Mass Loss Dynamics Research Articles

Thermal engineering and chemical kinetics of wood pellets torrefication

Relevance. The widespread distribution and availability of biomass in the regions of Russian Federation make it possible to consider it as a renewable energy source with a lower negative impact on the environment compared to fossil fuels, since biomass is recognized as a carbon-neutral fuel. The use of biomass as a fuel in the form of pellets is increasing, which provides increased density and heat value. At the same time, pellets as a fuel or as a technological raw material have a significant disadvantage – low hydrophobicity. This problem is solved by torrefaction – low-temperature pyrolysis at a temperature of 200–300°C to produce bio-carbon. The study of the wood pellets torrefaction in order to improve it is an urgent task. Aim. To identify the impact of the parameters of the torrefaction of wood pellets on the thermal characteristics of the product (the highest heat value of bio-coal) and the regime parameters of the process (mass and energy yields), as well as to determine the parameters of the chemical kinetics of low-temperature pyrolysis as the basis for mathematical modeling and development of efficient torrefaction reactors. Object. Torrefied coniferous wood pellets of domestic production (Moscow region). Methods. Experimental study of the low-temperature pyrolysis thermal characteristics; synchronous thermal analysis in an inert atmosphere. Results. It was found that during the torrefaction of wood pellets in an inert atmosphere, a change in the holding time in the range of 30–60 minutes does not significantly affect the higher heat value, mass and energy yield of bio-coal, while an increase in temperature from 250 to 300°C reduces mass and energy yield, and the higher heat value increases by 26%. The dynamics of mass loss and thermal effects when heated to 600°C at a rate of 10 K/min are determined by means of the synchronous thermal analysis. It is established that the chemical kinetics of the process is described by a generalized reaction of the order n=1.507, in the Arrhenius equation the activation energy E=71.25 kJ/mol, the pre-exponential factor A=4772 s–1.

Experimental and numerical analysis of the pyrolysis dynamics of a single wood particle: presentation of the radiographic technique

Pyrolysis is an oxygen-free process for the thermal decomposition of raw materials. The heat conduction and flow of pyrolysis products (i.e., the gas fraction and liquid vapour generated during pyrolysis) influence the process and products. In this work, the influence of the orientation of wooden particle fibres with respect to the direction of the heat source on the dynamics of the process was investigated, where there were two particle sizes oriented along or across the heat source. The novelty of this work lies in the use of a radiographic technique for analysing the influence of wooden fibres' orientation on the degradation process. The research showed that during pyrolysis, the mass loss rate in the particles with fibres oriented across the heat source and along the heat source was different. A similar tendency was characteristic for the drying process. The dynamics of pyrolysis of a single wood particle depends on many factors—particle size, process parameters, arrangement of fibres in wood, etc. The analysis of the dynamics presented in the publications is based on the analysis of the dynamics of mass loss, which is a very large simplification. The publication contains experimental analysis and mathematical calculations of the pyrolysis process for samples of various sizes and samples with different fibre arrangement. The result of the research is the determination of trends regarding the shape of the particle and the arrangement of fibres on the process, which provides knowledge that can be translated into industrial pyrolysis processes.

The Dynamics of Mass Loss and Nutrient Release of Decomposing Fine Roots, Needle Litter and Standard Substrates in Hemiboreal Coniferous Forests

