Exergy analysis of an integrated solar combined cycle system

Exergetic analysis has become an integral part of thermodynamic assessment of any power generation system. Energy and exergy studies for power plants optimum design and for combined chemical industries received much attention recently. An Integrated Solar Combined Cycle System (ISCCS) is proposed as a means of integrating a parabolic trough solar thermal plant with modern combined cycle power plants. In this study attempt will be made to analyze the Integrated Solar Combined Cycle in Yazd, Iran using design plant data. Energy and exergy analysis for the solar field and combined cycle is carried out to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram, and compared to the energy flow diagram. The causes of exergy destruction in the plant include: losses in combustor, collector, heat exchangers, and pump & turbines which accounts for 29.62, 8.69, 9.11 and 8% of the total exergy input to the plant, respectively. Exergetic efficiencies of the major plant components are determined in an attempt to assess their individual performances.     

Analysis of wind flow around a parabolic collector (1) fluid flow

Applications of parabolic collectors for solar heating and solar thermal power plant increased in the recent years. Most of the solar power plants installed with parabolic collectors are on flat terrain and they may be subjected to some environmental problems. One of problems for large parabolic collector is their stability to track the sun with respect to time very accurately. Any small off tracking as well as the collector structure stability will be affected by strong wind blowing for the regions where the wind velocity is high.In the present study, a two-dimensional numerical simulation of turbulent flow around a parabolic trough collector of the 250 kW solar power plants in Shiraz, Iran is performed taking into account the effects of variation of collector angle of attack, wind velocity and its distribution with respect to height from the ground.Computation is carried for wind velocity of 2.5, 5, 10, and 15 m/s and collector angles of 90°, 60°, 30°, 0°, −30°, −60°, and −90° with respect to wind directions. Various recirculation regions on the leeward and forward sides of the collector are observed, and both pressure field around the collector and total force on the collector are determined for each condition. The effect of absorber tube on the flow field was found negligible, while the effect of the gap between the two sections of parabola at midsection and the gap between the collector and ground were found considerable on both flow field and pressure distribution around the collector.     

Due-date assignment for multi-server multi-stage assembly systems

In this paper, we attempt to present a constant due-date assignment policy in a multi-server multi-stage assembly system. This system is modelled as a queuing network, where new product orders are entered into the system according to a Poisson process. It is assumed that only one type of product is produced by the production system and multi-servers can be settled in each service station. Each operation of every work is operated at a devoted service station with only one of the servers located at a node of the network based on first come, first served (FCFS) discipline, while the processing times are independent random variables with exponential distributions. It is also assumed that the transport times between each pair of service stations are independent random variables with generalised Erlang distributions. Each product's end result has a penalty cost that is some linear function of its due date and its actual lead time. The due date is calculated by adding a constant to the time that the order enters into the system. Indeed, this constant value is decided at the beginning of the time horizon and is the constant lead time that a product might expect between the time of placing the order and the time of delivery. For computing the due date, we first convert the queuing network into a stochastic network with exponentially distributed arc lengths. Then, by constructing an appropriate finite-state continuous-time Markov model, a system of differential equations is created to find the manufacturing lead-time distribution for any particular product, analytically. Finally, the constant due date for delivery time is obtained by using a linear function of its due date and minimising the expected aggregate cost per product.     

Organic Semiconductor Nanotubes for Electrochemical Devices

Electrochemical devices that transform electrical energy to mechanical energy through an electrochemical process have numerous applications ranging from robotics and micropumps to microlenses and bioelectronics. To date, achievement of large deformation strains and fast responses remains challenging for electrochemical actuators wherein drag forces restrict the device motion and electrode materials/structures limit the ion transportation. Results for electrochemical actuators, electrochemical mass transfers, and electrochemical dynamics made from organic semiconductors (OSNTs) are reported. The OSNTs device exhibits high-performance with fast ion transport and accumulation in liquid and gel-polymer electrolytes. This device demonstrates an impressive performance, including low power consumption/strain, a large deformation, fast response, and excellent actuation stability. This outstanding performance stems from the enormous effective surface area of nanotubes that facilitates ion transport and accumulation resulting in high electroactivity and durability. Experimental studies of motion and mass transport are utilized along with the theoretical analysis for a variable–mass system to establish the dynamics of the device and to introduce a modified form of Euler-Bernoulli's equation for the OSNTs. Ultimately, a state-of-the-art miniaturized device composed of multiple microactuators for potential biomedical applications is demonstrated. This work provides new opportunities for next-generation actuators that can be utilized in artificial muscles and biomedical devices.     

