Relative Humidity Range Research Articles

Ternary nanocomposite comprising MnO2, GQDs, and PANI as a potential structure for humidity sensing applications

Humidity sensing has been offering a noticeable contribution in different industrial, medical, and agricultural activities. Here, graphene quantum dots doped with polyaniline (PANI) and MnO2 were successfully prepared. The synthesized system is exposed to a set of structural, morphological, and optical investigations. The apparent crystallite size is less than 30 nm, reflecting the nanoscale of the structure, and thus validating the preparation route as evident on XRD pattern. SEM images show a fibrous structure where polyaniline dominates and covers most of the structure’s surface. The evident bands of the FTIR spectrum are designated to the component used in synthesis confirming the chemical structure of the fabricated system. The humidity sensing study of the synthesized structure is carried out through a wide range of relative humidity (RH) levels range of 11–97%. The response and recovery times of the fabricated structure are found to be around 120 and 220s, respectively.

Ti3C2-MXene used to enhance response/recovery speed and thermal stability of acrylate copolymer humidity sensor under abnormal temperature changes

MXene is a typical kind of 2D material with high specific surface, electrial conductivity, self-lubrication and abundant surface groups, which has received wide attention in the fields of electrochemistry, lubrication, sensors and electromagnetic shielding. In this work, MXene-containing polymer matrix composites (MHMA@ Ti3C2) are prepared to enhance the humidity response properties of conventional polyacrylate humidity sensitive materials. The result shows that the humidity response curve of MHMA@ Ti3C2 humidityfilm shows good linearity (R2 = 0.9992) in the relative humidity range of 30–90 %RH, with a high sensitivity of 63.7 kΩ/%RH. Meanwhile, the humidity response/recovery time of the MHMA@ Ti3C2 humidity film shortened from 310 s/312 s to 30 s/35 s, resulting in a much faster response speed. The wet hysteresis was reduced from 2.1 %RH to 0.34 %RH, and the lowest temperature change coefficient was reduced from 0.60 %RH/℃ to 0.44 %RH/℃ compared with MHMA. In the composites, MXene component significantly enhances the electronic migration capability during the humidity response, which improved the humidity-sensitive properties of the composites, and at the same time enhanced the response speed and temperature change resistance of the composites.

Salicylic acid and putrescine treatments reduce yellowing, decay and retain postharvest quality of bitter gourd (Momordica charantia L.) during cold storage

Bitter gourd is a valuable cucurbitaceous vegetable rich in various beneficial phytochemicals such phenols, antioxidants, saponins, charantin etc. In spite of high medicinal value bitter gourd faces significant postharvest losses due to factors such as mass reduction, tissue softening, yellowing, and fungal contamination, especially when stored under ambient conditions. To combat these issues, immature green bitter gourd fruits (16 DAP) were subjected to different concentrations of salicylic acid (SA) at 5, 7.5, and 10 mM) and putrescine (PUT) at 1, 2, and 3 mM, through a 15-minute dipping process. In contrast, untreated fruits were dipped in distilled water and served as the control group. These treated and control fruits were subsequently stored at 10 ºC with a relative humidity range of 85–95 % for 20 days. Results showed that among all treatments, bitter gourd fruits treated with 10 mM SA exhibited the most noteworthy outcomes. They retained higher levels of total phenols (26.28 μg GAE 100 g-1), radical scavenging activity (27.95 %), ascorbic acid content (50.0 mg 100 g-1 FW), and total chlorophyll (0.32 mg g-1 FW) on the 20th day of storage. Additionally, the 10 mM SA treatment demonstrated the highest inhibition of α-amylase and α-glucosidase activity, as well as the lowest decay percentage when compared to the control. On the other hand, 3 mM PUT treatment resulted in greater fruit firmness (27.45 N), lower per cent postharvest loss weight (6.60 %), and reduced pectin methyl esterase (PME) activity (0.0075 µmol min-1 g-1 FW). These findings were further validated through principal component analysis (PCA), which highlighted that bitter gourd fruits could be effectively stored for up to 20 days at 10 ºC with pre-storage treatment involving 10.0 mM SA and 3.0 mM PUT. Overall higher quality and shelf-life of bitter gourd were obtained in bitter gourd treated with 10.0 mM SA. Consequently, it is recommended that the application of SA and PUT represents an environmentally friendly approach to preserve the quality of bitter gourd during storage, benefiting both retailers and consumers alike.