Litter decomposition is a key process that drives carbon and nutrient cycles in forest soils. The decomposition of five different substrate types was analyzed in hemiboreal coniferous forests, focusing on the mass loss and nutrient (N, P, and K) release of fine roots (FR) and needle litter in relation to the initial substrate and soil chemistry. A litterbag incubation experiment with site-specific FR and needle litter and three standard substrates (green and rooibos tea, α-cellulose) was carried out in four Norway spruce and four Scots pine-dominated stands in Estonia. Substrate type was the primary driver of mass loss and the decay rate of different substrates did not depend on the dominant tree species of the studied stands. Alpha-cellulose lost 98 ± 1% of the mass in 2-years, while the FR mass loss was on average 23 ± 2% after 3-years of decomposition. The FR decomposition rate could be predicted using a corresponding model of green tea, although the rate of FR decomposition is approximately five times lower than the rate of green tea in the first 3-years. The annual decomposition rate of the needle litter is rather constant in hemiboreal coniferous forests in the first 3 years. The initial substrate of fine roots or needle litter and soil chemistry jointly had a significant effect on mass loss in the later stage of decomposition. The critical N concentration for N release was lower for pine FR and needle litter (0.9–1.3% and 0.7–1.1%) compared to spruce (1.2–1.6% and 1.5–1.9%, respectively). The release rate of K depended on the initial K of substrate, while the release of N and P was significantly related to the initial C:N and N:P ratios, respectively. The results show the central role of soil and substrate initial chemistry in the decomposition of fine roots and needle litter across hemiboreal forests, especially at later stage (after 2 years) of decomposition. The slower decomposition and higher retention of N in the fine roots relative to needle litter suggests that fine roots have a substantial role in the carbon and nitrogen accumulation in boreal and hemiboreal forest ecosystems.

Evidence for localized onset of episodic mass loss in Mira

Context. Mass loss from long-period variable stars (LPV) is an important contributor to the evolution of galactic abundances. Dust formation is understood to play an essential role in mass loss. It has, however, proven difficult to develop measurements that strongly constrain the location and timing of dust nucleation and acceleration. Aims. Interferometric imaging has the potential to constrain the geometry and dynamics of mass loss. High angular resolution studies of various types have shown that LPVs have a distinct core-halo structure. These have also shown that LPV images commonly exhibit a non-circular shape. The nature of this shape and its implications are yet to be understood. Methods. Multi-telescope interferometric measurements taken with the Interferometric Optical Telescope Array (IOTA) provide imagery of the LPV Mira in the H-band. This wavelength region is well suited to studying mass loss given the low continuum opacity, which allows for emission to be observed over a very long path in the stellar atmosphere and envelope. Results. The observed visibilities are consistent with a simple core-halo model to represent the central object and the extended molecular layers but, in addition, they demonstrate a substantial asymmetry. An analysis with image reconstruction software shows that the asymmetry is consistent with a localized absorbing patch. The observed opacity is tentatively associated with small dust grains, which will grow substantially during a multi-year ejection process. Spatial information along with a deduced dust content of the cloud, known mass loss rates, and ejection velocities provide evidence for the pulsational pumping of the extended molecular layers. The cloud may be understood as a spatially local zone of enhanced dust formation, very near to the pulsating halo. The observed mass loss could be provided by several such active regions around the star. Conclusions. This result provides an additional clue for better understanding the clumpiness of dust production in the atmosphere of AGB stars. It is compatible with scenarios where the combination of pulsation and convection play a key role in the process of mass loss.

Decomposition rate of peat-forming plants at the initial stages of destruction in peat deposits of the oligotrophic bogs “Bakcharskoe” and “Timiryasevskoe”

