Yazar "Karahan, Okan" seçeneğine göre listele

Listeleniyor 1 - 4 / 4
  • Küçük Resim Yok
    Öğe
    2 years of monitoring results from passive solar energy storage in test cabins with phase change materials
    (Pergamon-Elsevier Science Ltd, 2020) Cellat, Kemal; Beyhan, Beyza; Konuklu, Yeliz; Dundar, Cengiz; Karahan, Okan; Gungor, Caner; Paksoy, Halime
    Buildings are one of the major consumers of global energy with a significant share reaching to 40%. Phase change materials (PCMs) are used in building materials and structures for energy saving in buildings. PCM absorbs heat from solar energy during daytime and releases that heat when temperatures cool down at night. The benefits of using PCMs in building materials are to reduce peak load and energy demand for heating and cooling and attain smaller temperature fluctuations. The aim of this study is to demonstrate passive utilization of solar energy storage in buildings with a new microencapsulated bio-based PCM (mPCM). The demonstration involves several development steps, which start in the laboratory for development of mPCM suitable for concrete and go to the building application with an innovative panel design under real climate conditions in the field. Monitoring of the test buildings with and without mPCM showed that developed microencapsulated PCM-concrete composite panels helped to maintain thermal comfort in buildings with a change in indoor air temperature with respect to reference building reaching 2 degrees C, which corresponds to up to 13% energy savings.
  • Küçük Resim Yok
    Öğe
    Comparison of artificial neural network and fuzzy logic models for prediction of long-term compressive strength of silica fume concrete
    (ELSEVIER SCI LTD, 2009) Oezcan, Fatih; Atis, Cengiz D.; Karahan, Okan; Uncuoglu, Erdal; Tanyildizi, Harun
    In this study, an artificial neural network (ANN) and fuzzy logic (FL) study were developed to predict the compressive strength of silica fume concrete. A data set of a laboratory work, in which a total of 48 concretes were produced, was utilized in the ANNs and FL study. The concrete mixture parameters were four different water-cement ratios, three different cement dosages and three partial silica fume replacement ratios. Compressive strength of moist cured specimens was measured at five different ages. The obtained results with the experimental methods were compared with ANN and FL results. The results showed that ANN and FL can be alternative approaches for the predicting of compressive strength of silica fume concrete. (C) 2009 Elsevier Ltd. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Robust microencapsulated phase change materials in concrete mixes for sustainable buildings
    (WILEY-BLACKWELL, 2017) Beyhan, Beyza; Cellat, Kemal; Konuklu, Yeliz; Gungor, Caner; Karahan, Okan; Dundar, Cengiz; Paksoy, Halime
    For passive building applications, phase change materials (PCMs) are microencapsulated to avoid leakage of PCM from concrete structure. The primary challenge of using microencapsulated PCM (MPCM) is its weak shell structure. New MPCMs with different shell compositions to prevent breakage during mixing in fresh concrete are needed. In this study, free radical polymerization method to microencapsulate capric acid-myristic acid mixture as PCM with two different methyl methacrylate co-polymers is proposed to produce robust MPCMs for building applications. Two new microcapsules (MPCM-1 and MPCM-2) having latent heats of 91.9 and 97.3 J/g were synthesized. SEM analyses showed the size of microcapsules being in the range of 400-850 nm for MPCM-1 and 250-475 nm for MPCM-2. Analyses also reveal that the shells of MPCMs were not harmed, as they were added into concrete mixes. The microsphere's geometry was preserved, and distribution was homogeneous. The MPCMs were also studied under thermal tests of 1000 heating/cooling cycles. No significant changes in thermal properties were observed after thermal cycling tests. Copyright (C) 2016 John Wiley & Sons, Ltd.
  • Küçük Resim Yok
    Öğe
    Thermal enhancement of concrete by adding bio-based fatty acids as phase change materials
    (ELSEVIER SCIENCE SA, 2015) Cellat, Kemal; Beyhan, Beyza; Gungor, Caner; Konuklu, Yeliz; Karahan, Okan; Dundar, Cengiz; Paksoy, Halime
    An effective way to enhance the thermal storage capacity of buildings is to incorporate phase change materials (PCM) into building materials. Fatty acids are derivatives of materials readily found in nature and labeled as bio-based. In this study, we tested binary mixtures of capric acid (CA), myristic acid (MA), lauric acid (LA), and palmitic acid (PA) as candidate materials for building applications. The melting points of such fatty acid mixtures may further be adjusted, to agree with human comfort zone temperatures by regulating their compositions. We developed two binary mixtures of CA-LA and CA-MA as candidate PCMs for building applications. Thermal storage capacities were measured to be 109.0-155.4 J/g with a differential scanning calorimeter. Thermal cycle tests showed that both PCMs are thermally and chemically stable. Durabilities of PCM mixtures determined by the thermal gravimetric analysis indicated that degradation started at 120 degrees C. The compressive strengths of 1 wt.% PCM added to concrete mixtures were reduced by 12%, yet stayed within the desired limits for C35/45 concretes. However, when PCM contents were increased to 2 wt.%, compression strengths were reduced further, to be within the limits of C30/37 concretes. Both PCMs were suitable for self-compacting concrete mixtures used in buildings. (C) 2015 Elsevier B.V. All rights reserved.