Types Of Foams Research Articles

Influence of Enzymatically Hydrophobized Hemp Protein on Morphology and Mechanical Properties of Bio-Based Polyurethane and Epoxy Foams.

Biomass fillers offer the possibility to modify the mechanical properties of foams, increasing their cost-effectiveness and reducing their carbon footprint. In this study, bio-based PU (soft, open cells for the automotive sector) and epoxy (EP, hard, closed cells for construction applications) composite foams were prepared by adding pristine and laccase-mediated lauryl gallate-hydrophobized hemp protein particles as filler (HP and HHP, respectively). The fillers were able to modify the density, the mechanical properties and the morphology of the PU and EP foams. The addition of HP filler increases the density of PU foams up to 100% and significantly increases the σ values by 40% and Emod values. On the other hand, the inclusion of the HHP as filler in PU foams mostly results in reduced density, by almost 30%, and reduced σ values in comparison with reference and HP-filled foams. Independently from filler concentration and type, the biomass increased the Emod values for all foams relative to the reference. In the case of the EP foams, the tests were only conducted for the foams filled with HHP due to the poor compatibility of HP with the EP matrix. HHP decreased the density, compressive strength and Emod values of the composites. For both foams, the fillers increased the size of the cells, while reducing the amount of open cells of PU foams and the amount of closed cells for EP foams. Finally, both types of foams filled with HHP reduced the moisture uptake by 80 and 45%, respectively, indicating the successful hydrophobization of the composites.

PENGARUH PENAMBAHAN CACO3 DARI LIMBAH KULIT TELUR DAN WAKTU PENGADUKAN PADA PEMBUATAN ALUMINIUM FOAM MENGGUNAKAN METODE MELT ROUTE

Aluminum is a lightweight material that has good corrosion resistance and electrical conductivity. It can be used for making aluminum foam. One of the methods for making aluminum foam is the melt route method. Making aluminum foam using the melt route process, is called melting aluminum metal, adding foaming agent, and stirring. This study aims to determine the effect of adding CaCO3 from eggshells and stirring time on the foaming ability of aluminum foam. The characteristics that will be observed include the type of aluminum foam, height, pore size, density, porosity, and compressive strength. This research used the melt route method with adding variations in the mass composition of CaCO3 is 4, 5, and 6 wt% on smelted aluminum with stirring times of 30, 45, and 60 seconds. The process is carried out by heating aluminum to 760 °C and adding Al2O3 as a viscosity modifier then adding variations in the mass composition of CaCO3 and stirring with a variation of stirring time. The results show that the highest aluminum foam gets a value of 75 mm. The pore sizes of aluminum foam are obtained ranged from 0.287 to 1.109 mm. The optimal value obtained from the addition of CaCO3 with a mass composition of 4 wt% with a stirring time of 45 seconds, has a density value of 0.388 g/cm3, a porosity percentage of 85.848%, and a compressive strength of 1.777 MPa.

3D-Printed Graphene Nanoplatelets/Polymer Foams for Low/Medium-Pressure Sensors.

The increasing interest in wearable devices for health monitoring, illness prevention, and human motion detection has driven research towards developing novel and cost-effective solutions for highly sensitive flexible sensors. The objective of this work is to develop innovative piezoresistive pressure sensors utilizing two types of 3D porous flexible open-cell foams: Grid and triply periodic minimal surface structures. These foams will be produced through a procedure involving the 3D printing of sacrificial templates, followed by infiltration with various low-viscosity polymers, leaching, and ultimately coating the pores with graphene nanoplatelets (GNPs). Additive manufacturing enables precise control over the shape and dimensions of the structure by manipulating geometric parameters during the design phase. This control extends to the piezoresistive response of the sensors, which is achieved by infiltrating the foams with varying concentrations of a colloidal suspension of GNPs. To examine the morphology of the produced materials, field emission scanning electron microscopy (FE-SEM) is employed, while mechanical and piezoresistive behavior are investigated through quasi-static uniaxial compression tests. The results obtained indicate that the optimized grid-based structure sensors, manufactured using the commercial polymer Solaris, exhibit the highest sensitivity compared to other tested samples. These sensors demonstrate a maximum sensitivity of 0.088 kPa-1 for pressures below 10 kPa, increasing to 0.24 kPa-1 for pressures of 80 kPa. Furthermore, the developed sensors are successfully applied to measure heartbeats both before and after aerobic activity, showcasing their excellent sensitivity within the typical pressure range exerted by the heartbeat, which typically falls between 10 and 20 kPa.

