Wet Wall Research Articles

Review: How the Word is Passed: A Reckoning with the History of Slavery Across America, by Clint Smith

Review: <i>How the Word is Passed: A Reckoning with the History of Slavery Across America</i>, by Clint Smith

Nonlinear numerical assessments for the in-plane response of historic masonry walls

This study examines the in-plane cyclic response of historic masonry elements using a micro modelling approach that incorporates damage-plasticity and surface-based cohesive-contact interface approaches. The nonlinear procedures adopted are validated against tests on dry and wet panels in diagonal compression and large walls under reverse shear-compression loading. Considering the inherent material variability, the numerical results are shown to correlate well with the test results in terms of stiffness, strength, ductility, overall hysteretic response, and cyclic degradation. Based on the validated models, followed by exploratory sensitivity studies, detailed parametric assessments are carried out. The parameter ranges are selected to cover historical masonry materials, consisting of bricks and mortar, and address both dry and wet conditions. Four typical failure modes, namely, flexural strut crushing, diagonal cracking, flexural toe crushing, and mixed sliding, in an order of increasing ductility, are quantified and discussed. It is shown that wet masonry walls have an average reduction of 16% in terms of stiffness and capacity compared with the dry counterparts. Although the failure modes in dry and wet wall pairs are similar, some cases are identified in which the weaker moisture-affected joint strength results in a shift to a more brittle mode. It is also shown that the ductility of the flexural strut crushing mode, which often governs the failure of historical masonry due to its low strength, is considerably overestimated in existing guidelines. Based on the results of the parametric investigations, analytical models for predicting the inelastic response are evaluated, and suggestions for modifications are proposed.

Experimental study and modified modeling on effect of SO2 on CO2 absorption using amine solution

Understanding the competitive mechanism in absorption process between SO2 and CO2 is essential for simultaneous absorption of SO2 and CO2. In this study, the effect of SO2 on CO2 absorption using amine solution was studied experimentally and theoretically. The CO2 absorption rates in MEA/MMEA/MDEA solutions were determined using wetted wall column. Results showed that the reduction of flue gas temperature was beneficial for CO2 absorption at the typical coal-fired flue gas CO2 concentration. On this basis, the effect of SO2 on CO2 absorption performance was studied. Firstly, the overall CO2 mass transfer coefficient decreased under exposure to SO2. Secondly, in the presence of SO2, pH variation of amine solution increased. In addition, the saturated CO2 capacity largely decreased when SO2 was continuously bubbled into the solution. Furthermore, the quantum chemical calculation showed that CO2 had little effect on the absorption performance of SO2 whereas SO2 greatly weakened the interaction between CO2 and amines. The overall CO2 mass transfer coefficient was modified considering the effect of SO2. The competitive absorption factor, χ, was introduced to modify the CO2 liquid phase diffusion coefficients. The average deviation of overall CO2 mass transfer coefficient narrowed to 1.76 % (0.5 mol/L MEA), 1.13 % (1.0 mol/L MEA), 1.88 % (1.0 mol/L MMEA) and 1.43 % (1.0 mol/L MDEA) respectively, which agreed well with the experimental results.

Effects of particle size and liquid film viscosity on characteristics of particles colliding with dry and wet walls

Particle-wall collisions frequently occur in fluidized beds, granulation processes, and the transportation of gas–solid two-phase flows in pipelines. Exploring the rebound characteristics of particles after colliding with the wall will enable more accurate calculation models of collision rebound, enhanced control of the collision–rebound process, and improved efficiency of industrial production. This paper studies the relationship between the energy consumed by the liquid film and the energy consumed in the collision and investigates the effects of different particle sizes and liquid film viscosities on the liquid bridge morphology, coefficient of restitution (COR), and critical capture angle (CCA). The results show that the normal COR is affected by particle size, incident velocity, and viscosity, while the tangential COR is only related to the existence of the liquid film. Additionally, the maximum size of the liquid bridge and the growth rate of COR change suddenly in a transition region. The particle size and liquid film viscosity have significant effects on the CCA of the particle. The numerical results enable us to propose a general form of the normal wet collision model.

