Buğra ŞİMŞEK, Sıtkı USLU, Mehmet Ali AK
Buğra ŞİMŞEK, Sıtkı USLU, Mehmet Ali AK
Validationof onedimensional aerodynamic heating and ablation prediction program, AeroheataBSto calculate transient skin temperatures and heat fluxes for highspeed vehicles has been performed. In the tool shock relations, flat plate convective heating expressions, Eckert’s reference temperature method and modified Newtonian flow theory are utilized to compute local heat transfer coefficients. Corresponding governing equations are discretized explicitly and numerically solved. Time varying flight conditions including velocity, altitude and angle of attack serve as input to the program. In order toexamine the accuracy of aerodynamic heating capabilities of AeroheataBS, calculated temperature histories are compared with flight data ofthe X15 research vehicle, a modified vonKarman nose shaped body, conecylinderflare configuration and results of conjugate computational fluid dynamics studies. Comparative studies show that computed values are in good agreement with the reference data and prove that methodology established in AeroheataBSis appropriate for estimating aerodynamic heating and structural thermal response.

Ece AYLI, Oğuzhan ULUCAK
Ece AYLI, Oğuzhan ULUCAK
Türbinler tasarım noktaları dışında mevsimsel yağış dalgalanmaları, zamana bağlı elektrik ihtiyacı farklılıkları sebebiyle kısmi yükleme şartlarında çalıştırılabilmektedir. Bu noktada tasarımcılar tepe diyagramları oluşturmakta ve farklı debi ve düşüler altında sistem verimini tahminlemektedir. Tepe diyagramı çalışması bir çok farklı ayar kanadı açıklığında ve düşüde test gerektirdiğinden oldukça maliyetli bir çalışmadır. Bu çalışmada Yapay Sinir Ağları (YSA) ve Uyarlamalı Sinirsel Bulanık Çıkarım Sistemi (ANFIS) metodu ile farklı çalışma koşullarında Francis tipi türbin verim tahminlemesi gerçekleştirilmiştir. Elde edilen sonuçlar Hesaplamalı Akışkanlar Dinamiği (HAD) yöntemi ile elde edilmiş verim değerleri ile kıyaslanmıştır. Sonuçlara göre, maliyetli bir test veya sayısal süreç yerine ANFIS metodu kullanarak tepediyagramı oluşturmak mümkündür. Sayısal veriler %25’i test ve %75’i modeli eğitmek için kullanılmak üzere ikiye ayrılmıştır. Geliştirilen YSA ve ANFIS modelleri ile verim tahminleri yapılmış ve elde edilen sonuçlar karşılaştırılmıştır. Çıktılar ortalama hata, maksimum hata ve regresyon katsayısı olmak üzere 3 farklı istatistiksel kriter ile test edilmiş ve ANFIS’in tepe diyagramı uygulamasında YSA’ya göre daha iyi sonuç verdiği tespit edilmiştir. ANFIS parametrelerinin optimize edilmesi ile ortalama hata %1.41, R2değeri ise 0.999 olarak hesaplanmıştır. Yazarların bilgisine göre YSA ve ANFIS uygulamasının türbinlere uygulandığı ilk literatür araştırması bu çalışmadır

Özge YETİK, Necati MAHİR
Özge YETİK, Necati MAHİR
In this study, the flow and heat transfer characteristics oftwo heated square cylinders in a tandem arrangement near a wall is investigated. The numerical computations are carried outby solving the unsteady two dimensional NavierStokes and energy equations. A fractional step method with CrankNicholson schema was employed to the convective and the viscous terms of the equations. At the inlet, fully developed laminar boundary layer is employed for longitudinal velocity over the plane wall while transverse velocity set to zero. The simulations are performed for Prandtl number (Pr) of 0.71 and Reynolds number (Re) of 150 where the flow is considered two dimensional. The flow field characteristics and heat transfer depend not only on the ratio of the space between the cylinders (L/D) but also on the distance between the cylinder center and the wall (G/D). The vorticity and isotherm curves are generated and discussed for various L/D and G/D ratios to clarify the connection with flow and heat transfercharacteristics.When the cylinders are within the boundary layer formed on the plane wall, the large difference between the velocities at the upper and lower side of the cylinders leads to noticeable variation at the flow and heat transfer characteristics.