Identification of marine debris from fishery activities in Nipah and Alue Riyeung beaches, Nasi island, Northern Aceh waters

It is believed that the debris discovered in the ocean originated on land and was unintentionally and purposely transported by a river. Marine debris will accumulate on the water’s surface and sink to the bottom over time, polluting the seawater if left mismanaged. The life of marine organism will be threatened by the existence of the debris. The purpose of this study is to quantify the quantity of macro-sized marine debris generated by fishing activities. This study was carried out on Nasi Island in Aceh Besar from February to April 2022. Sampling of marine debris was carried out using the shoreline method with a 100 meter long transect. Marine debris from fishing activities identified includes types of plastic, plastic foam, cloth and wood, with a total of 179 items.

Monthly microplastics change in European anchovy's (Engraulis encrasicolus) gastrointestinal tract in the Black Sea

To contribute to a better understanding of the regional dynamics of MP pollution and its potential effects on the anchovy population and human health, here we assessed the presence and characterization of microplastics (MPs) in European anchovy (Engraulis encrasicolus), which is the most caught/consumed species in the Black Sea and is of vital importance to the ecosystem. A total of 360 individuals (30 per month) were sampled from the eastern Black Sea continental shelf all year round (monthly from September 20 to Aug 21). We extracted and digested the gastrointestinal tracts (GITs) of the samples with H2O2 and characterized the MPs in the GITs by stereomicroscope and ATR-FTIR. MPs varied between 0 and 0.43 MP individual−1. The morphological structure of MPs was composed of 51 % fiber > fragment (32.7 %) > film (12.2 %) > foam (4.1 %) and polymer types as PP (42.9 %) and PE (22.4 %). In the prevalence of MP colors, black (26.5 %) > white (24.5 %) > red (22.5 %) was observed. The mean MP size was 735.32 ± 836.62 μm, with no significant correlation between the abundance and size of ingested MPs and anchovy height/weight and GIT weight. We determined that MP abundance showed substantial differences between the fishing season (0.18 ± 0.05 MP ind−1) and the banned season (0.05 ± 0.03 MP ind−1). It is essential to develop effective waste management strategies to protect the vulnerable marine ecosystems of the Black Sea and ensure sustainable exploitation of living resources in this region. These strategies should be accompanied by robust monitoring and enforcement measures to guarantee their effectiveness and compliance.

Effects of velocity on N2 and CO2 foam flow with in-situ capillary pressure measurements in a high-permeability homogeneous sandpack

The effects of velocity and gas type on foam flow through porous media have yet to be completely elucidated. Pressure drop and capillary pressure measurements were made at ambient conditions during a series of foam quality scan experiments in a homogenous sandpack while foam texture was simultaneously visualized. New insights into foam-flow behavior in porous media were discovered. Previously accepted “limiting” capillary pressure theory is challenged by the findings in this work, and the “limiting” terminology is replaced with the word “plateau” to reflect these novel observations. Plateau capillary pressure {(P}_{c}) and transition foam quality were found to increase with velocity. Transition foam quality was found to depend mostly on liquid velocity rather than gas velocity and is physically linked to foam type (continuous vs. discontinuous) and texture (fine vs. coarse). Distinct rheological behaviors also arose in the low- and high-quality foam regimes as a function of velocity. Foam flow was found to be strongly shear thinning in the low-quality regime where foam texture was fine and discontinuous. In the high-quality regime, the rheology was weakly shear thinning to Newtonian for coarsely textured foam and continuous-gas flow respectively. When all other variables were held constant, at ambient conditions, CO2 foam was found to be weaker with also lower capillary pressures than N2 foam and the differences in gas solubility is a likely explanation.

