Spreading Behavior Research Articles

The Effect of Inclined Conditions on the Consequences of Fires Caused by Spilled Flammable Liquids: Development of Inclined Spreading Extent Formulae

The accidental spillage of flammable liquids on in-service ships and offshore installations may lead to pool fires, which are likely to spread over a particularly large area in large compartments under ship motion, resulting in extensive damage. However, the effect of the spreading extent of liquid fuel due to inclined ship motion on pool fire consequences has not been considered in the existing literature. Thus, in this study, fuel discharge experiments were conducted to investigate the spreading behaviour under different substrate inclination angles and discharge rates. The experimental results were analysed to derive closed-form expressions to predict the spreading extent of liquid fuel in large compartments. Additionally, the effects of surface inclination on fire consequences were investigated using the Fire Dynamics Simulator in terms of the heat release rate. The findings can provide guidance for effective fire safety design and establishing a realistic fire modelling methodology for ships and offshore installations.

Horizontal flame spread behavior of densified wood: Effect of structural characteristics

Densified wood (DW) is a recently developed material with excellent mechanical properties, considered as an ideal construction material for high-rise timber buildings. However, its flame spread behavior has not been well understood limiting its applications. This work for the first time experimentally and analytically investigates the horizontal flame spread behavior of DW. The influences of material structural characteristics (e.g. density) on heat transfer characteristics are focused. Thermally thin DW with density ranges of 441–1025 kg/m3 and a constant thickness of 2 mm were tested. The flame spread rate, mass loss rate (MLR) and flame height decreased with the increased wood density. A power-law correlation between the dimensionless MLR and dimensionless density is proposed, which well predicts the experiments with an R2 of 0.922. The increased wood density decreases flame height and reduces flame radiation. The gas-phase heat transfer shifts from radiation-dominant to convection-dominant. The longitudinal and radial thermal conductivities of DW increased with wood density. Empirical equations are optimized to predict the thermal conductivities of DW with R2 of 0.870 (longitudinal) and 0.837 (radial). The preheating zone length and the temperature gradient per unit length don’t vary significantly with wood density. Their values are averaged to 25.62 mm and 9.312 K/mm respectively. The longitudinal heat conduction is increased with the wood density due to the increased conductivity. However, this conduction increase is lower than the radiation decrease as the wood density increases. Thus, the total heat flux is slightly decreased with the wood density. The gas phase heat transfer dominates the flame spread. However, the longitudinal heat conduction can account for more than half of the gaseous heat transfer, and thus cannot be negligible. Results of this work improve the understanding of DW flame spread, which helps to evaluate the fire behaviors of timber construction.

Laboratory investigation of dodecylbenzene diffusion from submarine cables

Oil-filled submarine cables have come to dominate the reliable delivery of electrical power today, but oil leakage still remain a challenge. This work focuses on the exploring of spill behavior of dodecylbenzene (DDB) after leakage and the detection of DDB. Static and dynamic spill model were established to study the spreading and migration behavior of underwater DDB. In still water, the spilled oil droplets can quickly reach the uniform floating speed of 0.13 m s-1 with no significant change under different oil spill rates. DDB can be dispersed as small droplets in seawater, which the diameter of DDB droplets increased from 60 nm to 200 nm with the increase of the concentration from 10 ppm to 1000 ppm. This study suggests a research basis for finding the leakage point of submarine cables, and explores the way for detection of DDB.

