Theses supervised by Prof. Dr. Mustafa Pınar Mengüç
13 theses · Özyeğin University
Near- and far-field thermal radiation in metamaterials and the development of NF-RT-FDTD algorithm
In this dissertation, analysis of near-field regime of thermal radiative transfer in metamaterials supporting surface phonon polaritons (SPhPs) is given. Solutions of electromagnetic fields at subwavelength distances are studied where combined effects of surface waves and total internal reflection, result in enhancement of thermal radiation by orders of magnitude when compared against far-field regime of thermal radiation which is obtainable through Planck's blackbody law. We have developed Near Field Radiative Transfer Finite Difference Time Domain (NF-RT-FDTD) algorithm which is developed based on Finite Difference Time Domain (FDTD) method specifically designed to provide full solutions to near-field radiative transfer problems by solving Maxwell's equations combined with fluctuation-dissipation theory. We have extensively investigated the near- and far-field thermal emission and heat flux profiles in different geometries with corrugations and porosities of various size and shapes and report on our findings which reveals a high degree of accuracy is attainable by NF-RT-FDTD method in complex geometries. We have compared our results against solutions of effective medium theory which makes effective medium theory's ability to provide accurate solutions highly questionable. NF-RT-FDTD could be used to provide solutions for complex geometries with different applications, including energy harvesting with near-field thermophotovoltaics, radiative cooling, thermal sensing, nano manufacturing and medical diagnostics.
Hesaplamalı akışkanlar dinamiği simülasyonlarını kullanarak yapı iç çevresinde ısıl konforun saptanması
Bu tez çalışmasında, içinde çeşitli eşyaların bulunduğu bir oda için, ısıl konfor seviyesinin belirlenebilmesi adına, zamana bağlı olarak üç boyutlu hazırlanmış modelin Hesaplamalı Akışkanlar Dinamiği (HAD) yöntemi kullanılarak, doğrudan güneşlenmeye maruz kaldığı zaman diliminde, malzemelerin ısıl kapasitesi de hesaba katılarak, analiz tamamlanmıştır. HAD hesaplamları için FloEFD yazılımı tercih edilmiştir. FloEFD tasarımcılar için hızlı ve güvenilir sonuçlar veren, ileri seviye HAD yazılım programıdır. Bu hesaplama aracı, iklimlendirme ve havalandırma cihazlarının oda içinde hava dağıtımında etkin olan kısımlarının modellenerek, akışın üç boyutlu görselleştirmesine imkanı vermektedir. Isıl konforun yorumlanması için gerekli parametreler olan, I) havanın dağılımı, II) havanın sıcaklık profili, III)) nemi ve IV) ortalama ışınım sıcaklığı bu vasıtayla hesaplamalara dahil edilebilmiştir. Bu çalışamada yapılan önemli farklılık ise ortamdaki malzemelerin yüzey yayıcılık değerlerinin ve camların ışınım geçirgenlik değerlerinin tayfsal olarak ele alınmasıdır. Kullanılan malzemelerin fiziksel özelliklerinin detaylı olarak yazılıma dâhil edilmesiyle, simülasyon sonuçları ve oda içinde belirlenmiş zamanda tamamlanan ölçüm sonuçları, karşılaştırıldığında yüksek tutarlılık göstermiştir. Değişik pencere özelliklerinin ve HVAC elemanı olan difüzörün farklı senaryolar altında değerlendirilmesi dört farklı parametrenin görselleştirilmesiyle yapılmıştır. Akabinde, ısıl konfor yorumu için, bu dört parametre insanların giydiği kıyafetlerin bilgisinin ve metabolik üretim değerlerinin Fanger Metod'la PMV ve PPD parametrelerine dönüştürülmesi yapılmıştır. Tamamlanan karşılaştırma analizleri, güneşlenmenin olduğu 8 saat süresince gerçekleştirilerek, oda içindeki malzemelerin sıcaklığının artmasının göz önünde bulundurulması sağlanmıştır. Böylece ısıl konforun etkilenmesinin sadece, doğrudan gelen güneş ışınıma bağlı değil, ısınan malzemelerin uzun dalga boylarıyla yaydığı ışınım sebebiyle de olduğu sonucu çıkarılmıştır. Yeni difüzör senaryosunda, gelen havanın doğrudan oturma alanına üflenmesi sayesinde kullanıcı ısıl konfor açısından lokal olarak olumlu etkilenmiştir. Fakat görülmüştür ki, 8 saat süresince konfor zonunda ısıl konfor daha hızlı azalmaktadır. Bunun sebebi ise kıyaslamanın yapıldığı birincil difüzörün, doğrudan camalara ve duvara üfleme yaparak, malzemenin ısınmasını geciktirmesidir. Bu çalışmanın sonucunda elde edilenler, büyük cam cephe giydirmeli mahaller için ısıl konforun değerlendirilmesinde kullanılabilir.
