Ahmet Koyun

Performance analysis of a solar-driven heat engine with external irreversibilities under maximum power and power density condition

Thermodynamic optimizations based on the maximum power and maximum power density criteria have been performed for a solar-driven heat engine with external irreversibilities. In the analysis, it is assumed that the heat transfer from the hot reservoir is to be in the radiation mode and the heat transfer to the cold reservoir is to be in the convection mode. The power and power density functions have been derived, and maximization of these functions has been performed for various design parameters. The obtained results for the maximum power and power density conditions have been compared.

Optimal performance characteristics of a two-stage irreversible combined refrigeration system under maximum cooling load per unit total cost conditions

In this paper, we report a study on the thermoeconomical performance optimization of a two-stage irreversible combined refrigeration system affected by the irreversibility of heat transfer across finite temperature differences, the heat leak loss between the external heat reservoirs and the internal dissipation of the working fluids. The cooling load per unit total cost is taken as an objective function for the optimization. The maximum of the objective function and the corresponding optimal performance and design parameters have been derived analytically. The global and the optimal performance characteristics curves are presented in terms of technical and economical parameters. The effects of the major irreversibilities and the economical parameters on the general and optimal performances have been investigated. Some new results, which may play an important role in determining the economical design conditions of real two-stage refrigeration systems, are obtained.

Determination of Optimum Design Parameters of Horizontal Parallel Pipe and Vertical U-Tube Ground Heat Exchangers

The most important part of a ground source heat pump (GSHP) is the ground heat exchanger (GHE) that consists of pipes buried in the soil and is used for transferring heat between the soil and the heat exchanger of the ground source heat pump. Soil composition, thermal properties and water content affect the length of ground heat exchanger. Another parameter affects the size of the ground heat exchanger is the shape. There are two basic ground heat exchanger configurations: vertical U-tube and horizontal parallel pipe. There are plenty of works on ground source heat pumps and ground heat exchangers in the literature. Most of the works on ground heat exchangers are based on the heat transfer in the soil and temperature distribution around the coil. Some of the works for thermo-economic optimization of thermal systems are based on thermodynamic cycles. This study covers comparative thermo-economical analysis of horizontal parallel pipe and vertical u-tube ground heat exchangers. An objective function has been defined based on heating capacity, investment and energy consumption costs of ground heat exchanger. Investment and energy consumption costs were taken into account as total cost in the objective function. The effects of the soil thermal conductivity, number of pipes, thermal capacity of ground heat exchanger, pipe diameter and the burial depth on the objective function were examined. The main disadvantage of U-tube ground heat exchanger is higher borehole cost that makes installation cost higher than parallel pipe ground heat exchanger. To make reference functions equal for both type of ground heat exchangers, the borehole cost must be under 20

Design and Implementation of Kalman Filter for Fuel Pipe Damping Test Machine Working Based on Variable Frequency Vibration Principle

/m (now 55

Design and servo control of a leak tightness machine working based on hydrostatic pressure aging method

/m) for a given heating or cooling capacity. The performance of ground heat exchangers depends on the soil characteristics especially the soil thermal conductivity.Copyright

Wear behaviour of Ti6Al4V alloy blasted with zirconia/hydroxyapatite powders

Fuel pipes popularly used in automotive industry applications carry fuel from the fuel tank to the engine and work under variable vibrations having different magnitude and frequency parameters due to the engine’s rotation frequency and road profile’s spontaneous change. Considering that the transfer of the fuel to the engine in the desired way has a crucial importance on the driving performance, any problem that may exist because of the vibrations cannot be acceptable in the pipe assembly. Because of this reason, all manufactured fuel pipes have to be well tested in terms of some industrial standards. The fluid excitement test is a very useful and commonly accepted method in the industry. However, this method produces enormous amount of noise that does not allow to obtain healthy pressure values from the sensors. In this study, Kalman filtering method has been used to interpret the data that have been obtained from the sensors. The usefulness and effectiveness of the proposed Kalman filtering method have been shown and discussed based on the test results.

