Impinging wind jets commonly occur in tunnels and passages, whose non-uniform flow can significantly alter flame behavior.This paper investigates flame spread over double wires under varying side-confined distances (D = 0~15 mm), wire spacings (S = 0~16 mm), and nozzle exit velocities (Uf = 0~0.4 m/s) generated by an impinging jet system. Results show that flame morphology is governed by flow regions, with forward flow zone exhibiting larger flames and distinct "flame displacement". Pm decreases with increasing D and S, and is significantly changed by Uf. The stagnation zone shows higher merging probability due to cross-flow dominance. Flame tilt angle is determined by wind drag force (Fw), buoyancy force (Ff), and interaction force (Fi). In the reverse and forward flow zones, the longitudinal tilt angle θ is determined by the competition between buoyancy and wind drag, following the relationship . Meanwhile, the transverse tilt angle α in these zones arises for the combined effects of flame interaction and buoyancy, expressed as. In the stagnation zone, Fr number effectively has the relationship with transverse tilt angle and Pm, following as . FSR can be sorted as: forward flow > reverse flow > stagnation zone, due to the inner/outer wire velocity difference governed by wall jet wind speed u. A heat transfer model based on heat feedback components is established to well predict the flame spread rate within ±15% errors.

Considering the variations of water thermal properties with temperature and pressure, semi-analytical heat and mass transfer models are developed for coaxial-type and U-type deep borehole heat exchangers (DBHEs) respectively, and the influences of temperature and pressure-dependent water thermal properties on the thermal and hydraulic performances of DBHEs are investigated. The proposed models match well with experiment data and Darcy-Weisbach equation, indicating that proposed models are feasible. Ignoring temperature and pressure-dependent water thermal properties would lead to non-negligible deviations: for given heat output rate, outlet temperature deviations at 120 d range from 0.36 °C to 0.62 °C, and relative deviations of pressure drops range from −6.1% to 25.7%. The thermal performance of DBHEs is mainly influenced by pressure-dependent water thermal properties, and is partly influenced by temperature-dependent water thermal properties; the hydraulic performance is mainly influenced by temperature-dependent water thermal properties, and is partly influenced by pressure-dependent water thermal properties. Ignoring temperature and pressure-dependent water thermal properties would lead to great deviations of the convective heat transfer coefficients of water, which would only slightly affect the thermal performance of DBHEs. The results indicate that it is necessary to consider the influences of temperature and pressure-dependent water thermal properties for DBHEs simulation.

Insulation materials are susceptible to being ignited by flame spreading electrical wires, which can lead to uncontrolled fire growth. This paper investigates the ignition and interactive fire behaviors between wires and two typical insulation materials, extruded polystyrene (XPS) and rigid polyurethane foam (RPUF), under different side-confined distances (3 similar to 50 mm). In PartI(wire influences XPS/RPUF), the ignition time of XPS increases significantly with the side-confined distance, reaching at approximately more than 40s, whereas for RPUF, it is typically smaller within 3s. Notably, due to the thermoplastic nature of XPS, the ignition time is evidently prolonged by a distinct shrinkage time tsh. Correspondingly, the ignition time model is established, which can well predict the ignition times of XPS and RPUF. In Part II (XPS/RPUF influences wire), for XPS, the pool fire is formed and the feedback heat flux (q)over dot ''(f(Pool)) will accelerate wire flame spreading greatly during the fully merged stage for the main flame and pool fire, owing to the strongest burning interaction. In contrast, RPUF exhibits no evident deformation during burning, resulting in the electrical wire's extinction during the connection part. Interestingly, after complete combustion of RPUF, the wire may be re-ignited depending on two factors as: the side confined distance s is relatively larger and the heat flux on its preheating zone is larger than a critical value ((q)over dot ''(t(RPUF-W) >=) (q)over dot ''(ig,crit)). Finally, the heat transfer models are built, which can well reveal the distinct interactive burning behaviors of XPS/RPUF on wires.