Radyant ısıtma sistemlerinin termal konfor performansının incelenmesi: Farklı ısıtma yüzey konfigürasyonlarının karşılaştırılması
This thesis is an experimental-numerical study for the thermal comfort assessment of radiant heating system for different heating configuration such as from a wall, ceiling and combination of both that is installed in a test room with dimensions of 4m x 4m x 3m. Comfort evaluation was done by using the PMV (The Predicted Mean Vote) - PPD (Predicted Percentage of Dissatisfaction) index developed by Fanger [1]. In addition, for each heating scenario, human body exergy balance was calculated and the effect of exergy consumption rate on thermal comfort was evaluated. The data generated during the tests are used in numerical model for the validation of it. Numerical model is used to investigate the air temperature distribution, velocity fields for different cases. Three different heating configurations were evaluated in numerical model as same as experimental study. Wall heating, ceiling heating wall and ceiling heating scenarios were explored in terms of PMV thermal comfort index and human body exergy balance approach. All the numerical analysis studies were conducted using the Academic version of ANSYS 17.1, which is a commercial package program for numerical modelling. It contains special modules for different stages of the modelling process. After the three-dimensional room geometry was created in the Design Modeler module, the meshing module was subjected to decomposition using the finite volume method. Numerical solutions were made in Fluent, a widely used computational fluid dynamics module. The temperature and velocity fields were visually inspected using CFD-Post software as the final processor program. The natural convection was modelled using the Boussinesq approach, and the standard k-ε model which is a common numerical solution was picked to model turbulence. A Discrete Ordinates model with no scattering was used for radiative heat transfer. Numerical solution results were compared with different mesh numbers and mesh independence was observed. Radiant panels have been investigated to provide and maintain thermal comfort at different surface set temperatures. In the given set values, temperature distribution in the vertical and horizontal direction, mean radiant temperature and air velocity values in the room were examined. It has been observed that the exergy consumption values in the radiant heating system are close to the lowest values stated in the literature. Also, the temperature distribution in the room is considerably lower than all conventional systems. This demonstrates that radiant systems using low quality energy sources provide efficient, environmentally-friendly comfort solutions. It should be stated that it is a preliminary study for the location-based heating technologies and this method can be an innovative solution for heating / cooling industry. Therefore, it can be further evaluated in future research studies.
Integrated design and application of a campus-wide distributed-photovoltaic system
After releasing the regulations on unlicensed electricity generation in Turkey, the main structure of the regulatory mechanism has just finished in 2014 and renewable energy generation started to grow dramatically. Ozyegin University Campus Wide Solar Energy Application is the first large-scale building integrated, grid-connected system. From the idea of the project to the implementation processes, it is a great success story for the development of the academic researches and solar energy market. The complete process of technical, economical and bureaucratic side will be investigated for the future development while giving insights about the operation period as well. Ozyegin University has completely rooftop PV system distributed on 4 buildings with a total capacity of 378 kWp. The whole system has a unique design that could be implemented on each buildings similarly. Solar energy production simulations with 4 different database systems, selection of the each component, complete system design, 3D models, financial analysis, static measurement and reports, governmental appointment mechanism, legal approval, installation, commissioning and operation are the main topics that will be covered within the thesis. The most important extraction over the analysis of system outputs is the Operational Performance Index, which should be used as a performance KPI for the photovoltaic system. At the end, the value and the originality will come from not only the system integrity but also modals generated for the development of the market.
