Varying Humidity Conditions Research Articles

Numerical Assessment of Earth to Air Heat Exchanger with Variable Humidity Conditions in Greenhouses

Earth to air heat exchangers are widely utilized to cool or heat passive buildings for energy savings. They often need to deal with high humidity air conditions, especially in the greenhouse due to plant transpiration, and the condensation phenomenon is frequently observed during the cooling process. To evaluate the effect of humidity and condensation on thermal performance, a three dimensional computational fluid dynamic (3D-CFD) model was developed. The distribution of relative humidity in each pipe was investigated, and the impact of inlet air relative humidity on the integrated performance of the earth to air heat exchanger was discussed. The effects of inlet air temperature and volume flow rate were also analyzed. Moreover, the influence of the heat exchanger configurations on the performance of the air condensation was researched. The results indicated that condensation had few effects on the airflow distribution uniformity of the earth to air heat exchanger, while it acted observably on the thermal performance. In addition, humid air in a small diameter pipe tended to condense more easily. Humidity and condensation should be taken into consideration for the design of earth to air heat exchangers in greenhouses during engineering applications.

Bending Strength of Wood Treated with Propolis Extract and Silicon Compounds.

The modification of wood and its treatment with various preservatives may affect its mechanical properties, hence the knowledge of the character changes in wood caused by impregnation is of great importance. Therefore, the aim of the research was to determine the effect of impregnation, with the propolis-silane preparation (EEP-MPTMOS/TEOS) consisting of the propolis extract (EEP) and silicon compounds: 3-(trimethoxysilyl)propyl methacrylate (MPTMOS) and tetraethoxysilane (TEOS), on the bending strength of treated wood. Moreover, in the study wood treated with components of the propolis-silane formulation was used, namely 70% ethanol, the propolis extract, and silanes (MPTMOS/TEOS). In order to determine whether the impregnation of wood affects its long-term bending, creep tests were performed depending on the humidity. The impregnation of wood with the propolis extract and the propolis-silane preparation (EEP-MPTMOS/TEOS) contributed to the increase in modulus of rapture and work to maximum load values compared to the untreated wood. In dry wood condition, the wood treated with EEP and EEP-MPTMOS/TEOS was characterized by lower modulus of elasticity values than the control samples. In turn, in wet wood condition, wood treated with the propolis-silane preparation showed an increase in the MOE value. Moreover, the impregnation of wood had an influence on the wood creep process under bending loads. The treated wood was characterized by higher relative creep compliance than the untreated wood. The exception was the wood impregnated with EEP-MPTMOS/TEOS, which showed comparable relative creep compliance to the control samples. The presented results indicate that wood treated with a bio-friendly preparation based on propolis and silicon compounds can be used in various application and also in variable humidity conditions.

Increase in humidity widens heat tolerance range of tropical Ceratosolen fig wasps

1. Fig wasps are the obligate mutualistic pollinators of fig trees, which are important components of tropical forests. The stability of these species interactions, in the face of environmental changes, relies heavily on the thermal tolerance of these wasps.2. This study determined the upper thermal limits of three tropical Ceratosolen fig wasp species. Humidity levels and collection season were varied to determine the effect of water availability on heat tolerance.3. Wasps were placed in incubators to simulate different temperature regimes (30–45 °C) with varying humidity conditions. Wasp populations from either the dry or wet seasons were tested. Upper lethal temperature was determined by recording wasp survival.4. All factors (temperature, humidity, season, wasp species, and their interactions) significantly affected wasp longevity. Exposure to high temperatures resulted in a significant decrease in wasp longevity: longest at 30 °C and the ratio decreased rapidly at 40 and 45 °C. An increase in temperature from 30 to 35 °C caused at least a two‐fold reduction in wasp lifespan. More surprisingly, humid conditions allowed survival for two to six times longer than non‐humid conditions in high temperatures (40–45 °C). Wasps obtained during the wet season also survived longer than those from the dry season. Increased water availability (i.e. during wet season and with high humidity conditions) thus increased wasp upper thermal limits.5. Relative humidity was a strong limiting factor in the heat tolerance of tropical wasps. Persistence of insect species that are narrowly‐distributed will depend on the presence of intact, high‐humidity habitats.

