Varying Humidity Conditions Research Articles

Assessing Durability in Automotive Fuel Cells: Understanding the Degradation Patterns of PEM Fuel Cells Under Variable Loads, Temperature, Humidity, and Defective Stack Conditions

Assessing Durability in Automotive Fuel Cells: Understanding the Degradation Patterns of PEM Fuel Cells Under Variable Loads, Temperature, Humidity, and Defective Stack Conditions

Ultra-Sensitive NO2 Detection at Room Temperature Enabled by ZnO@MoO3 Core-Shell Nanocomposite.

The sensitive detection of NO2 is crucial for environmental monitoring and improving quality of life. Herein, a ZnO@MoO3 core-shell nanocomposite was fabricated via a simple stepwise solution self-assembly and heat-treatment process. Remarkably, the ZnO@MoO3 sensor exhibited a high response value of 5.4 to 2 ppm NO2 at room temperature. Furthermore, it displayed excellent selectivity against interference gases such as CO2, NH3, methanol, ethylene, and trimethylamine, along with outstanding stability and repeatability under varying humidity conditions. The exceptional sensing performance of the ZnO@MoO3 sensor is attributed to the synergistic effects between ZnO and MoO3, as well as the enhanced electron transfer rate enabled by the heterostructures. This work provides an effective strategy for advancing NO2 sensing capabilities in metal oxide composite sensors.

Development of swelling pressure in paulownia and Norway spruce during moisture absorption

Wood hybrid materials have gained significant attention for advanced technical applications over the past decade. In contrast to other materials, wood’s hygroscopic nature causes swelling and shrinkage, leading to differential expansion in hybrid systems under varying humidity conditions. When wood’s swelling is restrained by surrounding materials, stresses develop within both the wood and its adjacent components. To study this phenomenon, swelling tests were conducted on kiln-dried paulownia (Paulownia elongata) and Norway spruce (Picea abies) in a climate chamber at 20 °C and 98% relative humidity, with expansion restricted in one direction. Moisture absorption initially exhibited a steep, linear increase, levelling off after approximately 2 h. Swelling pressures rose sharply, peaking after 30 h for paulownia and 19 h for spruce, before gradually decreasing due to increased moisture content and relaxation. The measured stresses were lower than the compressive strengths of both wood species at their respective moisture contents. Microscopic examinations showed no cellular damage in paulownia during moisture absorption due to swelling pressure. In contrast, spruce wood displayed cell wall deformations and ray’s kinking in the early wood region of radial samples, as well as cell wall bending in tangential samples. This indicates that maximum stress is determined by the localised failure of the wood’s cellular structure rather than its overall properties. Such local effects were more pronounced in spruce than in paulownia due to their different structure. As a result, paulownia shows excellent potential for use in hybrid structures due to its low swelling and shrinkage properties and uniform structure.

Carbonation under Varying Humidity Conditions: A 3D Micro-Scale Kinetic Monte Carlo Approach.

This paper investigates the impact of varying humidity conditions on the carbonation depth in hardened cement paste using a 3-dimensional microscale kinetic Monte Carlo (kMC) approach. The kMC algorithm effectively simulates the carbonation process by capturing the interplay between CO2 diffusion and relative humidity at the microscale, providing insights into macro trends that align with historical models. The study reveals that the maximum carbonation depth is achieved at relative humidity levels between 55 and 65%, where the balance between water and CO2 diffusion is optimized. At lower relative humidity levels (<55%), a lower carbonation depth is observed. Conversely, at higher relative humidity levels (>65%), increased water content impedes CO2 diffusion, resulting in reduced carbonation depth for cement paste. The kMC model demonstrates a parabolic relationship between relative humidity and carbonation depth. Time series analysis shows that Fick's law is consistently followed, with carbonation depth following the relationship x = k√t at constant relative humidity. The kMC also breaks down the event cycle which shows that after an equilibrium (in terms of rate of events) is achieved between CO2 and H2O at a relative humidity of 75%, a shift occurs in the dominance from reactive to transport processes at a relative humidity of 85%. These findings highlight the importance of humidity in influencing carbonation rates on the one hand and demonstrate the effectiveness of the kMC approach in simulating these complex interactions at the microscale on the other hand.

Comprehensive Physicochemical Characterization and in Vitro Human Cell Culture Studies of an Innovative Biocompatible and Biodegradable Silk-Derived Protein Hydrolysate, SDP-4.

