Wet Wall Research Articles

How Does the Japanese Water Shrew Chimarrogale platycephalus Cross the Concrete Walls of Check Dams?

The concrete walls of check dams are considered a physical barrier for aquatic and semiaquatic animals that inhabit mountain streams. Traveling behaviors around concrete check dams by the Japanese water shrew Chimarrogale platycephalus, a semi-aquatic mammal, were directly observed via radio-tracking in Kamikoshi Stream in central Honshu, Japan. Traveling behaviors were mainly observed on the wet concrete walls and in the backfill sediments of check dams. Chimarrogale platycephalus generally crossed the wall directly, and route selection was affected by the traveling direction of C. platycephalus and the surface wetness of the concrete wall. Detouring behavior around the concrete walls was observed visually only once during the survey period. Using modulation of sounds on a FM receiver, the movements of C. platycephalus were detected in their hiding places along the stream. Some individuals frequently ceased movement within the backfill sediments. Our results suggest that existing concrete check dams do not prohibit the shrew's movements between upstream and downstream of the river and that backfill sediments may be utilized as resting places.

Measurement of acoustic dissipation occurring in narrow channels with wet wall.

The acoustic dissipation that occurs in a porous medium is experimentally investigated. Two conditions are tested. One is that the wall of the porous medium is wet by water, and the other is that it is dry. Experimental results show that water does not affect viscous dissipation; however, it affects the dissipation caused by pressure oscillation. Furthermore, it is found that the effect of water on the dissipation due to pressure oscillation increases with the temperature of the working gas. A theory that can consider the effect of condensation and evaporation on sound propagation is used to investigate the result. The theoretically and experimentally obtained values of dissipation are in good agreement. The reason for the effect of water is analyzed using the theory.

Testate Amoebae in Karst Caves of the Dinaric Arc (South-Eastern Europe) with a Description of Centropyxis bipilata sp. nov.

Karst freshwater caves are subterranean habitats characterized by the constant absence of light and relatively small variations of temperature and air humidity. They are mostly food deprived environments, with the exception if large bat colonies are present or if they are intensively supplied with organic matter by sinking rivers. Even though these habitats are often described as harsh, they have enabled the evolution of highly specialized and often endemic animals. The cave eukaryotic micro-organisms, on the other hand, are scarcely researched. The results of research of testate amoebae in the caves of the Dinaric arc detected 23 species, 12 of which were first found in caves. Also, a description of Centropyxis bipilata sp. nov. is presented. This species is clearly distinguished from other described species based on shell size, the presence of two struts and the usually dark ring around the aperture. Testate amoebae were registered on aquatic and terrestrial cave sediments and transitional habitats (like hygropetric and wet walls). The most frequent species within the samples were: Trinema lineare, Cryptodifflugia oviformis and Centropyxis bipilata sp. nov. Maximum diversity of testate amoebae was registered in Ponor Kovači with twenty species. In 24.4 % of the investigated samples microphototrophs were found, implying good surface-subsurface connectivity that could also affect testate amoebae diversity. This research showed that caves are underestimated habitats that can provide us with new data about the testate amoebae biogeography and diversity.

Numerical simulation of liquid mass collision with a wall

Numerical simulation of high-speed liquid mass collision with dry or wetted rigid walls by the CIP-CUP method on dynamically adaptive Soroban grids is studied. A number of specially selected 1D and 2D test problems is used for validating the resolution of the main features of the collision separately. The results of their calculations are in good correlation with the corresponding analytical and numerical solutions. A problem of hemispherically-ended high-speed jet collision with a wall covered by a thin liquid layer is considered to illustrate the capabilities of the CIP-CUP/Soroban-grid approach to resolving the main features of the high-speed liquid collision together. Its numerical solution is in good agreement with the known similar results.

