Mohamed Gadalla

Energy and exergy analyses of an integrated fuel cell and absorption cooling system

In this study, we carry out detailed energy and exergy analyses of a PEM fuel cell integrated with triple effect ammonia-water absorption cooling system and investigate the effect of different operating parameters such as pressure, temperature, membrane thickness and current density of the fuel cell on the outputs of the fuel cell, and COP of the cooling system. The results show that fuel cell efficiencies decrease by increasing the current density, temperature, and membrane thickness and increase by increasing cell pressure and cathode stoichiometry. Furthermore, both energetic and exergetic COPs increase with an increase in cell temperature and membrane thickness and decrease with an increase in cell pressure, current density and cathode stoichiometry.

Assessment of solar electricity production in the United Arab Emirates

In this work the possible large-scale integration of photovoltaic (PV) systems and parabolic trough concentrated solar power (CSP) technologies in the United Arab Emirates (UAE) power system is investigated in technical, economic and environmental terms. The analysis takes into account the available solar potential for UAE and in particular for the Emirate of Sharjah. In order to identify the least-cost feasible option for each renewable energy source for power-generation (RES-E) technology, a parametric analysis is carried out by varying each RES-E candidate system capital cost. From the analysis it is evident that an alternative cost-effective technology to the installation of a 50 MWp PV system might be the utilisation of a 50 MWe parabolic trough CSP system with either a 14.5 h thermal storage system or a 24/7 operation. The advantages of the latter are the dispatchability and the increased electricity output due to the utilisation of a thermal storage system, which leads to higher amounts of annual CO2 avoided emissions. However, the electricity selling prices are higher than the current UAE electricity tariffs; therefore, for the promotion of solar RES-E technologies in the UAE, relevant financial supporting mechanisms need to be developed such as feed-in tariffs or feed-in premiums.

Thermodynamic analysis of a pyroprocessing unit of a cement plant: a case study

The cement industry is one of the most intensive energy and cost industries in the world that consumes about 3800 MJ per tonne of cement produced. To achieve an effective energy management scheme, energy and exergy analyses were employed on the pyroprocessing unit of Gaziantep Cement Plant in Turkey. Energy and exergy efficiencies are determined to be 52.2% and 35.9%, respectively. Application of insulation on the unit reduced rate of heat loss from 22.7 MW to 17.3 MW. This in turn increases both the energy and the exergy efficiency values to 63.6% and 47.3%, respectively. The effect of weather conditions on the efficiency values is studied. It is estimated that 1056.7 kW of electricity can be generated by using the waste heat from the unit. The application of waste heat recovery steam generator prevents the emission of 5183 tons of CO2 to the atmosphere, representing a reduction of 8.2%.

On the Performance of Air-Lift Pumps: From Analytical Models to Large Eddy Simulation

The present study investigates a hierarchy of models for predicting the performance of air-lift pumps. Investigated models range from simplified one-dimensional analytical models to large eddy simulation (LES). Numerical results from LES and from two different analytical models are validated against experimental data available from the air-lift pump research program at Alexandria University. Present LES employs the volume of fluid (VOF) method to model the multiphase flow in the riser pipe. In general, LES is shown to provide fairly accurate predictions for the air-lift pump performance. Moreover, numerical flow patterns in the riser pipe are in good qualitative and quantitative agreement with their corresponding experimental patterns and with flow pattern maps available in the literature. On the other hand, analytical models are shown to provide results that are of surprisingly comparable accuracy to LES in terms of predicting the pump performance curve. However, due to the steady one-dimensional nature of these models, they are incapable of providing information about the different flow patterns developing in the riser pipe and the transient nature of the pumping process. [DOI: 10.1115/1.4027473]

Simulation of intermittent thermal compression processes using adsorption technology

Abstract This paper presents a dynamic model to simulate the adsorption–desorption processes associated with intermittent heat pump systems. This simulation plays an important role in sizing the adsorption systems for various types of applications in the design stage. A mathematical model that is based on the control volume approach was first developed and then discretized using the finite difference implicit scheme. The equations for the conservation of mass, momentum, and energy in the bed were derived for high-pressure and low-pressure segments, including the adsorbate (refrigerant), the adsorbent (Linde 13X), and the vessel wall. A pseudo-homogeneous model for the compression system was adopted. The numerical results that describe the adsorption–desorption history were obtained. It was found that the amount of the refrigerant recovered in the desorption process at the end of the cyclic operation is smaller than the amount adsorbed during the adsorption process. This indicates that the time for the regeneration process should be longer than the time for the adsorption process in order to raise the sieve temperature. In order to compare the simulated results with experimental data, numerical values for the heat transfer coefficients were theoretically evaluated. To assure the stability of the simulated results, the incremental time of system operation is kept equal or less than the value obtained from the minimum stability requirement. The simulated results of the temperature distribution history during system operation are in good agreement with the conducted experimental results, which led to the conclusion that the model can be used as an effective tool during the design stage and for the system development.

Performance assessment of an integrated absorption cooling-hydrogen liquefaction system using geothermal energy

An integrated geothermal based triple effect absorption cooling and Linde–Hampson system for hydrogen gas liquefaction is proposed and analysed thermodynamically. The effect of various operating conditions and parameters on the system performance is studied. The results show that the mass of hydrogen gas pre–cooled by the absorption system per unit mass flow rate of geothermal water flowing through the system (n) and the amount of hydrogen liquefied per unit mass flow rate of geothermal water flowing through the system (y) increase with an increase in the geothermal source temperature. Also, both energetic and exergetic coefficients of performance decrease from 1.33 to 0.12 and 0.92 to 0.08, respectively with an increase in the mass flow rate of geothermal water from 1.5 kg/s to 3.0 kg/s. The energetic and exergetic utilisation factors decrease from 0.06 to 0.009 and 0.19 to 0.006, respectively as the mass flow rate of geothermal water increases.