Estimating the hydratable surface area of building materials from water vapour sorption

The specific surface area of a building material controls its physical, chemical, and biological functions and services, including its moisture regulating potential. The Hydratable Specific Surface Area (H-SSA) of a building material can be estimated from its primary water vapour adsorption and desorption isotherm at a given relative humidity (RH) value or range of RH. The concept is illustrated for 12 mineral and bio-based building materials. The estimated H-SSA for only 1 kg of some building materials can approach the area of a typical agricultural field (500,000 m2, 50 ha.), which helps explain and illustrate the great moisture regulating properties of many bio-based materials. The H-SSA appears useful to help characterize and classify building materials.

Effect of relative humidity on the thin-layer chromatographic separation of E 472 emulsifiers

E 472 emulsifiers are organic acid esters of mono- and diacylglycerides. These emulsifiers are categorized into six subgroups (E 472a-f) based on the specific acid component, e.g., acetic acid, lactic acid, citric acid, tartaric acid, or mixtures of tartaric and acetic acid. The present study investigated the effect of relative humidity (RH) on the thin-layer chromatographic separation of four E 472 emulsifier subgroups, addressing practical concerns due to RH variations between seasons and within laboratories. Three RH-setting techniques affecting plate activity and chamber climate were assessed using saturated salt and aqueous sulfuric acid solutions. Aqueous sulfuric acid solutions for RH adjustment resulted in decreased hRF values, while no trends in hRF value changes were observed for saturated salt solutions. Unlike RH itself, the RH setting technique led to substantial changes in the chromatographic fingerprint. Thus, the choice of the RH setting method should be tailored to the specific analyte and analysis goal. Despite variations in chromatographic fingerprints between the three RH setting techniques, the fingerprint remained consistent within the same technique across the tested RH range.

Coupled effects of temperature and relative humidity on desiccation curling of a clayey soil

Soil curling caused by drying is a common phenomenon in nature, and it can vary depending on different atmospheric effects. To investigate the coupled effects of temperature and relative humidity on soil curling, a sequence of desiccation experiments were performed by using elongated strip soil samples in the laboratory. The soil curling process is divided into five stages: vertical settlement stage, lateral contraction stage, concave-up curling stage, curling recovery stage and convex-up curling stage. In this study, the soil evaporation characteristic and curvature curves are obtained under different temperature and relative humidity conditions. The findings revealed that a lower relative humidity results in a higher evaporation rate and a smaller maximum concave-up curling curvature for soil samples. Additionally, as the temperature increased, the water content associated with concave curling decreased. The maximum concave-up curling curvature was determined by the transition from the appearance of concave-up curling to the maximum curvature of concave-up curling. Under the coupled effect of temperature and relative humidity, all the water content associated with the occurrence of concave-up curling, maximum concave-up and convex-up curling appearance are reduced with increasing temperature and decreasing relative humidity. As the temperature ranged from 20 °C to 40 °C, the maximum concave-up curling curvature initially decreased and then increased. Conversely, the maximum concave-up curling curvature increased within the relative humidity range of 30% to 45%.

Color-changing and optical spectra based “humidity test paper”

We present a tilted fiber Bragg grating (TFBG) sensor coated with crystal violet/perfluorinated sulfonic acid (CV/Nafion) composite film for relative humidity (RH) monitoring. The composite film demonstrates the characteristics of an optical "humidity test paper" by exhibiting a color transition from yellow to green within a RH range of 10 % to 80 %. This color variation indicates its potential to effectively monitor RH levels in diverse environments. To achieve a quantitative RH sensing, we coat CV/Nafion composite film on an etched TFBG (ETFBG), where surrounding RH changes can be measured from spectral responses of ETFBG transmission. In experiments, the proposed the CV/Nafion-coated ETFBG sensor exhibits RH sensitivities of 0.068 dB/%RH and 3 pm/%RH for intensity change and wavelength shift measurements, respectively, within a relative humidity (RH) range of 10 % to 80 %. Additionally, based on intensity measurement, short response and recovery times of ∼4.4 and ∼4.6 s are estimated from a continuous RH monitoring.

