Hygroscopic Materials Research Articles

Numerical and experimental investigation of thermosyphon-driven liquid desiccant loop performance for sustainable indoor humidity removal

Indoor humidity management is one of the most challenging aspects of the control of indoor environment and is energy intensive, especially in hot and humid climates. A promising approach is the removal of the water vapor from the room using hygroscopic materials, otherwise known as desiccants. Desiccant cycles are thermally driven but require a heat sink and electricity-driven mechanical parts for desiccant circulation. Accordingly, this work proposes a thermosyphon-driven membrane-based liquid desiccant loop for sustainable humidity pumping between two areas at different humidity conditions. Mathematical models were developed for the different system subcomponents, which were validated with published data and in-house experiments. The models were used in a parametric study to determine the influence of the design and operation parameters on the system performance under different air conditions surrounding its various sections.It was found that the system was able to pump the air moisture from high to low and low to high humidity areas. Four cases were considered with outdoor conditions raging from moderate and hot and humid to semi-arid climates. The latent load removal density per unit area of the exposed membrane varied between 4 W/m2 to 35 W/m2 over the entire range of considered cases at required heat inputs varying between 150 W and 570 W respectively. The heat input increased with the channel height and the air humidity surrounding both system sides. The added sensible load depended on the heat sink temperature and was more than 65 % lower than removed latent load in most considered cases.

Moisture-Enabled Electricity from Hygroscopic Materials: A New Type of Clean Energy.

Water utilization is accompanied with the development of human beings, whereas gaseous moisture is usually regarded as an underexploited resource. The advances of highly efficient hygroscopic materials endow atmospheric water harvesting as an intriguing solution to convert moisture into clean water. The discovery of hygroelectricity, which refers to the charge buildup at a material surface dependent on humidity, and the following moisture-enabled electric generation (MEG) realizes energy conversion and directly outputs electricity. Much progress has been made since then to optimize MEG performance, pushing forward the applications of MEG into a practical level. Herein, the evolvement and development of MEG are systematically summarized in a chronological order. The optimization strategies of MEG are discussed and comprehensively evaluated. Then, the latest applications of MEG are presented, including high-performance powering units and self-powered devices. In the end, a perspective on the future development of MEG is given for inspiring more researchers into this promising area.

Waste plastic-derived aerogel modified with graphene oxide for hygroscopic material and oil spill treatment

Plastic bags, also known as nylon bags, plastic packaging, latex bags, and bubble bags, are one of the most harmful segments of plastic waste to the ecosystem. Researchers estimate that plastic bags in natural surroundings take between 500 and 1000 years to fully decompose. Therefore, the recycling of non-biodegradable plastic products such as plastic bags is always a prime topic. In this study, plastic bags were used as raw materials for the synthesis of aerogel (PBA) and modified with graphene oxide (GO/PBA) to increase mechanical strength. Young's module results show that GO/PBA can withstand a maximum compression of about 55 N while PBA has a compressive force of only about 10 N. GO/PBA has a porous 3D structure, low density (0.026 g/cm3), and the major elements are C, O with the existence of C − O, which are suitable as hygroscopic materials. GO/PBA are able to absorb moisture up to 17 g/g compared to that of PBA with 10 g/g. Besides, GO/PBA is hydrophobically modified with PDMS (PDMS/GO/PBA) to increase selectivity in oil/water systems, oil spill treatment application with high oil adsorption capacity reaching 27 g/g, about 10 times the mass of the material. Thus, GO/PBA and PBMS/GO/PBA were successfully synthesized for the application of desiccant and oil adsorbent, respectively. The kinetics of the two adsorption processes are shown by pseudo-order first and second models.