Hydroxyapatite Coating on Cp-Ti Implants by Biomimetic Method

The leakage problem, which occurs due to the high hydrostatic pressure values of the fluid inside the pipes, is a serious issue in most of the pipeline systems. Therefore, the leak tightness test is required in different standards for verification of almost every kind of pipes used in both academic researches and industrial applications. The behavior of the hydrostatic pressure parameter in the test pipe has to be as smooth as possible during the leak tightness test. The conventional control loops of the servo mechanisms used for pumping the test fluid into the test pipe are weak to provide the minimum overshoot, the rise time and the steady-state error. In this situation, hydrostatic pressure tests are not capable of giving meaningful results. In this study, a leak tightness test machine working with a servo control loop to provide the optimum hydrostatic pressure pattern is designed. The efficacy of the designed leak tightness test machine and proposed optimized servo control loop have been shown with both simulation and experimental results.

Linear matrix inequality-based model matching H2 output feedback control of a new leak tightness machine working based on hydrostatic pressure aging method

Purpose – The purpose of this paper is to investigate the effect of blasting treatment with zirconia/hydroxyapatite powders on the surface roughness, in vitro bioactivity and wear behavior of Ti6Al4V alloy (Grade V). Design/methodology/approach – Ti6Al4V specimens were sandblasted with ZrO2 and HA [Ca10(PO4)6(OH)2] powders in a commercial blasting cabinet. Surface analysis was performed evaluating eroded surfaces by scanning electron microscopy. Roughness surface analysis of the samples was performed with a surface roughness tester and in vitro bioactivity of titanium surfaces was examined in the simulated body fluid (SBF) solution before and after blasting. Wear resistance is evaluated by the weight loss during the test. Findings – The highest value of surface roughness is obtained with a mixture of 25 percent ZrO2+75 percent HA (Z25). Z25 exhibited also lower weight loss than Ti6Al4V and other treated samples. These results indicate that surface treatment with 25 percent ZrO2+75 percent HA provides the ...

The DMA, TG/DTA and FT-IR Characteristics of Wood Polymer Composites

Hydroxyapatite (HA) is the main inorganic component in the human hard tissues, such as bones and teeth. The use of HA in load-bearing orthopedic applications has been extensively studied to achieve a biocompatible coating layer on implant metals. Commercial pure titanium (cp-Ti) is the most commonly used metallic material in the manufacture of orthopedic implants. Uncoated metal surfaces generally show numerous toxic effects to the surrounding tissues. However, coating of the metallic surfaces before implantation may prevent the interference of implant surfaces in biological media and also could accelerate the new bone formation. The present study focused on the coating of HA on cp-Ti implants, using novel biomimetic sol-gel method. The surfaces of cp-titanium substrates were coated with novel biomimetic sol gel (BSG) method under biological conditions (37°C and pH= 7.4). A bone-like apatite with a nanosized and pure HA structure was formed on the substrates under atmospheric pressure. The pre-coating results indicate that the novel biomimetic sol gel method is definitely a promising coating route in case that optimum coating parameters are established in detail.

Statistical Evaluation Tensile Properties of High-Density Polyethylenes

Fluid leaks owing to broken pipes can be a serious problem for any hydraulic system. The main reasons for pipe breakage are spontaneously changing hydrostatic and hydrodynamic pressure values inside the pipe or faults occurring during the pipe manufacturing process. Therefore, different kinds of leak tightness tests are required in many standards for approval of the pipes used in both academic researches and industrial applications. Hydrostatic pressure aging is the most common method among leak tightness test procedures. However, conventional test machines cannot reach above 700 bar owing to their mechanical specifications. In this study, the design of a new leak tightness test machine that can reach above 1200 bar and its Linear matrix inequality-based model matching H2 output feedback control have been achieved. The efficacy of the test machine and proposed controller have been shown with both simulation and experimental results.