Numerical study on phase change behavior of liquid nitrogen droplets impinging on solid surface

The distinct physical properties of liquid nitrogen make liquid nitrogen spray cooling a promising technique in aerospace engineering, the electronic industry, superconductor cooling, cryobiology, etc. In-depth study of the dynamics and thermodynamic behavior of liquid nitrogen droplets impinging on the wall surface is helpful to understand the heat transfer mechanism of spray cooling technology with liquid nitrogen. Therefore, the mathematical model of single-liquid nitrogen droplet impacted solid surface is developed by Level Set-VOF method. The effects of wall wettability (30°－150°), initial velocity (0.1, 1.6 m/s) and wall temperature (300－500 K) on the phase change behavior during the evolution of droplets are investigated, and the mathematical model of film thickness is established. The results show that enhancing the wall wettability and increasing the impact speed facilitate the spreading of the droplets in the radial direction, thereby increasing the heat exchange area and reducing the thermal resistance. Ultimately, the heat exchange performance is significantly improved. Increasing the wall temperature results in an increase in the difference between temperatures of the solid surface and the liquid, thereby significantly increasing the wall heat flux density. The lower thermal resistance at the three-phase contact line results in a higher heat flux density at the edge than in the center; the difference among the heat flux distributions on different wetted walls decreases due to the increase of initial velocity, showing a significant velocity effect. In the film boiling region, the heat transfer process is mainly concentrated in the initial stage of impact, and the gas film is the main heat transfer resistance. Based on conservation of mass and energy, a numerical model of film thickness is developed in this paper. The model predictions are in good agreement with the simulation results of this paper and others.

Comparison of Liquid Desiccants for Air Cooling Systems Using Wetted Wall Column

Desiccant dehumidification refers to the use of chemical for absorption of water vapor to dehumidify air, and thus reduce the latent cooling load in a building’s Heating, Ventilation and Air-Conditioning system. There are two

A NUMERICAL STUDY OF TWO-PHASE FLOW AND INTERFACIAL MASS TRANSFER IN A WETTED WALL COLUMN FOR COUNTER-CURRENT GAS ABSORPTION

A NUMERICAL STUDY OF TWO-PHASE FLOW AND INTERFACIAL MASS TRANSFER IN A WETTED WALL COLUMN FOR COUNTER-CURRENT GAS ABSORPTION

Gloeobacter violaceus: primitive reproductive scheme and its significance

Gloeobacter violaceus is a simple unicellular cyanobacterium believed to be basal to all cyanobacteria. It is unique among the cyanobacteria in various features, but most significantly in the absence of thylakoids and a circadian clock. We found additional features which support the basal status of the clade of G. violaceus in samples from a wet wall in a waterfall cave in central Mexico. We encountered a high morphological and morphometric variability in the populations studied. In trying to explain the reasons for this, we discovered that it can be attributed basically to two phenomena: a lack of synchronicity, circadian or other, in the cell cycles of the organisms; and the presence of a scheme with three simultaneous reproductive options. These two characteristics interfere with the development of a life cycle comparable to that found in other organisms. We coined the term “reproductive routes” for the alternative to a life cycle and discuss the consequences of having several routes instead of a cycle. Our results open avenues for studies to understand how the rest of the cyanobacteria acquired circadian clocks, organized life cycles and evolved complex regulating mechanisms.

Desmonostoc danxiaense sp. nov. (Nostocales, Cyanobacteria) from Danxia mountain in China based on polyphasic approach

The recently established genus Desmonostoc was characterized by forming macroscopic colonies with diffluent mucilaginous envelopes embedding long vegetative filaments and possessing long chains of akinetes. The establishment of this new genus was further supported by the clustering of the 16S rRNA gene, which have a distinctive phylogenetic placement outside of Nostoc. In this study, a new cyanobacterial species was isolated from a wet rocky wall in Danxia mountain, Guangdong province, southern China, and the novel strains of this new species were evaluated by combining morphological characteristic and molecular data on the 16S rRNA gene and 16S-23S internally transcribed spacer (ITS). This new taxon was found to be closest to Desmonostoc species. The separation of the new species described here as Desmonostoc danxiaense, using morphological and molecular traits, was based on differences in phenotypic, 16S rRNA gene, ITS sequence and its secondary structure.