Nanopartikül süspansiyonlarda pH'ın partikül topaklaşmasına ve ışınımla ısı transferine etkisi
Nanoparticle suspensions (NPSs) are solid-fluid mixtures where small dielectric or metallic particles (with sizes <100 nm) used in a base fluid. NPSs have unique and tunable thermo-optical properties, and for that reason they can be used extensively to improve the thermal efficiency of different systems where they show remarkable enhancement in heat transfer compared with those of a base fluid. The effectiveness of solar thermal systems used for photo-thermal energy conversion is measured by their ability of absorb radiative energy by the working medium; for such applications NPSs are much better choice than traditional fluids. NPSs have also been used in coatings as they can be tuned to improve or alter the appearance of an object, as radiative and optical properties play significant roles. Although NPSs are considered very promising for these applications, there is some concern about their stability and their long-term use. Particle agglomeration in NPSs remains one of the most important challenges faced in terms of their usage. In all of these applications, the pH value and its effects on the particle agglomeration may have significant impact on the nanoparticles stability behavior, and consequently on the radiative transfer of energy. Steric and electrostatic stabilization methods are among the two approaches used for particulate suspensions to avoid such problems. In thermal applications, especially in high temperature ones, electrostatic stabilization method is usually preferred. In this dissertation, both experimental and theoretical investigations were carried out to determine the stability and optical properties of individual (water/TiO_2 and water/Al_2 O_3) and hybrid (water/TiO_2+Al_2 O_3) nanoparticle suspensions. The experimental studies include the preparation, characterization, and optical property measurements of the nanoparticle suspensions. The impact of the electrostatic stabilization (zeta potential and pH values) on the size and structure of particles due to agglomeration behavior are explored. The particle size distribution and the average (effective) particle agglomerate size for the nanoparticle suspensions in different conditions (the pH and particle volume fraction) were measured by using the dynamic light scattering (DLS) technique. The effects of the different particle agglomerates under different pH values on the dependent and independent scattering and their boundaries are investigated and demarcated for different conditions, where the relationship between the distance between particle to particle surface and the incident wavelength for different particle types are explored. The effects of particle agglomeration (similar and dissimilar particle agglomerations), particle size distribution and their contributions to the radiative properties of the nanoparticle suspensions are determined using the UV-Vis spectroscopy technique. The numerical part included the study of the optical and radiative properties and thermal radiation transfer based on the average (effective) particle agglomerate size obtained from the experimental studies. The optical and radiative properties of nanoparticle suspensions are calculated based on the Lorenz-Mie theory applying the single-scattering approximation technique. The influence of the particle size distribution on the scattering coefficient of nanoparticle suspensions is studied theoretically to account for the effect of compact particle agglomerates. The thermal radiation transfer in the nanoparticle suspensions is assessed by solving the radiative transfer equation using the discrete ordinates method, where the volumetric radiative heat flux and the thermal flux efficiency are calculated. The results show the impact of pH value on the stability of individual and hybrid nanoparticle suspensions. The different particle agglomerate types, sizes, and shapes yield different behavior of suspensions, including their stability or sedimentation rates, which help formation of optically thicker media. Light scattering in such media is significantly different as a function of the proximity of particles to each other. If they are closer to each other roughly less than dominant wavelength of the radiation, then their behavior is defined as dependent scattering, which is explored in this study. It is shown that a significant enhancement in the radiative properties, specifically in the UV/Vis spectrum, can be observed , which has an important effect on the thermal radiation transfer of the incident solar radiation. The demarcation of dependent and independent scattering regimes is explained for the individual and hybrid nanoparticle suspensions based on their pH value. NPSs with different effective particle agglomerate sizes have a considerable effect on the volumetric radiative heat flux, where the losses in radiative energy were decrease in comparison to those of pure water. The results also show the effects of composite particle agglomerates in the hybrid nanoparticle suspensions on the radiative properties, which are produced from dissimilar suspended particles. The results of this dissertation show that the pH value has a dominant effect on the radiative transfer involving nanoparticle suspensions, compared to other parameters. Adjusting the pH value based on the isoelectric point of the nanoparticle is an efficient method when specific radiative properties are required for specific applications. Such impact of pH value on optical and radiative properties of NPSs is studied for the first time in the literature.
