Numerical Determination of Effects of Wall Temperatures on Nusselt Number and Convective Heat Transfer Coefficient in Real-Size Rooms

A modeled room was numerically heated from a wall and cooled from the opposite wall in order to create a real-room simulation. The cooled wall simulated heat loss of the room, and the heated wall simulated the heat source of enclosure. The effects of heated and cooled wall temperatures on convective heat transfer coefficient (CHTC) and Nusselt number in the enclosure were investigated numerically for two- (2D) and three-dimensional (3D) modeling states. Different hot wall and cold wall temperatures were applied in order to obtain correlations that contained characteristic length in Rayleigh numbers. Results were compared with the results of previously reported correlations that have been suggested for vertical room surfaces in enclosures. In addition, new correlations for Nusselt number and average CHTC for enclosures for isothermal boundary conditions within indicated Rayleigh number ranges were derived through solutions. Average deviations of new correlations obtained for CHTC and Nusselt number from the numerical data were found 0.73% and 1.76% for 2D study, 3.01%and 0.49%for 3D study. It was observed that the difference between the 2D and 3D solutions in terms of CHTC and Nusselt number was approximately 10%

Exergoenvironmental and exergoeconomic analyses of a vertical type ground source heat pump integrated wall cooling system

akbulut, ugur/0000-0002-9317-3298WOS: 000379270300092In this study, exergoenvironmental, and exergoeconomic analyses of wall cooling systems fed by a vertical type of ground source heat pump integrated wall cooling system for cooling were examined experimentally and theoretically in Yildiz Renewable Energy House at Davutpasa Campus of Yildiz Technical University. the examination includes energy, exergy, exergoenvironmental and exergoeconomic analyses, between the dates of 1 July and 30 September 2013. the main aim of this objective is to minimize energy usage in Residential Sector as low as possible. Therefore, a particular system working with low temperature regime was chosen. According to the outcomes; energy and exergy efficiency of all the system have been found as 74.85% and 29.90%. Part-based environmental factor values are calculated. the compressor and underground heat exchanger have the highest values calculated as 0.040 mPts/s, 0.026 mPts/s respectively. the exergoenvironmental impact values of all system are detected as 42.60%. on the other hand; the exergoeconomic factor values of all system are calculated as 77.68%. the value of exergoeconomic factor changes depending on some particular components: accumulator tank, undersoil heat exchanger, evaporator and condenser calculated respectively as 69.43%, 62.59%, 62.53% and 29.15%. As a result; it is found that in order to determine economic and environmental impacts of irreversibilities occurring in the system and its components, economic and environmental analyses of thermal system as well as wall cooling systems, should be done based on exergy concept. (C) 2016 Elsevier Ltd. All rights reserved

Exergy, exergoenvironmental and exergoeconomic evaluation of a heat pump-integrated wall heating system

akbulut, ugur/0000-0002-9317-3298WOS: 000378660500042In this study, a vertical ground source heat pump wall heating system belonging to the Yildiz Renewable Energy House on the Davutpasa Campus of Yildiz Technical University was experimentally and theoretically studied. the examination included energy, exergy, exergoenvironmental and exergoeconomic analyses from 1 January 2013 to 30 March 2013 (i.e., the "Winter Session"). Data were collected and uploaded to a MySQL database. "The moments when the heat pump is activated" was detected and "Monthly Average Values" were analysed. Theoretical analyses were conducted for the Winter Session and correlated with the experimental results. This study includes exergetically, exergoeconomically, and exergoenvironmental evaluate a building and its heating system from the generation stage to the envelope of the building. the findings are based on applying a low exergy, exergoenvironmental and exergoeconomic analysis to investigate the system" performance. the energy and exergy efficiencies of the entire system were 67.36% and 27.40%, respectively, and the energy and exergy efficiencies of the wall heating system panels were 86.61% and 82.90%, respectively. the monthly average exergy-based environmental impact value was 0.212 mPts/s. the exergoeconomic factors changed from 74.97% to 75.77%. (C) 2016 Elsevier Ltd. All rights reserved

Modeling of the drying process of apple slices: Application with a solar dryer and the thermal energy storage system

WOS: 000408288100032In this study a solar air heater was developed to determine the drying rate of apple (Golden Delicious). In order to provide the drying process continuously a packed bed thermal energy storage system was designed and manufactured. Also, a recuperator unit was used for waste heat recovery. In the recuperator unit, it is provided the mixing of the fresh air with the drying air whose moisture content increases, at a specified rate. So at the rate of 50-60% waste heat is recovered and reutilized in the drying system. The advantage of the system is that it consumes less energy at the rate of 76.8% than other drying technologies. Experinients on the drying system were repeated twice a day. In the experiments the drying kinetics of apple slices (5 +/- 2 mm thick) was determined at constant temperatures ranging from 50-60 degrees C. Also, Diffusion Approximation model was used for drying of apple slices in constant temperature. A mathematical model was developed to calculate the prediction of the moisture ratio during time and it is observed that the model is complied with the studies in the literature. (C) 2017 Elsevier Ltd. All rights reserved.Republic of Turkey Ministry of Science, Industry and Technology as a San-Tez ProjectThe study was supported by Republic of Turkey Ministry of Science, Industry and Technology as a San-Tez Project