A B S T R A C T

Swirl stabilised combustion is one of the most successful technologies for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity

region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. The complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The

problem is even more acute when alternative fuels are used for flexible operation.

Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using isothermal case to recognize the the behavers of swirl.

The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by both the shear layer surrounding the Central

Recirculation Zones (CRZ) and outlet configurations.

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Abstract—Solar water heaters are used widely in places where solar energy is abundant. However, thermal energy storage systems are required due to the availability of solar energy only during day-time. The solution to this need is to design a thermal storage system with PCMs to provide hot water for domestic usage during night-time. This paper aims to provide a numerical simulation of the storage tank using ANSYS software, in which phase change materials are being utilized to find alternative ways to improve the thermal efficiency of hot water tanks. The factors that increase this efficiency, such as improving the thermal conductivity of paraffin wax using Encapsulated Phase Change Materials (PCMs) as spheres around the heat exchanger and the time for melting and solidification will be studied

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Abstract

Lean premixed swirl stabilized combustion is one of the most successful technologies for NOx reduction in gas turbines. The creation of inherent coherent structures such as recirculation zones is one of the main advantages of these flow-stabilized systems since these zones create regions of low velocity that allow heat transfer improvement between reactants and products while increasing residence time for unburned species. However, these effects can also affect the stability of the flame under lean conditions, with various instabilities that can appear during the combustion stage such as flashback, blowoff, autoignition, etc. These processes are even more complex when new alternative fuels are being used for power generation applications. Synthesis gases (syngas) are some of the most concerning out of the available range of fuels as their heating values, flame speeds, ignition energies, etc. are highly dependent on the combination of species that comprise them. Since new gas turbines need to deal with these new blends for fuel flexibility and current lean premixed swirled stabilized systems seem to be the most cost effective-technical option to keep NOx down, gas turbine designers need more information on how to properly design their equipment to achieve stable flames with low NOx whilst avoiding instabilities.

Therefore, this paper presents a study using numerical and experimental analyses to provide guidance on the use of CH4/H2/CO blends in tangential swirl burners. Methane content was decreased from 50% to 10% (volume) with the remaining amount being split equally between carbon monoxide and hydrogen. Ambient temperature conditions were assessed using a swirl number close to 1.0. Particle Image Velocity was used to experimentally validate numerical predictions and determine features of the coherent structures affecting the flame close to the nozzle. Modelling was carried out employing the k-ω SST turbulence model, providing more information about the impact of these structures and the flame turbulent nature close to blowoff limits. The study emphasizes the analysis of various nozzles with different angles and how these geometrical changes at the outlet of the swirl chamber affect the onset of blowoff. Recommendations on the use of RANS CFD modelling are provided on the basis of blend composition.

Abstract

Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions. 

Abstract

This paper provides a CFD comparison of tow turbulence modeling approaches (SST) and (K-epsilon), with application to the simulation of a teardrop. As well as, the study investigates and compares among 3 different models in a range these types in order to assess the suitability of CFD for use when calculating drag co-efficient. Moreover, the study focuses on 3 different velocities to be impacted with the drag co-efficient. Whereas, the pressure over the body was used to calculate the drag co-efficient for each of the 3 teardrops shapes.

This paper presents the dynamic crushing performance of corrugated composite plate with different profiles. Samples of sinusoidal, square, and triangular corrugated profiles were experimentally tested. They were subjected to axial impact load. A weight of 10.5 kg have been freely dropped from a height of 1m, 2m, and 3m. The idea is to understand the effect of corrugation geometry on energy absorption performance. All specimens have been manufactured by hand lay-up technique using woven roving E-glass fabric and polyester resin with six layers. Similar specimens have been tested before under the effect of quasi-static compression load. Quasi–static testing is simpler and less expensive than dynamic testing and facilities are more readily available. Quasi–static can provide good qualitative assessment as to the trend of different variables upon energy absorption. However, for useful design data, dynamic testing is essential to determine a quantitative measure of energy absorption. Results obtained from dynamic tests conducted showed that corrugation profile has high effect on energy absorption capability. It is also observed that, specimens of square profile recorded the highest capability of energy absorption characteristics compared with sinusoidal and triangular profiles. This result came exactly in conformity with the results of quasi-static load applied on similar specimen that performed in a previous research.

The quality requirements for concrete reinforcement have increased interest in optimizing the mechanical properties of reinforcing bars used for the construction of all types of structures such as buildings, bridges and other constructions. The variability of mechanical properties of reinforcing steel bars manufactured from scrap metals by local manufacturers in Libya have been investigated in this paper. Sydee-Assayh Steel Factory (SASF) is one of the private steel factories established recently in Libya. This factory uses mainly scrap metals as raw material. This was motivated by the fact that it has been noticed that the use of the substandard reinforcing bars in construction industry could lead to collapse of the structures reinforced with these bars in many developing countries. Therefore a series of experimental tests were conducted to find mechanical properties of Sydee-Assyh Steel Factory products. Steel rods samples of 12mm and 14mm diameter were selected randomly and tested. Results found were compared with Libyan specifications (LNS-75) and ASTM standard (A-615), and found almost satisfactory.

Due to the increased rate of failure of wind generators, condition-monitoring system plays a significant role in overcoming failures resulting from the harsh operation conditions. The mathematical, thermal, and electrical analyses may be utilized to detect the faults of wind generators by monitoring the changes in their characteristics under different operation conditions. The behavior of the rotating permanent magnet of the generator can indicate the wind generator’s condition. For instance, the torque of the permanent magnet of the generator is affected by the oscillation of the magnet temperature. Therefore, monitoring the torque of the permanent magnet with respect to the rate of change in the permanent magnet temperature defines the generator health. Furthermore, the rate of change in the generator temperature is considered an additional indicator to define the health of the wind generators with respect to the induced electrical torque. That is because of the negative effect of the elevated generator temperature on the induced electrical torque. In this study, a different methodology has been adopted to implement a proper condition monitoring system on the wind generators by evaluating the rate of change in the generator temperature and permanent magnet temperature with respect to the induced electrical torque and the

.driving torque of the rotating permanent magnet under different operation conditions.

A case study, which is based upon collected data from actual measurements, is presented in this work in order to demonstrate the adequacy of the proposed model.