The research presents quantitative estimates of the decomposition rate of plant residues at the initial stages of the decay of four plant species (Eriophorum vaginatum, Carex rostrata, Sphagnum fuscum, Sphagnum angustifolium) in peat deposits of the oligotrophic bogs in the southern taiga subzone of Western Siberia. We also studied the change in the content of total carbon, nitrogen and ash elements in plant residues and the activity of microflora at the initial stages of decomposition. The studies were conducted in the bogs characterized by various hydrothermal conditions. At the initial stage of the decay of peat-forming plants the maximum losses of mass occur in the first month of the experiment and reach 36-52% of the total loss of organic matter during the growing season. Sphagnum fuscum is the most resistant to decomposition. The most intense decomposition of Sphagnum fuscum at the initial stages of decomposition is characteristic for warmer and less humid conditions of the Timiryazevskoe bog. It was revealed that mass losses of organic matter correlate well with total carbon losses. The most intensive decreasing of the total carbon content as well as mass loss of organic matter are observed after the first month of the experiment. The maximal decline of carbon in plant residues was received for Eriophorum vaginatum. During the decomposition of plant residues, the nitrogen content was decreasing, and the most intense nitrogen losses were characteristic for Sphagnum mosses. Nitrogen loss in peat-forming plants during the first month of decomposition varies depending on the locality conditions, but it becomes equal during the later decomposition stages. At the first stages of decomposition of plant residues, both the accumulation and the loss of ash elements were observed in the samples. Both the Bakcharskoe and Timiryazevskoe bogs were characterized by the accumulation of ash elements in plant samples of Eriophorum vaginatum. Dynamics of mass loss and removal of elements are directly related to the activity of microorganisms. The maximum number of microorganisms was found in July and September. Peat and plant samples located in the peat deposit of the Timiryazevskoe bog are more saturated with microorganisms of the nitrogen cycle, and samples from the Bakcharskoe bog are richer in carbon cycle microorganisms. Microorganisms of the lignocellulosic complex were less active as compared with other groups of microorganisms. The number of microorganisms assimilating the mineral forms of nitrogen are on average 1.5 times less than the number of microorganisms assimilating the organic forms. The positive correlation between the nitrogen content and the number of fungi was found. In addition, correlation between the numbers of denitrifiers and oligotrophs was found. It is explained by trophic relationshipsbetween these groups of microorganisms.

Effect of expanded shrub litter on decomposition of graminoid litter in a temperate freshwater marsh

Shrub encroachment can alter litter decomposition in temperate graminoid-dominated wetlands, yet its influence on the direction of litter mixing effects is still elusive. We collected senesced aboveground tissues of two graminoid species (Deyeuxia angustifolia and Carex schmidtii) and leaf litter of two shrub species (Betula fruticosa and Salix floderusii) in a freshwater marsh of Northeast China, and measured litter mass loss dynamics in monocultures and shrub-graminoid mixtures (in mass ratios of 1:2 and 2:1) using a 730-day incubation experiment. In the monocultures, shrub litter had greater mass loss than graminoid litter presumably due to the relatively higher N, and dissolved organic C and N concentrations. Additive effects were observed in all shrub-graminoid mixtures after 182 days of decomposition, while nonadditive effects gradually became more prominent as litter decomposition proceeded. Salix floderusii leaves usually promoted decomposition of neighboring graminoid litter, especially when S. floderusii dominated, leading to a synergistic effect on mass loss of the whole litter mixtures. However, the effects of B. fruticosa on decomposition of graminoid litter varied with incubation time, species composition and species proportion. At the end of incubation, synergistic effects were observed in B. fruticosa-D. angustifolia mixtures, while additive effects occurred in B. fruticosa-C. schmidtii mixtures. The effects of shrub expansion on the direction of litter mixing effects are dependent on incubation time, shrub species and dominant graminoid types in this freshwater marsh. These findings help to predict the consequence of altered species composition on community-level litter decomposition in temperate graminoid-dominated wetlands.

Site-Specific Microbial Decomposer Communities Do Not Imply Faster Decomposition: Results from a Litter Transplantation Experiment.

Microbes drive leaf litter decomposition, and their communities are adapted to the local vegetation providing that litter. However, whether these local microbial communities confer a significant home-field advantage in litter decomposition remains unclear, with contrasting results being published. Here, we focus on a litter transplantation experiment from oak forests (home site) to two away sites without oak in South Tyrol (Italy). We aimed to produce an in-depth analysis of the fungal and bacterial decomposer communities using Illumina sequencing and qPCR, to understand whether local adaptation occurs and whether this was associated with litter mass loss dynamics. Temporal shifts in the decomposer community occurred, reflecting changes in litter chemistry over time. Fungal community composition was site dependent, while bacterial composition did not differ across sites. Total litter mass loss and rates of litter decomposition did not change across sites. Litter quality influenced the microbial community through the availability of different carbon sources. Additively, our results do not support the hypothesis that locally adapted microbial decomposers lead to a greater or faster mass loss. It is likely that high functional redundancy within decomposer communities regulated the decomposition, and thus greater future research attention should be given to trophic guilds rather than taxonomic composition.