Aytaç ŞANLISOY, Yahya Erkan AKANSU
Aytaç ŞANLISOY, Yahya Erkan AKANSU
In this study, the effects of the plasma actuator on flow control at varied Reynolds numbers and attack angles are examined. Plasma actuator is placed on the NACA2415 airfoil at x/C = 0.1. The effect of the actuator to active flow control is examined at Reynolds number between 8x103and 9x104in the wind tunnel. The lift force which acted on the airfoil was measured by using a force balance system. The velocity measurements were done by the hotwire probe, located at the wake region, and the flow around model was visualized by the smoke wire method. When the plasma was active, an increased lift force and a narrowed wake region are observed. The stall angle shifted to the higher attack angle by the effective active flow control at low Reynolds numbers. Prevent of the flow separation was enhanced up to 18° angle of attack and the maximum lift force occurred at the 14° angle of attack which is doubled when the plasma actuator is on.

Güven Hasret YILMAZ, Oğuz TURGUT, Burak TIĞLI, Nuri Eren TÜRKOĞLU
Güven Hasret YILMAZ, Oğuz TURGUT, Burak TIĞLI, Nuri Eren TÜRKOĞLU
The purpose of this studyis to destroy sphericalshape hepatic tumorsusing radiofrequency ablation method. Threedimensional finite elementsmethod has been employed. Five different radiofrequencyprobes for liver tissue have been used to create a sphericalshaped lesion. Investigated parameters are the electrical voltage, ablation time, geometry and number of electrodes. Results have been given as lesion volume and temperature distribution.Results have been compared with the literature results, and it is seen that present results are in good agreement with the literature results. Results showthat a spherical shape hepatic tumor can be destroyed using ahybrid electrode construction consistingof four Christmastree and four umbrellashaped electrodes. It is seen that approximately 20 mmdiameter of lesion can be destroyed using hybridelectrode design after eightminutes. It is hoped that hybridelectrode configuration can be usedfor treatment of spherical shape hepatic tumors in clinical applications.

Increase in demands for energy and discovered huge reserves of shale gas in the world cause countries and researchers to focus on it progressively. The amount of shale gas production has begun to rise by developing the techniques of gas extraction from shale rocks recently. In this paper, the nonpremixed combustion characteristic and emissions of shale gas and humid air with dilution effects are numerically investigated under different equivalence ratio, pressure and temperature. A two dimension model of cylindrical combustor is considered. It is concluded that NOxfor New Albany and Haynesville come to the maximum value at 1.025 and 1.02 of equivalence ratio and the maximum reaction temperatures are 2027 and 2014 K in turn. The rising equivalence ratio raises CO mass fractions. The increasing dilution rates decrease NOxand uplift CO mass fractions. The enhancing pressure rears NOxand diminishes CO fractions. The ascending wall temperature boosts NOx, CO and reaction temperatures. NOxand CO from environmental pollutants emerging at the end of shale gas combustion can be lowered by decreasing equivalence ratio, wall temperature, and pressure. The use of H2O dilution steps forward in compared with CO2and N2because of itsopposite effects on NOxand CO pollutants.

M. Nicem TANYERİ, S. Çağlar BAŞLAMIŞLI
M. Nicem TANYERİ, S. Çağlar BAŞLAMIŞLI
This study presents a detailed method to estimate the thermal load of an articulated electric urban bus. Thermal load, which consists of solar, metabolic, ambient and ventilation heat loads, is estimated hourly for a one year period. A mathematical model takes into account the hourly passenger occupancy rate, hourly weather condition of the line and hourly solar loads as input and predicts the heat load accordingly.In order to determine the importance and contribution of each thermal load, all loads are calculated individually. Calculations are made for each hour of a year in order to observe the change of the contribution of each load in time. With the proposed method, the thermal load of an electric bus can be predicted in the system design phase and theHVAC system of the bus can be selected accordingly.