SDP-4 is a soluble silk fibroin-derived protein hydrolysate extracted from the Bombyx mori silkworm cocoon and is a novel first-in-class biopolymer that is biodegradable, biocompatible, and shown to have regenerative properties. SDP-4 is currently used as a commercial wetting agent in topical eye drops, but it has also been shown to have anti-inflammatory properties that could be utilized in other biomedical applications. The purpose of this study was to comprehensively characterize the physicochemical properties that are necessary to design formulations and examine cell viability in response to varying doses of SDP-4 on different human cell types, with a particular attention toward respiratory applications. Lyophilized SDP-4 powder was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, differential scanning calorimetry (DSC), hot-stage microscopy (HSM), Karl Fisher (KF) coulometric titration, Raman spectrometry, confocal Raman microscopy (CRM), and Fourier transform infrared microscopy. The lyophilized powder exhibited a nonuniform, angular glassy flake morphology with uniform chemical composition and minimal moisture uptake when tested under varying humidity conditions. Crystalline character was evident through birefringence at ambient temperature which changed during phase transitions, as evidenced through qualitative and quantitative assessments. Dose ranging SDP-4 biocompatibility studies on different human lung cells, nasal cells, skin cells, and brain cells was assessed by the in vitro cell viability assay. Assay results showed that cell viability was maintained at the various doses studied for different human cell types. The transepithelial resistance (TEER) assay showed that SDP-4 leads to transient fluctuations in cell membrane integrity and barrier tightness, followed by a recovery phase as cells adapt or repair the junctions. These findings demonstrate that SDP-4 is biocompatible with different types of human cells and safe at all of the doses studied. The unique physicochemical properties of SDP-4 revealed in this study demonstrate its favorable formulating ability for a variety of potential therapeutic applications.

Preparation and initial condensation characteristics of superhydrophobic coating based on nano-SiO2 particles

Superhydrophobic surfaces can effectively inhibit the growth of droplets and reduce attachment, thus inhibiting the formation of frost. In this paper, using dimethyldimethoxysilane-modified silica nanoparticles, a superhydrophobic coating with a contact angle of 165.73 ± 1° and a rolling angle of 2 ± 1° was successfully prepared by the secondary spraying method, and the chemical composition of the substrate and the surface morphology of the coating were characterized by means of FT-IR, EDS, and SEM. A visualization test rig was constructed to investigate the condensation droplet growth characteristics on the superhydrophobic surface across various tilt angles (0°to 90°), cold surface temperatures (-1 ℃ to 5 ℃), and humidity levels (45% to 75%). The experimental results revealed that as the tilt angle increases, the forces acting on the condensed droplets change, resulting in a higher frequency of droplet merging, jumping, and slipping. Furthermore, a decrease in cold surface temperature accelerates the growth of condensed droplets. Under varying humidity conditions, droplets on the superhydrophobic surface nucleate and grow more rapidly in high humidity environments, where they exhibit a larger coverage area despite having a relatively small mean radius.

FlexSARCloak: A Flexible SAR Cloak Driven by Task-Oriented Learning.

Invisibility─the remarkable ability to render objects imperceptible─has long been a persistent dream of humankind. However, traditional cloaking materials are typically rigid and inflexible, limiting their adaptability to various shapes and requirements. Even when flexibility is achieved, uncontrollable scattering in complex electromagnetic environments continues to pose significant challenges in the design of flexible cloaks. In this paper, we present a task-oriented learning (TOL)-based metasurface design approach, successfully realizing a broadband, polarization-independent, flexible SAR cloak (FlexSARCloak). Experimental results reveal that the cloak achieves over 90% absorption efficiency across the 9-25 GHz frequency range for incidence angles ranging from 0 to 60°. Outdoor experiments further confirm that the FlexSARCloak achieves near-perfect invisibility under UAV-mounted SAR. Furthermore, a comprehensive series of environmental tests, including exposure to extreme temperatures, variable humidity, and sandstorm conditions, was conducted to simulate natural or extreme conditions, which successfully validated the stability of the electromagnetic performance. The proposed FlexSARCloak presents considerable potential for applications in electromagnetic protection and related domains. Moreover, the introduction of the TOL algorithm is expected to significantly accelerate the design and optimization of metasurfaces, paving the way for the physical realization of multifunctional metasurfaces.

