such as flow resistance and tortuosity that affect the sound absorption behaviour of the designed gypsum-based porous metamaterials. As a result of the experimental and numerical studies, it has been observed that the gypsum specimens produced in porous structure provide a significant sound absorption in comparison to non-porous reference specimen. It has been also noticed that the open-cell gypsum specimens, in which the cells are interaction with each other, are much more efficient in terms of sound absorption than the open-cell structure in which there is no direct interaction between the cells. In addition to this, it was found that the gypsum specimens having Octet unit-cell structure have the highest sound absorption performance in the open cell structures. In other respects, it was also found that the sound absorption behaviour of each unit cell structure is getting worse with the increasing porosity. The numerical flow analyses have indicated that increase in porosity reduces the flow resistance and tortuosity levels of the open unit-cell structures and consequently worsens the sound absorption behaviour.

Phenolic foam-derived magnetic carbon foams (MCFs) with tunable electromagnetic wave absorption behavior

• Magnetic porous graphitic carbon-based foams are synthesized. • Ultralight EMW absorbers with strong capacity, broad frequency and thin thickness. • The mechanism of the EMW absorption behavior has been discussed in depth. • Effect of internal cell-wall thickness on EMW absorption behavior is investigated. • Effective adsorption from C to Ku band is achieved via adjusting absorber thickness. By now, magnetic porous carbon-based composites have almost dominated recent development of electromagnetic wave (EMW) absorbers. Herein, we report on the fabrication of magnetic carbon foams (MCFs) via in-situ polymerization of iron acetylacetonate (Fe(acac) 3 ) N, N-Dimethylformamide (DMF) solution and phenolic resin, followed by in-situ carbonization processes, and the investigation of their EMW absorption behaviors and regulatory mechanism. MCFs display solid 3D foam architectures based on interconnected cells with narrow and smooth C/CFe 15.1 skeletons, where α-Fe, Fe 2 O 3 and Fe 3 Care formed on their surface. The EMW absorption capacity of MCFs varies with iron contents and internal foaming pressures. Among them, the absorber obtained with 0.12 g/mL Fe(acac) 3 and under a controlled pressure of 0.4 MPa possesses not only the strongest absorption capacity with the minimum reflection loss value of −54.02 dB and the relatively thin matching thickness (3.05 mm), but also the broadest effective absorbing bandwidth of 8.92 GHz. In addition, MCF-3 demonstrates the potential of simultaneously effectively absorbing EMWs from C-band to Ku-band by simply adjusting the thickness of the absorbers. The superior absorption behavior is proved to be attributed to the Maxwell-Wagner-Sillars (MWS) polarization and the residual loss. Besides, multiple reflections and scatterings inside the macroporous structures of MCFs increase the path of EMW propagation, being beneficial to the attenuation of EMW. This is the first time to investigate cell-wall thickness effect on EMW absorption capacities of porous absorbers. Our research hews out a facial way for preparing carbon-based foams embedded with metal/metal oxide and their application in EMW absorption.

Acoustic performance of countersunk micro-perforated panel in multilayer porous material

This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.

Micro-nano surface structure construction and hydrophobic modification to prepare efficient oil-water separation melamine formaldehyde foam

A superhydrophobic melamine formaldehyde foam (SMF) was fabricated via a simple green solution-dipping method in polyvinyl alcohol (PVA) aqueous solution and polydimethylsiloxane (PDMS) ethanol one respectively. The resulted phase-separated PVA during transferring MF from aqueous solution to ethanol one, can form micro-nano structure on MF skeleton, thus endowing the foam surface with considerable roughness. Along with the crosslinking of PDMS, hydrophobic coating on the surface was formed. The modified foam exhibited superhydrophobicity (water contact angle at 157° and water sliding angle at 7°). Its absorption capacity to different organic solvents was evaluated. Meanwhile, a simple device for oil-water separation by connecting the modified foam block with a vacuum system was designed to testify the oil-water separation efficiency. In addition to excellent oil-water separation ability, the modified foam also showed good compressive performances including excellent corrosion resistance with pH of solutions ranging from 1 to 13, remarkable recyclability (up to 150 cycles), improved mechanical properties and high flame retardancy. Compared with the conventional porous superhydrophobic absorbents involving complicated methods and nanomaterials, such efficient SMF fabricated via a simple, low-cost and eco-friendly way shows promising prospect in dealing with oil spillage and industrial organic pollution in the future.

