Air Vapor Research Articles

Insights into the Drivers and Spatiotemporal Trends of Extreme Mediterranean Wildfires with Statistical Deep Learning

Abstract Extreme wildfires continue to be a significant cause of human death and biodiversity destruction within countries that encompass the Mediterranean Basin. Recent worrying trends in wildfire activity (i.e., occurrence and spread) suggest that wildfires are likely to be highly impacted by climate change. To facilitate appropriate risk mitigation, it is imperative to identify the main drivers of extreme wildfires and assess their spatiotemporal trends, with a view to understanding the impacts of the changing climate on fire activity. To this end, we analyze the monthly burnt area due to wildfires over a region encompassing most of Europe and the Mediterranean Basin from 2001 to 2020 and identify high fire activity during this period in eastern Europe, Algeria, Italy, and Portugal. We build an extreme quantile regression model with a high-dimensional predictor set describing meteorological conditions, land-cover usage, and orography, for the domain. To model the complex relationships between the predictor variables and wildfires, we make use of a hybrid statistical deep learning framework that allows us to disentangle the effects of vapor pressure deficit (VPD), air temperature, and drought on wildfire activity. Our results highlight that while VPD, air temperature, and drought significantly affect wildfire occurrence, only VPD affects wildfire spread. Furthermore, to gain insights into the effect of climate trends on wildfires in the near future, we focus on the extreme wildfires in August 2001 and perturb VPD and temperature according to their observed trends. We find that, on average over Europe, trends in temperature (median over Europe: +0.04 K yr−1) lead to a relative increase of 17.1% and 1.6% in the expected frequency and severity, respectively, of wildfires in August 2001; similar analyses using VPD (median over Europe: +4.82 Pa yr−1) give respective increases of 1.2% and 3.6%. Our analysis finds evidence suggesting that global warming can lead to spatially nonuniform changes in wildfire activity.

Моделирование динамики контактных взаимодействий минералов во флотационной системе

Моделирование динамики контактных взаимодействий минералов во флотационной системе

RESULTS OF INDUSTRIAL TESTS OF A CONDENSING VAPOR RECOVERY UNIT AT AN OFFSHORE OIL TERMINAL

An effective method of reducing vapor emissions of liquid hydrocarbons, creating safe operating conditions for facilities for loading oil products into vehicles is the use of vapor recovery units (VRU). Among the available types of VRU, condensing installations are distinguished, the operation of which is based on the difference in the condensation temperatures of air and petroleum product vapors. To the advantages of condensing VRU developers refer: 1) safety; 2) low hydraulic resistance; 3) production of condensate of high commercial quality; 4) the possibility of accounting for the captured product; 5) the absence of secondary contaminated waste; 6) the practical absence of the need to purchase and dispose of consumables.
 The article presents the results of tests of the condensing VRU, called the «Condensation and Dispersion Complex», during the gasoline shipment at one of the offshore oil terminals in the spring and summer period.
 During the condensating VRU tests, the average degree of purification efficiency of the gas-air mixture (GAM) from gasoline vapors is established, which is significantly lower than the suppliers of condensing VRU declare and is
 completely insufficient to solve environmental problems. The content of hydrocarbons in the GAM at the output of the VRU turned out to be several times higher than was stated by the developer.
 The reason for this negative result is insufficient deep cooling of the gas-air mixture. It has been initially chosen incorrectly, because it does not take into account the accumulated experience in the world of using condensating URPs. The lowest achieved GAM temperature is several degrees higher than the coolant temperature in the condenser heat exchangers, which indicates an incorrect choice of condensation criteria.
 The amount of gasoline that was captured during the loading of one tanker was determined, as well as the amount of hydrate inhibitor required for this and the electricity consumption. It is established that the consumption of consumables during the operation of the condensing URP, called the «Condensation and Dispersion Complex», is rather high. Therefore, the developers' statement about the absence of consumption by the installation of consumables is a marketing technique.