How Bound Water Regulates Wood Drying

For most wood-based product uses it is essential to remove a large part of the water content from wet or green (fresh-cut) wood, to reduce further dimensional variations under varying humidity conditions, improve its mechanical characteristics, and protect it from biological attacks. However, the internal mechanisms of drying are not fully described. Here we observe drying at different scales using macroscopic measurements (weighing), nuclear magnetic resonance measurements allowing to distinguish bound- and free-water contents, and x-ray computed tomography images of air-liquid interfaces at the smallest pore scale (wood lumens). We show that during wood drying, even well above the fiber saturation point, bound-water diffusion in cell walls (instead of capillary effects) ensures the extraction of liquid water from pores and its transport towards the surface of evaporation, and thus controls the drying rate. The distribution of bound-water content (uniform or heterogeneous) along the main sample axis and the drying-rate evolution depend on the competition between the external conditions and a characteristic rate of transport due to bound-water diffusion. For sufficiently slow drying this distribution remains homogenous until free water is fully extracted. An original physical phenomenon is thus at work, which plays a major role in regulating water extraction, in that it maintains a constant drying rate and a homogeneous distribution of the (mean) water content throughout the material. These results provide sound concepts for modeling and controlling drying properties of wood materials. They open the way to the understanding or control of the properties of many other materials containing two water types in food or civil-engineering applications. Our results complete recent observations that bound-water diffusion also controls imbibition in hardwood and finally show that transfers between bound and free water play a major role in the interaction of plantlike systems with water.

Limitations of snapshot hyperspectral cameras to monitor plant response dynamics in stress-free conditions

Plants’ dynamic eco-physiological responses are vital to their productivity in continuously fluctuating conditions, such as those in agricultural fields. However, it is currently still very difficult to capture these responses at the field scale for phenotyping purposes. Advanced hyperspectral imaging tools are increasingly used in phenotyping, and have been applied to detect changes in plants in response to a specific treatment, phenological state or monitor its growth and development. Phenotyping has to evolve towards capturing dynamic behaviour under more subtle fluctuations in environmental conditions, without the presence of clear treatments or stresses. Therefore, we investigated the potential of hyperspectral imaging to capture dynamic behaviour of plants in stress-free conditions at a temporal resolution of seconds. Two growth chamber experiments were set up, in which strawberry plants and four different background materials, serving as controls, were monitored by a snapshot hyperspectral camera in variable conditions of light, temperature and relative humidity. The sampling period was set to three seconds, triggering image acquisition and gas exchange measurements. Different background materials were used to assess the influence of the environment and the camera in both experiments. To separate the plant and background data, static masks were determined. Two datasets were created, which encompass both experiments. One dataset was constructed after averaging over the entire mask to acquire one value per spectral band. These values were then used to calculate a set of vegetation indices. The other dataset used spatial subsampling to retain spatial information. From both datasets, linear models were constructed using ridge regression, which estimated the measured eco-physiological and environmental data. Leaf temperature and vapour pressure deficit based on leaf temperature are the two main eco-physiological characteristics that could be predicted successfully. Stomatal conductance, photosynthesis and transpiration rate show less promising results. We suspect that limited variation, and low spectral resolution and range are the main causes of the inability of the models to extract meaningful predictions. Furthermore, the models that were only trained on background data also showed good predictive performance. This is probably because the main drivers for good performing eco-physiological variables are temperature and incident light intensity. Environmental characteristics that have good performance are photosynthetically active radiation and air temperature. Current hyperspectral sensing technologies are not yet able to uncover most plant dynamic eco-physiological responses when plants are cultivated in stress-free conditions.