Selective extraction of thorium from uranium and rare earth elements using sulfonated covalent organic framework and its membrane derivate

Thorium, as a nuclear-power replacement for the uranium-based nuclear reactors and an effective avenue to produce uranium source, has become a key element for the increasing energy demand. However, we now are seriously restricted to gain thorium from mineral, due to co-existence of thorium, uranium, and rare earth elements. Accordingly, there is an urgent need to develop solid extraction technique with both large thorium adsorption capacity and high adsorption selectivity. In this work, a COF (covalent organic framework) adsorbent, namely [NH4]+[COF-SO3−] was prepared for selective extraction of thorium from uranium, and rare earth elements. The selective adsorption towards Th(IV) is reflected on the large distribution coefficient (Kd) of 1.34 × 105 mL/g, the big difference up to two orders of magnitude in the adsorption capacity, and the high selectivity (more than nine). This ultrahigh Th(IV) capture up to 395 mg/g presents the largest value for Th(IV) adsorption by porous absorbents. Furthermore, the practical separation of Th(IV) from U(VI) and rare earth elements (Eu3+ and Ce3+) was for the first time executed by both the breakthrough experiment and membrane-based separation experiment. Most importantly, upon this breakthrough separation a Th(VI) solution with high purity up to 93.5% was obtained.

Design, Experimental and Numerical Characterization of 3D-Printed Porous Absorbers.

The application of porous materials is a common measure for noise mitigation and in room acoustics. The prediction of the acoustic behavior applies material models, among which most are based on the Biot-parameters. Thereby, it is expected that, if more Biot-parameters are used, a better prediction can be obtained. Nevertheless, an estimation of the Biot-parameters from the geometric design of the material is possible for simple structures only. For common porous materials, the microstructure is typically unknown and characterized by homogenized quantities. This contribution introduces a methodology that enables the design and optimization of porous materials based on the Biot-parameters and connects these to microscopic geometric quantities. Therefore, artificial porous materials were manufactured using 3D-printing technology with a prescribed geometric design and the influence of different design variables was investigated. The Biot-parameters were identified with an inverse procedure and it can be shown that different Biot-parameters can be influenced by adjusting the geometric design variables. Based on these findings, a one-parameter optimization procedure of the material is set up to maximize the absorption characteristics in the frequency range of interest.

Loose cork granulates as possible new core element in noise barriers

This paper is a first study to evaluate the possible use of loose cork granulates as core element in noise barriers. To obtain the acoustical performance of loose cork granulates inside a noise screen, a small prototype of a noise absorbing barrier was designed and compared to commercial rock wool. The results obtained showed that these kinds of porous absorber, specially sorted and prepared, could be good sound absorbers with a certain broadband absorption spectrum.

NUMERICAL ANALYSIS OF SOLAR TOWER SYSTEM UTILIZED WITH FLAT PLATE AND POROUS ABSORBER

The performance of solar updraft tower investigates numerically by comparing between two solar collectors with and without porous absorber flat plate. In this study, copper metal foam (10 and 40) PPI at the same porosity (0.9) are used as an absorber plate. The effect of the absorbing porous medium is studied to increase the air flow towards the updraft tower by tilting of the porous absorber at an angle (2° and 6°) from the horizontal line for (10 and 40) PPI and compared with the horizontal absorber flat plate. To simulate the physical quantities inside the porous medium, at steady state, symmetry, three dimensional, Darcy model and energy numerical model with local thermal equilibrium (LTE) assumption are adopted and numerical models is approximated by a RNG (Re-Normalization Group) k- ϵ turbulent model and discrete ordinates (DO) radiation model equations. The numerical study is analyzed by Fluent software package (version 18.2) to solve the governing equations. The results showed that the tilting of a porous absorber plate at an angle (2° and 6°) from the horizontal line lead to increase in the mass flow rate inside the solar updraft tower and the maximum performance is found by using 40 PPI at tilt angle 2°.The performance of solar updraft tower investigates numerically by comparing between two solar collectors with and without porous absorber flat plate. In this study, copper metal foam (10 and 40) PPI at the same porosity (0.9) are used as an absorber plate. The effect of the absorbing porous medium is studied to increase the air flow towards the updraft tower by tilting of the porous absorber at an angle (2° and 6°) from the horizontal line for (10 and 40) PPI and compared with the horizontal absorber flat plate. To simulate the physical quantities inside the porous medium, at steady state, symmetry, three dimensional, Darcy model and energy numerical model with local thermal equilibrium (LTE) assumption are adopted and numerical models is approximated by a RNG (Re-Normalization Group) k- ϵ turbulent model and discrete ordinates (DO) radiation model equations. The numerical study is analyzed by Fluent software package (version 18.2) to solve the governing equations. The results showed that the tilting of a porous absorber plate at an angle (2° and 6°) from the horizontal line lead to increase in the mass flow rate inside the solar updraft tower and the maximum performance is found by using 40 PPI at tilt angle 2°.