Investigating the reduction of rainfall intensity beneath an urban deciduous tree canopy

Trees have an indispensable role to play in the hydrological cycle. The process of interception by tree canopies alters the magnitude, pathway, and intensity of rainfall reaching the ground. This study investigates the rainfall intensity-attenuating effects of canopy interception by open-grown birch trees (Betula pendula Roth.) in an urban environment and the influence of atmospheric variables. Rainfall partitioning was measured in a research plot in the city of Ljubljana, Slovenia, from August 2021 to August 2022. Simultaneously, optical disdrometers above and below the birch tree canopy measured microstructures of rainfall and throughfall, from which the intensities were calculated. During the measurement period, the birch tree intercepted on average 25.6 % of gross rainfall, with the interception being twice as high during the leafed season than in the leafless season. Consequently, the total number and volume of drops under the canopy were reduced on average by 16.4 % and 48.7 %, respectively, indicating the interception and fragmentation of raindrops by the canopy. Owing to these processes, the leafed and leafless states of the birch tree canopy attenuate the average intensities of rainfall by 50.2 % and 41.6 %, respectively. Canopy interception also moderates the maximum 10-minute rainfall intensities by 11.6–83.8 % and 13.1–74.2 % during the leafed and leafless periods, respectively. This percentage of reduction in the rainfall intensities below the canopy decreases with rainfall amount and in the absence of foliage. Aside from phenoseasons, we also found that vapor pressure deficit and air temperature were among the atmospheric variables that exert the highest influence on the intensities of throughfall. Furthermore, the regression analysis between the maximum throughfall intensity and peak water level for each rainfall event indicates that the reduction of rainfall intensity by the canopy has a significant effect on runoff peak water level (R2 = 0.76, p < 0.001).

Evaluation of the Moisture Management, Air and Water Vapour Permeabilities of Knitted Fabrics for Garments

The market today offers a variety of fabrics that may be utilised to create any style of clothing. Fabrics are periodically altered as a result of technology’s continual growth, to the point that it became difficult for clothes makers to assess the fabric characteristics related to thermal comfort. This paper reports some investigations on the moisture management and permeability properties of several commercial knitted fabrics intended for garment application. The fabric’s ability to manage moisture as well as its air and water vapour permeability were assessed. A fabric rating index was used to combine the results from each test to determine the fabric’s thermal comfort characteristics. Among the five knitted fabrics, the fabric comprised of nylon &amp; polyester with jersey structure gave the highest assessment rating which is 5. The study serves as a future reference for future textile and garment industry, that implement the laboratory method used in this paper i.e moisture management, water vapour and air permeability in choosing the better thermal comfort qualities for general wear.

Seasonal and Daily Xylem Radius Variations in Scots Pine Are Closely Linked to Environmental Factors Affecting Transpiration.

Seasonal and daily radius variations in the xylem (XRV) and inner bark (IBV) of mature Scots pine trees (Pinus sylvestris) were determined during April 2019-October 2021 at a drought-prone inner alpine site (c. 750 m asl; Tyrol, Austria) by applying point dendrometers. XRVs were also related to environmental factors to evaluate the drivers of XRV during the growing season. XRV records revealed that the xylem width (i) started to shrink around the onset of radial stem growth in April, (ii) consistently decreased by c. 50 µm at the time when air temperature (T) and vapor pressure deficit (VPD) reached their maximum in late June through mid-July, and (iii) recovered until November/December. Although in daily cycles of radius variations XRV preceded IBV by about two hours and the daily amplitude of XRV was about 1/10 that of IBV, XRV and IBV (seasonal trends removed) were closely linked (ρ = 0.755; p < 0.001), indicating tight hydraulic coupling between these tissues. Furthermore, the daily amplitude of XRV was linearly and closely related to daily maximum T (ρ = 0.802; p < 0.001), mean daily solar radiation (ρ = 0.809; p < 0.001), and non-linearly related to daily maximum VPD (R2= 0.837; p < 0.001), indicating that the xylem of Pinus sylvestris reacts like a transpiration-driven passive hydraulic system.