Water-salt transport modeling and sulfate erosion mechanisms in cultural heritage under microclimate

The microclimate of the environment influences the characteristics of salt erosion in historical cultural heritage, determining the pattern of salt weathering and the mechanism of salt-action. The study focuses on the influence of cultural heritage microclimate on salt weathering, and the study aims to understand the weathering mechanism by combining the theory of crystalline weathering with temperature and humidity variation. The study comprised immersing sandstone from the Yungang Grottoes, a World Heritage Site, in a sulfate salt solution and simulation of salt deterioration under on-site cyclic variable temperature and humidity conditions. The article designs the accumulation of salt crystallization at the sandstone surface under the effect of salt evaporation and visualizes the water-salt migration and crystallization process by ion chromatography (IC), microelectrode, and hyperspectral techniques. The corresponding types of sulfate deterioration under different weathering simulation conditions are investigated to probe the mechanism behind different weathering patterns. In the first part, we construct a water-salt migration test, combining hyperspectral techniques and microelectrodes to visualize the weathering patterns, compositional characteristics, and spatial and temporal changes of water-salt transport based on Fick's law to establish a mathematical model and simulate it in COMSOL multi-physics field simulation software. Subsequently, tests were carried out on sandstone with sulfate solution at variable temperatures and humidity levels to simulate the process of salt weathering. The results demonstrated that different salt solutions, such as Na2SO4 and MgSO4, lead to the dissolution of clay minerals. At the same time, crystallization disrupts the sandstone structure, causing degradation of its physico-mechanical properties after several weathering cycles, and there are significant differences in the salt crystallization patterns at different temperatures and after cycling at different humidities.

Large eddy simulation of droplet dispersion and deposition over street canyons

Predicting droplet transport in the atmosphere is a major issue for a large number of dispersion problems such as spray cooling systems in streets, urban lawn sprinklers [Milesi et al., “Interferometric laser imaging for respiratory droplets sizing,” Environ. Manage. 36, 426–438 (2005)], and dispersion of virus such as COVID or from a terrorist attack [Balachandar et al., “Host-to-host airborne transmission as a multiphase flow problem for science-based social guidelines,” Int. J. Multiphase Flow 132, 103439 (2020)]. Here, we investigate the propagation of droplets issued from a source near the ground between square obstacles with different spacings. The aerodynamic field is determined by large eddy simulation coupled with an immersed boundary method for the obstacles. Droplets are tracked by a Lagrangian approach. An evaporation model is used to account for varying humidity conditions. Droplet concentration, mass flux, and deposition rates are obtained for different evaporation conditions and obstacle spacings. The results show high deposition rates on the internal wall of the first obstacle due to droplet advection by the reverse flow of the primary vortex. In addition to this, droplets may escape the canyon and propagate downstream as far as eight times the obstacle distance (8H). The concentration of air-borne droplets downstream the canyon is higher for smaller street canyon openings. When evaporation is accounted for, the ground-level droplet concentration may be reduced by up to 30% in the case of small canyon openings.

High Ion-Conductive Hydrogel: Soft, Elastic, with Wide Humidity Tolerance and Long-Term Stability.

Ion-conductive hydrogels have received great attention due to their significant potential in flexible electronics. However, achieving hydrogels that simultaneously possess high ionic conductivity and stability under varying humidity conditions remains a challenge, limiting their practical applications. Herein, we propose a thermally controlled chemical cross-linking strategy to prepare an elastic and conductive hydrogel (ECH) of poly(vinyl alcohol) (PVA) with high content of H2SO4. The covalent cross-links formed effectively tackle the instability issue in high humidity of physically cross-linked PVA/H2SO4 hydrogels with high ionic conductivity, which were previously developed via the polymer-in-salt strategy. We systematically investigated the reaction conditions and clarified the methods to optimize the hydroxyl dehydration of PVA, resulting in excellent mechanical properties and ion conductivity simultaneously. The ECH demonstrates impressive ionic conductivity (up to 392 ± 49 mS cm-1) and elasticity (over 80% resilience upon stretching and compression after being equilibrated at various humidity levels for 24 days). Thanks to the excellent water retention of the high H2SO4 content, the ECH maintains an ionic conductivity exceeding 210 mS cm-1 for over 420 days at 50% relative humidity (RH) and retains over 100 mS cm-1 even after 3 days under extremely dry conditions (7% RH). These remarkable properties make the ECH an ideal candidate for applications requiring reliable ionic conductivity in diverse environmental conditions. Additionally, we demonstrated that the ECH can function as a stretchable Joule heater with high conformability for heating up objects with curved surfaces. The heating rate could reach a fast rate of ∼12 °C s-1 even when a human-safe alternating current voltage is below 36 V, attributed to the high ionic conductivity. We believe that the high performance and ease of fabrication make our hydrogels a promising candidate for use as electrolytes in flexible energy storage devices, electrolyte gates in electrochemical transistors, and artificial skin, which often face long-term stability challenges under varying humidity conditions.