Ag@Fe3O4-coated U-shaped plastic optical fiber sensor for H2S detection

This work presents the fabrication of U-shaped plastic optical fiber (POF) sensors for hydrogen sulfide (H2S) detection, coated with Fe3O4 nanoparticles synthetized using the Pulsed Laser Ablation in Liquid (PLAL) technique. The Fe3O4 nanoparticles were synthetized in ultra-pure water and in silver nitrate solution, resulting in two colloidal samples with different morphological, optical, and structural properties. The Fe3O4 nanoparticles were coated onto one POF sensor, while the other sensor was coated with a nanostructure composed of Ag as the core and Fe3O4 as the shell (Ag@Fe3O4). The performance of both sensors was evaluated by exposing them to different concentrations of H2S and other gases such as CH4, H2, and CO2. All experiments were conducted at 25 °C. Results showed that the sensor coated with Ag@Fe3O4 was 12 times more sensitive to H2S compared to the sensor coated with Fe3O4, with a detection limit of 1 ppm and a rise time of 15 s. Moreover, the POF sensor coated with Ag@Fe3O4 presented high selectivity to H2S, making it a promising candidate for H2S detection in different applications. The sensor's performance was also evaluated with a relative humidity range of 20–90%, exhibiting a minimal 0.75% signal variation at 90% humidity.

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Analyzing and Modeling the Municipal Sewage Sludge Drying Process Using Python

The programming language Python offers the opportunity to analyze and model the municipal sewage sludge (MSS) drying process in an illustrative chemical engineering practice. The drying process is performed on a flat plate while maintaining a uniform, parallel drying air speed. The Python program helps to analyze the digitalized weight measurements from each sample. The program enables the sorting of input data, determination of the drying critical point, and evaluation of the first and second drying periods. Moreover, the model calculates the fundamental drying parameter and forms a drying master curve to support the transfer to different drying conditions. The basic parameters calculated are mass transfer coefficient, heat transfer coefficient, and diffusion coefficient. The results are consistent with published data for those coefficients over the drying temperature range of 19.4–52.4 °C and relative humidity range of 8.2–33.6%. The findings of this study demonstrate the potential of Python as a powerful tool for analyzing experimental data and modeling chemical processes, which can lead to improved process design, optimization, and control.

Sulfonated hypercross-linked porous organic polymer based humidity sensor

Humidity sensors are of great significance in industry, agriculture and human activities, and many nanomaterials are already used for humidity sensing. Linear ionic polymers with hydrophilic groups have exhibited good humidity detection performance because they can adsorb water and then dissociate charged carriers. However, it suffers from the instability under high relative humidity that caused by polymer chain swelling and disengagement. To overcome this shortage, in this work, a new sensor based on hypercross-linked porous organic polymer (POP) with sulfonic acid group was fabricated to humidity detection in wide humidity range. The POP with strong covalent bonds exhibits remarkable chemical and thermal stability, and sulfonic acid group in the pore can act as fully accessible active site to enhance its ability to adsorb water. The obtained sensor shows high response (∼77) in a wide relative humidity range (11%−95% RH), short response/recovery time (9 s/21 s) and good stability. Complex impedance curves and density functional theory have been carefully investigated to understand its sensing mechanism. This work provides a new direction for the development of the impedance-type humidity sensitive materials in subsequent research and practical applications.

Relating three-decade surge in space cooling demand to urban warming

Rising demand for space cooling has been placing enormous strain on various technological, environmental, and societal dimensions, resulting in issues related to energy consumption, environmental sustainability, health and well-being, affordability, and equity. Holistic approaches that combine energy efficiency optimization, policy-making, and societal adaptation must be rapidly promoted as viable and timely solutions. We interpret the 30 year climatic-induced upward trend and spikes in urban space cooling demand from the perspective of climate change, urbanization, and background climates, through the lens of five major populated cities: Hong Kong, Sydney, Montreal, Zurich, and London. An unequivocal, worrying upward trend in cooling demand is observed in meteorological data, using cooling degree hours (CDHs) as a city-scale climatic-induced metric. The surge in cooling energy demand can be largely attributed to climate warming and urban heat islands, with the most abrupt spikes associated with intensified extreme heat events. Further, our quantification of the impact of the base temperature, in relation to the historical CDH, reveals that a 20% energy saving could be achieved instantly within a rather broad range of air temperature and relative humidity by increasing the setpoint temperature by one degree. With the rise in background temperatures due to climate change, the potential for energy saving diminishes for the same level of increase in setpoint temperature. For instance, an increase from 26 °C to 27 °C results in about 10% energy savings, while an increase from 22 °C to 23 °C could yield over 20% in energy savings. To reduce cooling energy demand rapidly in a warming climate, we highlight the necessity of promoting hard and soft behavioral adaptation along with regulatory intervention for the operation of space cooling systems.

Self-Powered, Highly Sensitive, and Flexible Humidity Sensor Based on Carboxymethyl Cellulose for Multifunctional Applications.