Comparative Study of Reversal Flow during the Evaporation or Condensation of Water and Ethanol Film in a Vertical Channel

A comparative study of reversal flow is carried out to investigate the effect of thermal and mass buoyancy forces with evaporation or condensation along a vertical channel. The highlight is focused on the effects of phase change of two different liquid films having widely different properties, on heat and mass transfer rates in the channel. The evaporation occurs along isothermal and wetted walls. The induced laminar upward flow consists of a mixture of blowing air and vapour of water or ethanol. Various combinations of thermal and solutal boundary conditions (cooling and heating modes) are considered to investigate extensively their influence on the flow development. A two-dimensional steady state and elliptical flow model is used and the liquid film is assumed extremely thin. The governing equations of the model are solved by FVM and the velocity-pressure fields are treated with the SIMPLER algorithm. The results show that the buoyancy forces have a significant effect on the hydrodynamic, thermal and mass fields of both gas mixtures. In addition, the flow reversal is predicted with a relatively high temperature difference between the air-mixture and the wetted walls.

Damping effect on impact pressure from liquid droplet impingement on wet wall

Damping of the impact pressure from liquid droplet impingement (LDI) on a wet wall was studied by numerical simulation and experiment. The numerical simulation was carried out for the impact of an axisymmetric spherical droplet on a wet wall using a compressible form of the Euler equations combined with the stiffened gas equation. The impact pressures on the wall were highly damped by the influence of the liquid film prevailing over the wet wall, and the damping effect was formulated as a function of the liquid-film thickness to droplet diameter. The physical mechanism of the liquid-film damping effect is due to the two-stage compression during LDI and its weakening by the diffraction of the shock wave propagated in the liquid film. In order to understand the liquid-film damping effect obtained from the numerical simulation, experiments on LDI erosion on a wet wall were carried out for various liquid temperatures, which generated a thinner liquid film on the wall at higher temperatures by the viscous effect. The experimental results indicated that the LDI erosion rate increased with rising liquid temperatures, which corresponds to the erosion-rate growth at thinner liquid-film thicknesses. This result is consistent with the liquid-film damping effect obtained from the numerical simulation.

Sweeping of the entrapped fluid out of the groove in a three-dimensional channel using lattice Boltzmann method

The entrapment of fluid inside a groove is an important topic of research from past few decades. In many engineering applications, it is seen that the droplet is displaced under the action of gravitational force on one of the wetted grooved wall of a rectangular three-dimensional channel. It is reported in literature that the entrapment of droplet fluid inside groove is undesirable in various applications. Thus, the present study deals with the method of sweeping out the entrapped fluid inside the groove by the displacement of a large size three-dimensional immiscible droplet under gravity. To analyze this problem, a three-dimensional lattice Boltzmann method (LBM) is used and Shan–Chen (S-C) model has been implemented to incorporate multiphase-multicomponent flow. The present problem deals with the single grooved wetted wall of a rectangular three-dimensional channel. The wettability of the groove surface is considered as uniform hydrophobic in two different cases, whereas the wettability of the three-dimensional channel wall outside of the groove is considered as uniform hydrophilic. The analysis shows that the sweeping of entrapped fluid out of the groove largely depends on the capillary number and groove dimensions. It is also observed that sweeping of entrapped fluid takes place only for uniform hydrophobic surface of the groove with contact angle equal to 118°. In case of hydrophobic surface with contact angle equal to 90°, the large size droplet completely trapped inside the groove and does not able to sweep out the previously entrapped fluid.

