IJE TRANSACTIONS A: Basics Vol. 30, No. 10 (October 2017) 1573-1582    Article in Press

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S. T. G. Krishna Teja, C. P. Karthikeyan and M. B. Shyam Kumar
( Received: April 26, 2017 – Accepted in Revised Form: August 28, 2017 )

Abstract    The objective of this study is to design and analyse materials which are capable of harvesting water from thin air using condensation phenomenon which employs the radiative cooling approach. These passive cooling materials not only solve the water generating problems, but also employed in various cooling applications. The fundamental concept of radiative cooling is analysed and the performance parameters were identified to test the passive cooling ability of the designed material for water harvesting. The field of Photonics is studied which has the potential to obtain the surface temperature significantly lower than the atmospheric temperature by radiation phenomenon. Important parameters are identified to validate the performance of the proposed materials. ANSYS FLUENT is used to analyse the surface temperature for the given boundary conditions and the potential material which is capable of obtaining a significant temperature difference with respect to the ambient temperature is identified. A sandwich material is designed and its performance is evaluated using Computational Fluid Dynamics (CFD) by which we could achieve temperature difference of 15C. To reduce the heat gain losses by conduction and convection, we designed a physical system which could maintain significant temperature difference even in the broad day-sunlight. CFD analysis of the designed system under similar boundary conditions gave satisfying results of maintaining the temperature difference of about 15C for a prolonged period of time due to minimal heat gain losses. Later, two potential materials are manufactured and the performance parameters of these materials are characterized using U-V/Vis (Ultraviolet-Visible) and FTIR (Fourier Transform Infrared) Spectroscopy experiments. The results of absorption phenomenon in the U-V/Vis spectrum and the transmittance phenomenon in the FTIR spectrum of the two materials explain the reason for the passive cooling ability of materials.


Keywords    Radiative cooling, CFD, Photonic material, Pigmented Foil,UV-Vis, FTIR


چکیده    هدف از این مطالعه طراحی و تحلیل موادی است که قادر به جذب آب از هوا با استفاده از پدیدهی تقطیر است با بهره گیری از اصل خنک کردن تشعشعی است. این مواد خنک کننده غیر عامل نه تنها مشکلات تولید آب را حل میکنند، بلکه در کاربردهای سرمایشی مختلف خنک نیز به کار میروند. مفهوم اساسی سرد شدن تشعشعی تحلیل شده و پارامترهای عملکرد برای اندازهگیری قابلیت خنک کنندگی غیر عامل مواد طراحی شده برای برداشت آب شناسایی شد. حوزهی فوتونیک مطالعه شده است. این حوزه قابلیت به دست آوردن دمای سطح در حد چشمگیری پایینتر از دمای جو با پدیده تابش (تشعشع)است. پارامترهای مهم برای تایید عملکرد مواد پیشنهاد شده شناسایی می شوند. از نرمافزار ANSYS FLUENT برای تحلیل دمای سطح برای شرایط مرزی مورد استفاده استفاده شده و مواد بالقوهای که می توانند اختلاف دما را با توجه به درجه حرارت محیط به دست دهند معرفی شدهاند. یک مادهی ساندویچی طراحی و عملکرد آن با استفاده از دینامیک سیالات محاسباتی (CFD) ارزیابی شده است. به این ترتیب می توانیم تفاوت دمایی در حدود 15 درجه سانتیگراد به دست آوریم. برای کاهش تلفات گرما از طریق هدایت و جابهجایی، یک سیستم فیزیکی را طراحی کردهایم که می تواند این اختلاف دما را حتی در زیر نور خورشید روز نیز حفظ کند. تحلیل CFD سیستم طراحی شده تحت شرایط مرزی مشابه نتایج رضایت بخش برای حفظ اختلاف دمایی در حدود 15 درجهی سانتیگراد را برای یک دوره طولانی مدت به دلیل کم شدن تلفات حرارت نشان داد. سپس، دو مادهی بالقوه مناسب تولید شده و پارامترهای عملکردشان با استفاده از آزمونهای طیف سنجی U-V / Vis (Ultraviolet-Visible) و FTIR (Transform Infrared) اندازهگیری شد. نتایج پدیده جذب در طیف U-V / Vis و پدیده انتقال توان در طیف FTIR از دو ماده که دلیل قابلیت خنک کنندگی غیر عامل مواد را توضیح میدهد.


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