Mechanical properties of polyurethane foam for potential application in the prevention and treatment of pressure ulcers

The viscoelastic property is a crucial parameter for evaluating the feasibility of the foam to be used as pressure relief. This work aims to perform experimental measurements to determine the dependence of the viscous behavior of polyurethane foam on density and energy dissipation. Experimental measurements were realized for three types of polyurethane foams with different densities soft, medium and hard. The compression tests at room temperature characterized the mechanical properties of these samples. Furthermore, the structures of the samples were characterized using scanning electron microscopy (SEM). A proportional relationship was observed between the density of polyurethane (PU) foam and the tolerated strength at 90% compression. This material has an excellent remanence (persistence) which showed by the creep experiments at constant stress (2, 5, 10 N) for 6 h. Young Modulus, relaxation time and dissipation coefficient (DE) were also calculated from the stress-strain curve. Moreover, softening behavior, which is responsible for pressure relief, was measured by a cyclic compression test. This paper assesses the capacity of polyurethane to effectively maintain interfacial pressure below the critical threshold of 32 mm of mercury, which represents a significant risk level for the development of pressure sores.

Highly Stable Polymer-Enhanced Pickering Foams for Hydraulic Fracturing Applications

Foams have been used as fracking fluids for decades, but their thermodynamic instability has always restricted subsurface applications, particularly in harsh reservoir conditions. Therefore, this study comprehensively investigated the role of commonly used stabilizers in foaming behaviors, including the surfactant (APG), nanoparticle (CNCs), and polymer (XG), and their stabilizing behavior at the interface was also explored using molecular dynamics (MD) simulations. Our findings indicated that the 0.5% XG-enhanced Pickering foam (0.5% APG + 1.0% CNCs) would be an exceptional fluid for fracking applications. The formation of APG–CNC–XG gel-like networks among bubbles significantly improved the stability of this liquid foam, and the liquid half-life could be extended by nearly 24 h, while the foam can last for several days at 80 °C. Using MD simulations, we showed that the coexistence and intramolecular interactions among APG, CNCs, and XG molecules generate a stronger hydrogen bonding network in the thin film, significantly reducing water mobility, corresponding to the experimental observations. To explore the potential of foams as fracking fluids, the sand-carrying capacity of two types of foams was also evaluated; the polymer-enhanced Pickering foam was able to suspend the sands for more than a day without participation. In the lab fracturing test, despite requiring a higher breakdown pressure, the polymer-enhanced Pickering foam reduces water consumption by almost 20%. Moreover, the highly viscous foam also induced the wing-shaped fracture with a wider width along the hole. The deep insights gained from this study will advance the application of foams as the fracking fluid in unconventional oil/gas reservoirs.

Vibration behaviours of foam-filled grille composite sandwich cylindrical shells

In this study, a novel lightweight composite sandwich cylindrical shell, namely an all-composite sandwich cylindrical shell (ACSCS) with a hollow grille core (HGC) filled with polyurethane foam (PF), is designed and prepared, and its free and forced vibration behaviours are investigated for the first time. First, an analytical model of the PFHGC-ACSCSs subjected to both base excitation and single-point pulse excitation loads is developed by employing the shear deformation theory enriched by the layerwise method, virtual artificial spring technique, Rayleigh-Ritz approach, modal superposition principle, Newmark-Beta approach, and improved cross-fill equivalent theory. Furthermore, the solution procedures for the natural frequencies, mode shapes, and vibration responses in the time and frequency domains of the PFHGC-ACSCSs are defined. Convergence investigations are performed to determine the appropriate truncation numbers and stiffness values for the virtual artificial springs used in the prediction model. Both literature and experimental validations are conducted on the current model, the results of which indicate that it is reliable for predicting the concerned dynamic parameters. Finally, the effects of the critical parameters on the free and forced vibrations of the PFHGC-ACSCSs are studied. The results suggest that the vibration suppression capability could be significantly strengthened by adopting a large core-to-skin thickness ratio, high ratio of the circumferential length of the hollow grille ribs to the whole thickness, large axial and circumferential number of the hollow grille ribs, high ratio of the wall thickness to the circumferential length of the hollow grille ribs, and type of foam with a high elastic modulus. The modelling and solving techniques, preparation processes, testing methods, and conclusions of this study pave the way for the application of such shell structures.

