International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 10, October 2017, pp. 19 24, Article ID: IJMET_08_10_003 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=10 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed OPTIMIZATION OF SOLAR THERMAL ENERGY STORAGE PERFORMANCE BY USING ASPEN AERO GEL AS INSULATOR Rasim Abbas Ahmmed*, Khalil Alwan.Hussien Directorate of Renewable Energies, Ministry of science and technology, Baghdad, Iraq Sabah Mohammed Hadi, Aed Ibrahim Owaid Directorate of Renewable Energies, Ministry of science and technology, Baghdad, Iraq ABSTRACT: The concept of research includes developmental process for current solar energy storage within solar evacuated tube collector system. many parameters must be considered on increasing the system performance and decreasing the heat losses to the lowest value by using new insulator. the insulator with remarkable properties, (aspen aero gel) was used to insulate the cylindrical solar storage tank system with 1m length and diameter 0.5 m with insulator thick of 0.01m, and to study the change temperature difference through the solar collector with the environmental conditions and the temperature of the storage media, and effect that change on the whole system, it was studied under standard conditions. It was noted the alteration of specific heat and density of storage media will effect on solar energy gain in collector that also will effect on heat losses from the storage. All these results were achieved with temperature range (30 ⁰C to 100 ⁰C) by MATLAB program. Keywords: Energy storage, Heat losses, Insulators, Thermal conductivity, MATLAB Cite this Article: Rasim Abbas Ahmmed, Khalil Alwan.Hussien, Sabah Mohammed Hadi and Aed Ibrahim Owaid, Optimization of Solar Thermal Energy Storage Performance by Using Aspen Aero Gel as Insulator, International Journal of Mechanical Engineering and Technology 8(10), 2017, pp. 19 24. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=10 1. INTRODUCTION: The sun is a sphere of intensely hot gaseous matter with a diameter of 1.39 x 10 9 m. the solar energy strikes our planet a mere 8 min and 20 s after leaving the giant furnace, the sun which is 1.5 x10 11 m away. The sun has an effective blackbody temperature of 5762 K. The temperature in the central region is much higher and it is estimated at 8 x 10 6 to 40 x10 6 K. In effect the sun is a continuous fusion reactor in which hydrogen is turned into helium. The sun s total energy output is 3.8 x 10 20 Mw which is equal to 63 MW/m 2 of the sun s surface. This energy radiates outwards in all directions. Only a tiny fraction, 1.7 x 10 14 kw, of the total http://www.iaeme.com/ijmet/index.asp 19 editor@iaeme.com
Rasim Abbas Ahmmed, Khalil Alwan.Hussien, Sabah Mohammed Hadi and Aed Ibrahim Owaid radiation emitted is intercepted by the earth. However, even with this small fraction it is estimated that 30 min of solar radiation falling on earth is equal to the world energy demand for one year [1]. Solar energy being transmitted from the sun through space to earth by electromagnetic radiation must be converted to heat before it can be used in a practical heating or cooling system. Since solar energy is relatively dilute when it reaches the earth, the size of a system used to convert it to heat on a practical scale must be relatively large. Solar energy collectors, the devices used to convert the suns radiation to heat, usually consist of a surface that efficiently absorbs radiation and converts this incident flux to heat which raises the temperature of the absorbing material. A part of this energy is then removed from the absorbing surface by means of heat transfer fluid that may either be liquid or gaseous [2].one of important part in solar collector systems is the energy storage which is not only play an important role in conservation the energy but also improves the performance and reliability of wide range of energy systems, and become more important where the energy source intermittent such as solar. Energy storage process can reduce the rate mismatch between energy supply and energy demand. The thermal energy storage can be used in places where there is a variation in solar energy or in areas where there is a high difference of temperature between day and night [3]. The amount of energy stored is given by the following equation: (1) Where, Q is the energy stored, m is the mass of the storage medium, c p