Enhancement in carbon monoxide sensing performance by reduced graphene oxide/trimanganese tetraoxide system

The article reports enhanced sensing response of reduced graphene oxide (rGO)-trimanganese tetraoxide (Mn3O4) nanocomposite gas sensor towards carbon monoxide (CO) at 298 K in a humid background. The outstanding performance of this sensor is mainly due to its high gas absorbing nature owing to uniform morphology and increased conductivity of rGO-Mn3O4 network. The sensor exhibits high sensitivity, good stability, quick response and rapid recovery. Furthermore, rGO-Mn3O4 sensor is showing better response time and reduced recovery time. The sensor response time for 50 ppm of CO is 3 s at 298 K, whereas for 20 ppm, it is 8 s. Gas sensing response at room temperature is around 70 % for 50 ppm of CO. The sensor also showed enhanced sensing at 473 K for low concentration (4 ppm of CO) with response time of 2 s and recovery time 5 s, respectively. Humidity independent sensor signal along with reduced response time, especially at a low operating temperature makes this sensor a very promising material for CO detection in conditions of variable humidity.

WATER VAPOR TRANSPORT IN PLASTERS CONTAINING SUPERABSORBENT POLYMERS

A proper characterization of material properties represents an important step towards an efficient building design. Considering the present issues in the construction sector, moisture loads pose a risk not only to increased material deterioration but also to the health of building inhabitants. In this paper, modified plaster mixtures with superabsorbent admixture are designed in order to improve passive moderation of finishing layers against varying humidity conditions. The relationship between the amount of applied superabsorbent admixture and resulting water vapor transport properties is identified and the influence of temperature on water vapor transport is analyzed. The steady-state cup method is used for the determination of water vapor transport properties, namely the water vapor diffusion permeability, water vapor diffusion coefficient and water vapor diffusion resistance factor. The obtained data show temperature as a very significant factor affecting water vapor transport in the analyzed plasters. Considering the dry-cup method arrangement, relative humidity probes should be used for monitoring relative humidity under the sealed sample for a sufficiently precise determination of water vapor pressure gradient.

Phylo‐biogeographical distribution of whitefly Bemisia tabaci (Insecta: Aleyrodidae) mitotypes in Ecuador

AbstractThe Bemisia tabaci complex in Ecuador was studied with respect to phylogenetic relationships and eco‐geographical distribution. Whitefly samples were collected from natural and agricultural environments in nine provinces of Ecuador (latitude, 2° N–5° S; longitude, 78°–81° W). Mitotypes were identified based on phylogenetic analysis of the 3′‐mtCOI‐tRNAleu region (832 bp) and corrected pairwise distance analysis. The distribution of mitotypes was modeled using MaxEnt, and their predicted niches were characterized according to environmental gradients. Four B. tabaci mitotypes were identified, of which three are endemic, herein ECU1–3, and the other is the introduced B mitotype. Mitotypes ECU1 (44%), ECU2 (0.74%), and ECU3 (1.47%) grouped in the American Tropics (AMTROP) species and diverged by as much as 10%, which was higher than previous estimates for the AMTROP clade of 7–8.6%. Although haplotypes of ECU1 and ECU2 are known from the American Tropics, this is the first report of the ECU3 mitotype, which may possibly be restricted to southern Ecuador. The distribution of the three ECU‐endemic mitotypes spanned the high‐altitude niches of the western slope of the Andes, rich in microclimates with variable temperature and humidity conditions. The non‐endemic B mitotype (47%) occurred only in the irrigated cropping systems located in hot and/or dry‐tropical ecological niches. Of the endemic mitotypes, ECU1 occupied the most ecological niches. Among variables contributing to ECU1 and B mitotype niche range assignments, the most significant to influence ecological range was rainfall. The B. tabaci endemic to Ecuador were more diverse with respect to mtCOI‐tRNAleu sequence than previously known, and occupied distinct microclimate niches suggestive of ecological resilience.