High strain-rate deformation analysis of open-cell aluminium foam

This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.

Evaluating Earplug Performance over a 2-Hour Work Period with a Fit-Test System.

Workers rely on hearing protection devices to prevent occupational noise-induced hearing loss. This study aimed to evaluate changes in attenuation over time for properly fit devices when worn by workers exposed to hazardous noise. Earplug fit testing was accomplished on 30 workers at a brewery facility with three types of foam and three types of premolded earplugs. The personal attenuation ratings (PARs) were measured before and after a 2-hour work period while exposed to hazardous noise levels. The minimum acceptable initial PAR was 15 dB. Average decreases in PAR ranged from -0.7 to -2.6 dB across all six earplug types. Significant changes in PAR were observed for the Foam-1 ( p = 0.009) and Premold-3 ( p = 0.004) earplugs. A linear mixed regression model using HPD type and study year as fixed effects and subject as random effect was not significant for either fixed effect ( α = 0.05). Ninety-five percent of the final PAR measurements maintained the target attenuation of 15 dB. Properly fitting earplugs can be effective at reducing worker's noise exposures over time. The potential for a decrease in attenuation during the work shift should be considered when training workers and establishing the adequacy of protection from hazardous noise exposures.

115 Laboratory Performances of the CIP 10 Personal Aerosol Sampler for the Collection of Submicron Particles

Abstract The CIP 10 is a personal aerosol sampler designed to sample conventional dust or specific occupational inorganic or organic substances such as crystalline silica, isocyanates or mycotoxins. It is widespread used, especially in France. Within the CIP10, the rotating cup contains a porous polyurethane foam devoted to the collection of airborne particles and rotates inside its housing at a speed close to 6700 rpm to induce a 7 or 10 L/min sampling airflow, depending on the particle-size selector. Despite several published works regarding its physical performances, no experimental data exist regarding the sampling efficiency for submicron particles. This study aimed to measure the collection efficiency of the CIP 10 for different types of foam (60 or 75 ppi, functionalized or not) and for the three selectors (inhalable, thoracic, respirable). Polydisperse particles with aerodynamic diameters between 20 nm and 10 µm were produced using various generators and different materials (DEHS, glass beads) in a specific test rig. For a given diameter, the collection efficiency was calculated by comparing the number concentrations measured alternatively upstream and downstream of the rotating cup, using APS (TSI 3321) or SMPS (Grimm DMA Vienna Type, CPC 5.403) spectrometers. While collection efficiency was 100% for particles > 3 µm, it progressively decreased to around 50 % and even below 10 % for aerodynamic diameters of 800 mm and 150 nm, respectively. Collection efficiency was unaffected by the type of foam or sampler flow rate used. Bias maps and consequences on workers aerosol exposure assessment will be discussed.

Study on Sound Absorption Performance of Aluminum Foam Combination

Aluminum foam is a kind of new material with a large number of holes distributed in aluminum alloy. It has the characteristics of lightweight, sound absorption, energy absorption and vibration reduction, and other porous materials. Aluminum foam has good acoustic performance. However, its excellent sound absorption ability is only reflected in the middle and high-frequency bands. Besides, the low-frequency sound absorption ability is very poor and the frequency band is narrow. Therefore, in this paper, different types of perforated aluminum foams with different parameters are combined to explore the influence on acoustic performance and find that the combination of large porosity perforated sample and aluminum foam has a better sound absorption effect. The unperforated sample is placed in front of the perforated sample to improve the sound absorption coefficient of the low and medium frequencies. Finally, different types of perforated aluminum foam samples were properly combined, and it was found through the test that almost all sound waves in the band of 1200 HZ~2000 Hz could be absorbed by the combined structure.