Self-powered humidity sensors based on friction electric and piezoelectric principles have been proposed in recent years. However, the complicated structure and preparation processes usually involved in these power generation humidity sensors limit their wider application. Herein, we developed a self-powered flexible humidity sensor with a simple structure and facile preparation process based on the primary battery principle. The self-powered humidity sensor consists of copper conductive tape as the positive electrode, nickel conductive tape as the negative electrode, and a carboxymethyl cellulose film dissolved with lithium chloride and sodium chloride as the sensing layer. The sensor exhibits good sensing linearity (R2 = 0.99791) in a wide relative humidity range (11-95%) with a satisfying response voltage of 41 mV (RH 95%) and excellent flexibility. Furthermore, the conduction mechanism of the sensing film was investigated by the complex impedance and phase angle-frequency spectral measurement and analysis. Multifunctional applications of human respiration monitoring to determine the respiratory rate and type, noncontact sensing, diaper and soil moisture detection, and power generation were demonstrated. The low-cost and facile preparation method in this work could provide a useful strategy for developing a self-powered, flexible, and multifunctional humidity sensor.

Capillary sorption, thermo physical characterizations and simulation study of an eco-friendly building material reinforced with Chamarrops humilis fibres

ABSTRACT This research introduces an environmentally friendly building material combining clay and Chamaerops humilis fibres, demonstrating substantial potential for enhancing thermal and energy efficiency in construction across diverse climates. The study aims to align construction materials with the heating and cooling requirements mandated by the Moroccan Thermal Building Regulations. Hygroscopic behaviour of the material was evaluated through experiments using gravimetric methods at varying temperatures and humidity levels. The assessment covered a wide air relative humidity range (5.72%–89.8%), enabling measurement of water absorption through capillarity. Thermal conductivity, density, and heat capacity were determined, critical for understanding the material’s thermal and energetic characteristics. Dynamic thermal simulations for a single thermal zone were performed to analyze the material’s impact on heating and cooling loads in different Moroccan climate zones: humid Agadir (zone 1), dry Marrakech (zone 5), and semi-arid Ouarzazate (zone 6). The analysis revealed substantial energy savings potential. The findings demonstrating comply with Moroccan Thermal Regulations, highlighting the efficacy of this composite material in meeting regulatory heating and cooling requirements.

PEMFC-Performance of Unsupported Pt-Ni Aerogel Cathode Catalyst Layers under Automotive-Relevant Operative Conditions

Unsupported, Pt-based electrocatalysts hold great potential for implementation in polymer electrolyte membrane fuel cell (PEMFC-) cathodes owing to their enhanced durability under startup/shutdown conditions entailing high potential excursions. Among such materials, the recently developed Pt-Ni aerogel consisting of tridimensional nanochains of interconnected nanoparticles has already been shown to feature an initial PEMFC–performance comparable to that of C-supported Pt-nanoparticles (Pt/C) along with a much better startup/shutdown durability. However, all PEMFC characterization of this materials has been carried out at 80 °C and using fully humidified gases, and its behavior under more demanding conditions concomitant to its potential implementation for automotive applications remains unexplored. Thus, in this work aerogel catalyst layers (CLs) are characterized under a wide range of temperatures and relative humidities, as well as submitted to fast current up-transients. These extensive tests showed that the performance of the aerogel CLs is comparable to that of a commercial Pt/C benchmark, except at high current densities and low temperatures at which the thin aerogel layers suffer from a low water storage capacity.

Highly efficient and stable NiSe2-rGO composite-based room temperature hydrogen gas sensor

The widespread consumption of hydrogen in commercial and industrial applications has resulted in the development of different hydrogen gas sensors. However, their practical application is restricted due to their non-cost efficiency, low sensitivity, poor selectivity and high temperature sensing properties. Thus, the development of a sensor capable of overcoming the aforementioned limitations is critical for commercial deployment. As a result, a NiSe2-rGO composite-based H2 gas sensor has been prepared for the first time using a simple hydrothermal technique. The developed material has been systematically characterized for its morphological properties and thoroughly investigated for H2 gas sensing applications. The findings show that the developed NiSe2-rGO composite exhibited enhanced H2 gas sensing properties, besides possessing appreciable selectivity, repeatability as well as long-term stability. Furthermore, the results demonstrate a stable sensor response of 254% within 43 s and 13 s of response and recovery time respectively at a hydrogen concentration of 500 ppm which is 8 and 500 times higher than that of its individual counterparts (NiSe2 and rGO) over a wide relative humidity range, indicating the material's potential for application in industrial environments. Thus, this work paves the way for the development of stable, effective, fast-responding, and selective hydrogen gas sensors that are functional at room temperature.