is the specific heat of the material and T is the temperature change during the process [4,5]. the efficiency of the solar systems effected by the heat losses from the storage tank of these systems so the insulator play important role to increase this efficiency in other words decrease heat losses. One of promised material that can be used as insulator for the this purpose is aspen aerogel which is defined a synthetic porous ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas, for example, grapheme aerogels. The combination of high porosity and extremely small pores provides aerogels with their extreme properties, solid with extremely low density and low thermal conductivity Aerogels are sometimes also known by different names such as frozen smoke, solid smoke, solid air, or blue smoke owing to translucent nature and the way light scatters in the material [6]. in order to optimize energy consumption, use of thermal insulation is one of the most attractive issues in different industries. Heat transfer mechanisms include conduction, convection and radiation. Therefore, blanket insulators can reduce heat transfer through all above mechanisms due to highly porous structure[7]. Production of aerogel in the production of an aerogel is used chemical method involving the reaction of tetrafunctional alkoxysilanes extremely diluted with water vapor (for example, Si(OCH3)4) in an inert atmosphere. In the first step, as a result of hydrolytic condensation is soft silica gel. Before the created silica foam is completely congeal, slowly is reducing the pressure in the reactor, until the almost complete vacuum and as a result is a rapid increase in volume of the gel. In the final stage of production, the reactor is carefully filled by inert gas again and at the same time the temperature is increasing, which leads to the end of the condensation reaction, and the durable aerogel is ready[8] as shown in the figure(1). Figure 1 Aerogel Manufacturing Process [8] http://www.iaeme.com/ijmet/index.asp 20 editor@iaeme.com
Optimization of solar thermal energy storage performance by using aspen aero gel as insulator Heat transfer from fluid to another separated by an intervening wall is of great practical importance.calculation of the rate of heat transfer in such a case is done by using an overall heat transfer coefficient. The heat losses from energy storage can be calculated by the following equations: ( ) (2) ( ) ( ) (3) Where UA=the overall heat losses coefficient in (w/⁰c), T i The initial temperature of the storage. T a is the ambient temperature, and R 1 is the thermal resistance for the cylindrical part of tank Where R 2 is the thermal resistance of the flat part in (⁰C /w), ( ) ( ) (4) ( ) ( ( )) (5) Where: r i,r o are the inner and outer radius respectively for the storage tank in (m), and k, is the thermal conductivity of the insulator in w/m.⁰c [9]. In this research it was selected an solar collector with known specifications in order to study the alterations of the density and specific heat of the storage media with the heat losses by conduction in the storage with aspen aerogel as insulator, and that will be within the working temperature range and standard environmental conditions for solar energy. 2. RESULTS AND DISCUSSION: The solar collector assumed in this study is vacuum tube CPC with optical efficiency 0.745 and heat transfer coefficient is 2.007 at (T m - T a ) = 0 [Wm -2 K -1 ], temperature-dependent heat transfer coefficient is 0.005 [Wm -2 K -2 ], the collector has gross surface area 2.32 m 2, the Thermal energy output of the this collector in (w) founded by using MATLAB program under standard conditions 1000w/m 2 and ambient temperature 30 ⁰C, and with difference of mean collector fluid and ambient temperature from 0 ⁰C to 70 ⁰C shown in the figure(2) Figure 2 Relation of change collector output with change difference of mean collector fluid and ambient temperature. The solar collector, already mentioned, provide energy to solar storage tank which is insulated by aspen aero gel with thickness 0.01m. The storage tank has 1m length, diameter 0.5 m, and filled with pure water. http://www.iaeme.com/ijmet/index.asp 21 editor@iaeme.com