Simulated Rainfall Reduces the Insulative Properties of Bird Nests

Bird nests are variable in design but all are constructed for the purpose of incubation. The potentially onerous energetic costs of incubation have meant that previous studies have focussed on thermal insulation but nests are often exposed to a variety of environmental factors, including rainfall. Those few studies that have investigated the effects of water on nests have saturated the walls by soaking but this may not reflect what a nest would typically encounter in situ during rainfall. Here, nests of four species of songbird (Common Chaffinch Fringilla coelebs, Common Linnets Linaria cannabina, Meadow Pipits Anthus pratensis, and Whinchats Saxicola rubetra) were investigated using temperature loggers to determine the effect of simulated rainfall on nest wall insulation. Simulated rainfall, produced by water dripping through a coffee percolator, significantly reduced the insulatory values of nests, and significantly increased the rate of cooling of temperature loggers inside the nest cup. No significant effect of species, or nest mass, was observed. Even when wet nest walls provided some insulation but whether this is attributable to the nest materials chosen by each species was not clear. The nest site chosen by the birds may also offer considerable protection from the weather. Further research is needed to better understand how rainfall affects the insulative properties of nests in situ.

Droplets Tracing in a T-junction Microchannel

Emulsions consist of small liquid droplets immersed in another liquid, typically either a mix of oil in water or water in oil. Emulsions have wide applications in the production of pharmaceutical products, food and cosmetics. The properties and quality of an emulsion typically depend on the size and the distribution of the droplets. Thus, the objective of this study was to investigate in detail the formation and behaviour of droplets in a T-junction microchannel. By setting up a model and applying a laminar two-phase flow in ANSYS© simulation, the particle droplets distribution was observed. The model used the predefined wetted wall boundary condition at the solid walls, with a contact angle of 135°. In this study, the behaviour and flow pattern of the particles along the T-junction microchannel were observed with regard to the effect of the initial particle concentration, the flow rate of the particles, and the initial velocity feed through the inlets of the microchannel. From the results, the effects of the velocity, mixing time and flow rate of the particles on the particle distribution and mixing were studied. It was shown that the optimization process was achieved at a flow rate of 0.025 mL/s, with the mixing process occurring within 1.6 seconds and the velocity feed at the two inlets being VA = 0.02 m/s and VB = 0.04 m/s, where the particles experienced less lift shear and compressive forces near the outlet, which caused the mixing process to become efficient.

Spiradiclis lui, a new species of Rubiaceae from Guangxi, China

Spiradiclis lui, a new species of Rubiaceae growing inside limestone caves and on wet shaded limestone walls in Guangxi, southwestern China is here described as most similar to S. umbelliformis, but differing from the latter in its glabrous stems, ovate or oval leaf blades, and the position of stamens and stigmas inside corollas. The conservation status of the novelity is asessed as ‘Vulnerable’ (VU) according to the IUCN red list categories and criteria. A diagnostic key to the species of Spiradiclis with corolla tubes longer than 12 mm is also provided.

Dynamics of wet particle–wall collisions: Influence of wetting condition

Particulate processes are characterised by intense contacts between particles and particles with the apparatus walls, where often liquid is present on the surfaces in form of droplets or liquid layers, e.g. in granulation and agglomeration processes. However, the influence of the liquid on collision dynamics is still not fully understood. Therefore, the influence of the liquid on wet particle–wall collisions is investigated via the coefficient of restitution (CoR). The CoR characterises the total energy dissipation during a collision and is defined as ratio of rebound velocity to impact velocity. In most literature regarding collision dynamics of wet particles, a target plate is covered by a liquid layer before the collision. However, this approach is often questioned of its similarity to real wet particle collisions. Therefore, during this work the particle was wetted before colliding with a dry or wet plate.Normal CoR was higher for a wet plate than for a wet particle. The case of a wet–wet collision is comparable to a superposition of collisions where a wet particle or a wet plate was used. Furthermore, during oblique collisions the tangential CoR was found to be smaller for a wet wall compared to a wet particle impacting on a dry wall.

