Nurdil Eskin

Transient performance analysis of cylindrical parabolic concentrating collectors and comparison with experimental results

This paper presents the unsteady, one-dimensional performance analysis of cylindrical parabolic concentrating collectors through the first and second laws of thermodynamics. These laws, together, help to define the optimum system that satisfies the imposed thermal and economical constraints and minimizes exergy loss. The analysis considers the thermal masses of the absorber pipe, pyrex envelope and the working fluid of the system individually, in an unsteady state. The instantaneous exergetic and energy efficiencies for the cylindrical parabolic collectors are compared for daily insolation at different flow rates. The values measured using the MKE Institute Collector Test Facility are in good agreement with the predicted simulation results. The simulation results indicate that the exergetic efficiency is highly dependent on the mass flow rates and the arrangement of the cylindrical parabolic collector array. The optimum flow rates which provide minimum exergy loss were obtained from the simulation model.

The Characteristics That Define Wind as an Energy Source

Abstract In many countries, present energy resources are insufficient, and the need for energy is growing rapidly. These countries do not possess enough conventional fossil fuel reserves but possesses rich renewable energy resources. Wind energy is one of the most significant and rapidly developing renewable energy sources in the world, and it provides a clean energy resource. This study is aimed at summarizing the studies carried out on the characteristics that define wind as an energy source, to detect insufficiencies of these studies, and to come up with new suggestions concerning wind energy implementations and future wind energy production plans. In order to provide a broad wind resource assessment, the wind characteristics must be studied in detail at each site separately. Considering the development of wind energy in the country, it may be concluded that the number of wind power plant installations will considerably increase in the future.

Performance analysis of a solar process heat system

This paper describes the results of a simulation study, validated by experimental results of a solar process heat system and represents the unsteady performance analysis of the system. The study focuses on the effect that the collector flow rates, temperature distribution and stratification have on the overall thermal and exergetic performance of the particular systems. The simulation is performed for the process heat system established in Izmir, Turkey. The analysis considers the unsteady-state thermal and exergetic analysis of the collector and the storage tank individually. The variation of the storage tank temperature is evaluated along the height of the storage tank at every hour during a day. The values obtained from the measurements at the Izmir Organize Sanayi Bolgesi-Industrial Process Heat System are compared with the predicted simulation results. The effects of the mass flow rates and temperature distribution of the load and collector on the performance of the system are discussed. The simulation results indicate that the exergetic efficiency is highly dependent on the ratio of mass flow rates and the use of an auxiliary heater in the system.

Analysis of a high temperature heater in a false twist texturing process

Abstract The production of textured filament yarns by false twist texturing is an important commercial method that requires heating. In this study, the transient two dimensional modeling of the yarn, heated by high temperature heaters in a false twist texturing process was developed in order to investigate the influence of various heating conditions on the yarn temperature distribution and to quantify the relative contribution of thermal radiation to the total heating. The surface temperatures and the residence time of yarns of different diameters were measured and compared with the simulation results. The temperature distribution in the cross-section of the yarns was calculated for various yarn speeds and for different heater temperatures. The temperature difference between the surface and the center of different types of yarns along the heater was found. For a yarn in a heater, energy is transferred from the heater surface to the yarn by both convection and radiation. As the yarn approaches its heat setting temperature, the total heat rate decreases. However, the calculated results show that the relative contribution of radiation increases up to 60% of the total with yarn temperature and diameter.

Estimation of cooling tube location in fluidized bed coal combustors through exergy analysis

Abstract This paper presents the exergy analysis of fluidized bed coal combustors (FBCCs) under different arrangements of cooling tubes. Considering changes in the heat transfer coefficient due to the particle movement and coal combustion and drag coefficient changes due to the particle movement in the bed and in the freeboard, the second-law efficiency of combustors has been examined and the effect of cooling tube locations on effectiveness has been analyzed. The location of cooling tubes in an FBCC has been analyzed with exergy analysis of the combustor. In performing the simulations, two parameters were defined: the volume ratio ϵ, which is the ratio of the volume of cooling tubes to combustor volume; and the height ratio H e,o H , which is the ratio of the starting height of cooling tube surfaces to the height of the combustor. The effects of cooling tube location on combustor effectiveness were examined under the various conditions of heat exchanger surfaces and at different superficial velocities. The combustor effectiveness decreases along the bed height at every ϵ value, and its value at every level in the combustor decreases as the value of ϵ decreases. On the other hand, the decrement in effectiveness was observed at every point along the combustor height as the height ratio increases. Combustor effectiveness was not affected by the superficial velocity as the location of cooling tubes was changed from 0.6 H to higher values. Also, at higher values of ϵ, the height ratio had no major effect on combustor effectiveness.

Development and Applications of Clean Coal Fluidized Bed Technology

Power generation in Europe and elsewhere relies heavily on coal and coal-based fuels as the source of energy. The reliance will increase in the future due to the decreasing stability of price and security of oil supply. In other words, the studies on fluidized bed combustion systems, which is one of the clean coal technologies, will maintain its importance. The main objective of the present study is to introduce the development and the applications of the fluidized bed technology (FBT) and to review the fluidized bed combustion studies conducted in Turkey. The industrial applications of the fluidized bed technology in the country date back to the 1980s. Since then, the number of the fluidized bed boilers has increased. The majority of the installations are in the textile sector. In Turkey, there is also a circulating fluidized bed thermal power plant with a capacity of 2 × 160 MW under construction at Can in Canakkale. It is expected that the FBT has had, or will have, a significant and increasing role in dictating the energy strategies for Turkey.