Moisture ageing effects on the mechanical performance of eco-friendly sandwich panels made of aluminium skins, bamboo ring core and bio-based adhesives

Recent research has been focused on developing high-performance sandwich structures using renewable resources. The adoption of bamboo rings as a core material and bio-based adhesives has emerged as a promising sustainable design solution for panel construction. It is therefore critical to conduct accelerated ageing tests on these materials to evaluate the impact of environmental humidity on their degradation and durability. This study assessed the effects of moisture ageing on the physic-mechanical properties of eco-friendly sandwich panels and their constituents (aluminium skins, bamboo ring core and castor oil bio-adhesive). Mechanical evaluations of sandwich panels with compacted and spaced bamboo ring cores were performed under varying humidity conditions. Bamboo rings exhibited variable bulk density due to swelling and loss of organic material over time. They also demonstrated increased compressive properties after 2 years of natural ageing but reduced performance after 30 days at 100 % relative humidity. The mechanical properties of the bio-based polymer were enhanced through water-ageing exposure. Sandwich panels constructed with compacted bamboo ring cores exhibited higher bending properties than those with spaced ring core architecture, with the latter showing failures characterised by a wrinkling effect on both skins followed by debonding.

Effect of relative humidity on passive spore release from substrate surfaces

Fungal spores are abundant in ambient air and exposure to this type of bioaerosols are found to cause significant health and climatic effects. In this study, we investigated the influence of air relative humidity (RH) on the passive release of spores from solid substrates. Preliminary investigations into the effect of RH on fungal spore release indicated an increase in spore flux with reduced air RH. The change in spore emission flux occurred very quickly in response to a change in ambient RH. To verify the hypothesis of extremely rapid drying under lower RH, experiments were conducted using a quartz crystal microbalance with dissipation (QCM-D) to understand the timescales of spore moisture uptake and drying. The analysis of mass transfer of water to and from the spores indicated that the bulk of the transfer occurred within a minute of exposure to any RH. The effect of the ambient RH was explained using a mathematical model with the spotlight on the parameter, E, that represented the energy required to aerosolise one spore. This study demonstrates the application of QCM-D to study interaction between ambient aerosol particles and various vapor phase and gas phase environments. The study enhances the overall understanding and capability to characterise passive fungal spore release under varying humidity conditions in the natural environment.

Humidity-independent NO2 gas sensors based on ZnO-NiOFx nanocomposites and the synergistic humidity-immune effect of fluorine doped NiO

Clean, alternative energy sources, especially fuel cells, are gradually attracting global attentions while the produced toxic nitrogen dioxide (NO2) is a greatly hazardous chemical impacting their energy efficiencies. Metal oxide semiconductors (MOS) hold significant promise as NO2 sensors. However, intensive humidity interaction intensifies signal drifts and reliable response inhibitions under variable humidity conditions. In this study, we present a novel approach to address this issue by engineering in-situ F-doped NiO nanocomposites (NiOFx) decorated on ZnO snowflakes achieved through decomposition modulation of ZnOHF precursors. The optimized NO2 sensor demonstrates unparalleled humidity-independence across a wide operating temperature range with prime sensitivity, low detection limit and rapid response/recovery. Matrix algorithm is also implemented in highly precise NO2 identification under complicated atmospheric and humid conditions. Mechanism studies based on temperature programmed desorption (TPD), quasi in-situ X-ray photoelectron spectroscopy (Quasi in-situ XPS) reveal that F− dopants facilitate interfacial electron transferring and inhibit oxygen activity. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) demonstrates that hygroscopic NiO and electronegative F− synergistically obstruct hydroxyl adsorptions on sensing materials. The innovative approach offers a promising solution for enhancing moisture resistance of MOS sensors for real-time NO2 concentration monitoring in fuel cells and provides valuable insights into anti-humidity mechanisms.