Thermodynamic and economic analysis of an integration system of multi-effect desalination (MED) with ice storage based on a heat pump

In this study, an innovative system that combined a heat pump, multi-effect desalination, and ice storage subsystem is proposed. The heat pump provides both thermal energy and cold energy for the system to achieve desalination and ice generation. The performance of the proposed system is compared with the conventional mechanical vapor compression and air conditioning systems. The thermodynamic, economic, and environmental analysis is also carried out of both proposed and conventional systems. Moreover, the impacts of the different refrigerants, the condensation temperature of the first effect, and the different areas are carried out to evaluate the effects of several vital parameters on the proposed system. Results showed that the specific energy consumption for the proposed and conventional systems is 4.71 kWh/t and 8.94 kWh/t, respectively. For the economic performance, the payback period of the proposed system is 3.85 years, while it is 5.90 years for the conventional system. For the environmental performance, the unit profit CO2 emission is 15.50 kg/$ of the proposed system, which is 7.68% lower than the conventional system (16.79 kg/$). Hence, the proposed system shows higher economic and environmental performance.

Viscose nonwoven fabric with copper and its multifunctional properties

The antimicrobial functionalization of textile structures with copper and its compounds carried out by various methods increased significantly during the SARS-CoV-2 pandemic. So far, in order to obtain antiviral properties the magnetron technique using copper was applied mainly to flat textile structures; polypropylene, polyester and cotton nonwovens, and polyester and cotton woven fabrics. In this study, magnetron sputtering with copper was applied to modify the spatial viscose needle-punched nonwoven fabric. We found that the spatial nonwoven structure made of regenerated cellulose fibers and one-side sputtered with copper has strong antimicrobial activity against Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae. In the case of herpes simplex virus type 1 (HSV-1) McKrae strain, vaccinia virus (VACV) WR strain, influenza A virus H1N1 (IFV) and mouse coronavirus (MHV) JHV strain used in the study, Cu modified nonwoven fabric has only weak activity against herpes simplex virus type 1 (HSV-1). It also has no significant toxicity compared to the control medium and pristine nonwoven fabric. The modified nonwoven fabric is characterized also by hydrophobic properties, high electrical conductivity, good air and water vapor permeability, and meets the requirements of breathing resistance for all protection classes (FFP1, FFP2 and FFP3) specified in the EN 149-2001 standard.

The rate of temperature increase in the inner layers of meat products during heat treatment in steam-air environments

Studies have been conducted to study the rate of temperature increase in the subcortical and central layers of meat products with a different ratio of moisture/fat content when heated in steam-air environments. Skinless chicken fillet (wet fat- free sample) was selected as the objects of research SBI, humidity – 74.5%, fat content – 1.4%) and the meat of the shoulder part of the pork carcass (low-moisture, greasy sample), humidity – 55.1%, fat content - 29.4%). The products were molded in the form of a one-dimensional cylinder and plate. Heating was carried out in an environment of dry air and a vapor–air mixture with a moisture content of 80-85% at coolant temperatures of 160 ... 240 °С. Measurements were carried out in the subcortical layer (upper moist) and in the center (inner moist). The general rates of temperature increase in the studied layers are determined, the observed patterns are described. For a more complete description, the process was divided into periods of heating and bringing to readiness; a variant of separation by heating rate was selected, which was carried out based on the results of an analysis of changes in excess temperature over time. To analyze the presented data, the ratios of the rates of temperature increase were calculated depending on the type of coolant and the sample. It is shown that the rate of temperature increase increases with an increase in the temperature of the coolant at both treatment periods for all the studied variants. At the initial stage, a higher rate of temperature increase is observed when heated in a vapor–air mixture (due to the predominant heat transfer due to condensation), at the main stage - in the air (due to the predominant heat transfer due to convection). For the subcortical layer, at the initial stage, a higher temperature increase is observed for the low-moisture, greasy sample, at the main stage – for the wet fat- free sample (due to the evaporative capacity of the material). For the center, a higher increase is observed for the wet fat- free sample in both periods (due to the inhibitory effect of the fat melt of the low-moisture, greasy sample).

