Dry Ambient Conditions Research Articles

Dying of thirst: Osmoregulation by a hawkmoth pollinator in response to variability in ambient humidity and nectar availability

Climate-induced shifts in flowering phenology can disrupt pollinator-floral resource synchrony, especially in desert ecosystems where rainfall dictates both. However, baseline metrics to gauge pollinator health in the wild amidst rapid climate change are lacking. Our laboratory-based study establishes a baseline for pollinator physiological state by exploring how osmotic conditions influence survivorship in a desert hawkmoth pollinator, Manduca sexta. We sampled hemolymph osmolality from over 1000 lab-grown moths at 20 %, 50 %, and 80 % ambient humidity levels. Starved moths maintained healthy osmolality of 350–400 mmol/kg for 1–3 days after eclosion regardless of ambient humidity, but it sharply rose to 550 mmol/kg after 4–5 days in low and moderate humidity, and after 5 days in high humidity. Starved moths in low humidity conditions perished within 5 days, while those in high humidity survived twice as long. Moths fed synthetic Datura wrightii nectar, synthetic Agave palmeri nectar, or water, maintained osmolality within a healthy range of 350–400mmol/kg. The same was true for moths fed authentic floral nectars from Datura and Agave plants, although moths consumed more synthetic than authentic nectars, possibly due to non-sugar constituents. Simulating a 4-day mismatch between pollinator emergence and nectar availability, a single nectar meal osmotically rescued moths under dry ambient conditions. Our findings highlight hemolymph osmolality as a rapid and accurate biomarker distinguishing dehydrated from hydrated states in insect pollinators.

Flow characteristics and resistance coefficients of local components of building heat-moisture-oxygen transport pipelines in the Tibetan Plateau

The Tibetan Plateau is characterized by low-pressure, cold, hypoxic, and dry ambient conditions. Thus, in addition to heating, buildings in the region need humidification and oxygenation. It is noted here that the existing specifications of the resistance coefficients of the gas flow in the HVAC pipeline do not consider the effect of the variation in air components on the local resistance of the pipeline due to the low air pressure conditions as well as the humidification and oxygenation. In this paper, the effects of various parameters on the local resistance loss are investigated and reported, including the atmospheric pressure, inlet velocity, humidity, oxygen concentration, pipe diameter, wall roughness, velocity ratio, and area ratio between the branch and the main pipes. The results showed that the decrease in atmospheric pressure leads to a shorter longitudinal distance of effective dissipation of the secondary flow, primarily concentrated in 25D-27D. Additionally, the resistance losses generated in the elbow, the tee straight branch pipe, and the side branch pipe are reduced, with a maximum reduction of 42 %, 33 %, and 46 %, respectively, under low pressure conditions. Also, with the increase in the inlet velocity and the decrease in the pipe diameter, the local resistance of the elbow pipe is increased by a maximum of 14 times and 22 %. Moreover, when the velocity ratio increases and the area ratio between the branch pipe and the main pipe decreases, the local resistance loss of the straight branch pipe and the side branch pipe increases. Based on this study, the recommended value of the local resistance coefficient of the elbow and tee under low pressure is identified. This can provide a reference for the proper design of heat-moisture-oxygen transport pipelines in the plateau area.

A Spatial Assessment of Current and Future Foliar Hg Uptake Fluxes Across European Forests