The Puzzling Behavior of Spreads During Covid

The Puzzling Behavior of Spreads During Covid

Investigation of SEIR model with vaccinated effects using sustainable fractional approach for low immune individuals

<abstract><p>Mathematical formulations are crucial in understanding the dynamics of disease spread within a community. The objective of this research is to investigate the SEIR model of SARS-COVID-19 (C-19) with the inclusion of vaccinated effects for low immune individuals. A mathematical model is developed by incorporating vaccination individuals based on a proposed hypothesis. The fractal-fractional operator (FFO) is then used to convert this model into a fractional order. The newly developed SEVIR system is examined in both a qualitative and quantitative manner to determine its stable state. The boundedness and uniqueness of the model are examined to ensure reliable findings, which are essential properties of epidemic models. The global derivative is demonstrated to verify the positivity with linear growth and Lipschitz conditions for the rate of effects in each sub-compartment. The system is investigated for global stability using Lyapunov first derivative functions to assess the overall impact of vaccination. In fractal-fractional operators, fractal represents the dimensions of the spread of the disease, and fractional represents the fractional ordered derivative operator. We use combine operators to see real behavior of spread as well as control of COVID-19 with different dimensions and continuous monitoring. Simulations are conducted to observe the symptomatic and asymptomatic effects of the corona virus disease with vaccinated measures for low immune individuals, providing insights into the actual behavior of the disease control under vaccination effects. Such investigations are valuable for understanding the spread of the virus and developing effective control strategies based on justified outcomes.</p></abstract>

BARA: cellular automata simulation of multidimensional smouldering in peat with horizontally varying moisture contents

Background Smouldering peatland wildfires can last for months and create a positive feedback for climate change. These flameless, slow-burning fires spread horizontally and vertically and are strongly influenced by peat moisture content. Most models neglect the non-uniform nature of peat moisture. Aims We conducted a computational study into the spread behaviour of smouldering peat with horizontally varying moisture contents. Methods We developed a discrete cellular automaton model called BARA, and calibrated it against laboratory experiments. Key results BARA demonstrated high accuracy in predicting fire spread under non-uniform moisture conditions, with >80% similarity between observed and predicted shapes, and captured complex phenomena. BARA simulated 1 h of peat smouldering in 3 min, showing its potential for field-scale modelling. Conclusion Our findings demonstrate: (i) the critical role of moisture distribution in determining smouldering behaviour; (ii) incorporating peat moisture distribution into BARA’s simple rules achieved reliable predictions of smouldering spread; (iii) given its high accuracy and low computational requirement, BARA can be upscaled to field applications. Implications BARA contributes to our understanding of peatland wildfires and their underlying drivers. BARA could form part of an early fire warning system for peatland.

Spreading of volatile droplets in a humidity-controlled environment.

When a pure ethanol droplet is deposited on a dry, wettable and conductive substrate, it is expected to spread into a thin, uniform film. Here, we demonstrate that this uniform spreading behaviour can be altered significantly by controlling the ambient relative humidity. We show that higher relative humidity not only promotes faster spreading of the droplet, it also destabilizes the moving contact line, resulting in a fingering instability. We observe that these effects primarily emerge due to the hygroscopic nature of the pure droplet, which eventually leads to solutal-Marangoni effects. Additionally, heat transfer between the evaporating droplet and the underlying substrate also plays a crucial role in the overall dynamics. Thus, the overall spreading of a pure hygroscopic droplet is determined by a delicate interplay between solutal and thermal Marangoni effects.

A Computational Approach to Evaluate the Effect of Shelter Construction Material and Fuel Load on the Fire Spread Behavior in Rohingya Refugee Camp

A Computational Approach to Evaluate the Effect of Shelter Construction Material and Fuel Load on the Fire Spread Behavior in Rohingya Refugee Camp

Bacteria-surface interactions: role of impacting bacteria-laden droplets.

Understanding the interactions of pathogenic droplets with surfaces is crucial to biomedical applications. In this study, using E. coli as the model microbe, we investigate the impact of a bacteria-laden droplet on different substrates, both bare and antimicrobial. In doing so, we unveil the significance of kinetic energy and spreading parameters of the impacting droplet in determining the microbes' proliferation capabilities. Our results indicate an inverse relationship between the impact Weber number and the bacterial ability to proliferate. We reveal that the mechanical stress generated during impact impedes the capabilities of microbes present inside the droplet to create their progeny. Following an order analysis of the mechanical stress generated, we argue that the impact does not induce lysis-driven cell death of the bacteria; rather, it promotes a stress-driven transition of viable bacteria to a viable-but-non-culturable (VBNC) state. Furthermore, variations in the concentration of particles on the antimicrobial surfaces revealed the role of the post-impact spreading behaviour in dictating bacterial proliferation capabilities. Contrary to the conventional notion, we demonstrate that during the early stages of interaction, a bare substrate may outperform an antibacterial substrate in the inactivation of the bacterial load. Finally, we present an interaction map illustrating the complex relationship between bacterial colony-forming units, bactericide concentration on the surface, and the impact Weber number. We believe that the inferences of the study, highlighting the effect of mechanical stresses on the soft cell wall of microbes, could be a useful design consideration for the development of antimicrobial surfaces.