Parabolk güneş toplayıcılarında ısınım ve ışınım transferi bazlı enerji/ekserji analizleri
The concept of exergy is used to determine the maximum energy that can be extracted from a system. It is based on both the first and the second laws of thermodynamics and allows us to determine the irreversibilities throughout a process and the losses from the system. In this dissertation, the fundamentals of spectral radiative exergy are developed and applied to determine the maximum conversion of solar energy in concentrated solar power (CSP) systems. There are five primary objectives of this study. First, a new formulation is developed for the maximum efficiency of the solar radiation conversion by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Exergy of spectral radiative transfer is determined, and the formulation for the exergy efficiency maximization is presented in a direct and practical manner. For the calculation of maximum efficiency, the mean temperature of the environment and the sink temperature are used. Second, a new methodology is presented for spectral radiative energy and radiative exergy calculations to evaluate the performances of CSP systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are considered in these analyses. The fundamental quantities needed for the spectral radiative energy and radiative exergy formulations are introduced, and then the spectral performances of five selective coatings are assessed. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. The third objective is to introduce a new approach for estimating the exergy value of the monthly average daily horizontal global radiation, including several parameters, such as the monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The concept is applied to four locations in Iraq and Turkey, to help predicting the maximum available solar radiation based on different weather parameters. The fourth objective is to outline a comprehensive energy analysis for a parabolic trough collector (PTC) system. The analysis considers all heat transfer modes, optical components, and the details of spectral absorption and reflection of solar radiation on the glass envelope. The energy performance of the PTC system is investigated using five gases in an annular space, five selective coatings of the absorber surface, and four common heat transfer fluids following a two-dimensional approach. A model is built using Engineering Equation Solver (EES). The results obtained are compared against the available results from experimental tests and analytical models. This analysis shows the effects of the properties of the absorbing gas, the selective coating and the working fluid on the energy performance of PTC as the key parameters of energy for various operating conditions. The fifth objective of the study is to establish a methodology to analyze PTC systems using the principles of spectral radiative exergy. The fundamental relations for spectral exergy analyses are derived starting from the first and second law of thermodynamics, and the key performance parameters, including exergy losses, destructions, consumption and efficiency are determined using the same parameters mentioned above in the fourth objective. It is noted that the exergy destruction is directly related to irreversibility throughout processes while the exergy losses are due to the thermal and optical losses. Based on these findings, an improvement of PTC design parameters are discussed.
Tesis yönetimi stratejisinde kullanıcı odaklı döngüsel operasyon modeli
Facility management (FM) concept should be re-considered for the next generation of strategic operations of buildings and should be human-focused. Traditional FM strategies are based on designs by the stakeholders and engineers and aim to have the optimum operational strategy from the financial point of view. However, this concept should include broad long-term strategic planning and focus on the users in a building, in addition to the daily tasks of building operations. The transdisciplinary innovation challenges in FM sector necessitate the consideration of human behavior during the process. The objective of this paper is to offer an optimum facility management strategy to make the actual residents of a building comfortable and productive. This can be achieved by designing a supportive management model for the core business processes. Our studies indicate that there are gaps between what building managers provide and what the users desire. This gap can only be closed by effectively considering different levels of behavior models. The study aims to design an optimum strategy for coupling human behavior models and building managers' decisions. Towards that end, we introduce a conceptual framework to enable the occupant engagement in buildings. The proposed "Circular Operation" model in a building is defined as a closed loop system which is actively engaging its users in the FM process. It is based on a business model replacing the end-of-life concept with linear frames, and increasing the building energy efficiency along with the comfort of the residents. The methodology is discussed with the help of multiple case studies based on qualitative research. This work provides guidelines for the managers by quantifying individual responses as a preliminary measure and by mapping user behavioral choices for the optimum operation strategy of a high performance, energy efficient and comfortable building.
