Yazar "Hekimoğlu, Gökhan" seçeneğine göre listele

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    Activated carbon nanotube/polyacrylic acid/stearyl alcohol nanocomposites as thermal energy storage effective shape-stabilized phase change materials
    (Elsevier, 2022) Göksu, Haydar; Aydınlı, Elif; Hekimoğlu, Gökhan; Sarı, Ahmet; Gencel, Osman; Subaşı, Serkan; Tozluoğlu, Ayhan
    Stearyl alcohol (SA) as one of organic phase change materials (PCMs) has promising thermal energy storage prospective. However, the leakage issue during solid-liquid phase change period and low heat harvesting and releasing rate significantly attenuates its TES potential. Towards to overcome these drawbacks, the SA was shape stabilized using the cross-linked poly acrylic acid (PAA) and activated single walled carbon nanotubes (aSWCNTs) at three different weigh ratio of 1:1:2, 1:3:4 and 1:5:6 (a-SWCNTs:PAA:SA). The chemical/crystalline and morphologic structures of the produced shape stabilized-nano composite PCMs (SS-NCPCMs) were investigated by FT-IR, XRD and SEM analyses. The latent heat storage (LHS) features and thermal stability of the SSNCPCMs were measured by DSC and TGA techniques. The thermal cycling effect on the LHS properties and chemical structures of the SS-NCPCMs was also estimated. The DSC findings indicated that the SS-NCPCMs had melting temperature of around 55-56 C and latent heat capacity of about 135 J/g. TGA measurements disclosed that the thermal degradation temperatures of the nano composite PCMs were prolonged somewhat compared to the SA. A 500 heating-cooling cycling test revealed that the SS-NCPCMs had great chemical and LHS stability. The heat harvesting and releasing performance of the NCPCMs were considerably shortened compared to those of pure SA. The obtained results exposed that the synthesized SWCNTs/PAA/SA composites can be evaluated as promising LHS materials for thermal management of electronic systems, automobile modules, food carriers, solar PV panels etc.
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    Development, characterization and thermo-regulative performance of microencapsulated phase change material included-glass fiber reinforced foam concrete as novel thermal energy effective-building material
    (Pergamon-Elsevier Science Ltd, 2022) Gencel, Osman; Subaşı, Serkan; Ustaoğlu, Abid; Sarı, Ahmet; Maraşlı, Muhammed; Hekimoğlu, Gökhan; Kam, Erol
    Thermal energy storage (TES) materials present very crucial role for heating and cooling load of building envelopes. This investigation focused on manufacturing of novel TES materials as a lightweight concrete by integration of microencapsulated PCM (MPCM) with foam concrete (FC) to improve thermal mass of buildings. Novel hybrid building material design is presented by combining static insulation property of FC and dynamic thermoregulation property of MPCM. In production of MPCM-included innovative FC, MPCM was used at 5%, 10% and 15% by weight. MPCM increased bulk density up to 592.1 kg/m(3), compressive strength up to 2.52 MPa and thermal conductivity up to 0.153 W/mK. Fourier transform infrared spectroscopy (FTIR) analysis confirmed that any chemical interaction did not occur between MPCM and ingredients of FC. Onset melting temperature and energy storage capacity were measured as 11.88 degrees C and 204 J/g for MPCM and 12.27 degrees C and 30.8 J/g for FC-MPCM, respectively. Center temperature of room with MPCM impregnated foamed concrete became about 1.9 degrees C lesser according to reference room through daytime. Moreover, it achieved about 1.72 degrees C higher room center temperature after sunset hour. Advantageous physico-mechanic and thermal properties make FC-MPCM as promising energy effective material for manufacturing thermo-regulative building components. (c) 2022 Elsevier Ltd. All rights reserved.
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    Effect of carbon nanotube and microencapsulated phase change material utilization on the thermal energy storage performance in UV cured (photoinitiated) unsaturated polyester composites
    (Elsevier, 2023) Subaşı, Azime; Subaşı, Serkan; Bayram, Muhammed; Sarı, Ahmet; Hekimoğlu, Gökhan; Ustaoğlu, Abid; Gencel, Osman
    The utilization of phase change materials in the synthesis of polyester is an economically viable approach for the production of polymer composites with remarkable thermal and mechanical characteristics, thereby facilitating thermal energy savings. This study manufactured a series of unsaturated polyester resin (UPR)/carbon nanotubes (CNT)/MPCM composites via mechanical mixing and ultrasonication processes and the produced composites were cured with ultraviolet (UV) curing technology. The unsaturated polyester resin was utilized as a support matrix, and to improve the thermal conductivity of MPCM-UPR composites, CNT were introduced into the matrix. This paper discusses the effect of CNT and MPCM on the mechanical, thermal, and thermal regulative performance of polyester composites. A 10 wt% incorporation of MPCM led to an almost 77 % and 15 % drop at Charpy impact strength and Shore D hardness values of reference UPR, respectively. Similarly, the introduction of substitution of 0.005 wt% of CNT reduced the impact strength of the specimen with 10 % MPCM by 31 %, while it increased the Shore D hardness by almost 5 %. Although the thermal conductivity of reference resin was reduced by 15 % with a 10 % addition of MPCM, CNT content increased the thermal conductivity values by almost 20 % regardless of MPCM concentration. The onset melting and freezing temperatures of MPCM were found to be 21.71 and 22.74 degrees C, respectively; while for the composites with and without CNT, this value ranged between 20.70 and 22.39 degrees C and 22.45-22.90 degrees C, respectively. Thermoregulation test results indicate that MPCM improved the thermal energy storage capacity of composites. The results of this research will be of great sig-nificance in order to gain a more comprehensive understanding of the thermal properties of polyesters with MPCM/CNT, thus allowing for the utilization of this material as a latent heat thermal energy storage system for energy conservation.
