Iyad Al-Zaharnah

A New Study for Hybrid PV/Wind off-Grid Power Generation Systems with the Comparison of Results from Homer

This article presents the development of a computational model for the sizing optimization of an off-grid hybrid solar wind electric power generation system. The model includes a PV model, wind power model, and a model for the required battery. The developed mathematical model also comprises a model for a diesel generator as an alternative for the storage battery. A simulation code has been developed using MATLAB to solve the mathematical model and simulate the performance of the hybrid system with different configuration for performance analysis and optimal sizing purpose. The mathematical model and the computer code have been developed using a general approach. This approach can be used to simulate, analyze and optimize any hybrid solar/wind/battery/diesel off-grid electric power generation systems. Also, it can be utilized for any remote area in the world depending on the weather data used as input to the developed simulation code. The results obtained via the presently developed model and code have been validated against previously published work and also against that obtained via the widely used software (HOMER). The model is used for the sizing optimization and assessment of a hybrid solar wind system based on the weather conditions for Dhahran city in the eastern province of the Kingdom of Saudi Arabia.

Thermal Analysis in Pipe Flow: Influence of Variable Viscosity on Entropy Generation

Flow through pipes and heating situations find wide applications in industry. Depending on the fluid properties, temperature field in the pipe changes. This in turn results in thermodynamic irreversibility in the flow system. Thermodynamic irreversibility can be quantified through amount of entropy generation in the thermal system. Consequently, in the present study, the influence of fluid viscosity on the entropy generation due to pipe flow heated from the pipe wall at constant temperature is examined. The turbulent flow with conjugate heating situation is accommodated in the analysis. The governing equations of flow and heat transfer are solved numerically using a control volume approach. Entropy generation rate due to different pipe wall temperatures is computed. It is found that the volumetric entropy generation rate in the pipe is higher for variable properties case; however, total entropy generation rate in the pipe wall attains considerably lower values for variable viscosity case as compared to that corresponding to the constant viscosity case.

Entropy Analysis in Pipe Flow Subjected to External Heating

In the present study, heat transfer and entropy analysis for flow through a pipe system is considered. The Reynolds number and the pipe wall temperature effects on entropy distribution and total entropy generation in the pipe are investigated. Numerical scheme employing a control volume approach is introduced when solving the governing equations. Steel is selected as pipe material, while water is used as fluid. It is found that increasing pipe wall temperature and Reynolds number increases the entropy production rate, in which case, entropy generation due to heat transfer dominates over that corresponding to fluid friction.

Boilers Optimal Control for Maximum Load Change Rate

In many cogeneration systems, one or more boilers are used in hot standby to meet the plant demand of steam in case of failure or upset in the cogeneration unit. Such boilers need to quickly respond to sudden and large steam load changes. However, fast changes in the firing rate cause transient changes in both the drum-boiler steam pressure and drum level, in addition to the potential of developing of thermal stresses in the walls of steam risers. A genetic algorithm (GA) based optimization scheme is proposed for tuning the conventional boiler control loops to maximize the ability of the boiler to respond to large steam demand while keeping the fluctuations in pressure, drum level, and feed rate within acceptable operation limits. A nonlinear model for an actual boiler is first built, validated, and then, it is used to demonstrate the performance of the boiler with the proposed control loop optimization.

Thermal Stresses in Thick Walled Cylinders Subjected to a Periodic Moving Heat Source

This paper presents numerical investigation on thermally developed stresses in a titanium cylinder when heated internally by a constant speed moving ring heat source, which has a periodic content. Effects of moving heat source speed on temperature gain and thermal stress distribution are investigated. This research reveals that a nonlinear relation exists between speed of moving heat source and both the temperature gain and thermal stress levels at the cylinder inner wall. Speeds larger than 20 and less than 45 mm/s are found to cause higher temperature gain and stress level.

Influence of Heat Flux and Friction Coefficient on Thermal Stresses in Risers of Drum Boilers under Dynamic Conditions of Steam Demand

Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of friction factor and heat flux. Diagrams for the influence of friction factor of the boiler tubes and the heat flux, that the tube is subjected to, on the maximum swing rate were examined.

Effect of Temperature Field on Flexural Wave Characteristics of a Bar Resembling Welding to Rigid Body

The flexural motion of a bar changes during the welding process because of the temperature field, which modifies the modulus of elasticity. Depending on the duration of heating during the welding process, the wave characteristics of the flexural motion changes; therefore, the wave characteristics can be related with the heating durations. In the present study, welding of one end of a bar to a rigid body is simulated and flexural motion generated at the free end of the bar through impulse force is analyzed. Temperature field and flexural wave characteristics are computed for different heating durations. It is found that temperature decays sharply in the region next to the heat source, and this decay becomes gradual as the heating progresses. The effect of temperature decay on the characteristics of the flexural wave is significant in the early heating period and gradual decay of temperature in the bar modifies the wave characteristics considerably.

Boiler dynamic control with optimized nitric oxides and efficiency

Boiler is a steam generating device that is used to generate electricity and provide heat in process industry and buildings. The generation of steam is carried out by harnessing thermal energy generated via combustion process. The key challenges that are posed in this process are harmful nitric oxide emissions and the energy losses from the total energy contained in the fuel. It is highly required to reduce these losses to improve boiler efficiency; however, when the operational parameters are adjusted to maximize boiler efficiency, the nitric oxide formation is adversely affected, that is, nitric oxide formation also goes up. Moreover, a little change in demand of steam may cause disturbance in all the dynamics of boiler which may go unstable if not controlled properly. All these issues necessitate measures to be taken to optimize boiler efficiency and nitric oxide as well as to regulate operational parameters like drum pressure and drum level all at the same time. In this work, a detailed study has been carried out to investigate how thermal nitric oxide emissions, combustion process and dynamics of boiler interact with each other. In this respect, dynamic models of nitric oxides, efficiency and other operational variables of boiler have been investigated, and these models have been combined to form a joint model of whole boiler system. This model is then utilized to form an efficient control of boiler variables along with trade-off-based optimization between efficiency and thermal nitric oxide emission. The results have been formed using an experimental input data from a typical package boiler to ensure the practicability of the proposed technique.

Flexural Motion Due to Laser Heating Applications

Laser evaporative heating of solid surfaces involves phase change process and recoil pressure generation in between the vapor and liquid phases. Recoil pressure remains high during a short period of time, which in turn causes mechanical vibration of the body irradiated by a laser beam. When the body resembles a cantilever arrangement and if the laser radiation takes place at the free end of the cantilever beam, the body undergoes a flexural motion. Depending on the laser pulse intensity and duration, the displacement characteristics of the cantilever beam provide information on the mechanical properties of the irradiated beam. In this chapter, laser pulse heating is formulated and thermal stress developed in the heated region is analyzed. In addition, flexural behavior of the cantilever beam is presented in detail.

HVOF Coating and Characterization

HVOF Coating is one of the thermal barrier coatings to protect surfaces from high temperature, corrosion, and erosion environments. Coating characteristics including thickness, metallurgy, elemental composition, and morphology play an important role in practical applications. In this chapter, a brief description of HVOF coating process and coating characteristics is presented. The practical applications of HVOF coating and coating properties are also included in detail.