Effects of the physical characteristics of foams on conditioned soil’s flow behavior: A case study

Earth pressure balance shield (EPBS) is the excavation technique responding to the technical construction complexity of the future line 16–1 of the Grand Paris Express project. Its principle is based on the capacity of the excavated ground to transmit the forces needed to counterbalance the earth and water pressures of the working face. Additives are injected into the soil; on the cutting wheel, in the excavation chamber and in the screw conveyor. Their role is to assure the soil conditioning by modifying the soil’s workability and its hydromechanical and rheological parameters. Therefore, the soil conditioning produces a plastic medium able to transmit the pressure to maintain the front face. In addition, as a second objective, the additives aim to overcome uncertainties in the soil. Depending on the case, the additives can reduce the clogging, internal friction, abrasiveness, and permeability of the soil. The additives can include water, surfactant, polymer and bentonite. The combination of water and surfactant with or without polymer produces the foam. In order to increase the excavation perfomance, laboratory prelimenary tests are performed to deduce the optimal foam parameters. Since no test measuring the foam characteristics is standardized yet, this article sums up the tests mostly used in foam characterisation; half-life measurements, rheological tests, microstructural observations. As for the conditioned soil, slump test is frequently used by the tunnelling industry to recommend the optimal soil conditioning parameters in terms of workability. This test has been adapted in this study and the results are verified by rheological tests, then compared to the real foam injection data used for the project and their effect on mechanical parameters. For a specific type of excavated soil, the quality (type) of foam recommended by the laboratory work falls into the same choice of additive based on in-situ tunnelling excavation data. These findings are explained by the foams characteristics. Therefore, a correlation between foam and the conditioned soil (sandy soil with silt and low percentage of clay) with foam is deduced at different levels: micro, meso and macro (real) scales.

A numerical study on mitigation of sloshing in a rectangular tank using floating foams

In this paper, the feasibility of using floating foams as a mitigation device to suppress water sloshing in a rectangular tank is numerically investigated. The sloshing in the tank is initiated using a harmonic excitation. To perform 3D numerical simulations, the Arbitrary Lagrangian-Eulerian technique (ALE) in the commercial software ABAQUS is utilized. The results of the model are validated by comparing the results of simulations with those of the experiments both quantitatively and qualitatively. Next, the efficacy of floating foams in suppressing water sloshing is evaluated for different cases with various layers of foam ranging from zero to three layers. In addition, the effects of various parameters on the wave height and kinetic energy variations are comprehensively analyzed. These parameters include water depth, density, friction factor, diameter of plastic foam spheres, frequency, amplitude and type of excitation. The numerical results show that the interactions between floating foams play a major role in mitigating water sloshing. Furthermore, the effects of plastic foam densities on decreasing the wave height are minor. A twofold increase in the foam density decreases the maximum kinetic energy by 9.68% and an almost threefold increase in the foam density reduces the maximum kinetic energy by 29.03%.

Kinetic Improvement of the Gel-sol Transition of Thermoresponsive Hydrogels Utilizing a High Surface Area Host

Rapid reversible phase transitions of biocompatible thermoresponsive sealants (TRS) upon cooling are required for their practical application in many sectors. The gel–sol transition rate of the TRS studied here [poly(N-isopropylacrylamide-co-butyl acrylate 95:5, number-averaged molecular weight = 7–64 kg mol–1] after being heated to 50 °C is slowed dramatically. The unheated materials return to a free-flowing sol form in a matter of minutes, while the heated materials remain in a gel or solid form for hours. The gel–sol transition of these polymers is enhanced in the presence of a high surface area host in the form of open-cell foams such as polyurethane (PUR), polyimide (PIM), hydrophilic polyurethane Aquazone (AQZ), and neoprene (NEO). An enhanced rate of sol formation on cooling and high TRS recovery (74–99%) were observed across a range of foam types and pore sizes when compared to samples stored without a host (9% recovery). Polyurethane demonstrates the greatest increase in TRS recovery (∼10-fold) after storing the TRS solution at 50 °C followed by cooling for 10 min at 0 °C, maintaining the thermally reversible gelation and mechanical strength of the TRS. Crucially, rheological measurements demonstrate that the viscosity, storage modulus, and loss modulus are not significantly affected by storage in a foam host. This work may be potentially extended to other injectable in situ forming hydrogels, which have suitable mechanical strength but less ideal phase transition times.