Visualization study on oil retention and flow characteristics of R32/PVE oil in suction lines with different flow orientations

Oil retention characteristic and flow patterns of R32/PVE lubricant oil mixture in compressor suction lines were investigated. Smooth copper tubes with 10.7mm inner diameter and four tube orientations including horizontal flow, vertical upward flow and inclined upward flow with 45° and 60° inclined angles, were utilized as test samples. Saturation temperature and superheat degree were maintained at 7.5°C and 12°C, respectively. The operation conditions of refrigerant mass flux and nominal oil mass fraction covered ranges of 48.5−230 kg•m−2•s−1 and 1−5%, respectively. The oil retention amount was measured by the remove and weight technique. Based on the visualization technique, flow patterns of R32/oil mixture were also observed, identified and analyzed. The characteristic of flow patterns was greatly influenced by the thermophysical properties of refrigerant-oil mixture. Comparisons of existing flow pattern maps and wet wall fraction correlations were conduct to investigate the applicability. The experimental result showed that oil retention in suction lines increased with the decrease in refrigerant mass flux and increase in oil mass fraction. The oil retention amount of 60° inclination suction line was slightly higher than that for 45°. Additionally, the difference of oil retention among the four configurations becomes limited at high mass flux conditions.

Monitoring SARS-CoV-2 in air and on surfaces and estimating infection risk in buildings and buses on a university campus.

BackgroundEvidence is needed on the presence of SARS-CoV-2 in various types of environmental samples and on the estimated transmission risks in non-healthcare settings on campus.ObjectivesThe objective of this research was to collect data on SARS-CoV-2 viral load and to examine potential infection risks of people exposed to the virus in publicly accessible non-healthcare environments on a university campus.MethodsAir and surface samples were collected using wetted wall cyclone bioaerosol samplers and swab kits, respectively, in a longitudinal environmental surveillance program from August 2020 until April 2021 on the University of Michigan Ann Arbor campus. Quantitative rRT-PCR with primers and probes targeting gene N1 were used for SARS-CoV-2 RNA quantification. The RNA concentrations were used to estimate the probability of infection by quantitative microbial risk assessment modeling and Monte-Carlo simulation.ResultsIn total, 256 air samples and 517 surface samples were collected during the study period, among which positive rates were 1.6% and 1.4%, respectively. Point-biserial correlation showed that the total case number on campus was significantly higher in weeks with positive environmental samples than in non-positive weeks (p = 0.001). The estimated probability of infection was about 1 per 100 exposures to SARS-CoV-2-laden aerosols through inhalation and as high as 1 per 100,000 exposures from contacting contaminated surfaces in simulated scenarios.SignificanceViral shedding was demonstrated by the detection of viral RNA in multiple air and surface samples on a university campus. The low overall positivity rate indicated that the risk of exposure to SARS-CoV-2 at monitored locations was low. Risk modeling results suggest that inhalation is the predominant route of exposure compared to surface contact, which emphasizes the importance of protecting individuals from airborne transmission of SARS-CoV-2 and potentially other respiratory infectious diseases.ImpactGiven the reoccurring epidemics caused by highly infectious respiratory viruses in recent years, our manuscript reinforces the importance of monitoring environmental transmission by the simultaneous sampling and integration of multiple environmental surveillance matrices for modeling and risk assessment.