Laser‐Triggered Degradation of Silicon Circuits by Lithiation and Moisture Uptake for On‐Demand Transient Electronics

Data security risks of unauthorized access of confidential information have attracted considerable attention. Transient electronics capable of physical disappearance or disintegration upon external stimuli could potentially offer an alternative solution at the device level. Despite great advances, smart, efficient, wireless, and nonrecoverable degradation of foundry‐compatible silicon (Si)‐integrated circuit (IC) chips remains a challenge. Herein, a laser‐triggered degradation of Si circuits by lithiation and moisture uptake is proposed. By integrating IC chips with a small amount of lithium sources and a fluidic reservoir consisting of hygroscopic materials, on‐demand, wireless, rapid, and complete degradation of Si IC chips built at 600 nm node is achieved upon activation by laser irradiation. This work paves a new route to accomplish smart, tether‐free, and thorough degradation of devices compatible with existing foundry processes, offering an essential baseline for the development of intelligent transient electronics for secured hardware.

Hygrothermal Properties Analysis of Bamboo Building Envelope with Different Insulation Systems in Five Climate Zones

Laminated bamboo lumber (BLL) and bamboo scrimber (BS) are potential environmentally friendly building materials, considering that they are hygroscopic materials and that their hygrothermal performance is closely related to the occupants’ comfort, their building durability, and building energy consumption. This study carried out material property tests on bamboo-based materials (BLL and BS) and analyzed hygrothermal performance simulations on bamboo exterior wall constructions in five major climatic zones using WUFI. Results show that BS had a greater heat storage capacity than BLL. However, BLL showed a relatively higher moisture sorption capacity, and BLL was more easily permeated by vapor than BS. The water content (WC) of 12 walls of BLL and BS was below 20%. BLL and BS met the requirements of the envelope, and the WC of BS was lower than that of BLL. Based on the results, the walls designed in this study are suitable for the corresponding climate zones. In the cold and severe climate zones especially, the external insulation system walls performed better than the internal insulation system. The external insulation system was recommended for these two climate zones. The design and simulation results of walls made of two types of bamboo-based materials provide a scientific basis for the application of the material.

The Characteristics of Green-synthesized Magnesium Oxide Nanoparticles (MgONPs) and their Biomedical Applications.

In the current epoch, noble metals/metal oxides with precise structures are needed to develop sustainable products to improve the welfare of human beings and the environment. Nanomaterials in the regime 1 -100 nm scale are a promising material for the research fraternities owing to their stupendous properties. The metallic/metal oxide nanoparticles (silver, gold, copper oxide, iron oxide, magnesium oxide) are gaining significant momentum and need to be extensively studied. Magnesium oxide nanoparticles (MgONPs) are a periclase, white hygroscopic material consisting of Mg2+ ions and O-2 ions in lattice arranged. These nanoparticles can be fabricated through physical, chemical and biological methods. The development of green synthesized MgONPs needs to be ascertained and explored its ultimate in medicine, health, cosmetics, environmental protection, chemical industries, and energy. Therefore, the present review manifests the green synthetic approaches of MgONPs and their impact on crystalline structure and shape. Further, we have provided the antibacterial and anticancer activities of MgONPs thoroughly reported in various kinds of literature. Overall, the unique MgONPs can be plausibly used as safe biomaterials in biomedical applications.

Metal–Organic Frameworks (MOFs) Based Electrospun Nanofiber Membrane for Passive Indoor Moisture Control

Metal–organic frameworks (MOFs), an emerging class of porous sorbents, have become one of the most promising functional materials for indoor moisture regulation. However, the practical application of MOFs in building environments is challenging. Common shaping forms of MOFs (e.g., pellets, tablets, monoliths, granules, coating, etc.) may lead to agglomeration of MOF particles, higher usage costs, low efficiency, and material waste. Here, we report a new MOF-based electrospun nanofiber membrane with high porosity, light weight, and a large surface-area-to-volume ratio. MOF nanoparticles distributed on the fibers can fully contact moisture in the air, thus significantly enhancing MOFs’ utilization and performance. The results of the moisture adsorption test show that the improved MOF membrane has significantly higher water vapor uptake than most conventional hygroscopic materials and textiles in built environments. A building energy model was established to evaluate the MOF membrane’s effect on building energy consumption under different climates worldwide. The simulation results show that the MOF membrane can efficiently moderate indoor moisture fluctuation and has excellent energy-saving potential. The latent heat load reduction rate in summer can be up to 80–90% in arid/semi-arid climates and around 50% in temperate climates in a purely passive manner.