Polyols and Polyurethane Foams Based on Water-Soluble Chitosan.

At present, majority of polyols used in the synthesis of polyurethane foams are of petrochemical origin. The decreasing availability of crude oil imposes the necessity to convert other naturally existing resources, such as plant oils, carbohydrates, starch, or cellulose, as substrates for polyols. Within these natural resources, chitosan is a promising candidate. In this paper, we have attempted to use biopolymeric chitosan to obtain polyols and rigid polyurethane foams. Four methods of polyol synthesis from water-soluble chitosan functionalized by reactions of hydroxyalkylation with glycidol and ethylene carbonate with variable environment were elaborated. The chitosan-derived polyols can be obtained in water in the presence of glycerol or in no-solvent conditions. The products were characterized by IR, 1H-NMR, and MALDI-TOF methods. Their properties, such as density, viscosity, surface tension, and hydroxyl numbers, were determined. Polyurethane foams were obtained from hydroxyalkylated chitosan. The foaming of hydroxyalkylated chitosan with 4,4'-diphenylmethane diisocyanate, water, and triethylamine as catalysts was optimized. The four types of foams obtained were characterized by physical parameters such as apparent density, water uptake, dimension stability, thermal conductivity coefficient, compressive strength, and heat resistance at 150 and 175 °C. It has been found that the obtained materials had most of the properties similar to those of classic rigid polyurethane foams, except for an increased thermal resistance up to 175 °C. The chitosan-based polyols and polyurethane foams obtained from them are biodegradable: the polyol is completely biodegraded, while the PUF obtained thereof is 52% biodegradable within 28 days in the soil biodegradation oxygen demand test.

Experiment Study on the Effectiveness of Various and Mixed Kinds of Low Expansion Foam of 120# Gasoline Pool Fire Suppression

Storage tank fires can endanger society and the environment by generating intense heat radiation, rapidly spreading blazes, and cataclysmic explosions. Various types of foam and even two or more mixed foams are commonly used in storage tank fire disposal sites. This research aims to experimentally and analytically assess the efficacy of various and mixed forms of foam in putting out 120# gasoline pool fires. A series of foam fire extinguishing and re-ignition tests were conducted using a laboratory fire-extinguishing device that gently released low-expansion foam. In this work, a 2.4 m-diameter steel round tray was utilized to model the full-surface fire of an oilcan in a large oil depot base. The non-dimensional (T* = TExtinguishing/Tboiling point) average temperature of 0.62–0.66 is used in this study to represent the fire extinguishing temperatures of 120# gasoline fuel. The power law is still followed during the spreading phase as the length of the foam spreads further with time. When combined, 6% aqueous film-forming foam solution and alcohol-resistant aqueous film-forming foam solution (AFFF + AFFF/AR) have the highest flow velocity of 0.0189 m s−1. According to the results, synthesis foam solution combined with alcohol-resistant fluoroprotein foam (S + FP/AR) provided the greatest cooling effect, followed by S + S/AR (alcohol-resistant synthetic foam solution), AFFF/AR, S + AFFF, S/AR + AFFF, and finally S/AR + AFFF. According to the results, foam with an expansion ratio of 8.7:1 (FP (fluoroprotein foam solution) + AFFF/AR) has greater re-ignition resistance and burn-back protection. A referable tactic for choosing foam for liquid fire suppression is shown in this paper. The results suggested that FP and AFFF should be used for effective fire suppression in this hydrocarbon fuel fire rescue. Then, we can use synthetic foam and AR foams to provide continuous cooling and prevent the fire from re-igniting through efficient foam coverage.