Semi-laboratory scale investigation of energy efficiency of masonry wall drying process by applying a thermo-injection method

Excessive wall dampness causes damage to buildings, increases energy consumption for heating and cooling, and favors breeding microorganisms dangerous for people's health. In that case, moist walls must be dried and renovated, including making them waterproof. However, present methods for drying are highly time- and energy-consuming and its optimal implementation should be searched. This paper investigates the behavior of wet masonry wall specimens during the drying process in the semi-laboratory scale. The study aimed to examine the influence of different operating parameters of the considered masonry wall drying method on samples' drying rates and propose an optimal drying strategy. Small-scale masonry wall samples made of red ceramic bricks, cement-lime binder, and plaster were considered. Specimens had similar dimensions of approximately 1000×1000×600 mm and a dry mass of roughly 1050–1150 kg. Two types of constructions were studied, i.e., plastered and unplastered. The drying process was conducted by applying the thermo-injection method and using a dedicated device that ventilated and heated the wet sample. Different drying device operating conditions and drying process implementations were tested, i.e., single-phase drying without and with heating for two constant mass flow rates of drying air and two-phase drying initially without and then with heating and with two different mass flow rates of drying air. Moisture mass change in the wet specimen, temperatures in several locations in the sample, relative humidity and temperature of the surrounding air in the room, as well as the drying device electrical parameters, were monitored to have insight into the drying phenomenon and assess the energy efficiency of the process. In both tested constructions, the lowest amount of energy was consumed during drying with ventilation mode on and without heating. However, much less moisture was removed from samples in these implementations than for drying implementations with heating. The drying with heating mode activated showed the highest moisture removal efficiency, but energy consumption increased significantly. The drying strategy with a two-phase drying process, i.e., initially without and later with heating of the specimen, showed promising efficiency and a good perspective for the future optimization of the process.

Numerical Study of Consecutive Drop/Wall Impacts Using Smoothed Particle Hydrodynamics

A fundamental understanding of drop/wall interactions is of vital importance to many engineering applications, particularly in internal combustion engines; the outcomes of drop/wall interactions directly affect an engine's overall performance. Numerical models developed for drop-wall interactions are mostly based on the impact of a single drop on dry or wet walls. To accurately mimic and model real engine conditions, it is necessary to have a comprehensive study of drop/wall interactions with consecutive droplets. A theoretical splashing criterion based on the K parameter incorporating the impingement frequency is presented in this paper. In this study, a numerical method, based on Smoothed Particle Hydrodynamics (SPH), is used to simulate the impact of a droplet train on a heated wall at different impingement frequencies. The present SPH method is validated against the experimental results on the propagation of the crown rim's diameter as a function of the non-dimensional time. Impact regimes are identified for various impact conditions based on the study of the time evolution of the post-impingement process. In this work, simulations were conducted for n-heptane drops at different impingement frequencies and diameters. It is found that the K parameter provides a better prediction for the impingement outcomes and the effect of impingement frequency is seen as the kinematic discontinuity among the spreading lamellae, film formation, and rapidness of drop impact. Additionally, the inhibition by high ambient pressure on the crown rim propagation is also quantified. The results of this study can be used to further improve spray/wall interactions models at realistic engine conditions.

Super-resolution imaging of Douglas fir xylem cell wall nanostructure using SRRF microscopy

BackgroundThe nanostructure of plant cell walls is of significant biological and technological interest, but methods suited to imaging cell walls at the nanoscale while maintaining the natural water-saturated state are limited. Light microscopy allows imaging of wet cell walls but with spatial resolution limited to the micro-scale. Most super-resolution techniques require expensive hardware and/or special stains so are less applicable to some applications such as autofluorescence imaging of plant tissues.ResultsA protocol was developed for super-resolution imaging of xylem cell walls using super-resolution radial fluctuations (SRRF) microscopy combined with confocal fluorescence imaging (CLSM). We compared lignin autofluorescence imaging with acriflavin or rhodamine B staining. The SRRF technique allows imaging of wet or dry tissue with moderate improvement in resolution for autofluorescence and acriflavin staining, and a large improvement for rhodamine B staining, achieving sub 100 nm resolution based on comparison with measurements from electron microscopy. Rhodamine B staining, which represents a convolution of lignin staining and cell wall accessibility, provided remarkable new details of cell wall structural features including both circumferential and radial lamellae demonstrating nanoscale variations in lignification and cell wall porosity within secondary cell walls.ConclusionsSRRF microscopy can be combined with confocal fluorescence microscopy to provide nanoscale imaging of plant cell walls using conventional stains or autofluorescence in either the wet or dry state.

