Browsing by Author "Okulu, D"

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    Review on nanofluids and machine learning applications for thermoelectric energy conversion in renewable energy systems
    Okulu, D; Selimefendigil, F; Öztop, HF
    This review is about applications of nanofluids technology and different machine learning algorithms on the potential improvement of system performance and computational efficiency of thermo-electric device installed systems. Brief information about the thermo-electric energy conversion principles, construction materials and different application areas in energy system technologies are presented. The applications of nanofluid technology in thermoelectric conversion starting from the basic information on the common nanofluid types, modeling aspects and thermophysical properties are presented. Potential of using nanofluid in diverse thermoelectric installed system on the conversion efficiency and performance improvements are discussed. Applications of different machine learning algorithms with the basic information on the most common applied ones are presented. The computational efficiency of using different machine learning methods have been analyzed. The gap in the present literature and future trends are discussed. As thermoelectric devices, which are among the clean energy technologies, gain importance with the many advantages they offer and draw attention with their adaptability to different systems, the results summarized here, and future aspects will be beneficial for efficient design and optimization of energy related technologies.
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    Numerical analysis for performance enhancement of thermoelectric generator modules by using CNT-water and hybrid Ag/MgO-water nanofluids
    Selimefendigil, F; Okulu, D; Mamur, H
    The aim of this study is to investigate the performance enhancement of thermoelectric generator module with different nanofluids. CNT-water nanofluid and Ag/MgO-water hybrid nanofluids are used in a 3D channel where thermoelectric generator modules are mounted. 3D coupled multi-physics simulations are performed by using Galerkin weighted residual finite element method. It was observed that the power output of the module enhances with the inclusion of nanoparticles. Configuration with hybrid nanofluid produces the highest output power. At Reynolds number of 500, increasing the solid volume faction from 0.005 to 0.2, the output power of the thermoelectric generator rises by about 5.84% and 9.30% for CNT-water and hybrid nanofluid. However, at Reynolds number of 1500, using CNT-water nanofluid becomes effective and the amount of increment will be 6.6%. The efficiencies of the module rise with Reynolds number and solid particle volume fraction, while the values are low.
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    Three dimensional numerical study of PV module cooling by using thermoelectric effects and nano-enhanced confined multiple slot jet impingement
    Selimefendigil, F; Okulu, D; Oztop, HF
    In this study, 3D numerical study of photovoltaic (PV) module cooling is analyzed by combined utilization of thermoelectric generator (TEG) and nano-enhanced slot jet impingement system. For the relevant parameters of interest, such as Reynolds number (between 10 and 100), nanoparticle loading (solid volume fraction between 0 and 0.02), non-dimensional vertical distance between the slots and upper plate (between 2.5 and 8), non-dimensional spacing between the slots (between 2.5 and 8), and cold NF inlet temperature (between 20oC and 30oC), finite element method is utilized. Using only TEG and nano-jet assisted cooling with TEG result in PV -cell temperature reduction by about 43.33oC and 69.55oC as compared to un-cooled PV module. It is observed that cell temperature decreases by about 2.4oC-2.9oC when considering the minimum and maximum Reynolds number cases. When nanoparticle loading is increased to 0.02, output TEG power rises while cell temperature decreases by about 0.75oC. When varying the vertical distance between the slot to the impinging surface, cell temperature changes up to 1.9oC while distance between the slots has very slight impact on the temperature variation. Decreasing the inlet fluid temperature by about 10oC decreases the cell temperature by about 8.5oC.
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    Effects of using a finned cylindrical cooler in the nano-enhanced cooling channel on the exergetic performance of a PV/TEG-coupled system
    Selimefendigil, F; Okulu, D; Öztop, HF
    In this study, three different nano-enhanced channel models were integrated into the 3D photovoltaic (PV)/thermoelectric generator (TEG) system and the effect of the channel models on the PV/TEG system performance was examined. The flat rectangular channel, Model 1 while the cylindrical and fin-reinforced cylindrical object accommodated in the flat rectangular channel are defined as Model 2 and Model 3, respectively. A comparison of water and ternary nanofluid with various nanoparticle (solid particle volume fraction between 0.01 and 0.03) loading was performed in each channel model. In addition, impacts of cooling fluids at different inlet temperatures (Tg between 25 degrees C and 12.5 degrees C) were considered in the simulations. Among different cooling channels, lowest PV cell temperature and the highest PV output power were obtained in Model 3. The highest PV power (0.51 W) was obtained with Model 3 with ternary nanofluid (%3 volume fraction) at Tg = 12.5 degrees C. This value is is 3.66% and 4.03% higher than Model 2 and Model 1, respectively. Under the same conditions, TEG output power reached its highest value with Model 2 and it was followed by Model 1 and Model 3, respectively. With the reinforcement of fins to the cylindrical object, an improvement in thermal performance was achieved, but a decrease in total output power was observed.