A beta-cyclodextrin-functionalized magnetic metal organic framework for efficient extraction and determination of prochloraz and triazole fungicides in vegetables samples

A β-cyclodextrin-functionalized magnetic zinc-metal organic framework (M-MOF/β-CD) was synthesized via a facile one-pot reaction. M-MOF/β-CD was used as a magnetic porous absorbent for the extraction and determination of prochloraz and three triazole fungicides in vegetable samples. M-MOF/β-CD was prepared by creating MOF layers on the surface of a Fe3O4–graphene oxide (GO) nanocomposite and bonding them with β-CD molecules. Characterization suggested that a 3D porous structure was formed, with M-MOF/β-CD exhibiting high superparamagnetism and a large surface area. As a new strategy, integrating MOFs with Fe3O4–GO could improve their water-resistance and mechanical strength by providing a rigid nanosupport interface. Combining M-MOF and β-CD resulted in excellent selective adsorption capacities for prochloraz and three triazole fungicides. The static adsorption process was evaluated and the results were in good agreement with the Freundlich model. Subsequently, M-MOF/β-CD was applied to extracting prochloraz and triazole fungicides from tomato and lettuce vegetables, followed by HPLC-MS/MS determination. The limits of detection for the above fungicides were found to be 0.25–1.0 μg/L at a signal-to-noise ratio of 3, with spiked recoveries of 74.13%–119.83%, indicating that M-MOF/β-CD was promising for application to the extraction and determination of fungicides in complex matrices.

Physical and mechanical properties of RAFT-stabilised collagen gels for tissue engineering applications

Cell behavior is influenced by the mechanical and structural properties of their substrate environment. Also, materials mechanically resistant to surgical handling and similar to the host site are required in tissue engineering to minimise the chance of an adverse host response. RAFT-stabilisation is a commercially available technique for creating stabilised hydrogels. Properties of RAFT-stabilised collagen (RsC) gels are governed by size, composition and arrangement of fibrils and their interaction with the fluid trapped within the matrix. The stabilisation process, using hydrophilic porous absorbers, produces dense matrices by rapid expulsion of fluid, and the structure obtained has mechanical properties suitable for tissue engineering. However, protocols to define and compare the physical properties and mechanical behavior of RAFT-stabilised collagen gels are not standardised across the field. Here, we investigate the fundamental mechanical and structural properties of RsC gels, and propose a new empirical relationship that correlates the measured stiffness of gels to varying frequency of strain oscillation. The results provide quantitative data characterising this extracellular environment for future tissue engineering studies.

Effect of pore size and porosity distribution on radiation absorption and thermal performance of porous solar energy absorber

In this paper, experimental and numerical study were both conducted to investigate the effect of pore size and porosity distribution on radiation absorption and thermal performance of porous solar energy absorber. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometer was used to measure the transmittance of porous media to reflect its radiation absorption capabilities. Numerical model was established based on the assumption of thermal nonequilibrium condition as well as using P1 model to consider the radiation heat transfer. The UV-Vis-NIR spectrophotometer measurement showed that: (1) With smaller pore size, the spectral transmittance of the porous media would be lower and the solar radiation absorption would be better; (2) Among the materials with different pore size distributions, pore-size-decreased combo and pore-size-increased combo have almost equal absorption coefficient which are higher than that of uniform structure. Numerical simulation demonstrated that: (3) For materials with different pore size distributions, pore-size-decreased structure has the best radiation absorption due to its ability of maximizing the volumetric absorption effect, which is agreed with the UV-Vis-NIR spectrophotometer experimental results; (4) For materials with different porosity distributions, porosity-gradually-increased structure has the highest mean fluid/solid temperatures because it can utilize the enhanced convective/conductive heat transfer to improve the overall thermal performance of porous receiver; (5) Porous structure with pore-size-decreased distribution and porosity-gradually-increased distribution has the best thermal performance of which the mean temperatures of fluid/solid phases are the highest among all the studied cases.

