Flame propagation and burning rates of methane-air mixtures using schlieren photography

Different methodology have been shown to produce different results for Markstein length and laminar burning velocity of methane-air mixture. This study attempts to determine the aforesaid parameters using the newly developed closed vessel combustion chamber with Schlieren photography. Markstein length and burning rate of methane-air mixture was determined under the initial pressure of 1 atm, temperature range of 298-302K and equivalence ratio range of 0.7-1.3. Experiments were performed in a centrally ignited 29.16L cylindrical constant volume combustion chamber. Ignition energy was set at 25mJ for each experiment. The images of spherically expanding flame were recorded using Schlieren photography technique at a speed of 2000 frame per second. Analysis of the flame area yield flame radii from which the flame speed and stretch rate could be obtained. These parameters would allow the determination of Markstein length and burning rate of the flame. Results show that Markstein length magnitude increases proportionally with equivalence ratio with a magnitude ranging from 0.125cm to 0.245cm. Maximum burning rate occurs at equivalence ratio of 1.1 with a magnitude of 0.366 m/s. Flame of each equivalence ratio also exhibits fluctuation arising from acoustic disturbance. This disturbance becomes more apparent at higher equivalence ratio

Cigarette smoking cessation increases plasma levels of several antioxidant micronutrients and improves resistance towards oxidative challenge

Cigarette smoking is associated epidemiologically with increased risk of cardiovascular diseases, but the pathophysiological mechanisms are still not fully understood. There is evidence that smoking is related to increased free radical production and antioxidant depletion, but the effects of smoking cessation on plasma concentrations of antioxidants and susceptibility to oxidative stress are largely unknown. Plasma levels of vitamins A, C, E, uric acid, total thiols, carotenoids (including lutein, zeaxanthin, β-cryptoxanthin, lycopene, α- and β-carotene) and malondialdehyde (MDA, a biomarker of lipid peroxidation) were measured in fifteen healthy, normolipidaemic subjects (seven males, eight females, 35·2 (sd2·3) years) before and 4 weeks after smoking cessation. To determine plasma resistance towards oxidative challenge, plasma was incubated for up to 5h with the peroxyl radical-generator 2,2′-azobis(2-amidinopropane) (AAPH); MDA and ascorbate levels were measured at various time points. The concentrations of all plasma antioxidants were lower before smoking cessation than afterwards; MDA levels were higher before than after termination of smoking. Upon AAPH exposure, the consumption of plasma ascorbate and the production of MDA occurred at a significantly faster rate before smoking cessation as compared with afterwards. Cigarette smoking cessation is followed by a marked increase in plasma antioxidant concentrations and substantially improves plasma resistance towards oxidative challenge. Given the importance of cigarette smoking as a risk factor for cardiovascular diseases and the pathophysiological role played by oxidative stress in these illnesses, quitting smoking represents an irreplaceable preventive strategy against tobacco-induced oxidative stress and vascular damage

Numerical evaluation of thermo-hydraulic performance in fin-and-tube compact heat exchangers with different tube cross-sections

This study examined numericallythe Thermal-hydrodynamic properties of airflow in the fin-and-tube compact heat exchangers (FTCHEs) with considering different shapes of tubes in lowReynoldsnumbers. The influence of applying flat, oval and circular tube adjustments on the thermal and hydraulic characteristics of air flow were analyzed on the in-line tube arrangements. Establishing standard conditions, the study compared different geometries based on circular tubes of 10.459 mm diameter tubes with 25.4 mm longitudinal pitches and 25.4 mm transverse pitches. The other geometries of tubes were assumed in a stable and constant state preparing the same heat transfer surface area per unit volume as that of the nominal case. The results showed that the FTCHE with flat tubes gives the best area goodness factor (j/f) with in a certainrange of Reynoldsnumbers. In addition, FTCHE with flat tubes shown the best thermo-hydraulic performance and a significant augmentation of up to 10.83% and 35.63% in the average area goodness factor achieved accompanied by a decrease in the average friction factor of 17.02% and 43.41% in the flat tube case compared to the oval and circle tube shapes, respectively. It is concluded that the average area goodness factorfor the oval tube is about 25.04% higher than that of the circular tube, while the average friction factor for the oval tube is about 26.9% lower than that of the circular tube. This means that the flat tube has a better-combined thermal-hydraulic performance than the oval and circle tube