The prediction of spontaneous oil-water imbibition in composite capillary

In view of the classical Lucas-Washburn equation, which can only describe the spontaneous imbibition of single wetted capillary, a tilted composite capillary model with circular cross section, composed of different wettability capillary wall was established. The model can describe the spontaneous oil-water imbibition of water-wet capillary, oil-wet capillary and mixed wetting capillary. Through numerical solution of the model equation, it is found that the component content of the capillary walls, the capillary radius and the oil-water viscosity ratio have great effects on the spontaneous oil-water imbibition. Effects of capillary inclination angle and inertia force on spontaneous oil-water imbibition are related to the capillary scale. Effects of capillary inclination angle and inertia force can be ignored in small radius capillary, while effects of inclination angle and inertia force can not be ignored in large radius capillary. • A composite capillary model composed of different wet walls was established. • Scale effects on spontaneous oil-water imbibition was considered. • The model is applicable to water-wet, oil-wet, mixed-wet pores.

Wet surface wall model for latent heat exchange during evaporation.

Air conditioning is a dual heat and mass transfer process, and the human nasal cavity achieves this through the mucosal wall surface, which is supplied with an energy source through the sub‐epithelial network of capillaries. Computational studies of air conditioning in the nasal cavity have included temperature and humidity, but most studies solved these flow parameters separately, and in some cases, a constant mucosal surface temperature was used. Recent developments demonstrated that both heat and mass transfer need to be modeled. This work expands on existing modeling efforts in accounting for the nasal cavity's dual heat and mass transfer process by introducing a new subwall model, given in the Supplementary Materials. The model was applied to a pipe geometry, and a human nasal cavity was recreated from CT‐scans, and six inhalation conditions were studied. The results showed that when the energy transfer from the latent heat of evaporation is included, there is a cooling effect on the mucosal surface temperature.

Heat Transfer and Residence Time in Lean Direct Injection Fuel Galleries

Abstract In radially staged lean direct injection (LDI) systems, pilot fuel plays an important role in cooling the mains fuel gallery in regions of the flight envelope where the mains fuel is stagnant. Under these conditions, managing wetted wall temperatures is vital to avoid the formation of carbonaceous particles, which become deposited on the surfaces of the fuel gallery and can lead to a deterioration in system performance. The prediction of wetted wall temperatures therefore represents an important aspect of the injector design phase. Such predictions are often based on injector thermal models, which tend to rely on the application of convective boundary conditions from empirical heat transfer correlations. The use of these correlations leads to questions over the accuracy of predicted wetted wall temperatures and therefore uncertainty over the probability of deposition. This paper seeks to improve on the current situation by applying the inverse conduction technique to determine heat transfer coefficients (HTCs) specific to the pilot fuel gallery. These HTCs are crucial for determining wetted wall temperatures in the pilot and mains fuel galleries and principally govern the risk of deposition in the stagnant mains. The pilot heat transfer data are further examined alongside measurements of the pilot residence time distribution, which together control the risk of pilot deposition at low fuel flow rates. Both the heat transfer and residence time measurements demonstrate the opportunity for future fuel gallery design refinement and provide the supporting data to facilitate this.