Detailed investigation on the insulation and permeability characteristics of rigid polyurethane foam loaded with micron-sized Turkey feather powder depending on the free volume change

This study brokes new ground to understand the insulation and permeability performances of rigid polyurethane foams (RPUFs) containing the different contents of micron-sized turkey feather powders (TFPs) depending on the free volume change for the first time. The effects of TFPs loading on the RPUFs were investigated by the examination of their structural and chemical features (particle size and ATR-FTIR analyses), free volume property (PALS analysis), insulation features (thermal conductivity and sound absorption tests), permeability performance (air and water vapor permeability tests) and cellular topology (SEM). PALS analysis results revealed that the addition of TFPs into the foams led to the sharp decrease in all free volume parameters since TFPs caused the formation of the disordered cells by occupying the holes in the matrix. Furthermore, both thermal conductivity and acoustic performance of the resulting foams get worse when compared to unfilled RPUF. This results were attributed to the formation of thinner and weaker cells during polymerization, reduction in the amount of CO2 inside the cells, enhancement in the solid-phase level in the matrix due to the increasing of volumetric density. Additionally, the foam samples with high content of TFPs showed considerably lower air and water vapor permeabilities when compared to neat RPUFs due to the dominant hydrophobic character of the keratin and reduction in the degree of vacancies in the matrix. SEM analysis also revealed that TFPs showed good compatibility with RPUF, but the distorted and irregular shaped cellular morphology was obtained at high contents.

Quality control criteria for gas permeability testing of concrete structures

AbstractCuring is a crucial process during the construction phase of concrete structures, as it plays a significant role in ensuring durability and strength. During the curing process, the concrete is kept moist to allow properly hydration and hardening. This process helps to prevent cracking, increase the concrete's compressive strength, and improve its resistance to weathering, abrasion, and other forms of wear. Therefore, it is essential that the curing process is carried out correctly to ensure the longevity and structural integrity of the concrete structures. The pore system within concrete plays a critical role in determining its durability and resistance to various types of degradation. One way to assess the quality and durability of concrete is by measuring its gas permeability. Gas permeability is a measure of how easily gases, such as air or water vapor, can pass through the concrete. If concrete has high gas permeability, it allows harmful substances, such as water, gases and chemicals, to penetrate into the concrete, causing damage and reducing its durability over time. Herein gas permeability testing is used for the evaluation of concrete curing quality.

Testing the suitability of Marginal Distribution Sampling as a gap‐filling method using some meteorological data from seven sites in West Africa

AbstractMeteorological data are useful in many fields related to climate change studies and their use often requires them to be continuous. To date, marginal distribution sampling (MDS), which consists of filling a missing value with an average of the data that are found in similar meteorological conditions over a flexible time window, is widely adopted in the FLUXNET community. In this work, we evaluate the performance of MDS at diurnal and monthly scales for the incoming shortwave radiation (Swin), relative humidity (RH), vapour pressure deficit (VPD), air and soil temperatures (Tair, Tsoil) acquired across seven sites in West Africa. The criteria tested are the MDS's ability to (i) fill gaps while reducing the error rate, (ii) represent proper variability within data and finally (iii) ensure homogeneity between its output and original data. We found during the daytime that MDS is adequate for filling gaps in Swin when both reducing error rate and a good representation of variability are targeted. If the goal is to have a small error rate, then this approach is recommended for all investigated variables except VPD. During nighttime, MDS is satisfactory to minimize the error when filling gaps in Tair, Tsoil and RH while to represent their variabilities it becomes more sensitive to the rate of missing data. At a monthly scale, the gap‐filled data are consistent with the original ones for all variables attributable to data size and a wider sliding window that allows more data under similar conditions to be considered.

Deep Reinforcement Learning DDPG Algorithm with AM based Transferable EMS for FCHEVs

Hydrogen fuel cell is used to run fuel cell hybrid electrical vehicles (FCHEVs). These FCHEVs are more efficient than vehicles based on conventional internal combustion engines due to no tailpipe emissions. FCHEVs emit water vapor and warm air. FCHEVs are demanding fast dynamic responses during acceleration and braking. To balance dynamic responsiveness, develop hybrid electric cars with fuel cell (FC) and auxiliary energy storage source batteries. This research paper discusses the development of an energy management strategy (EMS) for power-split FC-based hybrid electric cars using an algorithm called deep deterministic policy gradient (DDPG) which is based on deep reinforcement learning (DRL). DRL-based energy management techniques lack constraint capacity, learning speed, and convergence stability. To address these limitations proposes an action masking (AM) technique to stop the DDPG-based approach from producing incorrect actions that go against the system's physical limits and prevent them from being generated. In addition, the transfer learning (TL) approach of the DDPG-based strategy was investigated in order to circumvent the need for repetitive neural network training throughout the various driving cycles. The findings demonstrated that the suggested DDPG-based approach in conjunction with the AM method and TL method overcomes the limitations of current DRL-based approaches, providing an effective energy management system for power-split FCHEVs with reduced agent training time.