Study on Temperature Distribution and Smoke Spreading Behavior of Different Fire Source Locations in the Underwater W-Shaped Island-Crossing Tunnel

Study on Temperature Distribution and Smoke Spreading Behavior of Different Fire Source Locations in the Underwater W-Shaped Island-Crossing Tunnel

Investigation on the burning behaviors of the combustible ceiling with the impingement of an incipient fire source

This paper presents experimental and theoretical research on ceiling jet, burn-through, and flame spread behaviors of the combustible ceiling with the impingement of an incipient fire source. Medium-density fiberboard was utilized as the combustible ceiling in experiments, and the ceiling height above the fire source was varied. The flame radial length (rf), ceiling surface temperature, flame shape and spread rate after burn-through, and radiative heat flux were measured. Results showed that rf beneath the combustible ceiling was significantly longer than that of the non-combustible ceiling. Theoretical analysis was conducted for rf based on energy distribution, and an expression of rf beneath combustible ceiling was proposed. The burn-through behavior of the combustible ceiling was explored by combining the ceiling temperature, small-sized experiment and Fourier law. The advancement of char front along the ceiling thickness was calculated, which was the key point during burn-through. Upper surface flame spread in a circular shape after burn-through, and an expression of spread rate was obtained. A three-dimensional radiation model was adopted to calculate the radiative heat flux received by the unburned ceiling surface during the dynamic flame spread process, the calculated results agreed well with the experimental data.

Experimental study on the stable and dynamic characteristics during silicone oil spreading process on saline water sublayer with different salinities under various temperature conditions

This study investigated the influence of salinity on the spreading behavior of oil at varying temperatures on a calm sea surface through a series of experiments involving the spreading of silicone oil on saline water sublayers with salinities of 0, 5, 10, and 20 ppt (parts per thousand, equivalent to 1‰) across a range of temperatures from 5 to 35 °C. Real-time observations were made of the oil's morphology from both top and side perspectives. The top-view area of the oil slick was not only recorded, but also the side-view morphology of the oil slick was tracked and photographed during the whole process, and the dynamic process of the angle and thickness was measured. The results indicate that higher temperatures and salinity levels increase spreading area. The stable angle was determined by considering three-phase surface tension and Neumann’s rule. The stabilized thickness based on the angle is derived by combining capillary pressure analysis and the Young-Laplace equation. A dynamic thickness model was developed based on force analysis, primarily relying on differential pressure force and surface tension. This study offers valuable theoretical insights to aid in predicting the oil spread thickness of oil spills in various sea regions.

Experimental Analysis on the Behaviors of a Laboratory Surface Fire Spreading across a Firebreak with Different Winds