Energy and exergy efficiency analyses of high-performancebuildings
Reducing building energy density has become one of the global requirements to a decrease fuel consumption and emission production, and consequently making our world sustainable. The high value of energy consumed by buildings highlights the importance of the requirement to decrease building energy demand. The aim of this thesis is to analyze a well-designed existing building exegetically, exergo-economically and environmentally in order to determine the consequent effects of any options for improvement. In the first part of the study, the building was analyzed statically and dynamically (hourly) over a year for the heating season to specifically highlight the differences between them in addition to an accuracy estimation. In the second part, actual experimental processes for improvement that were applied to the buildings at different stages were investigated as well. For this study, the SCOLA Building at Ozyegin University Campus in Istanbul is considered. SCOLA was designed to be one of the least amounts of energy consuming buildings in Turkey. It includes 291 rooms with a floor area of 17,250 m2 and 6 floors. A natural gas boiler that produces hot water is used to heat the building with a distribution network and four fan coils. The hourly operational information about the heating system was recorded and used in tandem with the local weather data. The calculations were applied both in static and dynamic fashion, based on the recommendations from the facility management team. Improved pre-design tools were used to implement these details to the simulations. The simulations reveal that energy demand for the building can be as low as 1.38 MW and exergy is 1.34 MW at peak load, while their annual values are 8.9 GJ and 8.2 GJ, respectively. Based on the calculations, the specific heating demand at the building is found to be 25 W/m2 while the annual specific heating demand is 80 W/m2/yr (if heating is evenly distributed to the year; actual energy density for the building is determined to be 50 W/m2/year, considering summer months). The reduction in energy and exergy demand reaches 6% during working hours of the 21st January 2016, simultaneously reducing the cost and the CO2 emissions. The increase in exergetic cost coefficients reflect the reduction in the exergy efficiency of the heating system components based on the ambient temperature change. It is noted that a dynamic analysis using average monthly temperatures is preferred over a static analysis. However, if a simpler static analysis is to be used, an annual average temperature needs to be identified for a specific climate zone and building type. For Istanbul, an average temperature of 14oC is recommended for a static analysis. We also examine how different engineering implementation strategies, in addition to the original design, can improve the thermal performance of the building. Five different cases (scenarios) are investigated in addition to the original case which is considered to be the base case (1st case). The second is the use of a ground air heat exchanger, whereas the use of better insulation materials and the use of glass and roofs is the third case study representing the traditional approach. The use of solar PV-panels over the entire building constitute the fourth case, and the integration of a campus tri-generation system to the building energy modalities is considered as the fifth case. Applying all these processes to the building simultaneously is considered as the sixth scenario. All these changes have already been implemented in the building where the real time data are being collected. Performance simulations based on exergy, exergoeconomic, and environmental analyses are conducted and presented. Energy and exergy flow diagrams from all sources to the envelope for all cases are also outlined and conclusions are drawn. A Marginal Abatement Cost Curve (MACC) was constructed based on exergy analysis in order to achieve more accurate results. MACC analysis outlines the cost and carbon dioxide emission savings simultaneously. Its results help policymakers to employ the best potential option.
Giysilerin termo-fizyolojik konfor üzerindeki etkisi
This study investigates the effect of garment on human thermophysiological comfort. In this thesis simplified but effective model of heat transfer from human skin to the environment through clothing is proposed. A comprehensive and detailed literature search is provided. Thermal comfort models in literature are examined and based on the Fanger's comfort model, the simplified thermal comfort model is developed. The objective is improving an algorithm which is easy to calculate numerically yet gives best possible results by matching well with the experimental data in literature. The objective is developing a thermal comfort algorithm that can be used in IOT applications such as smart phones and smart buildings, so that a user can control his/her thermal comfort state by changing his/her clothing according to outputs of the algorithm. Therefore, the algorithm has to give fast but good results that do not require any use of measurement instruments. In buildings, the use of PMV control showed 7.3 % less energy consumption than the dry-bulb air temperature control and showed 28.8 % less energy consumption for the annual cooling electricity consumption (Hong, 2018). Therefore, this study can be used for such building control applications. Fanger's Predicted Mean Vote model is adopted to scale comfort values for this application. Different case studies that are focusing on clothing thermal resistance, evaporative resistance and PMV, are investigated. Codes are simulated in MATLAB. The main output of the algorithm in this study is suggestions on how a person should change his/her clothing to feel comfortable at any time in any environment. This algorithm is used for different strategies.
