Experimental study on flame propagation in a straight pipe

Flame propagation in a closed pipe with diameter 0.1 m and 5.1 m long, as well as length to diameter ratio (L/D) of 51, was studied experimentally. Hydrogen/air, acetylene/air and methane/air with stoichiometric concentration were used to observe the trend of flame propagation throughout the pipe. Experimental work was carried out at operating condition: pressure 1 atm and temperature 273 K. Results showed that all fuels are having a consistent trend of flame propagation in one-half of the total pipe length in which the acceleration is due to the piston-like effect. Beyond the point, fuel reactivity and tulip phenomenon were considered to lead the flame being quenched and decrease the overpressures drastically. The maximum overpressure for all fuels are approximately 1.5, 7, 8.5 barg for methane, hydrogen, and acetylene indicating that acetylene explosion is more severe

Numerical investigation on flame propagation in vented gas explosion

Explosion venting technology is one of the effective and widely used methods in protection measures against accidental internal gas explosions by relieving the pressure generated within the volume. Extensive studies have been carried out to investigate factors governing to the explosion development i.e. ignition position and vent burst pressure. However, the physical and dynamic process of explosion development during the venting to ambient air is yet not well understood. The primary motivation of this research was to gain improved understanding of turbulent flame propagation in vented gas explosion, with a view to develop improved models and methods for assessing explosion risks in the process industries. Computational Fluid Dynamic (CFD) analyses using FLUENT is adopted to study the phenomenology underlying vented gas explosions. Computations were run on deflagrating turbulent flames in small-scale combustion chambers with two different volumes (0.02 m3 and 0.0065 m3), with both closed at the rear end and open at the opposite face, in order to replicate the experimental work. All cases are initialised from stagnation. Only stoichiometric concentration of propane and methane-Air mixtures was considered with different ignition positions and vent static burst pressure, Pv. From the finding, end ignition gave higher reduced overpressure on both experimental and simulation results, compared to central ignition. The inclusion of vents in the enclosures provides significant reduction on the peak overpressures. However, it has been recognised on a tendency to a less effective reduction as the vent burst pressure, Pv was further increased. The competition between combustion rate and venting rate allows the explanation on both number and intensity of the overpressure peaks observed in propane-Air explosion

Hydrophilicity enhancement of metal oxide nanoparticles incorporated polysulfone ultrafiltration membrane

Hydrophilicity property of membrane is a crucial feature in preventing fouling by most organic components including proteins. In this work, two different metal oxide nanoparticles were selected and their effects on hydrophilicity of polysulfone (PSf) flat sheet membrane for ultrafiltration were investigated. Addition of copper oxide (CuO) and iron oxide (Fe2O3) of 0.25 wt% concentration in N-methyl-2-pyrrolidone (NMP) were also compared to a neat PSf membrane. The membranes were prepared via dry-wet phase inversion technique with 18 wt% of PSf with 5 wt% polyvinylpyrrolidone (PVP). The physical and chemical properties of the prepared membranes were observed by contact angle measurements, porosity, average pore size and scanning electron microscope (SEM). The membranes permeation performance was also examined in term of pure water flux (PWF) and protein rejection by using bovine serum albumin (BSA) solution. Contact angle value of CuO/PSf obtained was 67.1° that was lower than the neat PSf membrane of 87.9° whereas 68.1° for Fe2O3/PSf indicating that metal oxides addition did enhance the membrane hydrophilicity with CuO was slightly better than Fe2O3. The reduction in contact angle ensured that the pure water flux through the membrane with metal oxide additive would improve as well. For CuO, the PWF increased to 159.3 Lm-2hr-1 from 81.3 Lm-2hr-1 of neat PSf, while Fe2O3 showed the PWF at 93.4 Lm-2hr-1. Morphological analyses displayed asymmetric membranes with narrow finger-like structure were formed in this study. A well-formed dense top layer indicated that the membrane would possess good BSA rejection property with 92% of rejection achieved by CuO/PSf membrane. The incorporation of nanoparticles with the membrane is proven to be an effective mean to increase the membrane hydrophilicity with improved water flux and BSA rejection

Simulation of erosion rate in a reducer for liquid-solid flow system using computational fluid dynamics (CFD)

This research aims to simulate the influences of flow parameters such as particles size, stream velocities, and outlet reducer diameter on the erosion rate for a reducer in light crude oil (C19H30)-solid (sand) flow system. A commercially accessible ANSYS Fluent 2020 R1 (Academic Version)-computational fluid dynamics (CFD) was applied to numerically simulate the erosion rate in the reducer. Three separate models were used in the CFD approach called as a continuous flow modelling, Lagrangian particle tracking, and empirical erosion equation. The simulated parameters covered 100 - 500 μm particles size, 3 - 7 m/s stream velocities and 0.0762 - 0.1778 m outlet reducer diameter. It was found that the maximum erosion rate increased with the increasing size of the particles and stream velocities and decreased with the increasing of the outlet reducer diameter. For all the simulated parameters, the location of maximum erosion rate was found to be at the outlet location of the reducer except for the reducer with the diameter larger than 0.1270 m whereby it is located at the inlet location of reducer