Experimental studies on the interfacial shear characteristics between joint concrete and foamed polymer in cross-river shield tunnel

The inadequate grouting performance in cross-river shield tunnels is primarily due to the insufficient bonding strength between the grouting material and the tunnel segments. In this study, a series of tests were conducted to compare foamed polymer and common grouting materials, focusing on the tangential bonding performance of the interface with tunnel segment concrete under varying humidity conditions. The applicability of polymer for treating leaks in cross-river shield tunnels was explored. The effects of polymer density, interfacial humidity, interfacial roughness, and normal stress on the shear strength of the polymer-concrete interface were investigated. A mathematical model reflecting the interface shear characteristics between polymer and concrete was established and validated. The test results have shown that, due to the fast reaction speed and high expansion rate, foamed polymer was found to be a feasible solution for addressing leakage in cross-river shield tunnels. Compared with common grouting materials, the density of foamed polymer is controllable, and the shear strength between foamed polymer and concrete segments is less affected by humid conditions. The minimum shear strength of the interface between foamed polymer and concrete is 1.2 MPa, while the maximum is 2.0 MPa. Foamed polymer can meet the needs of leakage treatment of cross-river shield tunnel. The interfacial shear strength between foamed polymer and concrete segments is directly proportional to the polymer density, interfacial roughness, and normal stress, and inversely proportional to the level of humid in the tunnel. The influence of various factors on interfacial strength is ranked as follows: polymer density > interfacial humidity > normal pressure > interfacial roughness. The residual error of linear regression mathematical model for the shear strength of interface between foamed polymer and segment concrete follows a normal distribution. The fitting results were proven to be accurate, allowing for the intuitive prediction of the quantitative relationship between shear strength and multiple influencing factors.

Fabricating rapid proton conduction pathways with sepiolite nanorod-based ionogel/Nafion composites via electrospinning

The major limitation of conventional sulfonated polymer proton-exchange membranes (PEMs) is their strong reliance on water molecules for proton conduction, causing a significant reduction in proton conductivity under low-humidity conditions. In this study, a one-dimensional ionogel (IL@Sep) confined within sepiolite (Sep) nanorods was prepared using ionic liquid (1-butyl-3-methylimidazolium trifluoromethanesulfonate) and supercritical CO2. Subsequently, IL@Sep was blended with a Nafion solution, and electrospinning was used to fabricate the composite fiber PEM suitable for low-humidity environments. The results revealed that the electrospun (ES)-Nafion/IL@Sep composite fiber membrane exhibited significantly enhanced mechanical properties, water absorption, and proton conductivity. At an IL@Sep content of 2 wt%, the Nafion/2IL@Sep membrane exhibited a proton conductivity of 231 mS cm−1 at 80 °C/98 % relative humidity (RH) and 113 mS cm−1 at 80 °C/40 % RH. Moreover, the single-cell assembled with this composite membrane exhibited good gas tightness and achieved a peak power density of 779 mW cm−2 at 60 °C/80 % RH, which was ∼1.45 times that of the Nafion 212 membrane single-cell. This study indicates that electrospinning-assisted ionogel-modified ES-Nafion/IL@Sep composite fiber membranes have potential suitability for use in proton-exchange membrane fuel cells under varying humidity conditions.

Environmental aging effects on mechanical behavior of an hemp based biocomposite material for structural strengthening

Biocomposites are innovative materials usually made of natural fibers embedded in a natural matrix. The mechanical behavior of such materials when exposed to the environmental agents (i.e. UV radiations, high/low temperature, variable humidity conditions) is a crucial issue. This paper is aimed to investigate an hemp based biocomposite for structural strengthening, addressing a gap in the existing literature concerning the mechanical characterization of the composite constituents (i.e. hemp ropes and natural matrices) under accelerated weathering conditions. In particular, this research involves the mechanical behavior assessment of hemp ropes, four distinct types of matrices (i.e. two organic binder based matrices and two mortar based matrices) and the hemp/matrix interface. Tensile tests, three point bending tests, uniaxial compression tests and pull-out tests are carried out to characterize these components. To simulate accelerated weathering, samples of the biocomposite constituents are subjected to cycles of hygrothermal stress and UV radiation using an accelerated weathering testing apparatus. Subsequently, experimental mechanical tests are performed on the aged biocomposite components, and their mechanical properties are assessed and compared to those of the non-aged materials. The results reveal that aging leads to a significant reduction in the mechanical properties of the hemp ropes, and varying effects on the mechanical properties of matrices depending on their nature (organic binder-based or mortar-based matrices).