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    Application of ternary nanofluid and rotating cylinders in the cooling system of photovoltaic/thermoelectric generator coupled module and computational cost reduction
    Selimefendigil, F; Okulu, D; Oztop, HF
    Innovative cooling systems and solar panel modeling approaches have become critical for effective photovoltaic module performance and higher energy efficiency. In the present study, a novel cooling system for thermoelectric generator integrated photovoltaic module is proposed. Three dimensional coupled photovoltaic module/thermoelectric generator/cooling channel system is numerically analyzed by using Galerkin weighted residual finite element method. The cooling channels include rotating circular cylinders, with ternary nanofluid serving as the cooling medium. Three dimensional coupled numerical simulations are carried out for various values of cylinder's rotational speed (rotational Reynolds number, Rew between 0 and 5000), number of channels with rotating cylinders ( N between 2 and 8), size of the cylinders in the cooling channel ( RC between 0.006 H and 0.433 H) and nanoparticle amount in water (cp between 0 and 3%). Higher rotational speed of the cylinders, higher nanoparticle loading and higher channel number with cylinder contribute positively to the performance enhancement of the photovoltaic-thermoelectric generator coupled system. In the case of motionless cylinder in cooling channels, larger cylinder sizes have negative impact on the performance. By using cylinders that rotate at the fastest possible rate together with the usage of ternary nanofluid and only water, photovoltaic-cell temperature drops of 61.6 degrees C and 61 degrees C in comparison to un-cooled photovoltaic are achieved. When compared to motionless cylinder arrangements, cell temperature reductions of 4.3 degrees C and 3 degrees C are achieved by using the fastest rotation speeds for the base fluid and nanofluid. The temperature of the photovoltaic cells decreases and the thermoelectric power increases as the number of rotating cylinders in the cooling channels increases while temperature of the cell drops by 2 degrees C from N = 2 to N = 8 and becomes 4.3 degrees C as compared to motionless cylinder configuration. An efficient computational method by using proper orthogonal decomposition is proposed. While the computational time is reduced by a factor of 1/50, the approach is effective in properly predicting the variation in photovoltaic-cell temperature. The proposed cooling system and practical computational method are useful for further development and optimization of efficient thermal management of photovoltaic panels and integrated systems.
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    Energy and exergy performance improvement of coupled PV-TEG module by using different shaped nano-enhanced cooling channels
    Selimefendigil, F; Okulu, D; Oztop, HF
    In this study, impacts of using different cooling channels (L, T and U-shaped) on the energy and exergy performances of combined PV/TEG (photovoltaic/thermoelectric generator) unit are numerically assessed by using FEM based three dimensional high fidelity computational simulations. Cooling performance is boosted by using ternary nanofluid in the channels. The study is conducted for a range of Reynolds numbers (Re, between 50 and 500), nanofluid cooling inlet temperatures (between 15 degrees C and 23 degrees C), and nanoparticle loading amounts (between 0 and 3%). Evaluations are done on average PV-cell temperature, PV/TEG output powers, exergy efficiency, improve potential (IP), and sustainability index (SI). U-shaped and T-shaped channels are found to offer the greatest and worst cooling performances among various cooling channels. When comparing the lowest and maximum Re cases, the average temperature drops for PV cells are 3.54 degrees C for T channel and 2.55 degrees C for U channel. Exergy efficiency is determined to be 14.2% with T-channel at Re=50 and 14.6% with U-channel at Re=500. Taking into consideration different channels, an increase in the inlet temperature from 15 degrees C to 23 degrees C leads to an average rise in cell temperature of 6 degrees C. The IP rises with coolant inlet temperature while using T-channel. SI values fall as input temperature increases, although values between 1.164 and 1.175 may be achieved by using different cooling channels. Using nanofluid with higher loading results in higher exergy efficiency when comparing exergetic performances, with U-channel design exhibiting the highest performance. For the range of parameters considered, the coolant inlet temperature at the channel entry has the highest effect on PV cell temperature reduction; 8.5 degrees C of temperature reduction is feasible. By employing U-channel cooling, the maximum value of Re, the highest loading of nanoparticles, and the lowest inlet temperature yield the best exergy efficiency. The best and worst situations' respective exergy efficiencies are determined to be 15% and 14.1%. Utilizing T-channel cooling with water at a flow flow rate and a higher input temperature is the scenario with the biggest potential for exergy improvement; the value is 2.9. When different operational parameters are varied, the SI falls between 1.176 to 1.16.