AbstractAtmospheric mercury (Hg) is deposited to land surfaces mainly through vegetation uptake. Foliage stomatal gas exchange plays an important role for net vegetation Hg uptake, because foliage assimilates Hg via the stomata. Here, we use empirical relationships of foliar Hg uptake by forest tree species to produce a spatially highly resolved (1 km2) map of foliar Hg fluxes to European forests over one growing season. The modeled forest foliar Hg uptake flux is 23 ± 12 Mg Hg season−1, which agrees with previous estimates from literature. We spatially compared forest Hg fluxes with modeled fluxes of the chemical transport model GEOS‐Chem and find a good overall agreement. For European pine forests, stomatal Hg uptake was shown to be sensitive to prevailing conditions of relatively high ambient water vapor pressure deficit (VPD). We tested a stomatal uptake model for the total pine needle Hg uptake flux during four previous growing seasons (1994, 2003, 2015/2017, 2018) and two climate change scenarios (RCP 4.5 and RCP 8.5). The resulting modeled total European pine needle Hg uptake fluxes are in a range of 8.0–9.3 Mg Hg season−1 (min–max). The lowest pine forest needle Hg uptake flux to Europe (8 Mg Hg season−1) among all investigated growing seasons was associated with unusually hot and dry ambient conditions in the European summer 2018, highlighting the sensitivity of the investigated flux to prolonged high VPD. We conclude, that stomatal modeling is particularly useful to investigate changes in Hg deposition in the context of extreme climate events.

A Computational Perspective on Carbon-Carbon Bond Formation by Single Cu Atom on Pd(111) Surface for CO Electrochemical Reduction

This study focuses on the computational characterization of electrochemical C-C bond formation through the CO and CHO coupling process utilizing a dioxo-coordinated Cu single atom site ([CuO2]*) supported on a Pd(111) surface. The stable intermediate, [CuO2]*(CO)2, was identified as a tetradentate-and-tetrahedral species formed upon exposure to CO gaseous molecules. Electrochemically, the hydrogenation of the carbonyl group to CHO was found to be 0.87 eV, conceivably lower than the corresponding step for conventional Cu surfaces. This study observed a considerable charge transfer effect from the top layer of Pd atoms to the adsorbate moiety, especially at the TS structure. This phenomenon resulted in an accessible C-C bond formation barrier at 0.67 eV. Furthermore, the reaction energy of C-C bond formation was found to be exothermic at −0.21 eV, indicating a favorable chemical equilibrium condition. Considering the temperature effect and pressure of the gaseous molecules (CO, CO2, O2), the [CuO2]*(CO)2 intermediate was substantially populated at room temperature and was found to be chemically resilient under dry ambient conditions, as suggested by the kinetic modeling results.

Use of lidar aerosol extinction and backscatter coefficients to estimate cloud condensation nuclei (CCN) concentrations in the southeast Atlantic

Abstract. Accurately capturing cloud condensation nuclei (CCN) concentrations is key to understanding the aerosol–cloud interactions that continue to feature the highest uncertainty amongst numerous climate forcings. In situ CCN observations are sparse, and most non-polarimetric passive remote sensing techniques are limited to providing column-effective CCN proxies such as total aerosol optical depth (AOD). Lidar measurements, on the other hand, resolve profiles of aerosol extinction and/or backscatter coefficients that are better suited for constraining vertically resolved aerosol optical and microphysical properties. Here we present relationships between aerosol backscatter and extinction coefficients measured by the airborne High Spectral Resolution Lidar 2 (HSRL-2) and in situ measurements of CCN concentrations. The data were obtained during three deployments in the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project, which took place over the southeast Atlantic (SEA) during September 2016, August 2017, and September–October 2018. Our analysis of spatiotemporally collocated in situ CCN concentrations and HSRL-2 measurements indicates strong linear relationships between both data sets. The correlation is strongest for supersaturations (S) greater than 0.25 % and dry ambient conditions above the stratocumulus deck, where relative humidity (RH) is less than 50 %. We find CCN–HSRL-2 Pearson correlation coefficients between 0.95–0.97 for different parts of the seasonal burning cycle that suggest fundamental similarities in biomass burning aerosol (BBA) microphysical properties. We find that ORACLES campaign-average values of in situ CCN and in situ extinction coefficients are qualitatively similar to those from other regions and aerosol types, demonstrating overall representativeness of our data set. We compute CCN–backscatter and CCN–extinction regressions that can be used to resolve vertical CCN concentrations across entire above-cloud lidar curtains. These lidar-derived CCN concentrations can be used to evaluate model performance, which we illustrate using an example CCN concentration curtain from the Weather Research and Forecasting Model coupled with physics packages from the Community Atmosphere Model version 5 (WRF-CAM5). These results demonstrate the utility of deriving vertically resolved CCN concentrations from lidar observations to expand the spatiotemporal coverage of limited or unavailable in situ observations.