Effect of humidity on the friction and wear behavior of C/C-CuNi composites

The friction behavior and wear performance of C/C-CuNi composites under varying humidity conditions were investigated. Lower levels of humidity (30 %–50 % RH) resulted in the formation of a lubrication layer composed mainly of graphite and CuO, which led to adhesive wear of the composites together with stable and low coefficients of friction (∼0.144) as well as a low wear rate. However, when the relative humidity exceeded 70 %, there was an increased tendency for the formation of a brittle layer predominantly consisting of Cu(OH)2 and Cu2(OH)2CO3 compounds due to tribo-chemical reactions between the composites and H2O and CO2 in humid air. Subsequently, this brittle oxide layer caused abrasive wear accompanied by fluctuations in the coefficient of friction along with increased wear rates.

In situ X-ray and IR probes relevant to Earth science at the Advanced Light Source at Lawrence Berkeley Laboratory

Access to synchrotron X-ray facilities has become an important aspect for many disciplines in experimental Earth science. This is especially important for studies that rely on probing samples in situ under natural conditions different from the ones found at the surface of the Earth. The non-ambient condition Earth science program at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, offers a variety of tools utilizing the infra-red and hard X-ray spectrum that allow Earth scientists to probe Earth and environmental materials at variable conditions of pressure, stress, temperature, atmospheric composition, and humidity. These facilities are important tools for the user community in that they offer not only considerable capacity (non-ambient condition diffraction) but also complementary (IR spectroscopy, microtomography), and in some cases unique (Laue microdiffraction) instruments. The availability of the ALS’ in situ probes to the Earth science community grows especially critical during the ongoing dark time of the Advanced Photon Source in Chicago, which massively reduces available in situ synchrotron user time in North America.

Moisture actuated cobalt alginate discoloration artificial muscle

Artificial muscles have the ability to sense changes in the external environment and generate rapid and significant contraction deformation or rotational motion. However, most artificial muscles are limited to a single form of deformation, and there are still great difficulties in achieving complex dual response modes. Herein, a novel artificial muscle made of cobalt alginate fiber with both rotational/contraction deformation and discoloration functions was successfully prepared by a simple wet spinning and directional twisting methods. The wet-sensitive color change performance is achieved by the formation of different hydrates of cobalt ions in varying humidity conditions, while rotational motion is induced by radial untwisting resulting from fiber swelling upon moisture absorption. In addition, the artificial muscle fiber exhibited a transition from blue to purple to red as the environmental humidity changes from 35 % to 85 %. When the fibers were exposed to water, the twisted fiber with a twist count of 2500 truns provided a rotational speed of over 2000 rpm, and the actuating and discoloration performance did not significantly decrease in 50 repeated cycle tests. This stable shape and color dual response artificial muscle can simulate traditional windmill devices, while also providing a new design idea for smart textiles and humidity visualization devices.

Derivation of Ambient Enhancement Factors of Impregnated Twisted Pairs for Partial Discharge Risk Evaluation

Partial discharge (PD) is the main issue challenging the electrical machine (EM) insulation system for more electric aircraft (MEA) applications. Indeed, the trend of adopting higher DC link voltage and fast switching device further boost the risk of PD. Partial discharge inception voltage (PDIV) is mostly dominated by ambient conditions (i.e., temperature, pressure, and humidity), and their influence is accounted for through experimentally determined ambient enhancement factors. For non-impregnated windings, ambient enhancement factors are suggested by both IEC 60034-18-41 and recent literature. However, in many applications, EMs’ windings are often impregnated with resin to improve thermal performance, mechanical resistance, and electrical insulation. In this case, no indications of the enhancement factors for PD risk assessment are given. The ambient enhancement factors are experimentally determined in this paper to enable the PD risk evaluation for impregnated windings. These factors are obtained relying on an extensive PD investigation, where PDIV and partial discharge extinction voltage are measured under variable temperature, pressure, and humidity conditions. Finally, the tests are performed on different wire types and motorette samples to validate the applicability of the derived factors.