In this work, a series of laboratory surface fire experiments were performed over a pine needle fuel bed to investigate the effectiveness of a firebreak and the behaviors of a surface fire across a firebreak. Seven wind velocities of 0~3.0 m/s and six firebreak widths of 10~35 cm are varied. The behaviors of a surface fire across the firebreak, the heat flux received by fuel surface and fuel temperature before and after the firebreak are analyzed and compared simultaneously. The main conclusions are as follows: the behaviors of a surface fire spreading across a firebreak under different wind velocities are classified into three categories—no ignition, ignition by flame contact and ignition by spot fires. When the wind velocity is not more than 1.0 m/s, the surface fire cannot successfully cross the firebreak; as wind velocity changes from 1.5 m/s to 2.5 m/s, the fuel after the firebreak can be ignited by flame contact for relatively narrow firebreak conditions; when the wind velocity increases to 3.0 m/s, the burning fuel can be blown away along the fuel bed, and the fuel behind the firebreak will be ignited by spot fire. A linear relationship between the threshold of firebreak width and the fireline intensity is obtained, and the linear fitting coefficient in this paper is larger than the results reported by Wilson (0.36). For no ignition conditions, the fuel temperature and the heat flux received by the fuel after firebreak are significantly lower than those before the firebreak, whereas their variations over time are similar to those before the firebreak for ignition conditions. Moreover, for no ignition conditions, the maximum fuel temperature and the heat flux after the firebreak increase with wind velocity, but decrease with firebreak width. Additionally, when the fuel temperature (253 °C) and the heat flux received by the fuel considering the radiation and convection (43 kW/m2) after firebreak exceed a threshold value, the surface fire can successfully cross the firebreak.

Wetting behavior on wheat leaves surface by adding different surfactants

The wettability of chemical pesticides on the surfaces of crop leaves is crucial for enhancing the efficiency of chemical solutions. This work examined the wetting behavior of 28-Epimotabrassinolide (28-HB) combined with various surfactants on the adaxial and abaxial leaves at the jointing and boot stages of wheat. The microstructure of the leaf surface was characterized by ultra-depth microscopy, and the surface free energy (SFE) of the leaf was calculated by the Owens–Wendt–Rabel–Kaelble (OWRK) method. The surface tension of the 28-HB solution with different surfactants added and the contact angle on the leaf surface at the jointing and boot stages were measured. Compared with the boot stage, the wettability of the adaxial and abaxial wheat leaves was superior to that of the jointing stage. The addition of surfactants to the 28-HB improved the spreading behavior of droplets on the surface of leaves. Specifically, when fatty lcohol polyoxyethylene ether (AEO9) was added to 28-HB, the wettability of the droplets on the jointing wheat leaf surface was greatly enhanced. Additionally, cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (SDS) improve the wettability of 28-HB on wheat leaves at the boot stage. When the surface tension of the solution is lower than the free energy of the solid surface, the dispersion component in the free energy of the leaf surface aligns with the dispersion component in the surface tension of the solution, facilitating maximum wettability of the solution on the leaf surface. This work offers a fresh perspective on enhancing the efficiency of surfactants in achieving superhydrophobic leaf wetting.

Numerical analysis of liquid sodium spreading on sloped floor surface under pool fire scenario in SFR systems

The accidental leaks of coolant from the heat transport circuit of Sodium-cooled Fast Reactor (SFR) can create fire events due to the reactivity of sodium with atmospheric oxygen, which can pose threat to safe operation of the reactor. The leaked sodium eventually reaches the cell floor, spreads gradually, and forms a burning pool. The thermal consequences of pool fire depend on its surface area, which is determined by the spreading process of sodium on the floor surface. In this context, numerical investigation has been carried out on the spreading behavior of burning sodium pool on the plane/sloped cell floor by developing a 3-D numerical model based on the viscous-gravity current equation of the shallow layer model. The governing equations of the model have been solved numerically by implementing the Finite Volume Method. The model developed has been validated using the experimental results published on liquid pool spreading under burning and non-burning conditions on plane and sloped floors for different leak rates. Using this model, numerical simulations have been carried out on sodium pool spreading under various leak scenarios envisaged in SFR cells based on the specific burning characteristics of sodium pool fire. The time-varying pool size and shape, pool height profile, and maximum pool area have been estimated for a wide range of sodium leak rates and typical floor slopes of interest to nuclear power plants. These predictions contribute towards the numerical evaluation of sodium pool fire scenarios pertaining to the safety of SFR.