Development of a low environmental impact, porous solar absorber coating utilizing binary/ternary solvent blends for CSP systems

Concentrated solar power utilizes a field of mirrors to redirect solar rays onto a central receiver to generate thermal energy through heat transfer media and a Rankine steam cycle. To effectively transfer heat to the heat transfer material, the receiver has to efficiently convert/absorb the incoming solar flux without losing energy to radiation. Receivers are coated with a solar absorber coating evaluated with a figure of merit which weighs the energy absorbed by the sample against the total incident energy. The structure of the painted coating plays a large part in the long-term stability and optical properties of the solar absorber coatings. We investigated the effects of different solvents on the micro-structure of black oxide coated paint tiles and evaluated the stability of the paint colloid using the Gibbs free energy of mixing. We also investigated the use of low environmental impact solvents as potential alternates to standard solvents to create low-stress films. The results show that paint blends thinned by blends of dimethyl carbonate and tertbutylbenzene have low-stress surface morphology with pore-like structures due to the favorable Gibbs free energy value of the colloid and reduced evaporation rate of the primary solvents. These coatings also exhibited strong optical performance with figure of merit and solar absorbance values of 91.60% and 96.86%, making them ideal coatings for next generation concentrated solar power plants.

Enhancement of a solar still performance by inclusion the basalt stones as a porous sensible absorber: Experimental study and thermo-economic analysis

In the present study, a thermo-economic investigation was implemented to assess the enhancement of a solar distillation system (solar still) performance and productivity by inclusion a natural fine stone (black basalt) as a porous sensible absorber. The effect of stone size (1 cm, 1.5 cm and 2 cm) and porosity of the porous absorber on system performance and productivity was presented. Two models with the same design and specifications (conventional and enhanced) were tested and compared. The results illustrated that the yield of solar still for 1 cm, 1.5 cm and 2 cm stone size was about 0.901, 1.005 and 1.075 L/m2 with enhancement about 19.81, 27.86 and 33.37%, respectively compared to conventional solar still. Also, the highest daily thermal efficiency of a solar still was about 22.6% at 2 cm stone size with enhancement about 32.07%. The economic analysis revealed that the freshwater produced cost per liter by solar still utilizing 2 cm stone size was 0.017 $/m2.liter, whereas that for the conventional still is 0.020 $/m2.liter with reduction about 17.53%. So, the stone size of the heat storage absorber has a significant effect on solar still productivity and performance.

Structure-sound absorption property relationships of electrospun thin silica fiber sheets: Quantitative analysis based on acoustic models

In order to determine the sound absorption mechanism and characteristics of nonwoven sheets composed of thin silica fibers quantitatively, their structure and acoustic properties were characterized and the influence of their structure on the sound absorption characteristics were investigated based on conventional acoustic models (Delany–Bazley–Miki, rigid-frame, and limp-frame models). Nonwoven sheets with fiber diameters in the micrometer and nanometer ranges were prepared by electrospinning from sol-gel precursors. All the silica fiber sheets showed a superior sound absorption coefficient over glass wool. Our theoretical analyses clearly indicate that the sound absorption mechanism of the thin fiber sheets gradually approaches midway between porous-type and panel-type from typical porous-type with decreasing fiber diameter. In addition, the effect of the flow resistivity due to the friction between the air and the fiber, as well as the effect of sample vibration induced by the sound waves, is more substantial for fibers thinner than 3 μm. The insights provided by our quantitative analysis will be useful for the rational design of high-performance porous thin-film sound absorbers.

Comparison of acoustic absorption characteristics of coir and date palm fibers: experimental and analytical study of green composites

The use of natural biodegradable fibers in manufacturing of porous sound absorbers is an environmental-friendly approach employed by many researchers in the field of noise control and acoustics. The present study aimed to determine and compare the sound absorption coefficients of samples fabricated from fibers of coir and date palm by experimental and analytical methods. Experimental measurements of the sound absorption coefficients were performed in an impedance tube by modifying several parameters (thickness and air gap) of the samples. Prediction of sound absorption coefficient was determined by Delany–Bazley, Miki and Johnson–Champoux–Allard models along with differential evolution algorithm in MATLAB software and data from the experiments. The correlation between the sound absorption coefficients obtained from the experiments and the ones predicted by the existing models was examined by the Pearson correlation test. Samples from both type of fibers showed a poor and almost similar sound absorption in low-frequency range. In intermediate range (1000–3000 Hz), the sound absorption significantly increased to the maximum levels of 0.81 and 0.84 at 2000 Hz for the thickness of 40 mm. An increase in the samples thickness led to a fair agreement between values of sound absorption coefficient obtained from experimental and analytical methods. Correlation analysis showed that there was a significant and strong correlation between the outputs from the existing models and the experiments. The values approximated by Johnson–Champoux–Allard model demonstrated a better fit with the ones determined by the experimental tests.