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    Glass fiber reinforced gypsum composites with microencapsulated PCM as novel building thermal energy storage material
    (Elsevier Sci Ltd, 2022) Gencel, Osman; Hekimoğlu, Gökhan; Sarı, Ahmet; Ustaoğlu, Abid; Subaşı, Serkan; Maraşlı, Muhammed; Erdoğmuş, Ertuğrul
    A comprehensive study involving the fabrication and characterization of gypsum plasterboards combined with microencapsulated phase change material (mPCM) is introduced to evaluate their benefits regarding thermoregulation management and energy saving performance in buildings. For this purpose, the produced new type of gypsum plasterboard was subjected to the detailed chemical, morphological, mechanical, physical and thermal tests. The gypsum plasterboard incorporated with mPCM (7.5 wt%) and reinforced by glass fiber has latent heat capacities as high as 16.7 and 16.6 J/g at onset melting and solidification temperature of 11.90 ? and 12.09 ?, respectively. TGA analyzes revealed high thermal stability of gypsum plasterboard up to about 140 ?. Outcomes exhibited that mPCM-gypsum plasterboard can substantially diminish cooling load of a building during the daytime even at the high room temperature and offer decline in heat necessity of a house during night-time. During peak room temperature hours, the mPCM-gypsum plasterboard achieved 3 ? lower temperatures than the reference room, and it provided a cooler room temperature for about 7 h during the daytime while a warmer temperature of 0.3 ? was achieved at the cold weather. As a result, the produced gypsum-based composites can be considered as an energy-saving and indoor temperature regulating material in buildings.
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    Light transmitting glass fiber reinforced cementitious composite containing microencapsulated phase change material for thermal energy saving
    (Elsevier Sci Ltd, 2022) Gencel, Osman; Sarı, Ahmet; Subaşı, Serkan; Bayram, Muhammed; Danish, Aamar; Maraşlı, Muhammed; Hekimoğlu, Gökhan
    The energy utilization for artificial lighting, cooling, heating, and air conditioning in buildings results in the release of greenhouse gases and causes climate crises. In this regard, a novel light-transmitting cementitious composite (LTCC) was developed by substituting microencapsulated phase change material (MPCM) to reduce the building energy utilization via transmitted light through the composite and improve the solar thermal energy efficiency. The cementitious matrix is produced with cement, kaolin, silica sand, water, superplasticizer, adhe-sive polymer, glass fiber, different ratios of MPCM, and plastic optical grids to let inward sunlight transmittance. The current study thoroughly investigates the characteristics of light-transmitting composite, including MPCMs, via physico-mechanical, chemical, microstructural, thermal, light transmittance and solar thermoregulation tests. The thermal conductivity of the composite with 0 wt% MPCM decreased from 1.09 W/mK to 0.96 W/mK with 15 wt% MPCM addition. Incorporating 10 wt% of MPCM reduced the 28 days-compressive strength of specimens by almost 28 % due to the lower strength and density of microcapsules, as well as the voids formed by damaged MPCMs. On the other hand, the incorporation of MPCM did not dramatically affect the flexural strength of the cementitious composite. DSC analysis results revealed that the composite containing 15 wt% MPCM shows a latent heat of fusion of 14.6 J/g with a melting point of 17.65 degrees C. FTIR analysis disclosed that MPCM maintains its chemical structure in the composite. Composite slabs exhibited up to 12.4 % artificial light transmittance, which would translate to a considerable increase in the lighting efficiency of commercial and residential buildings. Thermoregulation performance test under ambient conditions indicates that the specimen containing 15 wt% MPCM can provide a cooler room temperature for 6.5 h when the room or surface temperatures increase above 21-23 degrees C, and a warmer room when the temperature decreases below these temperatures. The findings of the current study can be applied to enhance thermal energy saving and artificial lighting efficiency in buildings that inspire the design of environment-friendly constructions.
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    Utilization of waste apricot kernel shell derived-activated carbon as carrier framework for effective shape-stabilization and thermal conductivity enhancement of organic phase change materials used for thermal energy storage
    (Elsevier, 2022) Hekimoğlu, Gökhan; Sarı, Ahmet; Önal, Yunus; Gencel, Osman; Tyagi, V. V.; Aslan, Enes
    In this study, low-cost and eco-friendly AC obtained from waste apricot kernel shells (ACAS) was utilized to simultaneously solve the inherited drawbacks and enhance thermal conductivity of (Capric-Myristic acid (CA-MA), Lauryl alcohol (LAOH), n-Octadecane (OD) and Polyethylene glycol (PEG)) as different type organic PCMs. The ACAS/PCM composites had high PCM loading rates of up to 75 wt%, hence a high latent heat capacity of up to 193.7 J/g. Their melting and freezing temperatures varied in the range of 20.21-26.61 degrees C and 18.37-28.78 degrees C, respectively. All the prepared composites exhibited high thermal degradation resistance as well as high cycling stability even after 1200 melting-freezing cycles. The thermal conductivity of ACAS/CA-MA, ACAS/LAOH, ACAS/OD and ACAS/PEG was measured approximately 2.61, 2.40, 2.27 and 1.75 times higher than that of pure CA-MA, LAOH, OD and PEG, respectively. The advantageous TES characteristics of leak-proof composites make them favourable PCMs for low-temperature thermal management of buildings. (C) 2022 Elsevier B.V. All rights reserved.