Thermal runaway behaviour and heat generation optimization of the marine battery cabinet based on module thermal analysis

Currently, the application of lithium-ion batteries in electric vehicles has become common in recent years. Considering the adjustment and transformation of the future energy structure, the use of electric ships is increasing; however, the problem of heat production from the battery cabinet of electric ships must be solved. Therefore, in this study, the multi-scale and multi-domain solution method was used to analyse the heat production and heat transfer of a module-level battery to calibrate the basic calculation model in this study. A double-layer cooling arrangement was proposed to optimise the heat production of the model, which controlled the heat production rate of the battery module to be within 0.00497 K/s. Based on the thermal runaway (TR) module, a three-layer marine battery cabinet was visually analysed for the first time, and the influence of TR on the upper and lower layers and the thermal spread behaviour of the battery pack in the middle layer were studied. The results indicated that the temperature change in the battery in the first layer was more significant than that in the third layer. Furthermore, the proposed double-layer cooling scheme controlled the temperature of the battery in direct contact with the heat source to within 324.4 K. The findings of this study provide insights into the TR behaviour of a marine battery cabinet and its influence on heat generation as well as guidance for the thermal management of electric marine battery cabinets.

Numerical study of falling film flow and heat transfer on the horizontal tube with a porous coating layer

Porous surfaces often exhibit exceptional performance in liquid spreading and heat transfer, making them promising candidates for enhancing falling film heat transfer on solid surfaces. This paper delves into the flow and heat transfer characteristics occurring within falling films on horizontal tubes coated with a porous layer. To achieve this, a three-dimensional numerical model that couples the Volume of Fluid (VOF) method with porous media considerations was employed. The investigation comprehensively covers film spreading behavior, flow patterns, film velocity, film thickness, temperature distribution, and heat transfer coefficients, for both plain and porous tubes. Furthermore, we delve into the effects of key parameters, such as porosity, layer thickness, and material properties, on the overall heat transfer process. The results demonstrate the accuracy of our model in reproducing film thickness and heat transfer coefficients within falling films on horizontal porous tubes. When comparing plain tubes to porous ones, some key differences emerge. Specifically, the liquid film on porous tubes spreads more slowly, leading to increased film thickness and fewer occurrences of dry patches. Additionally, porous tubes result in lower film velocity and a more uniform temperature field compared to plain tubes. Interestingly, the findings reveal that smaller porosities yield thicker films and higher heat transfer coefficients, particularly when the porosity is below 0.4. Moreover, thicker porous layers result in thinner films, higher wetting ratios, and increased heat transfer coefficients. Among the materials we tested, aluminum and copper porous layers exhibit the highest heat transfer performance, while steel demonstrates the lowest.

Spreading process and characteristics of silicone oil with multi-viscosities on calm liquid surface with low temperature: Spreading length, stable thickness and morphology

Oil spreading on the sea has been a great focus, especially along with the intensification of oil development activities in arctic regions, leading to an increase in the frequency of oil spills in extremely cold regions. Currently, the effect of extreme low temperature on oil spreading behavior has not been fully studied, and the applicability of existing models of oil spreading characteristics in low temperature scenarios is not clear. An experimental platform was customized to set up low temperature liquid substrate environments (−20∼20 °C). A series of oil spreading experiments of silicone oil with viscosities of 50, 100, 350 and 1000 cs and five released volumes (1–5 ml) on low temperature substrates were carried out. The effects of experimental variables including temperature, viscosity and volume on oil spreading characteristics of spreading length, stable thickness, morphology, and cone angle were investigated. The entire spreading process of oil was displayed from the top and side views, and gave the variation curves of oil thickness and cone angle with time. Summarized the spreading law for multi-viscosity silicone oils, the values of the pre-exponential coefficient and the power-law exponent were determined, and detailed formulas for calculating the spreading length was proposed. An stable thickness prediction model that integrates all the forces on the oil spreading process was constructed, including surface tension, viscous force, inertia force and gravity. These forces all weakening with time, especially the inertial and viscous forces, which contain time terms, and weaken the most. The heat transfer between the oil and the liquid substrate was also monitored and discussed in the experiments, proposed that low temperatures may hinder the spreading behavior of the oil by decreasing the spreading coefficient of the oil. The findings of this study can provide a theoretical support for the oil spill cleanup.

