Muhammad Mahabat Khan

Large eddy simulation of a turbulent spray jet generated by high-pressure injection: impact of the in-nozzle flow

ABSTRACT The turbulence properties of a gas spray jet generated through the injection of a high-pressure atomising spray were studied in the context of the Euler–Lagrange formulation using a large eddy simulation (LES) approach. The studys main aim was to investigate nozzle flow effects on flow and turbulence statistics for a two-phase jet flow in the near and far fields of the spray. The study investigated the injection of an existing in-nozzle flow at the spray inlet. Simulation results were compared with measurements obtained for non-evaporating sprays under quasi-steady conditions, which, in practice, correspond to a long-duration injection. Both simulated high-injection pressure cases showed a good agreement with experimental data. A two-stage evolution of the spray was observed. The flow of the gas jet first developed along the spray cone, followed by the appearance of highly vortical structures around and within the spray. Cavitation in the nozzle flow resulted in an observed asymmetry of the generated gas spray jet: on the gas spray jet side of the nozzle (relative to the cavitation side), stronger jet spreading occurred, and droplets were smaller and slower. The spray jet typically exhibited an ellipsoidal cross-sectional shape. The paper provides a characterisation of the asymmetry that persisted for the duration of the spray evolution (at least for the distances considered here).

Performance Investigation of Air Velocity Effects on PV Modules under Controlled Conditions

Junction temperature of PV modules is one of the key parameters on which the performance of PV modules depends. In the present work, an experimental investigation was carried out to analyze the effects of air velocity on the performance of two PV modules, that is, monocrystalline silicon and polycrystalline silicon under the controlled conditions of a wind tunnel in the presence of an artificial solar simulator. The parameters investigated include the surface temperature variation, power output, and efficiency of PV modules under varying air velocity from near zero (indoor lab. conditions) to 15 m/s. Additionally, the results were also determined at two different module angular positions: at 0° angle, that is, parallel to air direction and at 10° angle with the direction of coming air to consider the effects of tilt angles. Afterwards, the thermal analysis of the modules was performed using Ansys-Fluent in which junction temperature and heat flux of modules were determined by applying appropriate boundary conditions, such as air velocity, heat flux, and solar radiation. Finally, the numerical results are compared with the experiment in terms of junction temperatures of modules and good agreement was found. Additionally, the results showed that the maximum module temperature drops by 17.2°C and the module efficiency and power output increased from 10 to 12% with increasing air velocity.

Exergetic optimization and comparison of combined gas turbine supercritical CO2 power cycles

For developing a sustainable power system, the key is to maximize the use of available resources with a minimal impact on the environment. One technique for achieving this is exhaust heat recovery. In this paper, three gas turbine exhaust heat recovery supercritical carbon dioxide combined power cycles are presented. They are combined gas turbine-recompression cycle, combined gas turbine-preheating cycle, and combined gas turbine-simple regenerative cycle. For all the cycles, thermodynamic models are developed and the influence of varying mass flow rates, compression ratio, and mass split/recompression percentages in different components of all three cycles are investigated. Using genetic algorithm, exergetic optimization is done to find the optimal configuration for each cycle. The reduction in CO2 emissions in presented cycles against fossil fuel power cycles is also assessed. Additionally, a comparison with a simple gas turbine (SGT) and an air bottoming combined cycle (ABC) is presented. The results indicate that owing to exhaust exergy recovery, there is a significant improvement in the energetic and exergetic performance of combined gas turbine-supercritical CO2 power cycles compared to that of SGT and ABC. The sum of exergy destruction and exergy loss in the combined cycles is lower as compared to the sum in SGT. The reduction in losses compared to SGT is 22.89% in the case of the combined gas turbine recompression cycle and 35.8% in the case of the combined gas turbine preheating cycle (CGTPHC). Moreover, the energetic and exergetic performances of the bottoming supercritical CO2 recompression cycles (BRECs) are better than those of the bottoming supercritical CO2 preheating cycle owing to lower exergy destruction in the components of BREC. As a result of comparative analysis based on the exergetic performance and environmental impact, the CGTPHC is selected as an appropriate option for gas turbine exhaust exergy recovery.For developing a sustainable power system, the key is to maximize the use of available resources with a minimal impact on the environment. One technique for achieving this is exhaust heat recovery. In this paper, three gas turbine exhaust heat recovery supercritical carbon dioxide combined power cycles are presented. They are combined gas turbine-recompression cycle, combined gas turbine-preheating cycle, and combined gas turbine-simple regenerative cycle. For all the cycles, thermodynamic models are developed and the influence of varying mass flow rates, compression ratio, and mass split/recompression percentages in different components of all three cycles are investigated. Using genetic algorithm, exergetic optimization is done to find the optimal configuration for each cycle. The reduction in CO2 emissions in presented cycles against fossil fuel power cycles is also assessed. Additionally, a comparison with a simple gas turbine (SGT) and an air bottoming combined cycle (ABC) is presented. The results i...