Effect of cathode channel structure on the performance of open-cathode proton exchange membrane fuel cell in dry environments

The open-cathode proton exchange membrane fuel cell (OC-PEMFC) is a promising power supply for mobile equipment and the design of the cathode channel structure has a significant effect on its water and thermal management. In this study, a three-dimensional multifield coupled OC-PEMFC single-cell model based on a graphite bipolar plate was used to investigate the performance of three types of cathode channel designs, namely, straight, divergent, and convergent channels, under dry ambient conditions. Under ambient conditions of 10 °C and 35% relative humidity, the divergent channel design exhibits the best performance, with the highest membrane water content and uniformity, even when the ambient temperature is increased. The performance of OC-PEMFCs can be improved by increasing the cathode stoichiometric ratio (CSR) under high-temperature and dry conditions. The divergent channel design has the best output performance under various CSRs. The growth percentage of the water content in the membrane ranges from 5.3 to 8.0%, and the average temperature in the membrane is reduced by 2.78–3.47 °C. Although the performance of the convergent channel design is improved, the uniformity of the water and electricity is significantly reduced. This study also provides guidance for the design of OC-PEMFC graphite bipolar plates.

Tribological properties of defect-rich molybdenum disulfide / graphene oxide composite coating under various environments

It is said that molybdenum disulfide (MoS2)/graphene oxide (GO) composite coating is a promising solid lubricant due to their synergetic effect. However, there is few reports on how the content of MoS2 affects the tribological performance of the composite coating. In addition, considering the requirements of production and environmental protection, more types of MoS2 nanomaterials, except the commonly used two dimensional MoS2, are needed to be developed. In this work, defect-rich MoS2 nanosheets obtained by a facile hydrothermal method are proposed to combine with GO nanosheets to form a robust solid lubricant. The influence of defect-rich MoS2 content on the tribological properties of GO/MoS2 composite coating is studied via sliding tests under dry nitrogen and ambient conditions, and its mechanism is revealed by analyzing the composition and microstructure evolution of the contacting interface. The results have implications for developing GO based nanocomposite coatings with excellent lubrication and wear-resistance performance for industrial applications.

Preliminary Exploration of Economic Polypropylene-Fiber-Reinforced ECC with Superfine River Sand (SSPP-ECC) Applied to a Bridge Pavement Leveling Overlay.

In response to the current common disease of concrete leveling overlays of bridge pavement in China, the feasibility of using an economic SSPP-ECC with local waste superfine sand as an alternative material for a leveling overlay was proposed in this study. To evaluate the interface bonding property in the girder between the SSPP-ECC and concrete, a slant shear test and split tensile test were designed to study the interfacial shear and tensile properties of the ordinary concrete/ordinary concrete (OC/OC) and ordinary concrete/SSPP-ECC (OC/ECC), where the results showed that SSPP-ECC could significantly improve the interface shear stress and split tensile strength compared to ordinary concrete. Furthermore, the damage status of OC/ECC no longer involved fracturing along the interface; instead, each of the two substrates was partially destroyed, which revealed that OC/ECC had a high bonding effect. Moreover, a restrained shrinkage test was carried out to evaluate the shrinkage property of SSPP-ECC, where the result showed that the shrinkage strain of SSPP-ECC was slightly lower than concrete, where the average cracking time for SSPP-ECC was far longer than for ordinary concrete under the same ambient drying conditions; furthermore, the stress rate for SSPP-ECC revealed that it was a low-cracking-risk material. Meanwhile, the crack width of SSPP-ECC was only 0.1 mm after 35 d, which showed that SSPP-ECC had a more substantial crack width control capacity relative to concrete. The test results initially verified the feasibility and great potential of economic SSPP-ECC applied in a bridge pavement leveling overlay.