Halil İbrahim YILMAZ, Mehmet Sait SÖYLEMEZ
Halil İbrahim YILMAZ, Mehmet Sait SÖYLEMEZ
The main contribution of this study is to present a novel thermal model for analyzingthe wheat cookingprocessand to propose a design procedure for an energyefficient cooking pot. A smallscale cooking potwas designed and an experimental setup was installed to verify the model under various operating conditions. The developed model was solved using the Engineering Equation Solversoftware. Results were compared with those of the experiments and good agreement was obtained. Additionally, a computational fluid dynamics model was developed to verify the thermal model and have a useful design toolfor largescale cooking pots. It was found that the energy efficiency of the cookingprocesscan be enhanced by initiating nucleate boiling (at ~5 °C minimum temperature difference between the heating element surface and saturation) which will supplythe minimum heat flux on the helicoidal heat exchanger of the cooking pot. Lessening the energy demandbut preserving the final product quality has decreased the 5day biological oxygen demand of wastewater at least 50%. It is proposed that the wheat to water ratio can be reduced to 1.0−1.2 once the energyoptimization and water recovery practices are satisfied. The estimated average specific energy consumption rate lies between 400‒475 ±5% W/kg (thermal power supplied for one kilogram of wheat) which can be reduced ~25% further by reducing the wheat to water ratio to 1.0. The results reported in the present study are expected to guide thermal and food engineers forthe design applications of industrial cooking pots, energy optimization with less harmful wastewater and process control strategies for cooking of wheat

Barış YILMAZ, Ebru MANÇUHAN, Deniz Yılmaz KARAPINAR
Barış YILMAZ, Ebru MANÇUHAN, Deniz Yılmaz KARAPINAR
In this study, a theoretical model is established usingEngineering Equation Solver (EES)software in order to investigate the effects of different design and operation parameterson the performance of the cascade systems for Ultra Low Temperature(ULT)between 50 oC and 100 oC.The analysis is performed for natural and synthetic refrigerant pairs to find an environmentallyfriendly alternative to commercial synthetic refrigerants. Effects of common parameters such as the evaporation temperature oflow temperature cycle (LTC), the condensation temperature of high temperature cycle (HTC) and the temperature difference in the cascade heat exchanger (HX)have been investigated with the proposed model.Furthermore, influence of operation parametersincluding vapor quality of the refrigerant after the expansion valve and the precooler heat exchanger(PCHX) capacity, crucial to reach ULT conditions, on the system performanceare examined. This study also contributes to the theoretical evaluation of the feasible natural refrigerant alternatives for ULT applications and the comparison of these refrigerants with synthetic ones in terms of performance and the environmental aspects.It is found that the natural refrigerant R1270/R170 pair results in about 5% better COPand almost half less CO2 emissions compared to synthetic refrigerant R404A/R508B pair.

Mehmed Akif PAKSOY, Salih Özen ÜNVERDİ
Mehmed Akif PAKSOY, Salih Özen ÜNVERDİ
An equation (29) is derived to calculate heat transfer rate of a heat pipe evaporator in terms of liquid pressure loss along and temperature difference across the wick and thermofluid properties, which shows that various wick profiles transfer same amount of heat under the constraints of pressure loss and temperature difference. It is proved by calculus of variations that among these profiles, wick weight is minimized in case of uniform wick thickness. Case studies are applied for a copperwater heat pipe with a wick of 0.5 porosity, 1.5x109m2permeability, 8.65 mm outer radius and around 1.96 W/mK thermal conductivity. A case study shows that sum of the pressure losses of the liquid and vapor phases of the adiabatic region is minimized at a certain ratio of vapor core radius to wick outer radius. Finally, 1D coupled flow and thermal analyses of the wick and vapor core of the heat pipe are performed for two types of designs with piecewise uniform wick thickness profiles which are proposed in this study. Under the constraint of constant total wick volume, heat transfer rate is plotted as function of wick thicknesses for each design. Without the wick volume constraint, increasing the adiabatic zone and condenser wick thicknesses while decreasing wick thickness of the evaporator enhances heat transfer rate up to 6.3%.On the other hand, increasing adiabatic zone wick thickness while decreasing that of the evaporator and condenser improves heat transfer rate up to 26.9% at capillary limit.