The Effects of Plant Secondary Metabolites from Coniferous Needle Leaf Litter on the Leaf Litter Decomposition of Betula albo-sinensis Burk

In this study, leaf litters of Betula albo-sinensis and 5 coniferous species were used as samples. The B. albo-sinensis leaf litter was buried in soil and termly treated with the water extracts of five types of coniferous leaf litter for a 6-month simulation decomposition experiment. The dynamics of mass loss and nutrients (C, N, P, and K) content of leaf litter and the soil enzymatic activities were measured to investigate the effects of plant secondary metabolites (PSM) from coniferous leaf litters on the decomposition processes of B. albo-sinensis leaf litter. The results indicated that the extracts of Pinus tabuliformis, Platycladus orientalis, P. armandii and Larix principis-rupprechtii leaf litters significantly inhibited the whole decomposition process and overall nutrients release of B. albo-sinensis leaf litter, while the extracts of Picea asperata leaf litter exhibited no significant influence. The general suppression of PSM on the soil sucrase, carboxymethyl cellulase and β-glucosidase activities might be the main reason leading to the inhibitory effects of the extracts of P. tabuliformis, P. orientalis, P. armandii and L. principis-rupprechtii leaf litter. The species causing inhibitory effects, especially L. principis-rupprechtii, was not recommended to be planted mixed with B. albo-sinensis, or their planting density should be lower in the mixed forests.

Prediction of higher heating values (HHVs) and energy yield during torrefaction via kinetics

Torrefaction is a promising process to upgrade biomass and produce solid biofuel. The purpose of this study is to predict the higher heating values (HHVs) of biomass and energy yield during torrefaction. A two-step model and a direct method are adopted to obtain the torrefaction kinetics and the prediction of elemental composition in the present study. The experiments were performed at the temperature range of 200-230 °C in a pilot-scale reactor, which can record the mass loss dynamics during the treatment. The results point out that the prediction of solid yield and elemental composition profiles are in good agreement with the experiments. The predicted HHVs are calculated from C, H, and O based on an empirical equation. As a while, the HHVs of torrefied wood are in the range of 19.85-20.71 MJ kg-1 and the energy yields are in the range of 92.3-97.4 %.

Heat treatment kinetics using three-stage approach for sustainable wood material production

The purpose of this study is to develop a numerical tool to predict the mass loss of a wood board during heat treatment as a marker of the process advancement. Mass loss dynamics during the wood heat treatment is experimentally obtained using a specially conceived equipment. The investigation method is applied on large scale wood samples whose radial and transvers dimensions are close to the boards used in industry. A two-step reaction mechanism is adopted to describe the behavior of wood thermodegradation. Model parameters are obtained by fitting the experimental data according to a new approach developed in this study for their optimal determination. The originality of the implemented modelling strategy is the establishment of a three-stage approach based on the analysis of wood thermal sensitivity depending on the treatment temperature range. Model equations are solved numerically by the commercial package Matlab® software. A good agreement is achieved between the numerical predictions and the experimental data. The developed model and established kinetics can be used for heat treatment process and reactor design in industry to produce wood materials for their applications.

Microbial Decomposer Dynamics: Diversity and Functionality Investigated through a Transplantation Experiment in Boreal Forests.