Dynamic and static drying temperatures for ‘Barton’ pecans: Impacts on the volatile compounds profile and kernel color

This study aimed to verify the effects of ambient, static, and dynamic drying temperatures on the volatile compounds (VC) profile and color preservation of ‘Barton’ pecan kernels. The static temperature of 60 °C used to dry the pecans to the desired moisture content (4.5%) reduced the drying period by 44.4 times compared to ambient drying conditions, as a combined effect of the higher temperature and lower air relative humidity (RH). Although, this drying condition increased aldehyde and ketone levels. Drying under ambient air conditions produced the best color parameter (greater hue angle) after drying, although without differing from 60 °C. Drying with a static temperature of 40 °C resulted in the lowest hue angle, and the static drying temperatures of 40 or 60 °C increased total aldehyde production. Our findings showed that the dynamic drying temperature of 40↔60 °C is recommended for ‘Barton’ pecans due to the lower color change, aldehyde and ketone abundance, and shorter drying times (22.2 times more efficient than ambient drying).

Performance analysis of small-scale direct expansion air conditioning system with indirect evaporative cooler as dedicated ventilator

Split-type and window-type air-conditioners are typical small-scale direct expansion air-conditioning (DXAC) system widely-used for household applications. However, lack of controllable ventilation can be a serious problem leading to health problems for such air-conditioning (AC) systems. To improve the indoor air quality of a home space equipped with small-scale DXAC system, an indirect evaporative cooler (IEC) is used as a dedicated ventilator, on one hand, to guarantee proper outdoor air supply and on the other hand, to provide sensible cooling under certain climatic conditions. Validated numerical component models of IEC, DXAC and indoor thermal balance were established and coupled in series to form a closed-loop model of DXAC with IEC ventilator (DXAC-IEC) system. The effects of ambient humidity, ambient temperature, sensible heat ratio and ventilation rate on the system performance were investigated, with comparison to the standalone DXAC system. The results show that the IEC can enhance the system performance under moderate hot and dry ambient conditions (tamb ≤ 33 °C, RHamb ≤ 60%) by reducing the cooling load of DXAC. But it would bring extra moisture from outdoor in humid conditions (tamb ≥ 30 °C, RHamb>50%) for sacrifice of improved indoor air quality. Optimal fresh air ratio exists for the DXAC-IEC system to achieve the maximum coefficient of performance. The findings will be beneficial for the design and optimization of DXAC-IEC system.

Mechanical properties of hydraulic lime mortars and fired clay bricks subjected to dry-wet cycles

This paper examines the influence of moisture and chlorides on the mechanical properties of natural hydraulic lime mortars, fired clay brick materials and masonry components. Besides assessing three types of mortars incorporating limes with different hydraulicity levels, a cement-only mortar was also investigated for comparison purposes. The test results indicate that all the hydraulic lime mortars had mass accumulation in the range of 11–14% after being subjected to wet-dry cycles in a sodium chloride solution, whilst the mass uptake was in the range of 3–8% for those made of cement. Salt accumulation produced a denser material leading to compressive cube and flexural strength enhancements by factors ranging between 1.6 and 4.7 in comparison to those in ambient-dry conditions, with even higher factors obtained for compressive cylinder strengths and elastic moduli. In contrast, lime mortar subjected to water-only wet-dry cycles showed constant mass or mass loss, due to cracking. Uniaxial compressive strengths of cylindrical brick cores were about 8.5% higher due to wet-dry cycles in chloride solution, and by about 14.9% lower due to wet-dry cycles in water, compared to the ambient-dry case. Complementary compressive tests on masonry cylinders in ambient-dry conditions were also used to assess the adequacy of existing compressive strength assessment expressions. After modifying the expressions by a set of proposed calibration factors, these are employed to undertake a sensitivity study using the mechanical properties of mortars and bricks subjected to wet-dry cycling. The results of the sensitivity study, combined with strength ranges available in the literature, lead to an identification of a suitable range of materials that can be considered for rehabilitation of some forms of historic masonry.