Long‐term observed changes of air temperature, relative humidity and vapour pressure deficit in Bolivia, 1950–2019

AbstractThis study analyzes the long‐term observed changes of mean (Tmean), maximum (Tmax) and minimum (Tmin) air temperatures, relative humidity (RH) and vapour pressure deficit (VPD) at different elevation ranges across Bolivia from 1950 to 2019. The linear trends in air temperature series present a significant increase, with no substantial seasonal or spatial differences. On an annual basis, RH exhibited a non‐significant decrease (−0.08% decade−1), while VPD showed a significant increase (0.01 hPa decade−1) (p &lt; 0.05). Although prior research has suggested that highland elevations experience faster warming than the global average, we have not identified a distinct correlation between elevation gradients and differential warming rates in Bolivia. Future research could investigate elevation‐dependent climate trends by examining seasonal and monthly patterns of climatic variables in relation to topographical gradients in various highland regions.

A cobalt-vacant Co3O4 as a stable catalyst for room-temperature decomposition of ozone in humid air

Conventionally ozone-decomposition catalysts such as MnO2 face the gradual deactivation due to occupation of reactive site, i.e., oxygen vacancy by intermediates like O22- or ubiquitous water vapor in air. Herein, we synthesized a Co2+-vacant Co3O4 (Co3−xO4) with dominant exposure of (110) facets, it maintained superior efficiency of 98% in decomposing 100 ppm ozone over 180 h under the space velocity of 1200 L/g·h at 25 ℃ and relative humidity (RH) of 50%, well beyond the performance of any reported metal oxides catalysts. Especially, it kept stable efficiency even under RH 90% and ultrahigh space velocity of 6000 L/g·h. A new ozone decomposition mechanism under humid conditions is revealed, i.e., the Co2+ vacancy significantly promotes O3 adsorption and the hydroxylation of coordination-unsaturated oxygen (CUO), and Co3+ work together with surface OH group to decompose ozone avoiding the deactivation. This study demonstrates a new way, i.e., creating metal vacancy rather than oxygen vacancy to design stable and efficient catalysts for ozone decomposition under humid conditions.

Surface Condensation Water under Salix psammophila Is the Main Water Source in Addition to Rainfall in the Kubuqi Desert

Amidst climate change, managing water and vegetation adaptability is vital in ecology and agriculture. Salix psammophila is key in deserts, maintaining ecological balance and combating desertification. Understanding its surface condensation and response to weather is critical for survival. This study aims to investigate the formation patterns of surface condensation water under S. psammophila at different irrigation levels and the influence of precipitation, temperature, relative humidity, and wind speed. Conducted in China’s Kubuqi Desert from June to September 2022, the study employed micro-lysimeters with four irrigation test sets and a control group, conducting detailed observations at various locations. The results indicate that S. psammophila significantly influences surface condensation water by blocking solar radiation and reducing wind speed. The drip irrigation system also regulates surface condensation water on S. psammophila. Moreover, meteorological factors such as 24 h maximum temperature, relative humidity difference, wind speed, and air vapor pressure deficit show significant correlations with surface condensation water formation. In conclusion, this study enhances the understanding of desert ecosystem water balance, vegetation adaptability, and efficient water resource utilization. It provides valuable scientific guidance for the conservation and restoration of desert ecosystems.