Litter decomposition is the main source of mineral nitrogen (N) in terrestrial ecosystem and a key step in carbon (C) cycle. Microbial community is the main decomposer, and its specialization on specific litter is considered at the basis of higher decomposition rate in its natural environment than in other forests. However, there are contrasting evidences on how the microbial community responds to a new litter input and if the mass loss is higher in natural environment. We selected leaf litter from three different plant species across three sites of different altitudinal ranges: oak (Quercus petraea (Matt.) Liebl., 530ma.s.l), beech (Fagus sylvatica L., 1000ma.s.l.), rhododendron (Rhododendron ferrugineum L., 1530ma.s.l.). A complete transplantation experiment was set up within the native site and the other two altitudinal sites. Microbial community structure was analyzed via amplified ribosomal intergenic spacer analysis (ARISA) fingerprinting. Functionality was investigated by potential enzyme activities. Chemical composition of litter was recorded. Mass loss showed no faster decomposition rate on native site. Similarly, no influence of site was found on microbial structure, while there was a strong temporal variation. Potential enzymatic activities were not affected by the same temporal pattern with a general increase of activities during autumn. Our results suggested that no specialization in microbial community is present due to the lack of influence of the site in structure and in the mass loss dynamics. Finally, different temporal patterns in microbial community and potential enzymatic activities suggest the presence of functional redundancy within decomposers.

Climate masks decomposer influence in a cross-site litter decomposition study

Leaf litter is a significant input of carbon and nutrients to forested systems. Rates of foliar decomposition, and cycling of carbon and nutrients, appear consistently explained by climate and litter quality. Although the soil decomposer community actually mineralizes litter, its independent role is often undetected in cross-site studies. At three sites along an elevational gradient in eastern U.S. temperate forest, we used a reciprocal litter transplant design to explore whether climate masks the functional influence of the decomposer community on litter decomposition dynamics in the short- and longer-term. Climate, measured as the climate decomposition index, best predicted mass loss in the longer term, over 23 and 31 months (the maximum incubation period). However, decomposer community function also predicted mass loss dynamics across the same time period. Therefore, climate effects on mass loss correlated positively with differences in the functional ability of the three soil decomposer communities. Our findings suggest that climate ‘masks’ the independent influence of the soil decomposer community over litter mass loss dynamics, because direct positive effects of more favorable climate on decomposition rates appear correlated with greater functional potential of the decomposer communities. These results fit within existing theory and experimental evidence that soil microorganisms both adapt to their climate regime, and are directly, through biotic activity, and indirectly, via community structure or function, affected by climate. These non-linear effects of climate may then amplify decomposer function in warm environments and suppress function in cool environments. Hence, our results suggest that decomposition relationships observed across spatial gradients may fail to adequately represent how decomposition will respond to changing climate across time.

AMBER/VLTI Snapshot Survey on Circumstellar Environments

AbstractOHANA is an interferometric snapshot survey of the gaseous circumstellar environments of hot stars, carried out by the VLTI group at the Paranal observatory. It aims to characterize the mass-loss dynamics (winds/disks) at unexplored spatial scales for many stars. The survey employs the unique combination of AMBER's high spectral resolution with the unmatched spatial resolution provided by the VLTI. Because of the spatially unresolved central OBA-type star, with roughly neutral colour terms, their gaseous environments are among the easiest objects to be observed with AMBER, yet the extent and kinematics of the line emission regions are of high astrophysical interest.

Foliar Litter Decomposition: A Conceptual Model with Focus on Pine (Pinus) Litter—A Genus with Global Distribution

The genus Pinus encompasses c 120 species and has a global distribution. Today we know more about the decomposition of pine needle litter than litter from any other genus. This paper presents a developed conceptual three-phase model for decomposition, based on pine needle litter, starting with newly shed litter and following the process until a humus-near stable residue. The paper focuses on the mass-loss dynamics and factors regulating the process in the early phase, the late one, and the humus-near phase. For the late phase, the hampering influence of N and the rate-enhancing effect of Mn on the decomposition are given extra attention. Empirical factors related to the limit value/stable residue are discussed as well as the decomposition patterns and functions for calculating limit values. The climate-related litter concentrations of N and Mn are discussed as well as their possible influence on the size of the stable residue, which may accumulate and sequester carbon, for example, in humus layers. The sequestration of carbon in humus layers is discussed as well as the effect of tree species on the process. Although the paper focuses on litter of pine species, there are comparisons to studies on other litter genera and similarities and differences are discussed.