Peering inside a cough or sneeze to explain enhanced airborne transmission under dry weather

High-fidelity simulations of coughs and sneezes that serve as virtual experiments are presented, and they offer an unprecedented opportunity to peer into the chaotic evolution of the resulting airborne droplet clouds. While larger droplets quickly fall-out of the cloud, smaller droplets evaporate rapidly. The non-volatiles remain airborne as droplet nuclei for a long time to be transported over long distances. The substantial variation observed between the different realizations has important social distancing implications, since probabilistic outlier-events do occur and may need to be taken into account when assessing the risk of contagion. Contrary to common expectations, we observe dry ambient conditions to increase by more than four times the number of airborne potentially virus-laden nuclei, as a result of reduced droplet fall-out through rapid evaporation. The simulation results are used to validate and calibrate a comprehensive multiphase theory, which is then used to predict the spread of airborne nuclei under a wide variety of ambient conditions.

Depth mapping of metallic nanowire polymer nanocomposites by scanning dielectric microscopy.

Polymer nanocomposite materials based on metallic nanowires are widely investigated as transparent and flexible electrodes or as stretchable conductors and dielectrics for biosensing. Here we show that Scanning Dielectric Microscopy (SDM) can map the depth distribution of metallic nanowires within the nanocomposites in a non-destructive way. This is achieved by a quantitative analysis of sub-surface electrostatic force microscopy measurements with finite-element numerical calculations. As an application we determined the three-dimensional spatial distribution of ∼50 nm diameter silver nanowires in ∼100 nm-250 nm thick gelatin films. The characterization is done both under dry ambient conditions, where gelatin shows a relatively low dielectric constant, εr∼ 5, and under humid ambient conditions, where its dielectric constant increases up to εr∼ 14. The present results show that SDM can be a valuable non-destructive subsurface characterization technique for nanowire-based nanocomposite materials, which can contribute to the optimization of these materials for applications in fields such as wearable electronics, solar cell technologies or printable electronics.

Investigation of Microstructure and Stress Corrosion Cracking in Al-6061-T6 Alloy at Different Loads

Stress corrosion cracking (SCC) refers to the damage of mechanical components which are under the combined action of static load and corrosive environment. This phenomenon occurs in various applications including naval and aerospace industry where aluminum and steel alloys experience mechanical loadings in the presence of corrosive environments. In this research work, microstructural and environmental influence on corrosion behavior of Al-6061-T6 at different static loads was investigated. A new test fixture was developed for stress corrosion cracking. Dog-bone shaped tensile specimens of Al-6061-T6 were manufactured using CNC milling machine. Tests were conducted at constant loads of 200 N, 500 N and 800 N, in three different environments: dry ambient conditions, distilled water and 3.5% NaCl solution. Testing continued for different intervals of time i.e. 96 hours, 68 hours and 4.5 hours respectively. After each set of experiments, specimens were observed for cracks using metallurgical microscope. Detailed fractographic investigation of all the tested specimens was carried out using Scanning Electron Microscope (SEM). Excessive corrosion and material degradation was observed in specimens tested in distilled water and 3.5% NaCl environments. Microstructural analysis depicted pitting corrosion and crack deformation. Some regions clearly showed that grain boundaries were attacked due to oxidation and chemical attack causing weakening of grain boundaries and resulted into intergranular corrosion. Precipitates and grain boundaries in Al-6061-T6 served as a reason of crack initiation due to hydrogen diffusion. Fractographic investigation provided the evidence of trans granular fracture as well as intergranular fracture which was observed as dimples and extensive ductile tearing.