Impinging wind jets in ventilation tunnels notably affect electrical wire combustion, with their unique flow structures further escalating fire risks. This paper investigates the impinging wind jets on the flame spread and extinction behaviors of wires by controlling the nozzle exit wind speeds (U-f = 0 similar to 0.8 m/s) and side-confined distances (y = 0 similar to 120 mm). Based on flow field characteristics, the flame spread will go through the wall jet zone (0 mm <= y < 70 mm), including of reverse, stagnation, and forward flow zones, and the free jet zone (70 mm <= y <= 120 mm). Results show that under the same wind speed, the flame longitudinal tilt angle theta in the reverse flow zone is significantly larger than that in the forward flow zone (theta(R) > theta(F)), which is mainly caused by the dynamic competition between flame burning and horizontal wind speed. In the wall jet zone, the flame spread rate (FSR) decreases with wind speed in the reverse flow and stagnation zones, but rises then falls in the forward flow zone. In the free jet zone, FSR also decreases as wind speed increases. Additionally, the Damkohler number Da* decreases exponentially as wind speed grows, resulting in flame extinction when u(w)(x, y) > 1.3m/s for the wall jet zone. Meanwhile, when the free jet wind speed u(f)(y) > 0.4m/s, the critical strain rate (a*(mix) = 120s (-1)) is surpassed, which leads to flame extinction in the free jet zone. Finally, the heat transfer models to predict the FSR and extinction limits are established, which show good agreement with experimental results.

Combustion characteristics of a partially premixed flame in a micro-combustor with a wall cavity were studied numerically under various conditions (primary air coefficient, α = 0.35, 0.5, and 0.65). The results show that the cavity has a significant effect on flame structure, establishing a typical double-flame structure (namely, a trapped-vortex flame and a main flame). The cavity effectively extends the operating range at a higher α. Although the trapped-vortex flame is relatively weak, it plays a crucial role in sustaining main flame through heat transfer. Specifically, the trapped vortex flame is dominated by the nature of the mixed gas flowing into the cavity, and assisted by the preheating effect. And the main flame is dominated by flow field and assisted by heat transfer. Research shows that with the increase of Vin, reaction zone area, temperature, and heat release rate (HRR) of both the trapped-vortex flame and the main flame are increased simultaneously. And as α increases, reaction zone area, temperature, and HRR of the trapped-vortex flame increase significantly, while those of the main flame decrease. According to the field synergy principle, a higher Vin does not necessarily lead to a better preheating effect of the fresh mixture.

This paper explores the characteristics of flame spread and the dominant heat transfer mechanism of vertically arranged wires in a tunnel with confined distance. The effect aspects including of wire spacing (0 cm and 5 cm), side wall confined distance (5 mm ~ 40 mm), and horizontal wind speed (0 m/s ~ 2.5 m/s) are well studied. The results show that the flame width and flame spread rate increase firstly and then decrease with the increase of wind speed, reaching at a maximum with a wind speed of 1.5 m/s. The flame height and inclination angle decrease continuously with the increase of wind speed and confined distance. When the wire spacing is 5 cm, each wire flame burns independently, and the upper flame, heated by ceiling thermal feedback and the lower flame, exhibits a higher heat flux. The heat transfer analysis shows that flame thermal convection contributes the most to flame spread, and ceiling thermal feedback is stronger than that of the side wall.Finally, a heat transfer model is well established, which can well reveal the triple wires heat transfer mechanisms during flame spread process in a wind tunnel. And the deviation between the predicted values of the heat transfer model and the experimental values is within ±15%, which verifies the effectiveness of the model.The results can give useful suggestions for the fire safety design and management for the triple or multiple electrical energy wires during energy transportation process.

This paper experimentally investigates the ignition behavior of three types of foam insulation materials when exposed to liquid droplets generated from the flame spreading wires under varying currents from 0 to 50 A. The results indicate that the individual droplet mass produced during wire combustion increases with current intensity. The larger thickness of PE for Type III wire will generate the larger droplet mass. The dripping frequency also increases with the increasing current, which can be well predicted with the theoretical analysis. When droplets drip onto the foam insulation materials, the total mass of RPUF and RPUF + EG10 foams will decrease due to combustion, whereas the mass of EPS foam increases as droplets penetrate the material without ignition. On the other hand, the number of droplets required to penetrate and ignite the foam decreases as the current increases. And the critical dripping mass for igniting insulation materials is proposed, which increases with current. The total ignition time t_ig is firstly divided into the dripping time of the critical mass t_dr and after the ignition time of the foams t_ig,0 , which also increases with current. Finally, a heat transfer model is established to reveal the ignition times of insulation materials by dripping droplets. It is demonstrated that, the calculated ignition time t_ig shows a good agreement with the experimental value.