Experimental and Modeling Study of Wall Film Effect on Combustion Characteristics of Premixed Flame in a Constant Volume Combustion Bomb

The primary objective of the present study was to investigate the impact of wall film on the combustion characteristics of premixed flames in internal combustion engines through the joint experimental and numerical techniques. The interaction between the premixed methane-air flame and n-dodecane film attached to the wall of a constant volume combustion bomb was experimentally examined. The flame propagation processes, as well as pressure evolution were quantitatively characterized. Then, computational fluid dynamic (CFD) simulation was performed incorporating the combustion chemistry model. To enable efficient simulation of the chemically reacting flow in engine chambers, a simplified modeling approach based on a two-step reaction scheme was developed. A compact reaction model for the selected model fuel n-dodecane was constructed and reduced to include 35 chemical species and 180 reactions. The flame propagation process of the premixed flame and its interaction with dry and wet walls was studied. The results showed that the propagation of the premixed flame could be divided into four stages, and the existence of the slit structure increased the instability of the flame structure in the near-wall region. The wall film tended to promote emissions, producing more unburned hydrocarbons, soot precursors and aldehydes.

Study of the influence of input parameters in an air channel on mass and heat transfer phenomena within a wall saturated with water: application to the renovation of old wet buildings

In order to control moisture in old buildings, a new technology consists in incorporating a ventilation system into the air space located between the thermal insulation and the wet wall. This technology is considered as one of the effective solutions to achieve the comfort of the occupants, the durability of the insulation. A mathematical approach based on the darcien model was developed, in order to analyse the influence of effective coupled parameters which are heat, moisture, and air on the evaporation performance of a porous layer. A hybrid coupling combining both the Boltzmann method and the finite volume method is proposed. The results show that blowing air in winter conditions affect markedly the heat and mass exchanges at the interface between the porous layer and the channel. However, blowing air in summer conditions provide drying the wall and decrease the risk of development of mould.

Hygrothermal Evaluation of Waterline Rising of a Masonry Tower based on Measurements and Simulations

Wet walls in ancient masonry buildings are common due to rainfall, groundwater and other environmental factors, and usually accompanied by the degradation phenomena such as powdering, shedding, salting out, which threatens the value and safety of ancient buildings. It is found that the bottom of Dayan Pagoda has been damp and gloomy for a long time. In recent 40 years, the waterline at the bottom has risen by about 0.5 ∼1m, and the wet area on the north wall is as high as 5m. This paper aims to clarify the cause of the rising waterline and the water source of Dayan Pagoda. The correlation between degradation of Dayan pagoda and environmental factors such as temperature, rainfall and solar radiation was established. Firstly, there was a field measurement on the waterline height in different orientations of Dayan Tower; Then, a coupled heat and moisture transfer model was developed to obtain the hygrothermal distribution in the brick wall, and the impact of rainfall and groundwater was evaluated, and the rising trend of waterline in the future was predicted. The field measured results show that during 2018-2020, the waterline of the west wall of Dayan Pagoda has the largest rise (about 20cm), while the south wall has the smallest rise (about 10cm). The simulation results show that the water source of rising waterline is mainly wind-driven rain rather than groundwater rising. The result contributes to propose environmental control measures to alleviate the degradation of masonry buildings caused by water.

New and interesting diatoms from the Shimen Wetwalls, Yunnan Province, China. I. Valve morphology of Melosira radiato-sinuata var. yunnanica Chen (Bacillariophyta: Melosirales) from Yunnan Province, China, with comments on its systematic position

We examine and describe the frustular morphology of the diatom originally described as Melosira radiato-sinuata var. yunnanica from a wet wall in Yunnan Province, China, based on light and scanning electron microscopy. This diatom has carinoportulae present in the central portion of the valve, and prominent caverns present internally around the periphery of the valves. The valve mantle height varies. Based on these features M. radiato-sinuata var. yunnanica is transferred to the genus Orthoseira and recognized as a distinct species. It is compared to other, similar ‘centric’ diatoms. Several other, similar taxa are also formally transferred to the genus Orthoseira, including M. radiato-sinuata, and Melosira undulata var. triocellata. ‘Orthoseira sp. #2' sensu Spaulding and Kociolek is formally described as a new species. A discussion of the morphological diversity within the genus Orthoseira is presented.