НАТУРНОЕ ИССЛЕДОВАНИЕ ПРОЧНОСТИ СКЛЕИВАНИЯ МАССИВНОЙ ДРЕВЕСИНЫ СОВРЕМЕННЫМИ КЛЕЯМИ ПРИ ЭКСПЛУАТАЦИИ В РАЗЛИЧНЫХ УСЛОВИЯХ

Abstract
 Glues are widely used to connect various materials, especially since in some cases other options for combining materials are not suitable. The paper deals with the bonding of solid hardwood with modern adhesive materials. Currently, a large group of adhesives of various brands from Russian and foreign manufacturers is presented on the market. In the woodworking industry, adhesives are used in the carpentry and furniture, manufacturing, in wooden house-building, in the production of finishing materials, etc., which are operated outside and inside the premises in constant and variable humidity conditions. Therefore, the correct choice of adhesives plays an important role both for the manufacturer and subsequently for the consumer of the resulting product. In this work, we have studied the dependence of the tensile strength when chipping along the adhesive layer on the type of glue, wood species, and operating conditions. We have selected the following adhesives based on polychloroprene, polyvinyl acetate and rubber. The greatest strength of the adhesive bonding when gluing solid hardwood is given by polyvinyl acetate adhesives. When using the product in conditions of changing temperature and humidity, the bonding strength decreases, in some cases significantly. In fairness, it should be noted that not only the type of glue, but also the type of wood affects the bonding strength

Microbiome in Cladonia squamosa Is Vertically Stratified According to Microclimatic Conditions.

Lichens are miniature ecosystems that contain fungi, microalgae, and bacteria. It is generally accepted that symbiosis between mycobiont and photobiont and microbial contribution to the ecosystem support the wide distribution of lichens in terrestrial ecosystems, including polar areas. The composition of symbiotic components can be affected by subtle microenvironmental differences within a thallus, as well as large-scale climate differences. In this study, we investigated fine-scale profiles of algal, fungal, and bacterial compositions through horizontal and vertical positions of the Antarctic lichen Cladonia squamosa colonies by next-generation sequencing of the nuclear large subunit rRNA gene (nucLSU) of eukaryotes and the 16S rRNA gene of bacteria. Apical parts of thalli were exposed to strong light, low moisture, and high variability of temperature compared with basal parts. Microbial diversity increased from apical parts to basal parts of thalli. Asterochloris erici was the major photobiont in apical positions of thalli, but other microalgal operational taxonomic units (OTUs) of Trebouxiophyceae and Ulvophyceae were major microalgal components in basal positions. Photochemical responses of algal components from apical and basal parts of thalli were quite different under variable temperature and humidity conditions. Several fungal OTUs that belonged to Arthoniomycetes and Lecanoromycetes, and diverse bacterial OTUs that belonged to Alphaproteobacteria, Acidobacteria_Gp1, and candidate division WPS-2 showed a clear distribution pattern according to their vertical positions within thalli. The overall lichen microbiome was significantly differentiated by the vertical position within a thallus. These results imply that different microclimate are formed at different lichen thallus parts, which can affect microbial compositions and physiological responses according to positions within the thalli.

Hygrothermal and mechanical characterisation of novel hemp shiv based thermal insulation composites

Abstract This study focuses on the development of advanced water resistant bio-based composites with enhanced hygrothermal performance for building applications. The highly porous structure of hemp shiv is responsible for low thermal conductivity and allows the material to adapt to varying humidity conditions providing comfortable indoor environment. However, the pore network and the hydrophilic nature of hemp shiv affects the compatibility and durability of the material in presence of excess moisture conditions. In this work, novel hemp shiv composites were prepared in a starch based or silica based matrix and characterised for their hygroscopic, thermal and mechanical properties. The hemp shiv based composites were resistant to water yet permeable to vapour and showed excellent moisture buffering capacity when compared to conventional hemp-lime composites. The composites prepared were light weight with low thermal conductivity values of 0.051–0.058 W/mK and showed good mechanical performance. Hemp shiv composites with superior hygrothermal characteristics have immense potential as robust thermal insulation building materials.

Microwave Sensing Schemes of CPW Resonators Fully Printed on Humidity Sensitive Substrates

This letter investigates the humidity sensing schemes of the transmission line-based resonators printed on the hygroscopic sheets. A serial resonator in the coplanar waveguide technology was designed, simulated, screen-printed with only one silver layer on a Kapton HN foil, and tested under variable humidity conditions. Sensing schemes in frequency and phase paradigm for integration within resonant or transmitting microwave systems were proposed and experimentally validated. The resonant frequency and $S_{21}$ phase were used as the measurement variables. The sensor was proven highly sensitive and wide range. In the 60–100 %RH range, the frequency sensitivity of the sensor reached 3.88 MHz/%RH, and its phase sensitivity reached 1.25°/%RH.