Role of bazaars as a unifying factor in traditional cities of Iran: The Isfahan bazaar

A city is a vital organism that lives and grows like other organisms. Therefore, implementing development plans that would provide a sense of unity and integration in relation to the city as a whole is necessary. Traditional Iranian architecture is full of samples evolved during the course of Iranian history that can serve as architectural paragons of the city. In Iran's traditional cities, a sense of unity exists in various urban areas. The traditional city of Isfahan is one of the most valuable samples and was selected as the case study in this research. Accordingly, the most important questions of this research are as follows: (1) What is the role of bazaars in creating a sense of unity in the traditional cities of Iran? (2) How do bazaars play out their role in the integration of these cities? This research focuses on the concept of a “traditional city” to determine the role of bazaars in such cities. The results show that bazaars are crucial in giving a sense of integrity to the concept of a traditional Iranian city. Bazaars provide cohesion among the different parts of cities, such as residential areas, as well as socio-political and trade centers. This condition means that traditional bazaars play two important roles in traditional cities: (1) they interconnect the different parts of the city's physical structure; and (2) the crucial role of bazaars in a city's social and cultural structure brings about unity among the citizens in the city. Bazaars as a unifying element connect the main urban functions and guarantee the city's economic and social life.     

Computational Fluid Dynamics of Co-Production of Zinc and Syngas in a Solar Reactor

In this paper, the production of Zn and H₂ in a 4 kW solar reactor has been investigated. Utilization of a renewable energy source increases the importance of this work. The effect of changes in reactor geometry was analyzed, and, with changing different parameters, their effects were investigated. At constant thermal energy rate, with increasing CH₄ inlet gas flow rate there is a decrease in reaction chamber temperature and therefore in reactor efficiency. Increasing rotation of reaction chamber causes its temperature to increase, where an increase of 150% in rotation caused a 1% increase in efficiency. With the increase in thermal energy rate, thermal efficiency was increased. Also, with increasing rate of thermal energy, the rate of chemical reaction that produces Zn and H₂ increased. The geometry used in the light beams concentrator section causes the occurrence of maximum temperature in the desired point (cylindrical chamber) which increases system efficiency significantly.     

Influence of channel geometry on the performance of a counter flow microchannel heat exchanger

Microchannel heat exchangers (MCHE) can be made with channels of various geometries. Their size and shape may have considerable effect on the thermal and hydraulic performance of a heat exchanger. In this paper numerical simulation is carried out to solve 3D developing flow and 3D conjugate heat transfer of a balanced counter flow microchannel heat exchanger (CFMCHE) to evaluate the effect of size and shape of channels on the performance of CFMCHE for the same volume of heat exchanger. The effect of shape of the channels on its performance is studied for different channel cross-sections such as circular, square, rectangular, iso-triangular and trapezoidal. Results show that for the same volume of a heat exchanger, increasing the number of channels lead to increase in both effectiveness and pressure drop. Moreover circular channels give the best overall performance (thermal and hydraulic) among various channel shapes. New correlations are developed to predict the value of heat exchanger effectiveness and performance index as a function of relative size of channels with overall heat exchanger volume, Reynolds number and thermal conductivity ratio.     

Air flow patterns around domed roof buildings

The wind has been regarded as an important criterion in designing building environments since the early days of human settlement. In hot, arid regions of Iran building is designed such as to have adequate protection against the wind storms and also they had provided summer time air conditioning by means of passive cooling. Most of such buildings are domed roof structures. In order to observe wind environment over such structures, simple models of these vaulted roof buildings are made and tested in a two dimensional low speed wind tunnel for low velocity smoke flows.Flow pattern over and around the models are visualized and photographed. From the observations, several features such as flow separation, turbulence, wind shadow area and flow circulation have been identified for different building configurations.     

Solar radiation for Shiraz, Iran: a comparative study for two periods

Instantaneous solar radiation data read from the chart of global solar radiation on a horizontal surface as well as sunshine hours in Shiraz during two periods (1980–1983 and 1988–1990) are analysed and compared with solar conditions in the early 1970s. It is apparent from the recorded data and subsequent analysis that while this area still possesses a relatively high abundance of sunshine, there has been a gradual decay in clearness index. Frequency of clear sky days, the average daily irradiation and the mean cumulative annual irradiation for the two periods under study are presented and a decrease in solar radiation received on a horizontal surface due to down grading of Shiraz from the clear sky conditions enjoyed in the 1960s and 1970s is demonstrated.     

Distribution of functionalized gold nanoparticles between water and lipid bilayers as model cell membranes

Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of nanoparticles with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assessed the affinity of functionalized gold nanoparticles (Au NPs) with sizes from 5 to 100 nm to lipid bilayers by determining the Au NP distribution between aqueous electrolytes and lipid bilayers. The Au NP distribution to lipid bilayers reached an apparent steady state in 24 h with smaller Au NPs distributing onto lipid bilayers more rapidly than larger ones. Au NPs distributed to lipid bilayers to a larger extent at lower pH. Tannic acid-functionalized Au NPs exhibited greater distribution to lipid bilayers than polyvinylpyrrolidone-functionalized Au NPs of the same size. Across the various Au NP sizes, we measure the lipid bilayer-water distribution coefficient (K(lipw) = C(lip)/C(w)) as 450 L/kg lipid, which is independent of dosimetric units. This work suggests that the nanoparticle-cell membrane interaction is dependent on solution chemistry and nanoparticle surface functionality. The K(lipw) value may be used to predict the affinity of spherical Au NPs across a certain size range toward lipid membranes.