Compressive behaviour of fired-clay brick and lime mortar masonry components in dry and wet conditions

This paper examines the fundamental mechanical properties of masonry elements incorporating fired-clay bricks and hydraulic lime mortars under ambient-dry and wet conditions, corresponding to 48 h submersion in water. In addition to complementary material characterisation assessments, two types of specimens are tested: cylindrical cores in compression, and wall elements in compression. Overall, a detailed account of more than 50 tests is given. Apart from conventional measurements, the use of digital image correlation techniques enables a detailed assessment of the influence of moisture on the constitutive response, confinement effects and mechanical properties of masonry components. The uniaxial compressive strengths of wet brick elements and brick–mortar components, resulting from tests on cylindrical cores with height-to-depth ratios of around two, are shown to be 13–18% lower than those in ambient-dry conditions. The tests also show that enhanced confinement levels in brick units mobilise 67–92% higher strengths than in the corresponding unconfined cylinders. Moreover, experimental observations indicate that the presence of significant confinement reduces the influence of moisture on the mechanical properties as a function of the brick and mortar joint thickness and their relative stiffness. As a result, the failure of wet masonry walls in compression is found to be only marginally lower than those in ambient-dry conditions. Based on the test results, the influence of moisture on the constitutive response and mechanical properties of masonry components is discussed, and considerations for practical application are highlighted.

Investigations on effect of elevated temperatures and reduced relative humidity on drying of grapes

Drying of grapes is a complex process involving physical or chemical pre-treatment to create micro-cracks in waxy cuticle on berry skin followed by drying to 15-16% moisture level by different methods. Weather factors prevailing during grape drying particularly temperature and relative humidity play a very important role in determining the quality of raisins. Since last few years, major grape drying areas in India are experiencing untimely rains during grape drying season resulting in the production of inferior quality raisin. To address such recurring problems, modified grape drying chamber containing heavy duty heaters and fans was fabricated at ICAR National Research Centre for Grapes, Pune. Berries of Thompson Seedless and Manik Chaman were dried in single layer in this chamber in March 2017 and April 2018. Average temperature and average relative humidity during the drying duration and drying periods required to reduce moisture level in the berries up to 15-16% moisture level were compared with drying in chamber having ambient conditions. Average temperatures and relative humidity in heated chamber were high and low, respectively than in ambient chamber in both the years. Thompson Seedless required 25% and 28.6% less drying period in 2017 and 2018, respectively. Whereas, Manik Chaman required 37.5% and 42.9% less drying period in 2017 and 2018, respectively. Under ambient drying conditions, both varieties exhibited similar drying periods (8 days in 2017 and 7 days in 2018) in both the years, however, faster drying of Manik Chaman in heated chamber in both the experimental years may perhaps be due to different wax structure on berry skin and its faster degradation under high temperatures in this variety. Drying under heated chamber conditions would be beneficial to grape growers as the grapes are dried at faster rate and are not exposed to unfavorable drying conditions created by the untimely rains for a longer time. The quality of raisins is also expected to be far better due to absence of dust and other debris which are otherwise present in open drying conditions.

Effects of the surface processing on the tribological performance of C/SiCs under dry friction

A new friction counterpart for carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiCs) and zirconia (ZrO2) toughened by magnesia ceramics is proposed. The effects of the C/SiC surface processing parameters friction on the tribological performance are investigated under dry friction and ambient temperature conditions. The wear tests are carried out using the pin-on-disc friction method. Scanning electron microscopy (SEM) on an instrument equipped with an energy dispersive spectroscopy (EDS) is used to observe the surfaces of the pins and discs before and after the application of friction to reveal the wear mechanism. The results show that surface processing influenced the tribological properties of C/SiC significantly. When the pressure is 30 N, the speed is 0.5 m/s, and the C/SiC surface is ground using 1500# sandpaper, the counterpart tribological performance is the best among the samples considered herein. It is found that the retention ability of the counterparts influenced the tribology performance significantly.

