Mahmoud A. Fouad

Efficiency Optimization of a Standing-Wave Thermoacoustic Heat Engine

Thermoacoustic heat engines (TAHE) are capable of producing acoustic energy from any source of heat energy. Thus, the primary energy source to drive the engine could be conventional or unconventional that includes industrial waste heat, solar energy and fossil fuels. It has no moving parts thus; chances of mechanical failure are extremely low. The present work main goal is to demonstrate an optimization process that would yield a better efficiency of thermoacoustic engine model. Computational investigations were carried out to improve the efficiency of a 1.05 meter thermoacoustic heat engine using air at atmospheric pressure and 900 K temperature as the working fluid. The efficiency optimization process was implemented by performing an optimization process of stack parameters, like stack shape (i.e. Rectangular, Honeycomb, Slab, and etc...), stack plates spacing, stack length and stack material. The present optimization process has shown that slab stacks made of Celcor (a Celcor material) demonstrated much better performance than other stack shapes and materials which resist such high temperatures. For a 1.124-meter-long and 0.011 m2 squareshaped resonator tube, a 7.75 cm long slab stack made of Celcor having 0.304 mm-thick-plates, spaced by 0.648 mm, giving a porosity ratio of 0.68067, will theoretically convert heat to acoustic power at an efficiency of 30.611% which is equivalent to 47.97% of Carnot’s efficiency. The paper ends with a brief summary of conclusions.

Effect of Shaped-Hole on Film Cooling Effectiveness of Gas Turbine Blade

Film cooling is vital to gas turbine blades to protect them from high temperatures and hence high thermal stresses. Improvements have been made to the cooling hole shaping of to provide higher heat transfer effectiveness. The present study of the impact of the film cooling turbine to protect from high temperatures through the Parametric study of blowing ratio, stream wise angle and the nature of the surface (concave and convex) on the film cooling effectiveness . In case study, it was taken three stream wise angles of 30, 60 and 90 with three blowing ratios 0.45, 1 and 2, and the sides of the turbine blade concave and convex. Using computational fluid dynamics software FLUENT ® and choosing the standard k-� model. It was concluded that the maximum centerline effectiveness with blowing ratio occurs at stream wise angle 30 on concave, convex and flat plate surface, the optimum blowing ratio on convex shape for

Effect of Fire Locations on the Performance of Impulse Ventilation System in an Underground Car Park

This paper investigates the effect of changing fire locations on the performance of Impulse Ventilation System (IVS) in an underground car park. The number of 40 N jet fans is influenced by different positions of fire source. The tested parameters are backlayering, visibility, temperature and visibility. Fire Dynamic Simulator (FDS) software version 5.5 is utilized to simulate 7 case studies in an 80.1 m long, 40.5 m wide and 3.3 m height domain with a car fire source simulated as a fire with a steady heat release rate of 4 MW resulted from burning polyurethane as a fuel in which soot yield equals 0.1 kg soot/kg fuel. Results show that impulse ventilation system helps in prevention of fire smoke spreading as well as maintaining a good visibility above 5 m at a height of 1.8 m to provide a clear access for fighters. The jet fans are distributed in a way to reduce backlayering and improve visibility. The air velocity inside the car park is maintained below 5 m/s at a height of 1.8 m. However, IVS may cause temperature rise on the downwind zone of fire source with a maximum value of 90 °C (70 °C above the ambient). Dividing the car park into zones assists in reduction of smoke spread inside the parking.

On The Calculations of Flat Plate Film Cooling Effectiveness

Film cooling is vital to gas turbine blades to protect them from high temperatures and hence high thermal stresses. Improvements have been made to the shaping of the cooling hole to provide higher heat transfer effectiveness. The present study of the impact of the film cooling turbine to protect from high temperatures through the Parametric study of blowing ratio , stream wise angle and the shape of hole on the film cooling effectiveness . Has been studied the following cases three blowing ratios 0.45, 1 and 2, the three stream wise angle of 30, 60 and 90 and study the impact of changing of lateral and forward diffusion angles on the hole cooling from 0 to 15 degrees on the film cooling effectiveness on adiabatic tested flat plate. Using computational fluid dynamics software FLUENT ® and choosing the standard k-� model. It was concluded the maximum centerline effectiveness with blowing ratio occurs at stream wise angle 30 on flat plate surface, the optimum blowing ratio for arrow of 30 degree jets is around 0.6, relatively less for a row of 60 degree jets is around 0.5 and relatively less for a row of 90 degree jets around 0.4 and the highest cooling lateral effectiveness is obtained in the case of LFDSA-15-15 with fan-shaped diffuser exists by 15-digree divergence angles on both lateral sides at all blowing ratio. NOMENCLATURE

Energy Modelling of District Cooling Plant in Egypt

Renewable energy resources and solutions are the main concern, nowadays; lack of energy is the future nightmare .The world HVAC associations are implementing codes from the beginning of the design stage for energy savings. The research paper investigates an existing energy problem in a district cooling plant in Egypt. The existing price for electricity is high which affected the price of the ton refrigerant produced by the district cooling plant which is sold to all the buildings in areas of the district .The research investigates and make use of an artificial lake and propose that the lake is a solution as heat sink instead of the existing cooling towers. The methodology for the above research was carried out by site temperature measurement and energy modeling perspective for a sample chiller of the district cooling plant.