Compared to open spaces, fires in confined spaces such as long tunnels are usually influenced by significant heat accumulation, large smoke generation and low burning efficiency. This paper investigates the flame spread and heat transfer over electrical wire under different wind speeds (V = 0,1.5,2.5 and 3.5 m/s) and fire source locations along diagonals of the tunnel(theta = 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees), respectively. The results show that the flame width and flame spread rate increase and then decrease with the wind speed. As the lower wind speed promotes the airflow and fuel mixing, while the higher wind speed enhances the cooling effect and inhibits the mixing. The closer the flame is to the sidewall or ceiling wall, the larger the heat feedback is, making the flame height higher.According to the heat flux feedback of flame, copper core, sidewall and ceiling wall at different space locations of Ds and Hc, the five regions are divided. Finally, a heat transfer model is established, which can accurately predict the flame spread rate. Meanwhile, the dimensional flame height and dimensional flame spread rate are proposed, with the terms of Hf & lowast;, D & lowast;c, Q(center dot)& lowast; and Vf & lowast;, which agree well with the experimental values.

It is common for multiple wires to be used together in energy transmission systems. In this paper, four types of electrical wires (copper core diameter:6mm and 8 mm;PE thickness:1mm and 2 mm, respectively) were used to study horizontal flame spread of triple parallel electrical wires with spacings of 0 mm, 2 mm, 5 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm and 20 mm. The results show that triple wires significantly contribute to the flame merging phenomenon during combustion as compared to double wires. The flame spread rate (FSR) and flame width are higher than those of double wires. The dynamic equilibrium stage is found, which illustrates that the FSR of flame 2 is a bit faster than that of flame1 or flame 3 firstly, while the FSR of the triple wires will be the identical at the end with a periodic cycle. In an addition, the heat transfer model over flame spread is established. By estimating the heat fluxes of feedback components, it is revealed that the total heat flux received in the preheating zone of wire 2 is greater than that of the wires on both sides, resulting in a faster flame spread rate at the intermittent stage. And the convective heat flux reaches at the maximum value when entering to the intermittent merging stage.The thickness of PE insulation layer will influence the flame spread much more than that of copper core diameter for the triple wires.

Soil thermal conductivity ()s) is a vital parameter for sizing vertical borehole heat exchanger (VBHE) of groundsource heat pump, which may vary dramatically with the depth. To measure the )sdistribution of coaxial VBHE, this study proposes an estimation method based on distributed thermal response test (DTRT). Firstly, a 3D numerical model is built and validated, which is utilized to simulate some DTRTs under various conditions. A 1D model is then developed for any layer of coaxial VBHE, which is discovered to agree better with the 3D model than the traditional infinite line source model. The proposed estimation method utilizes the 1D model to match DTRT data to identify the )s distribution, and then it is compared with the traditional direct method based on the simulated DTRT data. The results show that the traditional method probably has great errors, and that the proposed method could accurately estimate the )s of nearly all the soil layers, the errors of which are basically smaller than 4 %. The precision of the proposed method is slightly affected by the DTRT duration, number of split layers and errors of soil heat capacities. The proposed method is simple and concise, which is convenient for practical application.

The wire as an important carrier of energy transportation is widely used in many fields. This paper investigated the flame spread and mutual interaction behaviors over two energy wires under different side-confined distances of D = 0,3,6,9,12,15 and 18 mm, and wire spacings of S = 0,3,5,10,15,20 and 30 mm, respectively. The results show that the existence of sidewall leads to the competition mechanism of air entrainment restriction and heat feedback enhancement. When D <= 3 mm, the flame spread will be dominated by the air entrainment, as the sidewall will inhibit the burning; when D > 3 mm, oxygen supply is sufficient, and the sidewall will promote flame spread. Meanwhile, under the influence of the restricted sidewall, the flame merging will be enhanced. As the inner flame height is significantly stretched higher than that of the outer especially at D = 3-5 mm. Finally, a heat transfer model is built to quantitatively analyse the feedback heat fluxes of the gas zone, the solid zone and the sidewall zone. With the larger preheating length for the inner wire, the larger flame spread rate can be well predicted.