Exotic tree leaf litter accumulation and mass loss dynamics compared with two sympatric native species in south Florida, USA

The exotic tree Melaleuca quinquenervia (melaleuca) forms dense forests usually characterized by low plant diversities and dense litter biomass accumulations on forest floors of ecologically sensitive ecosystems, including portions of the Florida Everglades. We quantified litter accumulation in mature melaleuca stands and compared decomposition rates of melaleuca leaves with a sympatric native plant, either Cladium jamaicense (sawgrass) in sawgrass marshes or Pinuselliottii (slash pine) in pine flatwoods habitats that varied in soil types. Total litter accumulation in mature melaleuca forests prior to June 1997 ranged from 12.27 to 25.63 Mg ha−1. Overall, melaleuca leaves decomposed faster in organically rich versus arenaceous soils. Decomposition rates were lower for melaleuca leaves than for sawgrass in both melaleuca-invaded and uninvaded sawgrass marshes. In arenaceous soils of pine flatwoods, melaleuca leaf and pine needle decomposition rates were similar. Complete mineralization of sawgrass leaves occurred after 258 weeks, whereas melaleuca leaves had up to 14% and pine foliage had up to 19% of the original biomass remaining after 322 weeks. Total carbon (C) in intact decomposing leaves varied slightly, but total nitrogen (N) steadily increased for all three species; the greatest being a fourfold in sawgrass. Increases in N concentrations caused decreases in the C/N ratios of all species but remained within an optimal range (20–30) in sawgrass resulting in higher decomposition rates compared to melaleuca leaves and pine needles (C/N ratio >30). Slower decomposition of melaleuca leaves results in denser litter layers that may negatively affect recruitment of other plant species and impede their establishment in invaded communities.

Liquid-phase continuity and solute concentration dynamics during evaporation from porous media: Pore-scale processes near vaporization surface

Evaporation from porous media involves complex pore scale transport processes affecting liquid phase distribution and fluxes. Often, the initial evaporation rate is nearly constant and supplied by capillary flow from wetted zones below to the surface. Sustaining constant flow against gravity hinges on an upward capillary gradient and on liquid phase continuity with hydraulic conductivity sufficient for supplying evaporative flux. The pore scale liquid phase adjustments during evaporative displacement necessary for maintaining a constant flux have been postulated but rarely measured. In this study we employed detailed imaging using x-ray synchrotron radiation to study liquid phase distribution and dynamics at the most sensitive domain just below the surface of evaporating sand columns. Three-dimensional images at a resolution of 7 microns were obtained from sand column (mean particle size 0.6 mm) initially saturated with calcium iodide solution (4% by mass) to enhance image contrast. Detailed imaging of near-surface liquid phase distribution during evaporation confirmed phase continuity at micrometric scale and provided quantitative estimates of liquid conductance in agreement with values required to supply evaporative flux. Temporal variations in bulk salt concentrations determined from x-ray attenuation were proportional to evaporative water mass loss. Highly resolved salt concentration images revealed existence of evaporating chimneys that supply the bulk of evaporative demand. Delineated mass loss dynamics and salt distribution measured by the x-ray attenuation were in reasonable agreement with a simplified analytical convection-diffusion model for salt dynamics during evaporation from porous media.

Decomposition of pure and mixed foliage litter in a young lodgepole pine – Sitka alder stand in the central interior of British Columbia

A 7-year litterbag experiment examined mass loss dynamics of Sitka alder ( Alnus viridis (Chaix) DC. subsp. sinuata (Regel) A. Löve & D. Löve) and lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm. ex S. Watson) foliage litter in a young stand dominated by these species in the Sub-Boreal Spruce biogeoclimatic zone of central British Columbia. Although mass loss was initially faster for alder litter, the amounts of mass remaining for alder, pine, and mixed pine–alder (50:50 by mass) litter began to converge after 2 years. Mass loss by the mixed litter differed significantly from that predicted from the behaviour of its pure components, but the mechanisms responsible could not be determined from this experiment. Limit values for the projected maximum extent of mass loss ranged from 63.5% (alder) to 76.9% (pine), with the latter value considerably below estimates reported for lodgepole pine in Scandinavia. Despite these differing limit values, forest floor mass measurements prior to the experiment did not show significantly higher organic matter accumulations under long-established alder clumps on this site.