Rasim Abbas Ahmmed, Khalil Alwan.Hussien, Sabah Mohammed Hadi and Aed Ibrahim Owaid The specific heat of the water has small change with the difference of mean collector fluid and ambient temperature depending on increasing of the temperature of water caused by transferred energy from collector to storage tank. This change caused decreasing density of water in storage. As shown in figure (3) and figure (4) respectively. Figure 3 Change specific heat of water with increase temperature of storage according to difference of mean collector fluid and ambient temperature. Figure 4 Change density of water with increase temperature of storage according to difference of mean collector fluid and ambient temperature. When the difference of mean collector fluid and ambient temperature increases, this lead to decrease the raising of the storage media temperature under taking the change in specific heat and density of pure water as a shown in figure(5). that will give as indication, that the decreasing of heat losses, by aspen aerogel conduction, from the storage depending on the same increasing of the difference of mean collector fluid and ambient temperature as shown in figure (6) http://www.iaeme.com/ijmet/index.asp 22 editor@iaeme.com
Optimization of solar thermal energy storage performance by using aspen aero gel as insulator Figure 5 Illustrated increasing temperature of storage with transfer the energy from collector when using aspen aerogel as storage insulator. Figure 6 The heat losses by conduction from storage depending on mean difference of fluid collector and ambient temperature. 3. CONCLUSIONS: a) Aspen aerogel has remarkable properties which encourage the researchers and scientists to consider it as a good insulator for the energy storage units. b) It was noted from the mathematical side that the heat losses resulted from conductivity of aspen aerogel help to build efficient thermal storage system. c) Can be used as a new insulated material in solar storage to increase equality of solar systems. ACKNOWLEDGEMENTS: The authors are grateful to solar thermal department, for their kind support in providing assistance to achieve the research. http://www.iaeme.com/ijmet/index.asp 23 editor@iaeme.com
Rasim Abbas Ahmmed, Khalil Alwan.Hussien, Sabah Mohammed Hadi and Aed Ibrahim Owaid REFERENCES: [1] Soteris A. Kalogirou, Solar thermal collectors and applications vol.30, p.231 295 (2004). [2] Nosa Andrew Ogie, Ikponmwosa Oghogho, and Julius Jesumirewhe Design and Construction of a Solar Water Heater Based on the Thermosyphon Principle Journal of Fundamentals of Renewable Energy and Applications Vol. 3, Article ID 235592, 8 pages (2013). [3] Mahmud M. Alkilani, K. Sopian, M.A. Alghoul, M. Sohif, M.H. Ruslan Review of solar air collectors with thermal storage units Renewable and Sustainable Energy Reviews Vol.15, p.1476 1490 (2011). [4] Sarada Kuravi, Jamie Trahan, D. Yogi Goswami, Muhammad M. Rahman, Elias K. Stefanakos, Thermal energy storage technologies and systems for concentrating solar power plants Progress in Energy and Combustion Science Vol.39 p.285-319 (2013). [5] Lavinia Gabriela Seasonal Sensible Thermal Energy Storage Solutions Leonardo Electronic Journal of Practices and Technologies ISSN 1583-1078 p. 49-68 (2011). [6] Prakash C. Thapliyal and Kirti Singh Aerogels as Promising Thermal Insulating Materials Journal of Materials. Article ID 127049, 10 pages (2014). [7] M. Razzaghia, H. R. Hadizadeh Raeisia, A. R. Bahramiana, Improvement of Polyester Blanket Thermal Insulator Properties Using Phenolic Aerogel. Procedia Materials Science Vol.11 p. 522 526 (2015). [8] Lech Licholai, Jerzy Szyszka, Possiblities of the Aerogel Application in Building Lviv Polytechnic National University Institutional Repository p. 148-152, (2013). [9] Karwa, Rajendra Heat and Mass Transfer springer ISBN 978-981-10-1556-4 (2017). [10] Sandhya Jadhav and Dr. V. Venkat Raj. Simulation of Solar Thermal Central Receiver Power Plant and Effect of Weather Conditions on Thermal Power Generation. International Journal of Mechanical Engineering and Technology, 8(2), 2017, pp. 27 33. [11] Alo Mikola, Teet-Andrus Kõiv and Mikk Maivel. Production of Domestic Hot Water with Solar Thermal Collectors in NorthEuropean Apartment Buildings. International Journal of Mechanical Engineering and Technology, 7(1), 2016, pp. 58-66. [12] Malleboyena Mastanaiah, K. HemachandraReddy, Performance Characteristics of Solar Thermal Flat Plate Collector with Different Selective Surface Coatings and Heat Transfer Fluids, International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 309-318 http://www.iaeme.com/ijmet/index.asp 24 editor@iaeme.com