P.362 Antipsychotic treatment for the maintenance phase of schizophrenia: An updated systematic review of the guidelines and algorithms

There are limited studies on the tribological properties of SiAlON-TiN composites. Therefore, in the present study, tribology tests were conducted on a number of αı/βı-SiAlON-TiN composites with different αı/βı-SiAlON phase ratio and TiN content, fabricated with unique compositional design. The influence of αı/βı-SiAlON phase ratios, microstructure, mechanical properties and TiN content on friction and wear behavior was investigated and wear mechanisms were explained. Tribology tests were conducted on computer controlled tribometer under dry unlubricated ambient conditions with a linear reciprocating movement in a ball-on-disc sliding wear configuration and test parameters kept as constant. It was observed that TiN addition (17 wt.%) did not change the friction (CoF) of SiAlON and wear rate and wear volume were observed to increase. Wear mechanisms showed differences with αı:βı-SiAlON phase ratio. Fracture toughness had very pronounced effect on wear resistance.

Application of spore-forming probiotic Bacillus in the production of Nabat - A new functional sweetener

The basis of the present study was developing a novel type of functional sweet product with the additive probiotic spore forming bacteria that do not require cold chain or any specific storage condition. In this study, rock candy containing probiotic bacteria was produced in dry ambient condition. Spore-forming bacilli were selected as probiotics that are resistant to thermal processes and osmotic conditions. Rock candies were coated with an edible coating containing carboxymethyl cellulose, sucrose, glucose syrup, fructose syrup and a probiotic strain. After coating process, the parameters of turbidity (created by water dissolution of coated Nabat); effect of drying temperature on bacterial viability; moisture content, water activity, ash content of product; as well as product storage time were evaluated. Under thermal stress during both dissolution in hot liquid and drying, the survivability of the spores used in the coated rock candies did not fall significantly. Viability evaluation of the probiotic bacilli in the product after six months of storage at ambient temperature revealed 90.39 and 89.07% viability of Bacillus coagulans and Bacillus subtilis spores, respectively. Our results showed that spore-forming probiotics embedded in rock candy are highly stable during storage at ambient temperature and dry condition.

Evaluating performance of hybrid PCM-fan and hybrid PCM-desiccant vests in moderate and hot climates

Personal cooling vests containing phase change material (PCM) are commonly used for outdoor workers. They cool the human torso and provide a better rating of overall thermal comfort in hot environments. However, PCM cooling vests become less effective at conditions where a high sweat secretion is present, and at very humid or very dry ambient conditions. Therefore, design variations have been used to justify the use of the PCM cooling vest in such conditions. These mainly include the hybrid PCM-Desiccant cooling vest, containing thin solid desiccant packets attached to the PCM packets, and the hybrid PCM-Fan vest, formed of PCM packets and ventilation fans.The aim of this study is to develop criteria for comparing the performance of the three vests at different ambient conditions and human metabolic rates. The comparison used predicted values of torso skin temperature and overall thermal comfort using validated simulation models for heat and mass transfer in each of the vest layers, integrated with a validated bio-heat model. Steady state results were obtained at metabolic rates of 3 and 6 MET at ambient temperatures of 35, 40 and 45 °C with varying relative humidity (RH). Based on developed criteria, it was found that the use of the PCM-only vest is recommended at activity level of 3 MET in moderate ambient temperature of 35 °C and at ambient RH of 17% and 27%. At the higher ambient temperatures of 40 °C and 45 °C and low ambient RH, the use of the hybrid PCM-Fan vest is recommended. However, at moderate RH both hybrid vest types can be used while at higher ambient RHs, the use of hybrid PCM-Desiccant vest is justified. Similarly, it was shown that at higher metabolic rate of 6 MET, both hybrid vests can be used at moderate RH. However, at high RH, the hybrid PCM- Desiccant vest is recommended.