Biopolymers for Hygroscopic Material Development.

The effective management of atmospheric water will create huge value for mankind. Diversified and sustainable biopolymers that are derived from organisms provide rich building blocks for various hygroscopic materials. Here, a comprehensive review of recent advances in developing biopolymers for hygroscopic materials is provided. It is begun with a brief introduction of species diversity and the processes of obtaining various biopolymer materials from organisms. The fabrication of hygroscopic materials is then illustrated, with a specific focus on the use of biopolymer-derived materials as substrates to produce composites and the use of biopolymers as building blocks to fabricate composite gels. Next, the representative applications of biopolymer-derived hygroscopic materials for dehumidification, atmospheric water harvesting, and power generation are systematically presented. An outlook on future challenges and key issues worthy of attention are finally provided.

Effects of Visitor Influx on the Indoor Climate of the Milan Cathedral

The indoor climate of non-climatized churches is usually subject to cyclical fluctuations of temperature and relative humidity induced by external climate conditions which might be dampened by the high thermal capacity of their envelope. However, several phenomena affect their indoor climate (e.g., internal gains due to people and artificial lighting, air infiltration, etc.), which lead to environmental variations that might jeopardize the artworks contained within. In particular, one of the most influential parameters that may affect non-climatized churches is the massive and intermittent presence of people who constantly visit their spaces. In such regard, long-term monitoring allows the collection of environmental data with different building operation conditions and visitor fluxes. This paper analyses the indoor climate of the Milan Cathedral (Duomo di Milano) in Italy for three continuous years (including the lockdown period that occurred in 2020 caused by the COVID-19 pandemic), with a focus on visitors’ effects on the indoor environment and the conservation of the main artworks contained within. The results of the analysis have shown that spaces with huge volume are most influenced by the opening of the doors rather than the hygrothermal contribution of the intermittent presence of massive crowds. Moreover, the absence of visitors for a prolonged period correlates with an improvement in the indoor conservation conditions for artworks, especially those made of hygroscopic materials, due to the reduction in short, rapid climate fluctuations.

Design and performance research on the automatic sweat-treating fabrics used for ski suits

Skiers sweat a lot during training, and the sweat will create a wet-cold type environment between the ski suit and the athlete, reducing the wearer’s comfort. In this study, high hygroscopic materials and hydrophobic functional particles were integrated onto the inner fabric of the ski suit by dipping, scraping, spraying and other methods. A kind of fabric with automatic sweat-treating function used for ski suits was developed and the sweat-guiding, sweat-absorbing, sweat-holding, breathing and thermal insulation properties of the samples were tested by using a liquid guiding performance tester, a water content tester, an infrared thermal imager, a thermal plate, an air permeability tester, a moisture permeability tester and other equipment. The results show that the method of changing the hydrophobic properties of different areas of fabric surface and combining and distributing fabrics with different absorbing properties can be used actively to guide the flow direction of sweat on the fabric surface. The samples designed in this study can effectively delay the time for the ski suits to enter the wet-cold type state. Treated samples can effectively protect the insulation layer from being affected by sweat and steam. Before and after sweat absorption, the temperature of the insulation layer of treated samples changes relatively slowly compared with the control group. After finishing, the breathability of the sample decreased, while it still had a good breathability. In conclusion, the automatic sweat-treating fabric developed in this study has good sweat-treating performance.

