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    Characteristics of Some New Generation Refrigerants with Low GWP
    (Elsevier Science Bv, 2015) Devecioglu, Atilla Gencer; Oruc, Vedat
    In the present study, a comparison was considered about some characteristics of new generation low GWP value gases most of which are at the trial stage. Hydrofluoro-olefin (HFO) based mixed gases having low GWP value were investigated as alternatives to different four refrigerants used commonly in refrigerating and air conditioning equipments. In the study, R450A, R513A, R1234yf and R1234ze(E) gases were used instead of R134a; DR-33, L40, DR-7 and R448A were used instead of R404A; DR-5 and R447A were used instead of R410A; and N20 and R444B refrigerants were used as alternatives to R22. Refrigerants were compared within their own groups in terms of liquid density and viscosity properties. (C) 2015 The Authors. Published by Elsevier Ltd.
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    Effect on the thermodynamic performance using N20 and R444B refrigerants instead of R22 in a vapor compression refrigeration system
    (Gazi Univ, Fac Engineering Architecture, 2016) Oruc, Vedat; Devecioglu, Atilla Gencer
    In this study, the energy and exergy parameters were theoretically investigated for a vapor compression refrigeration system for which N20 and L20 (R444B) refrigerants were used instead of R22. The comparison of the energy parameters was carried out for different evaporation temperatures (-15 degrees C, -10 degrees C, -5 degrees C, 0 degrees C) and condensing temperatures (30 degrees C, 40 degrees C, 50 degrees C) under the same operating conditions. The coefficients of performance (COP) were seen to be in the same order of magnitude for three refrigerants, but the highest COP value was obtained with R22 case. It was seen that the equipments which will use N20 or R444B should have larger condenser surface areas compared to devices operating with R22. It was also determined that the exergetic efficiency of R22 was higher among the investigated refrigerants.
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    The Effects of Tragacanth Addition on the Thermal and Mechanical Properties of Lightweight Concretes Mixed with Expanded Clay
    (Budapest Univ Technology Economics, 2016) Devecioglu, Atilla Gencer; Bicer, Yasar
    The effects of adding tragacanth, which is a natural resin, as expanded clay aggregate and binder to specimens on the thermal and mechanical properties of lightweight concretes has been examined in this study. Expanded clay with diameters of 4-8mm and by proportion 5%, 10% and 20% of cement's weight was added to specimens in the study. As a binder, by addition of 1% tragacanth to cement at the rate of 1%, new lightweight concrete specimens with densities varying between 867 kg/m(3) to 1452 kg/m(3) were produced. Tragacanth with the same proportions of mixture was prepared in pure specimens in order to compare. Water/cement ratio was kept constant in all mixtures. At the end of a drying time of 28 days, thermal conductivity, specific heat capacity, compressive strength, modulus of elasticity, water absorption and drying quantities of specimens were confirmed. As a result, decrease of thermal conductivity, density and compressive strength of specimens was seen through adding tragacanth and raising the amount of expanded clay.
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    Modelling for determining the thermal conductivity of porous solid materials
    (Emerald Group Publishing Ltd, 2023) Bicer, Ayse; Devecioglu, Atilla Gencer
    The aim of this study was to develop an algebraic equation to calculate the thermal conductivity coefficients of porous solid materials. The components of the equation consisted of material porosity and density, and thermal conductivity coefficients of its Matrix and porous gas. The equation was applied to ten samples of organic sediment stones, volcanic rocks, and porous aggregates. The thermal conductivity coefficients given by the equation were higher than those measured experimentally (6.62%-16.89%). The proposed equation was also compared to six algebraic equations. Results suggest that the proposed algebraic equation can be used to calculate the thermal conductivity coefficients of solid materials containing complex geometrical pores.
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    Seasonal performance assessment of refrigerants with low GWP as substitutes for R410A in heat pump air conditioning devices
    (Pergamon-Elsevier Science Ltd, 2017) Devecioglu, Atilla Gencer
    In this study, the effect of the utilization of refrigerants with a low Global Warming Potential (GWP) instead of R410A in air conditioners on seasonal efficiency was evaluated theoretically. In the study, four different alternative refrigerants were used namely, R446A, R447A, R452B and R454B. The GWP values of all of the studied refrigerants were lower than 750. The calculations were made according to the EN 14825 standard. Average seasonal conditions were applied for heating. The results showed that R446A had the lowest heating capacity and electric consumption. R446A required electric energy consumption for extra heating due to its low heating capacity and therefore it had the lowest seasonal coefficient of performance (SCOP) value. The seasonal energy efficiency ratio (SEER) values of the refrigerants were very close to each other and their average was 6.56. R452B had the most suitable with 3.92 SCOP value among the alternative refrigerants. (C) 2017 Elsevier Ltd. All rights reserved.