Effect of Film cooling of HP and IP turbines on Performance of triple Spool Turbofan Engines

Present and future wide-body airliners (such as the Airbus 350, A380 and Boeing 787) are powered by high bypass ratio (HBPR) turbofan engines. To maximize its thrust force and performance parameters, turbine cooling is a necessity. Air bled from compressor is used for turbine cooling. Such bleed ratio is examined in his work to analyze both its effects on turbine and the overall engine performance. As a case study, three spool mixed and unmixed engine (similar to Trent 700) is examined. Operating conditions are flight Mach of 0.82, altitude 12,000 meters and the maximum temperature ranging from 1500 to 1700 Kelvin. A comparison between two cases of mixed and unmixed turbofan engines is performed. Matlab-7 is used to simulate and analyze thermal cycle of both cases. A case of 8% air bleed is employed for both engines. For uncooled mixed turbofan engine bleed air decreased specific thrust by 0.84% which is negligible compared with the increased maximum temperature of the engine from 1200 to 1700 Kelvin, which led to an increase specific thrust by 25%. Uncooled unmixed turbofan engine bleed air decreases specific thrust by 56% but this depletion increases the temperature of the turbine from 1200 to 1700 K, which increases the thrust by 565%. NOMENCLATURE List of symbols ec A Exit area for the cold stream eh A Exit area for the hot stream b Bleed air , / b le e d m m a o o

Resonator Shape Effect on the Performance of a Standing-Wave Thermoacoustic Heat Engine

This thesis demonstrates an attempt to make a design of an about 1-meter-long thermoacoustic heat engine that has an optimum efficiency. This will be done using DeltaEC, software which was developed especially for low amplitude thermoacoustic devices modeling. The optimization process includes geometrical parameters of the resonator tube and the stack, the working fluid, and the heat input to the engine. The present optimization process has shown that slab stacks made of Celcor (a Ceramic material) demonstrated much better performance than other stack shapes and materials. For a 1.1239-meter-long and 0.011 m2 square-shaped resonator tube, a 7.75 cm long slab stack made of Celcor having 0.304 mm-thickplates, spaced by 0.648 mm, giving a porosity ratio of 0.68067, will theoretically convert heat to acoustic power at an efficiency of 30.611% which is equivalent to 47.97% of Carnot’s efficiency. The thesis ends with a brief summary of conclusions. Thermoacoustics is a branch of science concerned mainly with the conversion of heat energy into sound energy and vice versa. The device that converts heat energy in sound or acoustic work is called thermoacoustic heat engine or prime mover and the device that transfers heat from a low temperature reservoir to a high temperature reservoir by utilizing sound or acoustic work is called thermoacoustic refrigerator. There are several advantages of heat engines based on thermoacoustic technology as compared to the conventional ones. These devices have fewer components with at most one moving component with no sliding seals and no harmful refrigerants or chemicals are required. Air or any inert gas can be used as working fluids which are environmentally friendly. Furthermore, the simple design of the devices reduces the fabrication and maintenance costs. However, significant efforts are needed to bring this technology to maturity and develop competitive thermoacoustic devices. The thermoacoustic (TA) procedure uses a sound wave to achieve local heat exchange between the gas in which it propagates and a solid medium. Heat transfer occurs simultaneously along the length of the solid walls of the structure in which the gas is held. A sound wave is the propagation of a disturbance, the passage of which induces a reversible variation in the local physical properties (temperature, pressure) of the medium in which it propagates. It transports energy, but not matter. The propagation medium undergoes macroscopic displacement in the same direction as the propagating wave, and is therefore a longitudinal wave. The pressure wave causes the volumes of gas to oscillate around a mean value. Thus, half-way through the cycle, the gas is on one side of this mean and is compressed and hot, whereas at the end of the cycle, it is on the other side of the mean and is expanded and cold. If a solid medium, such as a metal plate, is used, this solid medium is likely to accumulate heat or to slow heat transfer. During the phases of compression and expansion, heat is exchanged with the wall, generating a difference in temperature between the two ends. In this study, four different resonator shapes are investigated and compared for a thermoacoustic heat engine of 1.12 m length to select the resonator shape that gives the best efficiency of the device. The selected shape will then undergo some changes in the geometrical parameters in order to obtain further performance enhancement.

Comparative Study of Air Distribution systems in Offices: Flow Regime, Thermal Pattern

Comparative Study of Air Distribution systems in Offices: Flow Regime, Thermal Pattern George S. Youanas, Essam E. Khalil and Mahmoud A. Fouad, Department of Mechanical Power Engineering, Faculty of Engineering, Cairo University, Giza, Egypt, khalile1@asme.org Abstract The objective of this paper is to find the most efficient ventilation system to be used in an office room to give best temperature and velocity distribution for the same boundary and initial conditions. This is done by doing a comparison between different ventilation systems namely: mixing ventilation, displacement ventilation in which Under Floor Air Distribution UFAD is used, a combination of UFAD and Personalized Ventilation PV and a combination between mixing ventilation and chilled ceiling CC to see which of them gives the best air distribution in an office room. This office room is constructed in two different layouts. Layout 1 has two workstations located in the middle of the room and separated by a low-level partition, while Layout 2 has a low level-partition which separates the room into two volumes with one workstation at each corner. This is also another means of comparison to the see the impact of changing the layout on air distribution for each of the previously mentioned ventilation systems. The model built is of 6.6 m (L) × 3.7 m (W) × 2.6 m (H) dimensions used GAMBIT software to draw and mesh. Computational Fluid Dynamics CFD is used for it is easier and less time consuming than experimental testing, it is also validated with experimental data to be confident with the results. FLUENT software is used with Re-Normalization Group k– epsilon model. In general, the combination of the UFAD and PV gave the best velocity and temperature distribution and did not differ for both layout 1 and layout 2 as it directs the air flow to control properties in the micro-environment surrounding the occupant. Exactly the opposite happened with the mixing ventilation as the air distribution in it is not symmetric and great differences between the two layouts. Adding chilled ceiling to mixing ventilation did not affect much the air distribution but it did affect temperature distribution by making it more symmetrical.