Thermally Insulating and Moisture-Resilient Foams Based on Upcycled Aramid Nanofibers and Nanocellulose.

Low-density foams and aerogels based on upcycled and bio-based nanofibers and additives are promising alternatives to fossil-based thermal insulation materials. Super-insulating foams are prepared from upcycled acid-treated aramid nanofibers (upANFA ) obtained from Kevlar yarn and tempo-oxidized cellulose nanofibers (CNF) from wood. The ice-templated hybrid upANFA /CNF-based foams with an upANFA content of up to 40wt% display high thermal stability and a very low thermal conductivity of 18-23mW m-1 K-1 perpendicular to the aligned nanofibrils over a wide relative humidity (RH) range of 20% to 80%. The thermal conductivity of the hybrid upANFA /CNF foams is found to decrease with increasing upANFA content (5-20wt%). The super-insulating properties of the CNF-upANFA hybrid foams are related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANFA and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar, and this study can hopefully inspire efforts to upcycle textile waste into high-performance products.

Characterization of an Impedance-Type Humidity Sensor Based on Porous SnO2/TiO2 Composite Ceramics Modified with Molybdenum and Zinc.

In this study, we report on the room-temperature characteristics of an impedance-type humidity sensor based on porous tin oxide/titanium oxide (SnO2/TiO2) composite ceramics modified with Mo and Zn. The SnO2/TiO2-based composites synthesized in the solid-state processing technique have been structurally characterized using X-ray diffraction, scanning electron microscopy, energy dispersive, and Raman spectroscopy. Structural analysis indicated the desired porous nature of the synthesized ceramics for sensing applications, with an average crystallite size in the nano range and a density of about 80%. The humidity-sensing properties were evaluated within a wide relative humidity range from 15% to 85% at room temperature, and the results showed that a better humidity response had a sample with Mo. This humidity-sensing material exhibits a linear impedance change of about two orders of magnitude at the optimal operating frequency of 10 kHz. Furthermore, fast response (18 s) and recovery (27 s), relatively small hysteresis (2.8%), repeatability, and good long-term stability were also obtained. Finally, the possible humidity-sensing mechanism was discussed in detail using the results of complex impedance analysis.

Polythiophene/ Reduced Graphene Oxide Nanocomposites for Humidity Sensing Application

A novel humidity sensing composite was synthesized using polythiophene (PTh) and graphene oxide by chemical oxidation process. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and investigations on humidity sensing were used to characterize the samples. XRD pattern of PTh demonstrated that it is amorphous in nature. The flaky character and more compact structure of composites were both confirmed by scanning electron microscopy. These findings show that the thiophene monomer successfully polymerized on graphene's surface. Polythiophene/graphene composites were studied for their humidity sensing performance in the relative humidity (RH) range of 11% - 97%.

High-Barrier, Biodegradable Films with Polyvinyl Alcohol/Polylactic Acid + Wax Double Coatings: Influence of Relative Humidity on Transport Properties and Suitability for Modified Atmosphere Packaging Applications.

Polyvinyl alcohol (PVOH) exhibits outstanding gas-barrier properties, which favor its use as a biodegradable, high-barrier coating on food-packaging films, possibly in combination with modified atmospheres. Nonetheless, its high sensitivity to water can result in a severe loss of barrier properties, significantly limiting its applications with fresh foods and in high-humidity conditions. In this work, the water vapor (PWV) and oxygen permeability (PO2) of high-barrier biodegradable films with PVOH/PLA + wax double coatings were extensively characterized in a wide range of relative humidity (from 30 to 90%), aimed at understanding the extent of the interaction of water with the wax and the polymer matrices and the impact of this on the permeation process. What is more, a mathematical model was applied to the PWV data set in order to assess its potential to predict the permeability of the multilayer films by varying storage/working relative humidity (RH) conditions. The carbon dioxide permeability (PCO2) of the films was further evaluated, and the corresponding permselectivity values were calculated. The study was finally augmented through modified atmosphere packaging (MAP) tests, which were carried out on double-coated films loaded with 0 and 5% wax, and UV-Vis analyses. The results pointed out the efficacy of the PLA + wax coating layer in hampering the permeation of water molecules, thus reducing PVOH swelling, as well as the UV-shielding ability of the multilayer structures. Moreover, the MAP tests underlined the suitability of the double-coated films for being used as a sustainable alternative for the preservation of foods under modified atmospheres.