Nanometal dust explosion in confined vessel: combustion and kinetic analysis

Extensive application of metal powder, particularly in nanosize could potentially lead to catastrophic dust explosion, due to their pyrophoric behavior, ignition sensitivity, and explosivity. To assess the appropriate measures preventing accidental metal dust explosions, it is vital to understand the physicochemical properties of the metal dust and their kinetic mechanism. In this work, explosion severity of aluminum and silver powder, which can be encountered in a passivated emitter and rear contact (PERC) solar cell, was explored in a 0.0012 m3 cylindrical vessel, by varying the particle size and powder concentration. The Pmax and dP/dtmax values of metal powder were demonstrated to increase with decreasing particle size. Additionally, it was found that the explosion severity of silver powder was lower than that of aluminum powder due to the more apparent agglomeration effect of silver particles. The reduction on the specific surface area attributed to the particles' agglomeration affects the oxidation reaction of the metal powder, as illustrated in the thermogravimetric (TG) curves. A sluggish oxidation reaction was demonstrated in the TG curve of silver powder, which is contradicted with aluminum powder. From the X-ray photoelectron spectroscopy (XPS) analysis, it is inferred that silver powder exhibited two reactions in which the dominant reaction produced Ag and the other reaction formed Ag2O. Meanwhile, for aluminum powder, explosion products only comprise Al2O3

Effect of pipe size on acetylene flame propagation in a closed straight pipe

The understanding of flame propagation mechanism in a tube or pipe as a function of scale is needed to describe explosion severity. Acetylene is an explosively unstable gas and will lead to a violent explosion when ignited. To achieve the goal, an experimental study of premixed acetylene/air mixture at stoichiometry concentration was carried out in a closed straight pipe with different sizes of L/D (ratio of length to diameter) to examine the flame propagation mechanism. Pipes with L/D=40 and 51 were used. From the results, it was found that the smaller pipe with L/D=40 enhanced the explosion severity by a factor of 1.4 as compared to that of the bigger pipe with L/D=51. The compression effect at the end of the pipe plays an important role to attenuate the burning rate, leading to higher flame speeds and hence, increases the overpressure. In the case of L/D=40, the compression effect is more severe due to the larger expansion ratio, and this phenomenon would decrease the quenching effect and subsequently promote flame acceleration. Fast flame speeds of up to 600 m/s were measured in the smaller pipe during explosion development. From the results, it can be seen that the compression effect plays a major role in contributing to the higher burning rate and affects the overall explosion and flame speed development. Furthermore, the compression effect is more severe in the smaller pipe that leads to the detonation-like event. This mechanism and data are useful to design a safety device to minimise explosion severity

Preliminary study on food-based dust explosion: Effect of physicochemical properties & thermal behaviour

Severe dust explosions occur frequently in the food processing industry, and explosion damage increases with the rate of flame propagation in pipes or plants. It is important for the food industry to recognize the potential hazards associated with food-based dust explosions. Appropriate investments are required to achieve sustainable industrial development and operational safety. In this study, the effect of the physicochemical properties of brown rice and tea powder on the severity of dust explosions was investigated over a size range of 1–138 µm. Thermogravimetric analysis (TGA) was applied to determine the physicochemical properties of the samples. Results showed that volatility, moisture content, and fixed carbon had a significant effect on the combustion. Brown rice, with a lower moisture content (6.52 wt%) and higher volatile matter (71.7 wt%) compared to tea powder, exhibited a higher explosion pressure (16.50 bar) and rate of pressure rise (95.0 bar/s). The lower moisture and fixed carbon content, combined with a higher volatile matter content, make it highly reactive in combustion. Its dryness also meant less agglomeration which contributed to its higher explosion pressure. It was observed that the physicochemical properties of the dust had a significant effect on the severity of the ensuing dust explosions. While there is a general understanding of the factors that contribute to dust explosions, there may be specific types of dust or mixtures of dust that require further study. Understanding the specific characteristics and behavior of these types of dust can inform safety guidelines and best practices for handling and processing them

Entropy analysis on convective film flow of power-law fluid with nanoparticles along an inclined plate

Entropy generation in a two-dimensional steady laminar thin film convection flow of a non-Newtonian nanofluid (Ostwald-de-Waele-type power-law fluid with embedded nanoparticles) along an inclined plate is examined theoretically. A revised Buongiorno model is adopted for nanoscale effects, which includes the effects of the Brownian motion and thermophoresis. The nanofluid particle fraction on the boundary is passively rather than actively controlled. A convective boundary condition is employed. The local nonsimilarity method is used to solve the dimensionless nonlinear system of governing equations. Validation with earlier published results is included. A decrease in entropy generation is induced due to fluid friction associated with an increasing value of the rheological power-law index. The Brownian motion of nanoparticles enhances thermal convection via the enhanced transport of heat in microconvection surrounding individual nanoparticles. A higher convective parameter implies more intense convective heating of the plate, which increases the temperature gradient. An increase in the thermophoresis parameter decreases the nanoparticle volume fraction near the wall and increases it further from the wall. Entropy generation is also reduced with enhancement of the thermophoresis effect throughout the boundary layer

Experimental study on premixed flame acceleration in closed pipe

An experimental study has been carried out to investigate the flame acceleration in closed pipe. A horizontal steel pipe, with 2 m long and 0.1 m diameter, giving length to diameter (L/D) ratio of 20 was used in this project. For test with 90 degree bends, the bend has a radius of 0.1 m and added a further 1 m to the length of the pipe (based on the centerline length of the segment). Ignition was affected at one end of the vessel while the other end was closed. Natural gas/oxygen mixtures were studied with equivalence ratio, Ф ranges from 0.5 to 1.8. It was demonstrated that bending pipe gave three times higher in overpressure (5.5 bars) compared to 2.0 bars of straight pipe. It is also shown that the flame speed is 63 m s-1, greater by factor of ~ 3 for explosion in bending pipe in comparison with straight pipe (23 m s-1). This is due to bending acting similar to obstacles. This mechanism could induce and create more turbulence, initiating the combustion of unburned pocket at the corner region, causing high mass burning rate and hence, increasing the flame speed