Scaffolded spheroids as building blocks for bottom-up cartilage tissue engineering show enhanced bioassembly dynamics

Due to the capability of cell spheroids (SPH) to assemble into large high cell density constructs, their use as building blocks attracted a lot of attention in the field of biofabrication. Nevertheless, upon maturation, the composition along with the size of such building blocks change, affecting their fusiogenic ability to form a cohesive tissue construct of controllable size. This natural phenomenon remains a limitation for the standardization of spheroid-based therapies in the clinical setting.We recently showed that scaffolded spheroids (S-SPH) can be produced by forming spheroids directly within porous PCL-based microscaffolds fabricated using multiphoton lithography (MPL). In this new study, we compare the bioassembly potential of conventional SPHs versus S-SPHs depending on their degree of maturation. Doublets of both types of building blocks were cultured and their fusiogenicity was compared by measuring the intersphere angle, the length of the fusing spheroid pairs (referred to as doublet length) as well as their spreading behaviour. Finally, the possibility to fabricate macro-sized tissue constructs (i.e. cartilage-like) from both chondrogenic S-SPHs and SPHs was analyzed.This study revealed that, in contrast to conventional SPHs, S-SPHs exhibit robust and stable fusiogenicity, independently from their degree of maturation. In order to understand this behavior, we further analyze the intersection area of doublets, looking at the kinetic of cell migration and at the mechanical stability of the formed tissue using dissection measurements. Our findings indicate that the presence of microscaffolds enhances the ability of spheroids to be used as building blocks for bottom-up tissue engineering, which is an important advantage compared to conventional spheroid-based therapy approaches. Statement of significanceThe approach of using SPHs as building blocks for bottom-up tissue engineering offers a variety of advantages. At the same time the self-assembly of large tissues remains challenging due to several intrinsic properties of SPHs, such as for instance the shrinkage of tissues assembled from SPHs, or the reduced fusiogenicity commonly observed with mature SPHs. In this work, we demonstrate the capability of scaffolded spheroids (S-SPH) to fuse and recreate cartilage-like tissue constructs despite their advanced maturation stage. In this regard, the presence of microscaffolds compensates for some of the intrinsic limitations of SPHs and can help to overcome current limitations of spheroid-based tissue engineering.

Interaction between droplet impact and surface roughness considering the effect of vibration

Droplet impingement is pivotal in several fields, such as agricultural spraying, ink printing and firefighting. Although droplet impact studies have received much attention, the combined effects of roughness and vibration on droplet dynamics still need to be explored. In this study, an in-depth analysis is carried out to address this issue, and high-speed photography is utilised to explore the droplet impact process under different roughness and vibration conditions. The results show that higher surface roughness dissipates the kinetic energy of droplet spreading, thus inhibiting droplet spreading. Conversely, vibration imparts additional inertial effects to the droplet, leading to sustained oscillations once the droplet stabilises, which in turn results in a more pronounced variation in the droplet's dynamic contact angle. Therefore, in this paper, the vibrational Weber number (Wev) is employed to characterise the interaction between the vibration-induced extra inertia force and the droplet's surface tension. Moreover, as the Wev increases, the relative velocity of the droplet impact also rises, further intensifying the droplet's spreading behaviour. At a Wev of 8.72 and a surface roughness of 0.4 μm, droplet spreading is enhanced by 33%. While at a surface roughness of 6.3 μm, droplet spreading was suppressed by 32% relative to a surface roughness of 0.4 μm. Ultimately, an empirical model was proposed to predict the droplets' maximum dimensionless spreading coefficient (βmax) under vibration conditions, with an error of ±9.5% in the model prediction. This study delves into the dynamic characteristics of droplets under the combined influence of surface roughness and vibration, offering crucial theoretical foundations and profound insights for engineering applications in the field.