Agar Foam: Properties and Cleaning Effectiveness on Gypsum Surfaces

In the past decade, the usage of soft materials, like gels, has allowed for a better control of the water release process into the substrate for cleaning interventions. Agar—a natural polysaccharide harvested from algae—has been used to perform cleaning of stone materials, gypsum works, and paintings with remarkably positive results. Agar presents the great advantage of being cheap, easily available, fast to produce and not toxic, allowing for more sustainable conservation works. More recently, a new type of agar fluid, agar foam, promises further control of the water release and ease of application on delicate surfaces. In the present study, this new type of agar, CO2 and N2O foams, has been characterized and compared with the conventional sol/gel agar system. Moreover, the cleaning effectiveness of the agar foam was tested both in laboratory conditions and in two case studies: a historical gypsum from the porch framing of the Abbey of Nonantola, and the 20th century gypsum cast of the Pietà Rondanini by Michelangelo, located in the Sforza Castle in Milan. The obtained results show that foaming changes the sol-gel transition temperature of the agar gel as well as incrementing its dissipative behavior. When freshly applied, the foams flow with a reduced velocity, thus allowing a better control and ease of application. Once gelified, they act as a soft solid-like material, as shown by their rheological properties. Moreover, it was found that CO2 foam slightly reduces the water release to the surface, while maintaining the moldability and ease of application. The study allows for the conclusion that agar foam offers an interesting alternative for delicate surfaces, with a non-coherent mineral deposit, and with complex geometries that often represent a challenge for the conventional agar applications

Thermal performance evaluation of PCM-MF composite heat sinks under varying ambient conditions

This study focuses on the effect of ambient conditions and choice of phase change material (PCM) on the thermal performance of a metal foam(MF)-PCM composite heat sink. The PCMs considered are paraffin wax (PF), docosane (DOC) and eicosane (EIC) and their melting temperature ranges are 44.5–60.1 °C, 40.3–44.5 °C and 36.3–38.1 °C, respectively, as obtained from differential scanning calorimetry measurements carried out at a heating/cooling rate of 0.5 °C/min. Experimental investigations are carried out at different ambient conditions (temperature varying from 25 to 45 °C) for three different heat input levels of 5, 10 and 15 W (1.39, 2.78, 4.14 kW/m2). Thermal performance of two types of metal foams (copper (Cu) and aluminum (Al)) are evaluated to arrive at the proposed composite heat sink configuration. Due to the introduction of metal foam into the PCM a maximum reduction of 15.1% in the peak temperature is observed (at heat flux of 2.78 kW/m2 at an ambient temperature of 25 °C) and the time taken to reach a set point temperature of 50 °C is enhanced by 1.8 times (at heat flux of 4.14 kW/m2 at an ambient temperature of 25 °C) for the considered fixed duration experiments. Furthermore, rise in ambient temperature is found to significantly increase the maximum temperature attained in the heat sink coupled with reduction in the duration of latent heat phase of PCM. Effect of ambient temperature on the thermal performance of the PCM-MF composite heat sink is demonstrated by evaluating the variation of Nusselt number as a function of modified Stefan and Fourier number during the PCM-charging (heating) process. Low melting point PCM-MF composite (EIC-MF-Cu) is recommended for normal (25 °C) and intermediate (35 °C) ambient conditions at low heat input load (≤ 1.39 kW/m2); while DOC-MF-Cu exhibits better performance if the conditions involve high heat input (2.78 to 4.14 kW/m2) and higher ambient temperature (≤ 45 °C). Also, high melting point PCM based composite heat sink (PF-MF-Cu) showed better readiness for subsequent charge-discharge cycles at elevated ambient temperature (35 and 45 °C) due to its higher melting/crystallization point.