Design of a water wash column in the CO2 capture process using a polyamine-based water-lean solvent

Amine-based water-lean solvents (WLSs) have been studied as energy-saving alternatives to existing aqueous amine solvents for the capture of CO2. However, despite the low energy requirements of WLS-based processes, WLSs are susceptible to amine vaporization loss due to the high amine concentration. In addition, the water content of WLSs is apt to increase, which is caused by the low vaporization pressure of water from the solvent due to the low water content of the solvent. When this happens, it is expensive to return the water content of the solvent to its original state. To address these problems, in this study, we investigated the design of a water wash section for a CO2 capture process based on a WLS consisting of 60 mass% of 3,3′-iminobis (N,N-dimethylpropylamine) (IBDMPA), 10 mass% of water, and a non-amine chemical as the final content. The heat and mass balance around the water wash section was analyzed, including the IBDMPA/water transfer from gas phase to liquid (water) phase within the water wash bed. To achieve this, the mass transfer coefficients of the IBDMPA and water were measured in a modified wetted wall column system, and the binary and ternary vapor–liquid equilibria for the WLS were also measured and modeled. The computation using the ASPEN Plus® simulator showed that IBDMPA emissions of less than 1 ppm and water balance in the WLS could be successfully achieved through the appropriate design of the water wash section.

Experimental and numerical mass transfer study of carbon dioxide absorption using Al2O3/water nanofluid in wetted wall column

In this study, the CO2 absorption by Al2O3/water nanofluid was investigated in laboratory-scale wetted wall column. Effects of important operation parameters such as, nanoparticle volume fraction, fluid flow rate and temperature on the mass transfer coefficient have been studied under laminar conditions and steady state. According to the experimental results, the mass transfer coefficient of nanofluid is higher than base fluid water and the mass transfer coefficient increases with the increase of nanoparticle concentration, temperature, and fluid flow rate. The mass transfer coefficients Al2O3/water nanofluid were increased by 40.3% and 67.16% with addition of 0.0125 and 0.025 %v/v nanoparticle, respectively. Then, the mass transfer behavior of Al2O3/water nanofluid in an axi-symmetric two dimensional domains was simulated by applying computational fluid dynamics considering Brownian motion mass diffusion coefficient in nanofluid. The CFD results have a good agreement with experimental results. Also, results have shown that the dimensionless CO2 concentration in film layer clearly increases with an increase in nanoparticle volume fraction and the temperature; but when the fluid flow rate increases, the CO2 concentration decrease.

In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

Melinacidin-Producing Acrostalagmus luteoalbus, a Major Constituent of Mixed Mycobiota Contaminating Insulation Material in an Outdoor Wall.

Occupants may complain about indoor air quality in closed spaces where the officially approved standard methods for indoor air quality risk assessment fail to reveal the cause of the problem. This study describes a rare genus not previously detected in Finnish buildings, Acrostalagmus, and its species A. luteoalbus as the major constituents of the mixed microbiota in the wet cork liner from an outdoor wall. Representatives of the genus were also present in the settled dust in offices where occupants suffered from symptoms related to the indoor air. One strain, POB8, was identified as A. luteoalbus by ITS sequencing. The strain produced the immunosuppressive and cytotoxic melinacidins II, III, and IV, as evidenced by mass spectrometry analysis. In addition, the classical toxigenic species indicating water damage, mycoparasitic Trichoderma, Aspergillus section Versicolores, Aspergillus section Circumdati, Aspergillus section Nigri, and Chaetomium spp., were detected in the wet outdoor wall and settled dust from the problematic rooms. The offices exhibited no visible signs of microbial growth, and the airborne load of microbial conidia was too low to explain the reported symptoms. In conclusion, we suggest the possible migration of microbial bioactive metabolites from the wet outdoor wall into indoor spaces as a plausible explanation for the reported complaints.