An Air Knife–Assisted Recrystallization Method for Ambient‐Process Planar Perovskite Solar Cells and Its Dim‐Light Harvesting

The photovoltaic performance of perovskite solar cells is highly dependent on the control of morphology and crystallization of perovskite film, which usually requires a controlled atmosphere. Therefore, fully ambient fabrication is a desired technology for the development of perovskite solar cells toward real production. Here, an air-knife assisted recrystallization method is reported, based on a simple bath-immersion to prepare high-quality perovskite absorbers. The resulted film shows a strong crystallinity with pure domains and low trap-state density, which contribute to the device performance and stability. The proposed method can operate in a wide process window, such as variable relative humidity and bath-immersion conditions, demonstrating a power conversion efficiency over 19% and 27% under 1 sun and 500-2000 lux dim-light illumination respectively, which is among the highest performance of ambient-process perovskite solar cells.

The impact of humidity on the generation and morphology of the 3D cotton-like nanofibrous piezoelectric scaffold via an electrospinning method

Three-dimensional (3D), highly porous, and low-density fibrous scaffolds have attracted significant interest in recent years for applications in tissue engineering. However, the fabrication of 3D fluffy fibrous piezoelectric scaffolds remains a challenge. In this study, we report the dramatic effect that relative humidity (RH) has on the deposition of 3D cotton-like constructs composed of polyvinylidene fluoride (PVDF) piezoelectric nanofibers mixed with Barium Titanate (BT) and multiwalled-carbon nanotubes (MWCNTs). The 30 mm diameter deposits were fabricated under variable humidity conditions while all other parameters were kept constant. Two types of fibrous architecture, 3D fluffy and two-dimensional (2D) membrane types, are recognized, as the RH during electrospinning varies. A fiber morphology transition takes place at certain RH, and the 3D cotton-like nanofibrous structure has been optimized above 90% RH. The fabrication of the 3D cotton-like fibrous piezoelectric scaffold may provide new insights for various applications in tissue engineering.

Phenotypic variation in egg survival in the predatory mite Phytoseiulus persimilis under dry conditions

The predatory mite Phytoseiulus persimilis is widely used for augmentative biological control, as an effective predator of the spider mite Tetranychus urticae. However, the biocontrol efficacy of P. persimilis decreases under dry conditions. One of the reasons for this decline concerns P. persimilis’ eggs, which are sensitive to low humidity. In this study, we investigated the possibility to select for a strain of P. persimilis adapted to dry conditions. To understand the potential sources of phenotypic variation in egg survival under dry conditions, we tested the effects of genetic and environmental factors on variation in this trait. We compared egg hatching of five P. persimilis strains, under constant as well as variable humidity conditions, at 25 °C. The results show no intraspecific genetic variation among the five tested strains in egg hatching under constant and variable humidity conditions. In all five strains, less than 20% of the eggs hatched when they were exposed to constant low (60% RH) humidity conditions. However, when eggs were exposed to successive cycles of low and high humidity, a common pattern observed in the field, significantly higher hatching rates were observed. Under variable humidity conditions, more than 73% of the eggs hatched successfully, even when exposure to high humidity was limited to only 13% of the egg developmental time. Although P. persimilis eggs suffered from a high rate of water loss under constant dry conditions, they were able to compensate for this water loss when exposed to high humidity conditions for a few hours during their development. A decreased biocontrol efficacy of P. persimilis under dry conditions may be explained by a higher egg mortality when relative humidity is constantly low. Yet, when relative humidity exhibits diurnal variation, periods of high humidity may mitigate the effects of periods of low humidity during development of P. persimilis eggs.