Heat and Mass Transfer in Hygroscopic Porous Media: Consequences of Invoking Tóth’s Sorption Isotherm

The thermal performance of ventilated beds of hygroscopic porous media depends strongly on the sorption properties of the solid phase. Furthermore, the published literature shows that the predicted performance of ventilated beds of hygroscopic porous media is extremely sensitive to the form and accuracy of the sorption isotherm. This is particularly apparent under idealized conditions when thermodynamic equilibrium is deemed to exist between the solid and fluid phases. When Tóth’s isotherm is invoked in an equilibrium model used to analyse the performance of a bed of initially warm and dry silica gel ventilated with cool, humid air, it is predicted that a shock wave develops downstream of air entering the bed. In contrast, it is shown that non-equilibrium solutions result in a transfer wave, the width of which decreases as the velocity of the interstitial air decreases. The Tóth isotherm gives rise to erroneous values of the integral heat of wetting of silica gel. Previously published studies of simultaneous heat and mass transfer in beds of hygroscopic materials refer to conceptual difficulties in interpreting the results, and some published mathematical analyses are somewhat terse. A secondary aim of this work is to assuage these difficulties by detailing the analyses in Supplementary Information.

Preliminary evaluation of the climate-induced fatigue in wood: A physical and computational approach

Wood is the organic hygroscopic material for excellence. Due to its extremely easy handling, it has always been used in many applications, especially as building material for artefacts and works of art. However, it is highly climate-susceptible as it swells or shrinks by exchanging moisture with the surrounding environment when natural or artificial microclimatic fluctuations occur. The shrinkage/swelling of wood, if repeated over time, may cause the arising of deformations or damage that may lead to catastrophic failures. For this reason, in this work, a preliminary study about the effect that repeated microclimatic loads have on wooden samples is carried out. To do so, well-established fatigue approaches have been implemented, with few simplifying considerations. The case study is a slice of Scots pine which is assumed to be stored inside Ringebu stave church (Norway). Ringebu indoor microclimate is reconstructed, through a proper transfer function, starting from outdoor temperature data downloaded from web platforms. The reconstructed indoor temperature timeseries cover three periods: far past (1948–1977), recent past (1981–2010) and far future (2071–2100). The results obtained for the three periods made it possible to gain insights about the climate-induced fatigue of wood and to preliminary assess the impact of climate change. It has been observed that successive similar temperature fluctuations can be potentially treated as a block of constant amplitude and constant frequency fatigue-like load. Finally, introducing few simplifying considerations, it has been assessed that the simulated behavior is coherent with the theoretical one coming from exploiting well-established thermo-based methods.

Estimation of the diffusion coefficient of hygroscopic materials using a contactless transient THz water vapour content imaging and excitation device

The investigation of humidity movement during drying or imbibition processes represents a serious challenge for several industries, such as the wood-based material industry and paper industry. Recently, several studies have been conducted on the efficiency contactless Terahertz technique (THz) to map the water content. In this study, this technique based on coupling infrared camera and developed Tera-Thermo-Converter, is used for the estimation of mass diffusion coefficient within hygroscopic materials initially dry. A water vapour water content excitation device is designed to excite the samples in a THz semitransparent enclosure during the monitoring. The recorded infrared films showed a pronounced mitigation of the signal over time, indicating penetration of vapour through the sample. Processing image techniques such as the four-image, algorithm and Singular Value Decomposition (SVD) and averaging are used to obtain the space-time water content map. A simplified one-dimensional model of mass transfer is proposed to estimate the diffusion coefficient using two inverse methods: a) a statistical method based on Bayesian approach, and b) a minimization method based on Levenberg‒Marquardt algorithm (LM). The results showed that THz imaging technique coupled with the appropriate processing and the adequate modelling, is able not only to map the water content field but also to monitor the transient transfer and estimate the diffusion coefficient without contact.