Influence of modified air on combustion characteristics in meso-scale vortex combustor

The need to supply power for miniaturized mechanical devices opens exciting new opportunities for combustion, especially in the field of micro-power generation. Because of the need for power supply devices with high-specific energy (small-size, low weight, long duration) and power. Meso/micro scale combustion has been considered as a potential solution for many small-volumes and energy demanding systems, such as power supplies for portable device. In this study the structure of turbulent diffusion flames in a meso scale combustor with different oxygen concentration has been investigated using a new design of vortex combustor. Methane gas was used as a fuel. Numerical investigations have been performed on the temperature distribution, swirl number, heat loss, and emitter efficiency in vortex combustion. The results have been obtained for various O2 concentrations in the air as oxidizer. The results shows that thermal flame behaves depend strongly on the oxygen content in the oxidizer. When the oxygen concentration increases from 15% to 30%, the flame temperature of the meso-combustion rises in all cases. Emitter efficiency is very high in the meso-combustor with high O2 concentration in oxidizer

Determine physical properties of an organic citric acid (processed lime juice) dissolve with water using experimental apparatus

This paper describes experimental studies on the physical properties of processed lime juice to dissolve with water. Lime juice as known as organic citric acid have many advantages in our life especially in food industries, pharmaceutical industries, anticancer and antioxidant and cleaning agent. Physical properties of liquid include pH, viscosity, density, molar mass and surface tension. This Study conducted using common laboratory apparatus such as Pycnometer, the pH device (HI 9811 pH), Viscolite700 etc. The additional organic citric acid by percentage in water was changed the physical properties of liquids. The future strategy of this research is to introduce organic lime juice mixed with water in spray system as cleaning agent, reduce air pollution and reduce water consumption for Commercial Restaurant Equipment

Characteristic study of flat spray nozzle by using Particle Image Velocimetry (PIV) and ANSYS simulation method

Water mist sprays are used in wide range of application. However it is depend to the spray characteristic to suit the particular application. This project studies the water droplet velocity and penetration angle generated by new development mist spray with a flat spray pattern. This research conducted into two part which are experimental and simulation section. The experimental was conducted by using particle image velocimetry (PIV) method, ANSYS software was used as tools for simulation section meanwhile image J software was used to measure the penetration angle. Three different of combination pressure of air and water were tested which are 1 bar (case A), 2 bar (case B) and 3 bar (case C). The flat spray generated by the new development nozzle was examined at 9cm vertical line from 8cm of the nozzle orifice. The result provided in the detailed analysis shows that the trend of graph velocity versus distance gives the good agreement within simulation and experiment for all the pressure combination. As the water and air pressure increased from 1 bar to 2 bar, the velocity and angle penetration also increased, however for case 3 which run under 3 bar condition, the water droplet velocity generated increased but the angle penetration is decreased. All the data then validated by calculate the error between experiment and simulation. By comparing the simulation data to the experiment data for all the cases, the standard deviation for this case A, case B and case C relatively small which are 5.444, 0.8242 and 6.4023

Study the velocity and pressure exerted in front of the filter surface in the kitchen hood system by using ANSYS

Commercial kitchen hood ventilation system is a device used to capture and filtered the plumes from cooking activities in the kitchen area. Nowadays, it is very popular in the industrial sector such as restaurant and hotel to provide hygiene food. This study focused at the KSA filter part which installed in the kitchen hood system, the purpose of this study is to identify the critical region which indicated by observing the velocity and pressure of plumes exerted at of KSA filter. It is important to know the critical location of the KSA filter in order to install the nozzle which will helps increase the filtration effectiveness. The ANSYS 16.1 (FLUENT) software as a tool used to simulate the kitchen hood systems which consist of KSA filter. The commercial kitchen hood system model has a dimension 700 mm width, 1600 mm length and 555 mm height. The system has two inlets and one outlet. The velocity of the plumes is set to be 0.235m/s and the velocity of the inlet capture jet is set to be 1.078m/s. The KSA filter is placed 45 degree from the y axis. The result shows the plumes has more tendency flowing pass through at the bottom part of KSA filter