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

Urban forest microclimates across temperate Europe are shaped by deep edge effects and forest structure

The urban heat island (UHI) causes strong warming of cities and their urban forests worldwide. Especially urban forest edges are strongly exposed to the UHI effect, which could impact urban forest biodiversity and functioning. However, it is not known to what extent the UHI effect alters edge-to-interior microclimatic gradients within urban forests and whether this depends on the forests’ structure.Here we quantified gradients of air temperature, relative air humidity and vapour pressure deficits (VPD) along urban forest edge-to-interior transects with contrasting stand structures in six major cities across Europe. We performed continuous hourly microclimate measurements for two consecutive years and analysed the magnitude and depth of edge effects, as well as forest structural drivers of microclimatic variation.Compared to edge studies in rural temperate forests, we found that edge effects reached deeper into urban forests, at least up to 50 m. Throughout the year, urban forest edges were warmer and drier compared to forest interiors, with the largest differences occurring during summer and daytime. Not only maximum, but also mean and minimum temperatures were higher at the urban forest edge up to large edge distances (at least 85 m). Denser forests with a higher plant area index buffered high air temperatures and VPDs from spring to autumn.We conclude that urban forest edges are unique ecotones with specific microclimates shaped by the UHI effect. Both forest edges and interiors showed increased buffering capacities with higher forest canopy density. We advocate for the conservation and expansion of urban forests which can buffer increasingly frequent and intense climate extremes. To this end, urban forest managers are encouraged to aim for multi-layered dense forest canopies and consider edge buffer zones of at least 50 m wide.

Unravelling the diversity in water usage among wild banana species in response to vapour pressure deficit.

The rise in global temperature is not only affecting plant functioning directly, but is also increasing air vapour pressure deficit (VPD). The yield of banana is heavily affected by water deficit but so far breeding programs have never addressed the issue of water deficit caused by high VPD. A reduction in transpiration at high VPD has been suggested as a key drought tolerance breeding trait to avoid excessive water loss, hydraulic failure and to increase water use efficiency. In this study, stomatal and transpiration responses under increasing VPD at the leaf and whole-plant level of 8 wild banana (sub)species were evaluated, displaying significant differences in stomatal reactivity. Three different phenotypic groups were identified under increasing VPD. While (sub)species of group III maintained high transpiration rates under increasing VPD, M. acuminata ssp. errans (group I), M. acuminata ssp. zebrina (group II) and M. balbisiana (group II) showed the highest transpiration rate limitations to increasing VPD. In contrast to group I, group II only showed strong reductions at high VPD levels, limiting the cost of reduced photosynthesis and strongly increasing their water use efficiency. M. acuminata ssp. zebrina and M. balbisiana thus show the most favourable responses. This study provides a basis for the identification of potential parent material in gene banks for breeding future-proof bananas that cope better with lack of water.

An Eulerian multiphase frost model based on heat transfer measurements

In this paper, a laminar numerical model is developed to predict frost formation over a horizontal cold flat surface. An Eulerian-Eulerian multiphase approach is followed to model humid air and ice phases separately. Frost accumulation on the cold surface is modeled with an empirical mass source term. Model constants were tuned in a systematic way using experimental heat flux and frost thickness data. A velocity dependent model constant is introduced into the mass source term. The heat flux rise observed experimentally at the initial stages of the frosting could be captured with the use of the velocity dependent model constant and the addition of this term considerably improved the accuracy of the frost model at the initial stages of frosting. It was also observed that the selected particle diameter for the solid ice phase has a considerable effect on the velocity profile over the frost layer. This requires tuning of the velocity dependent model constant parameters according to the selected ice particle diameter. The developed numerical model was tested with three different frost thermal conductivity models. Using the thermal conductivity of solid ice for the frost thermal conductivity resulted in the most accurate prediction at the early stages of the frost growth process indicating a rather column-wise vertical growth of ice crystals with very low lateral branching. However, the overprediction of the numerical heat flux with the thermal conductivity of solid ice points out a decrease in the thermal conductivity of the newly added frost layers indicating a more pronounced lateral branching of ice crystals within the frost layer. The effect of the diffusion coefficient of the water vapor in humid air on frosting is also investigated. An artificial increase in the diffusion coefficient improved the accuracy of the heat flux prediction of the model at the initial stages of frosting which might indicate an eddy-driven enhanced mixing in the boundary layer which might not be captured in the laminar flow model. Finally, the developed numerical model is also tested on another scenario with the surface temperature held at -30 °C. Detailed analysis of the numerical simulations showed a more porous frost layer with the surface temperature at -30 °C as compared to the frost porosity formed on the surface at -20 °C.