Thermal conductivity assessment of moist building insulation material using a Heat Flow Meter apparatus

Thermal conductivity is one of the most important parameters of building insulation materials. This parameter is dependent on the temperature, and on the moisture content for hygroscopic materials. When measured by steady-state methods (with the HFM device and the guarded hot plates), moisture will migrate from the hot side to the cold, influencing the measured heat flux and, thus, the measured thermal conductivity. This study aims to analyze the effects of moisture transfer on the thermal conductivity measurement of wet hygroscopic light building insulation material (namely wood fiber insulation). Several experiments are performed on instrumented samples to evaluate the influence of parameters like the thickness, the mean moisture content, the mean temperature, or the temperature gradient on the measured heat flux, on the temperature and relative humidity distributions and on the time to reach hygrothermal equilibrium. Particularly, the measurement errors made when shortening the experiment are discussed and the moisture dependence of true thermal conductivity is evaluated experimentally by considering the notions of apparent and diffusive thermal conductivities. Last, by using a validated heat and moisture transfer model, this dependency is compared to the one predicted by the methods proposed in the standards EN 12664 or ISO 10051.

Bio-Graphene Sensors for Monitoring Moisture Levels in Wood and Ambient Environment.

Wood is an inherently hygroscopic material which tends to absorb moisture from its surrounding. Moisture in wood isa determining factor for the quality of wood being employed in construction, since it causes weakening, deformation, rotting, and ultimately leading to failure of the structures resulting in costs to the economy, the environment, and to the safety of residents. Therefore, monitoring moisture in wood during the construction phase and after construction is vital for the future of smart and sustainable buildings. Employing bio-based materials for the construction of electronics is one way to mitigate the environmental impact of such electronics. Herein, a bio-graphene sensor for monitoring the moisture inside and around wooden surfaces is fabricated using laser-induced graphitization of a lignin-based ink precursor. The bio-graphene sensors are used to measure humidity in the range of 10% up to 90% at 25°C. Using laser induced graphitization, conductor resistivity of 18.6 Ω sq-1 is obtained for spruce wood and 57.1 Ω sq-1 for pine wood. The sensitivity of sensors fabricated on spruce and pine wood is 2.6 and 0.74 MΩ per % RH. Surface morphology and degree of graphitization are investigated using scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis methods.

Hygroscopic and Photothermal All-Polymer Foams for Efficient Atmospheric Water Harvesting, Passive Humidity Management, and Protective Packaging.

Environmental humidity and thermal control are of primary importance for fighting global warming, growing energy consumption, and greenhouse gas emissions. Sorption-based atmospheric water harvesting is an emerging technology with great potential in clean water production and passive cooling applications. However, sorption-based humidity management and their hybrid applications are limited due to the lack of energywise designs of hygroscopic materials and devices. Herein, all polymeric 3D foams are developed and evaluated as hygroscopic and photothermal materials. The gas-foaming method generates closed-cell structures with interconnected hydrophilic networks and wrinkled surfaces, expanding hygroscopic, photothermal, and evaporating areas of the 3D foams. These unique advantages lead to efficient water vapor sorption in a wide broad relative humidity (RH) range of 50-90% and efficient water release in a wide solar intensity (0.4-1 sun) and temperature range (27-80 °C). The reversible moisture sorption/release in 50 adsorption/desorption cycles highlights the excellent durability of the 3D foams compared to conventional inorganic desiccants. The 3D foams disclose passive and efficient apparent temperature regulation in warm and humid environments. Moreover, the use of the 3D foams as loose fill for fruit preservation and packaging is demonstrated for the first time by taking the merit of the 3D foams' moisture-absorbing, quick-drying, cushioning, and thermal-insulating properties. This work presents an integrated design of polymeric desiccants and scaffolds, not merely delivering stable water adsorption/desorption but also discovering innovative hybrid applications in humidity management and protective packaging.

In Situ All‐Weather Humidity Visualization by Using a Hydrophilic Sponge

AbstractHumidity visualization is of significant importance across both the living systems and the industrial processes, which remains a huge challenge. Herein, for the first time, a hydrophilic sponge, which is composed of rigid gel and super hygroscopic material, has been demonstrated capable of all‐weather humidity visualization in a portable, convenient, economical, and in situ manner. This promising aspect is attributed to the effective all‐weather humidity capture and various color display as a response to the humidity capture capacity, of the super hygroscopic material; as well as the rapid humidity transport and excellent humidity storage ability provided by the porous rigid gel. As a consequence, combined with a smartphone, the invisible information on the environment's relative humidity levels, on the one hand, can be correlated qualitatively with the specific color display of the sponge; on the other hand, it can be correlated quantitatively with the specific color intensity, providing a pretty good smart model for humidity visualization in various complex environments. The present humidity visualization technology may open up a new avenue for the development of novel humidity sensors with a wide range of practical applications.

