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Öğe An experimental investigation of the effect of thermophysical properties on time lag and decrement factor for building elements(Gazi University, 2020-06-01) Oktay, Hasan; Yumrutaş, Recep; Argunhan, ZekiThe time lag (TL) and decrement factor (DF) are essential for the heat storage capabilities of building elements, which strictly depend on the thermophysical properties of the elements. Many investigations are presented in literature arguing to find the influence of each thermophysical property on TL and DF by keeping the other properties constant. This study aims to investigate the effect of each property on TL and DF, utilizing relationships between the measurement values of the thermophysical properties of wall materials. Therefore, first, 132 new concrete wall samples were produced, and their thermophysical properties were tested. Secondly, TL and DF values for each building element are computed from the solution of the problem by Complex Finite Fourier Transform (CFFT) technique. Finally, a multivariate regression analysis has been performed, and the variations of each thermophysical property versus TL and DF are presented, and also the findings are compared with literature. The results show that each property alone (keeping the other properties constant) is not adequate to identify the thermal inertia and thermal performance of a wall element. Besides, 87.3 % decrease in thermal diffusivity corresponds to 6.03 h increase in the value of TL and 88.8 % decrease in value of DF; respectively, for W1 wall assembly.Öğe Effects of fuels produced from fish and cooking oils on performance and emissions of a diesel engine(Elsevier, 2014-07-15) Oktay, Hasan; Yumrutaş, Recep; Behçet, RasimIn this study, two fuels called as FOME (Fish Oil Methyl Ester) and COME (Cooking Oil Methyl Ester) were produced from waste fish and cooking oils using the transesterification method. Commercial D2 (Diesel fuel) and two fuel samples obtained by blending the FOME and COME with the D2 with a ratio of 25% on volume basis were used as fuels in a Diesel test engine. An experimental study was performed for investigating the performance and exhaust emissions of the Diesel engine using the fuels. According to the test results, it was observed that the fish oil based fuel indicated better performance and exhaust emission parameters than those of cooking oil. Results clearly showed that the engine power and torque values were lower than those of the Diesel fuel with values of 3.05% and 1.25% for FB25, and 4.07% and 2.2% for CB25, respectively. Also, brake specific fuel consumption for the produced fuels increased up to 5.69% compared to Diesel fuel. However, HC and CO emission reductions compared to the Diesel fuel were found to be around 16.24% and 19.81%, respectively. But, the amount of increase in NOx emissions for the same biodiesel fuels reached up to 17.2%.Öğe An artificial neural network model to predict the thermal properties of concrete using different neurons and activation functions(Hindawi, 2019-04-01) Fidan, Şehmus; Oktay, Hasan; Polat, Süleyman; Öztürk, SarperGrowing concerns on energy consumption of buildings by heating and cooling applications have led to a demand for improved insulating performances of building materials. The establishment of thermal property for a building structure is the key performance indicator for energy efficiency, whereas high accuracy and precision tests are required for its determination which increases time and experimental costs. The main scope of this study is to develop a model based on artificial neural network (ANN) in order to predict the thermal properties of concrete through its mechanical characteristics. Initially, different concrete samples were prepared, and their both mechanical and thermal properties were tested in accordance with ASTM and EN standards. Then, the Levenberg-Marquardt algorithm was used for training the neural network in the single hidden layer using 5, 10, 15, 20, and 25 neurons, respectively. For each thermal property, various activation functions such as tangent sigmoid functions and triangular basis functions were used to examine the best solution performance. Moreover, a cross-validation technique was used to ensure good generalization and to avoid overtraining. ANN results showed that the best overall R2 performances for the prediction of thermal conductivity, specific heat, and thermal diffusivity were obtained as 0.996, 0.983, and 0.995 for tansig activation functions with 25, 25, and 20 neurons, respectively. The performance results showed that there was a great consistency between the predicted and tested results, demonstrating the feasibility and practicability of the proposed ANN models for predicting the thermal property of a concrete.Öğe Mechanical and thermophysical properties of lightweight aggregate concretes(Elsevier, 2015-10-15) Oktay, Hasan; Yumrutaş, Recep; Akpolat, AbdullahIn this study, experimental investigation is performed for producing new cement-based with relatively high strength, low density and good thermal properties for energy efficient buildings. Different types of concretes containing silica fume (SF), superplasticizer (SP) and air-entrained admixtures are prepared with a constant water–cement ratio, and normal aggregates replaced by lightweight aggregates (LWAs) including pumice (PA), expanded perlite (EPA) and rubber aggregates (RA) at different volume fractions of 10%, 20%, 30%, 40% and 50%. 102 samples with different materials and compositions are produced, and their characteristics are tested in accordance with ASTM and EN standards. Based on the experimental results, equations are presented to determine the relation between the thermophysical properties of composite samples. The investigation revealed that the addition of PA, EPA and RA reduced the material bulk density and compressive strength, and improved the insulation characteristics of the composite concretes. Furthermore, it was found out that the reductions in thermal conductivity and diffusivity of the produced samples reached to 82% and 74%, respectively.Öğe Comparison of exhaust emissions of biodiesel–diesel fuel blends produced from animal fats(Journals & Books, 2015-06) Aydın, Hüseyin; Behçet, Rasim; Oktay, Hasan; Çakmak, AbdülvahapThe present paper examines two biodiesels named as fish oil methyl ester (FOME) and chicken oil methyl ester (CFME) produced from low-cost waste fish and chicken oils using the transesterification method, and their fuel properties were compared to EN 14214 and ASTM D6751 biodiesel standards. Then, each methyl esters were blended with the commercial diesel fuel (D2) with a ratio of 20% on volume basis, respectively and two fuel samples named as FOB20 (20% Fish Oil Methyl Ester and 80% D2 fuel) and CFB20 (20% chicken oil methyl ester and 80% D2 fuel) were obtained. An experimental study for investigating the effects of the blended fuels on engine performance and its exhaust emissions was performed by using a single cylinder, four stroke, direct injection and air-cooled diesel engine at different speeds under full load. According to the test results, it was observed that the brake power, torque values and the carbon monoxide (CO), unburnt hydrocarbon (UHC) and carbon dioxide (CO2) concentrations of blended fuels decreased while the NOx concentration and brake specific fuel consumption (bsfc) values increased compared to diesel fuel.