Adaptive observer-based control for an IPMC actuator under varying humidity conditions

As ionic polymer metal composites (IPMC) are increasingly applied to mechatronic systems, many new IPMC modeling efforts have been reported in the literature. The demands of rapidly growing technology has generated interest in advancing the intrinsic actuation and sensing capabilities of IPMC. Classical IPMC applications need constant hydration to operate. On the other hand, for IPMCs operating in air, the water content of the polymer varies with the humidity level of the ambient environment, which leads to its strong humidity-dependent behavior. Furthermore, decreasing water content over time plays a crucial role in the effectiveness of IPMC. Therefore, the primary challenge of this work is to accurately model this phenomenon. The principal contribution of the paper is a new IPMC model, which considers the change of moisture content. A novel nonlinear adaptive observer is designed to determine the unknown electric potential and humidity level in the polymer membrane. This approach effectively determines the moisture content of the IPMC during long-term continuous operation in air. This subsequently allows us to develop an effective back-stepping control algorithm that considers varying moisture content. Data from experiments are presented to support the effectiveness of the observation process, which is shown in illustrative examples.

Modelling and Control of Ionic Electroactive Polymer Actuators under Varying Humidity Conditions

In this work, we address the problem of position control of ionic electroactive polymer soft actuators under varying relative humidity conditions. The impact of humidity on the actuation performance of ionic actuators is studied through frequency response and impedance spectroscopy analysis. Considering the uncertain performance of the actuator under varying humidity conditions, an adaptable model using the neural network method is developed. The model uses relative humidity magnitude as one of the model parameters, making it robust to different environmental conditions. Utilizing the model, a closed-loop controller based on the model predictive controller is developed for position control of the actuator. The developed model and controller are experimentally verified and found to be capable of predicting and controlling the actuators with excellent tracking accuracy under relative humidity conditions varying in the range of 10–90%.

The Mechanical Properties of Jute/E-glass Fiber Reinforced Polymer Composites influenced by Hygrothermal Effects

During service, almost all materials suffer degradation in their properties when subjected to different conditions such as high temperature and moisture. Composite materials are no exception to this general degradation. Here it is proposed to study jute/E-glass fiber reinforced polymer composite at different temperatures with varying humidity conditions. The composite materials are tested for tensile and flexural properties at ambient conditions and in wet-hot conditions. Influences of these variables on microstructure of these composite materials are studied using scanning electron microscopy (SEM). It is found that tensile strength of the composites that have undergone treatments mentioned above is reduced which assigns the absorption of water molecules on the surface which weakened the composites.

Experimental verification of shrinkage due to drying in concrete under varying humidity conditions in accordance with the Eurocode2 standard

The concrete shrinkage depends on many factors. There are the concrete mixture, dimensions of the element and environment conditions, mainly humidity. All these factors can be imposed under laboratory conditions and controlled. In field conditions, however, a constant humidity is not possible to keep. The paper presents the impact of relative humidity changes on the values of shrinkage strains. The experimental results obtained on the specimens (with size 150x150x600 mm) were compared with the values calculated in accordance with the Eurocode 2 standard. The specimens were made with basalt aggregate without admixtures or additives. Two kinds of cement were used in preparing the specimens: Portland and blast-furnace slag cement. All specimens were treated in water for 10 days in the first days after demoulding and then subjected to testing. During the 56 days the temperature was 22 ± 2°C, while the humidity decreased proportionally from 91% to 47%. Strains were measured and the specimens were weighed to determine the mass loss. The experimental results were compared to the computational results. It should be concluded that they were not coherent in the case of ambient humidity exceeding 80% although it was accordance with the Eurocode 2 standard.

Effects of Variable Humidity on the Creep Behavior of Concrete and the Long‐Term Deflection of RC Beams

The influences of variable humidity on the creep behaviors of concrete and the long‐term deflections of RC beams are analyzed in this paper. A total of 6 prismatic specimens and 5 RC beams were subjected to sustained loads and 3 types of variable humidity conditions for 331 days. The creep strains of the prismatic specimens and the deflections of the RC beams were recorded to investigate the long‐term deformation characteristics. The test results reveal that both the creep strain and the deflection of specimens under cyclic humidity conditions exhibit approximately linear tendencies that are obviously less than those of specimens exposed only to natural air. During certain wetting cycles, the deformation rate became slower and the creep strain even recovered with an increase in the humidity, especially for shorter wetting‐drying cycles. Long‐term deflections predicted using the CEB‐FIP 90 and ACI 209R models were compared with the test results to evaluate the versatility of these current specifications. The findings included rather large errors between the predicted results and experimental data when the average relative humidity was adopted in the analytical models.