Experimental Validation of a Coupled Solid- and Gas-Phase Model for Combustion and Gasification of Wood Logs

A solid-gas-phase model for thick wood gasification/combustion is extensively studied, after a re-examination of the kinetic constants for the char gasification reactions. The solid-phase model, which includes the description of all the relevant heat and mass transfer phenomena and chemical reactions, is coupled with a CFD code for the gas-phase processes. Both the gasification and combustion of single wood logs are simulated (log radius in the range of 0.06-0.1 m, initial moisture content, on a dry basis, 1-81%, inlet gas temperature 1253-1613 K, inlet gas velocity 0.5-1.0 m/s, and various compositions of the gaseous mixture). For comparison purposes, a solid-phase model, with global heat and mass transfer coefficients and a constant-property gas phase, is also considered. Although both models predict the mass loss dynamics to be qualitatively similar, the solid-phase model overestimates the total heat flux and underestimates the char combustion rate. Extensive experimental validation of both models is carried out in terms of conversion time and average mass-loss rates. Acceptable agreement is obtained for the comprehensive model, whereas in the other case, the conversion times are generally underestimated and the average mass loss rates are overestimated. However, improvements in the predictive capabilities of the solid-phase model could be achieved through the introduction of corrective factors for the external heat and mass transfer coefficients.

Mathematical modelling of the combustion of a single wood particle

A mathematical model describing the thermal degradation of densified biomass particles is presented here. The model uses a novel discretisation scheme and combines intra-particle combustion processes with extra-particle transport processes, thereby including thermal and diffusional control mechanisms. The influence of structural changes on the physical–thermal properties of wood in its different stages is studied together with shrinkage of the particle during its degradation. The model is used to compare the predicted data with data on the mass loss dynamics and internal temperature of several particles from previous works and relevant literature, with good agreement.

On the structure of contact binaries. III - Mass and energy flow

view Abstract Citations (96) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the structure of contact binaries. III. Mass and energy flow. Shu, F. H. ; Lubow, S. H. ; Anderson, L. Abstract A variety of topics dealing with the mass and energy flow in contact binaries is examined. It is argued that the contact discontinuity hypothesis proposed in earlier communications is both necessary and sufficient to resolve Kuiper's (1941) paradox concerning the existence of contact binaries with unequal components. A detailed qualitative picture of the maintenance by fluid flow of the contact and weak discontinuities of zero-order models in presented. This discussion supplies a description of the mechanism by which the interior luminosities are redistributed to give common envelope luminosities. It also provides order-of-magnitude estimates for the thickness of the transition layer and mixing region that constitute the actual structure of the contact and weak discontinuities. The gas dynamics of mass loss that occurs if stellar evolution should cause a synchronously rotating common surface to try to expand beyond the outer critical surface is calculated. The role of various processes in the problem of the evolution of contact binaries is considered. Publication: The Astrophysical Journal Pub Date: April 1979 DOI: 10.1086/156948 Bibcode: 1979ApJ...229..223S Keywords: Binary Stars; Discontinuity; Energy Transfer; Hydrodynamics; Mass Flow; Stellar Structure; Gas Dynamics; Qualitative Analysis; Stellar Evolution; Stellar Luminosity; Transition Layers; Turbulent Mixing; Astrophysics; Contact Binaries:Hydrodynamics; Contact Binaries:Mass Exchange; Contact Binaries:Models; Contact Binaries:Structure full text sources ADS | Related Materials (3) Part 1: 1976ApJ...209..536S Part 2: 1977ApJ...216..517L Part 4: 1979ApJ...229..657L