Digital Repository for Faculty of Science

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. arabic 11 English 64
Adel Diyaf, Hesham Baej, Adel Akair, Salem Adeilla, Abdurahman Kraiem(9-2018)

Due to the global concerns on the depletion of fossil fuels and the negative effect of their use in environmental pollution and climate change, renewable energy resources are increasingly in demand. Global solar power generation has almost doubled during the last 2 years with countries, such as China, leading the way with huge investments. The first generation of solar cells are either single or multi crystalline silicon, and still have 59% market share; the second (amorphous silicon, copper indium gallium selenide, and cadmium telluride) is approaching in terms of cost and efficiency; and the third (dye sensitized solar cells, organic photovoltaic, quantum dots, and perovskite) all show promise yet are still to come to market. However, future solar cells (using copper oxide and zinc oxide) featuring the regular intrusion of one junction layer into the other in order to massively improve junction contact area are of particular promise. arabic 7 English 50
Adel Diyaf, Yahya Alajlani, Abed Alaswad, Frank Placido, Des Gibson(1-2018)

In this paper, considers a solution of Maxwell's curl equations by using the finite-difference time-domain (FDTD) method. We simulated electromagnetic waves propagation in free space. The electric and magnetic fields generated in two cases to make a comparison between the models. All models were computed using the same parameters. This study showed that the intensities of the fields affected when adding three excited sources pointed in three locations. However, it was noted that three sources placed in the same location improved the distributions of the fields. Therefore, this difference in excitation position leads to change the image intensity distribution. arabic 7 English 43
Adel G Diyaf, Sedig S. Farhat(4-2017)

Hybrid photovoltaic cells take the advantages of silicon in charge carrier separation and transport and organic dyes in strong complementary light absorption. Photovoltaic responses from a set of hybrid solar cells based on amorphous silicon and phthalocyanine dyes of double- or triple-layer heterojunction structures were investigated, which were found to have thickness dependence with the organic active layers. It was found that the photocurrent contributions from organic layers are limited, although they are strong light absorbers. The main photocurrent contributions are from the silicon counterpart. arabic 13 English 111
Adel Diyaf, Huan Zhao, Zhiqun He, Xiaojin Zhang, Zhi Zhang, John I B Wilson, Anna H N Lind(4-2015)

Integrating photonic microstructures into organic light-emitting diodes (OLEDs) has been a widely used strategy to improve their light out-coupling efficiency. However, there is still a need for optical modelling methods which quantitatively characterise the spatial emission pattern of microstructured OLEDs. In this paper, we demonstrate such rigorous calculation using the reciprocity theorem. The calculation of the emission intensity at each direction in the far field can be simplified into only two simple calculations of an incident plane wave propagating from the far field into a single cell of the periodic structure. The emission from microstructured OLED devices with three different grating periods was calculated as a test of the approach, and the calculated results were in good agreement with experiment. This optical modelling method is a useful calculation tool to investigate and control the spatial emission pattern of microstructured OLEDs. arabic 12 English 89
Adel Diyaf, Emiliano R. Martins, John I.B. Wilson, Graham A. Turnbull, Ifor D.W. Samuel, (7-2015)

Amorphous undoped intrinsic silicon, B-doped silicon and P-doped silicon hybrid bilayer structures with poly(3-hexylthiophene) have been fabricated and their photovoltaic responses have been investigated. Open-circuit voltages and fill factors of the devices are moderate, but strongly dependent on the doping type of a-Si:H films. The highest available open-circuit voltage from the hybrid solar cells within this investigation is 1.23 V in a standard test condition. Both inorganic and organic semiconducting layers contribute to the photocurrent generation. The short-circuit currents appear to be limited by unbalanced charged carriers collected from different sides of the semiconductors, which indicates a way forward in device optimization. arabic 9 English 56
Adel Diyaf, Zhiqun He, John I.B. Wilson, Anna H.N. Lind, Ying Peng, Zhi Zhang(9-2013)

A series of uniform polymer/amorphous silicon hybrid structures have been fabricated by means of solution-casting for polymer and radio frequency excited plasma enhanced chemical vapour deposition for amorphous silicon (a-Si:H). Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) functioned as a photoactive donor, while the silicon layer acted as an acceptor. It is found that matching the hole mobility of the polymer to the electron mobility of amorphous silicon is critical to improve the photovoltaic performance from hybrid cells. A three-layer p-i-n structure of ITO/PEDOT:PSS(200 nm)/i-Si(450 nm)/n-Si(200 nm)/Al with a power conversion efficiency of 4.78% under a standard test condition was achieved. arabic 11 English 61
Adel Diyaf, Zhiqun He, John I. B. Wilson, Ying Peng(3-2014)

In the present work, the authors have studied conductive surfaces on polyester fabrics by using two types of commercially available conductive polymers; polyaniline and poly (3,4-ethylenedioxythiophene)-poly (styrenesulphonate) (PEDOT: PSS) with 100 nm aluminium thin film evaporated on top of the polymer so the fabric becomes a conductive substrate for inorganic thin film solar cells. Conductive polymer surfaces on woven polyester fabrics were obtained by knife-over-table coating technique. Surface resistivities for polyaniline and PEDOT: PSS coated fabrics were measured and found in the range of 400 × 103 and 1 × 103 Ω/□, respectively. Thermal stability tests were carried out to evaluate the effect of specific periods of heal treatment at different elevated temperatures on resistance of polymer coated conducting textiles. PEDOT: PSS exhibited better stability than panipol. According to long term tests, PEDOT: PSS coated samples showed improvement in conductivity over 3 days whereas panipol showed the opposite. Transmission Line Model tests were performed to measure aluminium/polymer contact resistances which were found to be 120 × 103 Ω for polyaniline and about 46.3 Ω for PEDOT: PSS. Mechanical bending tests for aluminium/PEDOT: PSS/fabric samples showed that the polymer can maintain the conductivity of samples by bridging micro-cracks in the metal film. arabic 10 English 59
Adel G A Diyaf, John Wilson, Robert R. Mather(1-2014)