This study proposes a novel strategy for the value-added utilization of converter OG sludge by incorporating it as a flame-retardant additive in rigid polyurethane foam (RPUF). A series of RPUF/OG composites were fabricated via a one-step all-water foaming technique. The effects of OG sludge on the thermal stability, combustion behavior, and flame retardant properties of RPUF were systematically investigated using multiple analytical methods, including limiting oxygen index (LOI) test, vertical burning test (UL-94), thermogravimetric analysis (TG), and cone calorimeter test (CCT). The results show that OG sludge can significantly enhance the fire safety of the composites. While traditional metrics like the limiting oxygen index showed limited improvement, CCT results indicate that the peak heat release rate (pHRR), total heat release (THR), and total smoke production (TSP) of the RPUF/OG50 composite decrease significantly by 16.5%, 24.1%, and 43.6%, respectively. This confirms the effectiveness of OG sludge in suppressing fire intensity and smoke generation. TG reveals that OG sludge improves the thermal stability of RPUF composites, with a residual char yield of up to 21.7 wt% at 800°C. Scanning electron microscopy (SEM) and Raman spectroscopy analyses demonstrate that the complex metal oxides in OG sludge enhance the compactness of the char residue of RPUF composites, forming a stable barrier layer that inhibits the transport of heat and substances during the combustion of the composites. This study provides a new approach for the high-value and sustainable utilization of OG sludge, and offers directions for the development of flame-retardant RPUF composites for building thermal insulation applications.

This paper investigated the mutual interaction between two extra-thin line fires under different wind speeds of 0.4, 0.6, 0.8, 1.0 and 1.2m/s by using a small-scale wind tunnel. The experiments involved the spacing distances of 5, 10, 15, 20, 25, 30, 35 and 40 cm, and the heat release rates of 19.4, 25.7 and 32.7 kW, respectively. The results show that the flame merging probability increase, as the wind speed or the heat release rate increases. Compared with the two rectangular or square fires, the flame height and flame length will be smaller at the same heat release rate for the extra-thin line fires. Meanwhile, the line fires will decrease the flame merging, making the downstream flame temperature smaller than that of the upstream at the relatively larger wind speed or heat release rate.The interesting finding is that, with the increase of the heat release rate, the flame inclination angle will increase in the fully merging stage, which is opposite to that of square fires.Correspondingly, the flame merging model is built on the influences of the buoyancy force and inertial force of the horizontal wind,which can give the good explanation on this behavior.

This paper aims to investigate the confined distance near the floor(0 similar to 28 mm) and wire size (the ratios of copper core diameter to entire wire diameter are: 6mm/8 mm,6mm/10 mm, 8mm/12 mm and 6mm/12 mm for type I, type II, type III and type IV, respectively) on the flame spread over polyethylene (PE) wires. It is indicated that, when the confined distance is relatively small, the extinction occurs for all types. The typical parameters of flame shape including of flame width, flame height and flame area, flame spread rate and mass loss rate with the increase of confined distance s can be separated into continuous growth stage and stable fluctuation stage. At the continuous growth stage, the flame area shows an exponential relationship with s as: A similar to s(5/2). And at the stable fluctuation stage, the flame width is larger than that at the unconfined condition accounting for a large portion. While, the flame height is always smaller than that in the unconfined case. In order to explicitly describe the heat transfer, the upward large main flame and downward small flame are firstly introduced in this paper. Correspondingly, the heat flux feedback of components to the preheating zone is established with the upward main flame flux (q) over dot(f)''((up)) [includes of (q) over dot(vf(up))'' + (q) over dot(rf(up))''], the downward small flame heat flux (q) over dot(f(down))'' [includes of (q) over dot(vf) (down)) ''+ (q) over dot(rf(down))''], the conductive heat flux (q) over dot(c)'' and the gypsum board heat flux (q) over dot(g)''. With the increase of s, q(f(down))'' shows an increasing and then decreasing trend, making it take a second role during heat flux feedback. Meanwhile, the analysis demonstrates that for the larger copper core (type III) and the smaller of PE thickness (type I), the ratio of heat flux of (q) over dot(f(down))/(q) over dot(f(up)) +(q) over dot(f(down)) will be increased, which will enhance the heat transfer effect of downward small flame.