An Investigation into a Small Wind Turbine Blade Design

A small wind turbine blade was designed to be aerodynamically efficient, economical and easy to be manufactured. Aerodynamic analysis was conducted using commercially available software. The aerodynamic analysis suggested laminar flow airfoils to be the most efficient airfoils for such use. Blade geometry was determined after calculating baseline geometric values to have low weight and drag while yielding maximum torque. The blade span was constrained such that the complete wind turbine can be roof-top mountable. The blade was designed without any taper or twist to comply with the low cost and ease of manufacturing requirements. For low cost and favorable strength to weight ratio, fiberglass-epoxy was used as the blade material. Computer simulated structural test results suggested that skin thickness of 1 mm of fiberglass-epoxy can sustain the loads on the blade. The wind turbine blade produces 3.1 N lift with 6.3 N.m torque at 4 m/s wind speed. Since it uses a relatively inexpensive material, fiberglass-epoxy, the cost of the blade is low. Fiberglass-epoxy is also easy to work with hence it contributes towards manufacturing ease. Overall, the research was successful in designing a wind turbine blade that is easy to be manufactured, economical and has high torque.

Improvement in Spiral Heliostat Field Layout Thermo-Economic Performance by Field Zoning Implementation

Arguably, the most complicated and problematic mathematical formulation for solar collectors belongs to the heliostat field collectors. Consequently, extensive researches are carried out in order to develop several codes capable of providing heliostat field analysis and optimization. Noting that most of the aforementioned heliostat field codes are developed based on the radial-staggered field layout which is arguably the most popular and widely implemented heliostat field configuration in the literature. Nevertheless, a ground-breaking heliostat field layout based on the spiral patterns of phyllotaxis discs is recently proposed. It was argued that the transition between the areas with high and low heliostat field density is not continuous in radial-staggered configuration. In a study by the authors, the spiral and radial-staggered field layouts thermo-economic analyses are compared and the results points to the superiority of the radial-staggered layout. Nevertheless, it is believed that utilizing two design variables might be only sufficient for small number of mirrors. Therefore, more design variables must be implemented to fully control different areas of the field for larger capacity heliostat fields. In this paper, spiral field zoning is proposed and its impact on the spiral heliostat field layout performance is assessed. By dividing the heliostat field into multiple zones, each zone is designed with a set of design variables (two design variables: a and b). Consequently, the impacts heliostat field zoning might have on the field thermo-economic performance are investigated.Copyright

Design and Evaluation of a Rooftop Wind Turbine Rotor With Untwisted Blades

A small horizontal axis wind turbine rotor was designed and tested with aerodynamically efficient, economical and easy to manufacture blades. Basic blade aerodynamic analysis was conducted using commercially available software. The blade span was constrained such that the complete wind turbine can be rooftop mountable with the envisioned wind turbine height of around 8 m. The blade was designed without any taper or twist to comply with the low cost and ease of manufacturing requirements. The aerodynamic analysis suggested laminar flow airfoils to be the most efficient airfoils for such use. Using NACA 63-418 airfoil, a rectangular blade geometry was selected with chord length of 0.27[m] and span of 1.52[m]. Glass reinforced plastic was used as the blade material for low cost and favorable strength to weight ratio with a skin thickness of 1[mm]. Because of the resultant velocity changes with respect to the blade span, while the blade is rotating, an optimal installed angle of attack was to be determined. The installed angle of attack was required to produce the highest possible rotation under usual wind speeds while start at relatively low speed. Tests were conducted at multiple wind speeds with blades mounted on free rotating shaft. The turbine was tested for three different installed angles and rotational speeds were recorded. The result showed increase in rotational speed with the increase in blade angle away from the free-stream velocity direction while the start-up speeds were found to be within close range of each other. At the optimal angle was found to be 22° from the plane of rotation. The results seem very promising for a low cost small wind turbine with no twist and taper in the blade. The tests established that non-twisted wind turbine blades, when used for rooftop small wind turbines, can generate useable electrical power for domestic consumption. It also established that, for small wind turbines, non-twisted, non-tapered blades provide an economical yet productive alternative to the existing complex wind turbine blades.Copyright

Performance Improvement of a Simple Gas Turbine Power Station Using Pulse Combustion Technology

The retrofitting projects have been considered in many countries to convert simple gas turbine units into more advanced cycle units with higher efficiency and higher output. Among many proven technologies, such as inlet air cooling, intercooling, regeneration, reheat and steam injection gas turbine etc., pulse combustion is one of the promising technologies in boosting both the output capacity and thermal efficiency, and reducing carbon and nitrogen oxides emissions without additional pollution control equipment. This paper presents the analysis of potential and real benefits of pulse combistion technology applied in the combustion process of a simple gas turbine cycle under different operating conditions. In addition, this study investigates the utilization of converting part of chemical energy of fuel into pressure energy in the gas turbine pulse combustion chamber. The influence of the maximum pressure rise due to pulse combustion (pre-compression parameter), the ratio of combustion heat released in the isochoric process, maximum cycle temperature, and compressor pressure ratio on the performance paramenters such as net work output, cycle thermal efficiency, and fuel consumption were also investigated. Finally, the results of comparative analyses between a simple gas turbine cycle utilizing a pulse combustor and a conventional cycle show the thermodynamic advantages of applying this technology in simple gas turbine power cycles.Copyright