İnsan vücudu ısı değişim mekanizması ve görsel uyarım ile termal konfor
Thermal comfort is a combination of several components and can be described in many ways while for all definitions the precedence is human. In this thesis, thermal comfort is examined through the environmental differences and psychological changes via several experiments performed with human subjects while accounting for metabolic rates and clothing level. For the experimental study, three different test scenarios were considered, to examine if a human subject is feeling hot, cold or comfortable. To track the comfort level of subjects, skin temperatures were measured from four different body segments and TSV (Thermal Sensation Vote) questionnaires were given at certain intervals. To compose the required combinations of environmental parameters of the test room such as, relative humidity, air velocity, air temperature the Fanger Method was used and comfort level of the test rooms were described according to PMV (Predicted Mean Vote) indices. Participant's psychological changes were controlled with emotional stimulating pictures from IAPS (International Affective Picture System) data base. IAPS consists of several colorful images with different levels of stimuli (pleasant, unpleasant and neutral pictures). Each subject attended one of the case conditions randomly and during 15 minute long experiments, watched 3 different blocks of stimuli pictures. Consequently, the direct effects of human emotions on thermal comfort and thermal sensations were assessed throughout the experiments and with this study it is aimed to find a way to decrease energy usage on HVAC systems by controlling human psychology within certain limits.
Augmenting occupant thermal experience with cyber-physical-social systems: A case study on adaptive vents
Buildings use more than 30% of global energy, while 36% of this energy comes from direct combustion of fossil fuels. Hence, buildings constitute a considerable share of CO2 emissions and has a large contribution to climate change related problems. The highest share (almost half) of the total energy consumption in buildings is due to heating, cooling and air conditioning (HVAC). Particularly, the increasing demand for space cooling is pushing this share up. Thus, HVAC systems are considered as one of the key contributors of the total energy consumption and the adverse environmental impacts of buildings. Recent developments in technology offer promising tools to leverage interactions between occupants and the building systems. The energy efficiency of HVAC operations is not only a technical concern, what is more is that it requires to modifications considering human behavior. The convergence of physical systems in built environment with the information and communication technologies, as well as the human dimension makes it necessary to co-evaluate these distinct realms during the design and operation of building systems. The cyber-physical-social systems (CPSS) approach has a promising potential to facilitate this interdependence. A novel HVAC interface is presented in this thesis study. An Adaptive Vent System (AVS), is proposed to enable localized and customized thermal management in built environment for a better thermal experience of occupants and higher level of energy efficiency for building operators. The system is designed as a CPSS and composed of: (i) a novel diffuser design with individually operable flaps, (ii) thermal agents, (iii) a user interface, and (iv) a control and communication unit. It enables asymmetric air-inlet to manage indoor temperature distribution and aims to match varieties in temperature with the differences in occupant demands. The system is intended to decrease the conditioned air volume that results in HVAC energy efficiency without sacrificing occupant comfort. The design and operation of complex building energy systems like AVS is a challenging task. In order to assist this process, a methodological framework is presented that outlines the development process, from the early definition to prototyping and performance analysis. The framework is based on a novel CPSS modeling approach that combines hybrid dynamic modelling (for cyber and physical aspects) with human behavior modeling (for social aspects). A prototype of the proposed AVS was deployed in an office of an academic building in order to conduct experiments and validate CPSS and computational fluid dynamics (CFD) models. Both experiments and simulation based assessments of system operation shows that system can generate temperature difference between opposite sides of a room in a controllable manner. It is also shown that this difference results in considerable change in thermal sensation of occupants and can pave the way for energy savings with localization inside the rooms. The core reason for efficient HVAC operation with AVS is the usage of less amount of thermally conditioned air by minimizing the conditioning of unnecessary parts of the room. Moreover, the system leverages occupant interaction by delivering advanced control options (enhanced perceived control) for more customized practices. The interplay between the building energy management and the localization and customization of thermal management can maximize demand flexibility of buildings, that is a key concern for demand side management and energy planning. Hence, the new AVS system is to leverage overall thermal experience in built environment in an energy efficient way and help decreasing the environmental impact of buildings.