Water vapour condensation in a partly closed structure. Comparison between results obtained with an inside wet or dry bottom wall

We are interested in the determination of the more significant parameters acting on the water vapour condensation in a partly closed structure, submitted to external constraints (temperature and humidity), in view to recover the generated droplets as an additional source of potable water. External temperature variations, by inducing temperature differences between outside and inside of the structure, lead to convective movements and thermal variations inside this structure. Through an orifice, these movements permit a renewing of the humid inner air and can lead to the condensation of the water vapour initially contained in the inner air volume and/or on the walls. With the above hypotheses, and by using a numerical simulation [1] based on the ambient air characteristics and a finite volumes method, it appears that condensed water quantities are mainly depending on the boundary conditions imposed. These conditions are: 1) dimensions of the structure; 2) external temperature and relative hygrometry; 3) the phase φ (T/RH) linking thermal and hydrometric conditions; 4) the air renewing and its hygrometry for each phase; and 5) for each case, the fact that the inside bottom wall can be wet or dry. The resulting condensed water vapour quantities obtained, for the width section, point out clearly that they are very depending on this phase φ (T/RH) which appears as the more significant parameter and can be modified by the presence or not of a thin layer of water vapour on the inside bottom wall. Condensation phenomenon could be increased if φ could be optimized.

A fast multipole boundary element method implemented for wet single particle and wall interactions

The progress is described in developing a parallel computer code to study the dynamics of wet granular systems based on the Fast Multi-pole Boundary Element Method (FMBEM). Here, three examples are considered that have closed-form or numerical solutions and thus able to act as benchmarks. They involved capillary interactions, the formation of a solid-solid contact when a particle approaches a solid wall while immersed in a Newtonian fluid, and the isoviscous hydrodynamic and elastohyrodynamic sliding of a particle. While computationally more expensive than DEM, there are a number of advantages such as extending interactions from the pendular to more saturated states, the ease with which non-spherical particles can be modelled and the ability to model wet granular systems that may exhibit transitions from frictional to lubricated flow. Consequently, FMBEM is able to model wet agglomerates more realistically than DEM and this is important for improving the performance of twin screw granulation, which is the intended application of the current work.

Analytical meanders of selected systems for thermo-renovation of historical buildings

The article contains an analysis of selected systems for thermorenovation of vertical partitions in protected buildings. Historical buildings often require thermo-renovation, but in practice their "insulation" can be applied only internally on partitions without decorations. Internal thermorenovation methods can be classified according to heat exchange and moisture transport. For the purpose of this paper, the methods were analysed in terms of diffusion-open and diffusion-closed systems, and compared in a multi-variant aspect. The calculations were made assuming a wall with the moisture content up to 3%, a wall with the very high moisture content up to 11%, and for a wet wall with a constant inflow of water due to capillary action. They attempted to evaluate the effectiveness of various thermo-modernisation treatments in building partitions in the aspect of protection against permanent moisture growth, mould development and improvement of their overall heat protection, considering the 8-year time interval. Several different sets of materials were included in a multivariate analysis, as well as various scenarios of the possible effects of their use. The paper is summarised with conclusions regarding the effectiveness and risk related to the application of different internal methods of thermo-renovation of partitions.

Influence of slosh baffles on thermodynamic performance in liquid hydrogen tank

A calibrated CFD model is built to investigate the influence of slosh baffles on the pressurization performance in liquid hydrogen (LH2) tank. The calibrated CFD model is proven to have great predictive ability by compared against the flight experimental results. The pressure increase, thermal stratification and wall heat transfer coefficient of LH2 tank have been detailedly studied. The results indicate that slosh baffles have a great influence on tank pressure increase, fluid temperature distribution and wall heat transfer. Owning to the existence of baffles, the stratification thickness increases gradually with the distance from tank axis to tank wall. While for the tank without baffles, the stratification thickness decreases firstly and then increases with the increase of the distance from the axis. The “M” type stratified thickness distribution presents in tank without baffles. One modified heat transfer coefficient correlation has been proposed with the change of fluid temperature considered by multiplying a temperature correction factor. It has been proven that the average relative prediction errors of heat transfer coefficient reduced from 19.08% to 4.98% for the wet tank wall of the tank, from 8.93% to 4.27% for the dry tank wall, respectively, calculated by the modified correlation.