Hygrothermal behaviour of a room with different occupancy scenarios

The thermal and moisture properties of building partitions and the related possibility of moisture buffering affect the water vapour exchange between the superficial layers of the hygroscopic materials and the indoor environment, which results in energy consumption for different purposes. The paper describes an analysis of the hygrothermal behaviour of a roomunder different occupancy scenarios for four wall finishing variants (variable parameters of thermal conductivity index and diffusion resistance of the applied material). The application of gypsum board and cement-lime plaster was analysed with and without a paint coat. Computer simulations using WUFI Plus were used for the analysis. The application of cement-lime plaster without a top paint coat was shown to reduce fluctuations in the amplitude of indoor relative humidity more than the other solutions. Applying a paint coat to the interior surface of a building partition limits the material's buffering properties, and consequently, the indoor relative humidity amplitude increases. Upon improving thermal efficiency, the decrease in indoor relative humidity was higher for a nursery than for an office space. For the air conditioning dynamic operation mode, it was demonstrated that gypsum board walls with no paint coat could reduce energy demand for dehumidifying systems and increase it for humidifying systems. The painted variants are characterised by a higher total energy consumption for humidification and dehumidification purposes.

Numerical method for solving coupled heat and mass transfer through walls for future integration into an urban climate model

Numerous studies of hygrothermal transfers through walls have highlighted the impacts of this phenomenon on energy consumption and indoor conditions. However, urban scale models that aim to simulate weather conditions and urban heat island effects within cities neglect moisture transfer through walls. The objective of this paper is to propose a method for solving this phenomenon that could be integrated into an urban climate model. This kind of integration requires the numerical schemes to be adapted as well as the spatiotemporal scales. The proposed method is based on an Implicit/Explicit discretisation scheme and a decoupled numerical approach for solving. Numerical stability is ensured by reducing the time step in critical moments, which are detected by five tests. This method is validated by comparison with a reference model (Delphin ®), on several study cases using different wall compositions and climates. A mesh sensitivity analysis is performed and shows that low permeability walls require a finer mesh than walls made of highly hygroscopic or capillary active materials. Furthermore, the more layers there are in the wall, the finer the mesh size needs to be. This numerical method allowed a balance to be found between computational cost and accuracy level in accordance with the expectations for an urban climate model. The future integration of this method into an urban climate model will make it possible to carry out energy/climate simulations, including the hygrothermal behaviour of walls, and thus to study its impact at urban scale.

Design of Hygroscopic Bioplastic Products Stable in Varying Humidities

AbstractHygroscopic biopolymers like proteins and polysaccharides suffer from humidity‐dependent mechanical properties. Because humidity can vary significantly over the year, or even within a day, these polymers will not generally have stable properties during their lifetimes. On wheat gluten, a model highly hygroscopic biopolymer material, it is observed that larger/thicker samples can be significantly more mechanically stable than thinner samples. It is shown here that this is due to slow water diffusion, which, in turn, is due to the rigid polymer structure caused by the double‐bond character of the peptide bond, the many bulky peptide side groups, and the hydrogen bond network. More than a year is required to reach complete moisture saturation (≈10 wt.%) in a 1 cm thick plate of glycerol‐plasticized wheat gluten, whereas this process takes only one day for a 0.5 mm thick plate. The overall moisture uptake is also retarded by swelling‐induced mechanical effects. Hence, hygroscopic biopolymers are better suited for larger/thicker products, where the moisture‐induced changes in mechanical properties are smeared out over time, to the extent that the product remains sufficiently tough over climate changes, for example, throughout the course of a year.