This paper investigates the effects of wind speed(V=0.25, 0.5 and 0.75 m/s), length-width ratio(n=5,8,10,15,20,25,30 and 40) and spacing distance(0, 10, 20 and 30 cm) on the burning and flame merging characteristics of two-line fires fueled by n-heptane. Experimental results indicate that the flame merging probability Pm decreases gradually with the increasing length-width ratio. Meanwhile, Pm shows an increasing trend with the groove length(L).The correlation between P m with n and L is found. On the other hand, it is found that,flame height and length decrease with the increasing length-width ratio.The flame height and length of upstream flame are smaller than those of downstream flame for different length-width ratios, at the same n and V. With the length-width ratio increase, the flame inclination angle will increase, and that of upstream flame is consistently smaller than that of downstream flame. Based on heat transfer analysis, under the influence of wind speed, the m '' is closely related to (L+W)/LW, showing an increasing trend with length-width ratio.With the increase of spacing distance, the ṁ '' of downstream flame will be larger, equal and then smaller than that of upstream flame.

System resilience denotes the capacity to uphold desired system performance in the face of disruptions. Evaluating the resilience of a process system necessitates a thorough consideration of the intricate interplay between its components and the pivotal role of process parameters in reflecting the repercussions of disruptions on the system. This paper introduces an integrated methodology that takes into account component interactions and leverages process data for the resilience assessment of a process system. The proposed methodology comprises four key components: system structure analysis, disruption impacts analysis, process simulation, and resilience assessment. Firstly, the system structure is meticulously scrutinized using a P-graph model. This analysis encompasses the assessment of the significance and interplay of components, as well as the evaluation of how component failures affect the system's overall processes. Secondly, a Markov model is devised to examine the state transition process of components and quantifies the maintenance time needed for failed components. Subsequently, a simulation model is formulated to acquire real-time process parameters in the presence of disruptive events. Finally, the system's performance response function (PRF) is derived from the normalization of these process parameters. Building upon this foundation, a resilience assessment is conducted with a focus on the PRF. To illustrate the effectiveness of this methodology, an LNG terminal system is employed as an exemplar.

Stainless steel bolts (SSB) are increasingly utilized in bolted steel connections due to their good mechanical performance and excellent corrosion resistance. Fire accidents, which commonly occur in engineering scenarios, pose a significant threat to the safety of steel frames. The post-fire behavior of SSB has a significant influence on the structural integrity of steel frames, and neglecting the effect of temperature can lead to serious accidents in engineering. Therefore, it is important to evaluate the performance of SSB at elevated temperatures and their residual strength after a fire incident. To investigate the mechanical behavior of SSB after fire, 114 bolts with grades A4-70 and A4-80, manufactured from 316L austenitic stainless steel, were subjected to elevated temperatures ranging from 20 degrees C to 1200 degrees C. Two different cooling methods commonly employed in engineering, namely cooling at ambient temperatures (air cooling) and cooling in water (water cooling), were used to cool the bolts. Tensile tests were performed to examine the influence of elevated temperatures and cooling methods on the mechanical behavior of SSB. The results indicate that the temperature does not significantly affect the Young's modulus and the ultimate strength of SSB. Up to 500 degrees C, the yield strength increases with temperature, but this trend reverses when the temperature exceeds 500 degrees C. In contrast, the ultimate strain shows the opposite trend. The strain hardening exponent is not significantly influenced by the temperature until it reaches 500 degrees C. The cooling methods employed have an insignificant impact on the performance of SSB. When compared to high-strength bolts, 316L austenitic SSB demonstrate superior fire resistance. Design models for the post-fire mechanical behavior of 316L austenitic SSB, encompassing parameters such as the elasticity modulus, yield strength, ultimate strength, ultimate strain, and strain hardening exponent, are proposed, and a more precise stress-strain model is recommended to predict the mechanical behavior of 316L austenitic SSB after a fire incident.