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    A Novel Cooling System by Surface Corrugation and Nanofluid Utilization for the Performance Improvement of Photovoltaic Module Coupled with Thermoelectric Generator and Efficient Computations by Using Artificial Neural Network-Based Hybrid Scheme
    Selimefendigil, F; Okulu, D; Oztop, HF
    For a photovoltaic module coupled with thermoelectric generator, a unique wavy cooling channel is proposed, and its performance is numerically assessed by using three-dimensional computations. The cooling channel uses nanofluid of alumina-water with various shaped nanoparticles (spherical, cylindrical and brick). Numerical simulations are performed for a range of parameters for the corrugation amplitude (0 <= Amp <= 0.1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0 \le \text {Amp} \le 0.1$$\end{document}), wave frequency (2 <= Nf <= 16\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2 \le \text {Nf} \le 16$$\end{document}), nanoparticle loading quantity (0 <= SVF <= 0.03\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0 \le \text {SVF} \le 0.03$$\end{document}), and nanoparticle shape (spherical, brick, and cylindrical). We analyze the photovoltaic module's average temperature and temperature uniformity for a variety of parameter variations. When nanofluid and greater channel corrugation amplitudes are utilized, the average panel surface temperature is decreased more. A wavy shape of the cooling channel at the maximum corrugation amplitude yields a cell temperature reduction of 1.88 o\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>\text {o}$$\end{document}C, while frequency has little impact on average cell temperature and its uniformity. The best-performing particles are those with cylindrical shapes, and the drop-in average photovoltaic temperature with solid volume fraction is essentially linear. As utilizing cylindrical-shaped particles, the average temperature of corrugated cooling channels decreases by around 1.9 o\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>\text {o}$$\end{document}C as compared to flat cooling channels with base fluid at the greatest solid volume fraction. As compared to un-cooled photovoltaic, cell temperature drops by around 43.2 o\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>\text {o}$$\end{document}C when employing thermoelectric generator. However, temperature drop value of 59.8 o\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>\text {o}$$\end{document}C can be obtained by using thermoelectric generator and nano-enhanced wavy cooling channel utilizing cylindrical-shaped nanoparticles. An hybrid computational strategy for the fully coupled system of photovoltaic with cooling system is provided, which reduces the computational time by a factor of 75.
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    Photovoltaic Thermal Management by Combined Utilization of Thermoelectric Generator and Power-Law-Nanofluid-Assisted Cooling Channel
    Selimefendigil, F; Okulu, D; Öztop, H
    In this study, two different cooling systems for the thermal management of a photovoltaic (PV) module were developed. A PV/thermoelectric generator (TEG) and PV/TEG-mini-channel cooling systems were considered; in the later system, water and water-based Al2O3 nanofluids were used in the cooling channel. The effective cooling of the PV module was achieved by using higher-loading nanoparticles in the base fluid, while the nanofluid exhibited a non-Newtonian behavior. The PV/TEG with a cooling channel system was numerically assessed with respect to various values of Reynolds numbers (between 5 and 250), inlet nanofluid temperatures (between 288.15 K and 303.15 K), and nanoparticle volume fractions in the base fluid (between 1% and 5%). Variations in average cell temperature, PV power, TEG power, and efficiencies were computed by varying the pertinent parameters of interest with Galerkin's weighted residual finite element method. The most favorable case for cooling was obtained with TEG-cooling channel at f = 5% and Re = 250. In this case, PV electrical power increased by about 8.1% and 49.2% compared to the PV/TEG and PV system without cooling, respectively. The TEG output power almost doubled when compared to the PV/TEG system for all channel models at Re = 250. The inlet temperature of the nanofluid has a profound impact on the overall efficiency and power increment of the PV module. The use of the PV/TEG-cooling channel with the lowest fluid inlet temperature (288.15 K) and nanofluid at the highest particle loading (f = 5%) resulted in a PV efficiency increment of about 52% and 10% compared to the conventional PV system without cooling and the PV/TEG system. In this case, the TEG efficiency rises by about 51% in the PV/TEG nanofluid model compared to the PV/TEG model.