Kum ile radyatif soğutma
Passive radiative cooling is one of the upcoming technologies likely to help decrease the negative impacts of climate crises and reduce energy consumption in buildings. The principle of radiative cooling involves radiating heat from the surface of a building into space, thus reducing the reliance on air conditioning systems. Understanding the fundamentals of passive radiative cooling is important for thermal management related to buildings and industrial applications. The principle of radiative cooling in buildings involves selectively reflecting incident radiating heat from the surroundings and selectively emitting energy from a surface to the surroundings to achieve minimum heat load on the system. In the case of buildings, solar radiation incident on roofs can be reflected or absorbed. The absorbed heat is either transferred to the surrounding air by convection or it will be emitted back to the sky. If a surface is desired to be radiatively cooled it must have a large reflection of solar energy at the visible wavelength range and the highest radiation emission at the atmospheric window range (8-13 µm wavelength range) as discussed in detail in the thesis. This technique can significantly help reduce greenhouse gas emissions as it will help decrease air-conditioner use in warm climates during the summer months. Recently, the use of nanoparticles and different structures has been considered for passive radiative cooling applications. In this study, we investigate the radiative cooling properties of sand particles experimentally and compare their performance with other materials including silicon dioxide, titanium dioxide, and zinc oxide. Scanning electron microscopy (SEM) is used to analyze the morphology of the surface of sand the particles, and the other materials used in the study for comparison. Fourier transform infrared spectroscopy (FT-IR) experiments were conducted in order to measure the absorbance and transmittance percentage of the samples. In addition, the absorption coefficient was calculated from the FT-IR measurements. The absorption coefficient of the sand samples showed a high ratio (in the units of 1/m which was approximately between 0.4⨯10^4 and 0.8⨯10^4 for all the pellet samples at the atmospheric window range. Also, the behavior of the absorption profiles of the sand sample and ZnO were very similar in their ratios, especially in the atmospheric window range. Also, we observed that the emission shows the highest peaks at 6.78 µm, 9.24 µm, 11.69 µm, and 14.05 µm for all sand pellet samples. Thus, the properties of sand samples experimentally studied in this work show that they can be used for radiative cooling due to their abundance and thermal properties with better performance.
Kum ile Radyatif Soğutma
Passive radiative cooling is one of the upcoming technologies likely to help decrease the negative impacts of climate crises and reduce energy consumption in buildings. The principle of radiative cooling involves radiating heat from the surface of a building into space, thus reducing the reliance on air conditioning systems. Understanding the fundamentals of passive radiative cooling is important for thermal management related to buildings and industrial applications. The principle of radiative cooling in buildings involves selectively reflecting incident radiating heat from the surroundings and selectively emitting energy from a surface to the surroundings to achieve minimum heat load on the system. In the case of buildings, solar radiation incident on roofs can be reflected or absorbed. The absorbed heat is either transferred to the surrounding air by convection or it will be emitted back to the sky. If a surface is desired to be radiatively cooled it must have a large reflection of solar energy at the visible wavelength range and the highest radiation emission at the atmospheric window range (8-13 µm wavelength range) as discussed in detail in the thesis. This technique can significantly help reduce greenhouse gas emissions as it will help decrease air-conditioner use in warm climates during the summer months. Recently, the use of nanoparticles and different structures has been considered for passive radiative cooling applications. In this study, we investigate the radiative cooling properties of sand particles experimentally and compare their performance with other materials including silicon dioxide, titanium dioxide, and zinc oxide. Scanning electron microscopy (SEM) is used to analyze the morphology of the surface of sand the particles, and the other materials used in the study for comparison. Fourier transform infrared spectroscopy (FT-IR) experiments were conducted in order to measure the absorbance and transmittance percentage of the samples. In addition, the absorption coefficient was calculated from the FT-IR measurements. The absorption coefficient of the sand samples showed a high ratio (in the units of 1/m which was approximately between 0.4 ⨯ 10^4 and 0.4 ⨯ 10^4 for all the pellet samples at the atmospheric window range. Also, the behavior of the absorption profiles of the sand sample and ZnO were very similar in their ratios, especially in the atmospheric window range. Also, we observed that the emission shows the highest peaks at 6.78 µm, 9.24 µm, 11.69 µm, and 14.05 µm for all sand pellet samples. Thus, the properties of sand samples experimentally studied in this work show that they can be used for radiative cooling due to their abundance and thermal properties with better performance.