Design and testing of cooking vessels of solar box cooker for evening cooking

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In the present work, an attempt has been made to design and test the performance of box type solar cooker with cooking pots of different materials filled with latent heat energy storage mediums to perform the cooking in sun shine and off sun - shine conditions.

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Nội dung Text: Design and testing of cooking vessels of solar box cooker for evening cooking

International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp.1931-1938. Article ID: IJMET_10_04_196 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed DESIGN AND TESTING OF COOKING VESSELS OF SOLAR BOX COOKER FOR EVENING COOKING Ajeet Kumar Rai and Sanjay Kumar Srivastava Mechanical Engineering Department, VIAET, SHUATS, Prayagraj, 211007, (U.P.) India ABSTRACT In the present work, an attempt has been made to design and test the performance of box type solar cooker with cooking pots of different materials filled with latent heat energy storage mediums to perform the cooking in sun shine and off sun - shine conditions. The box type solar cookers are not common in use due to limited availability of solar energy. Latent heat energy storage materials are used to store solar energy available in day time to use in evening and off sunshine hours. Paraffin wax is used as energy storage material (PCM) to improve the performance of the system in off sunshine conditions. PCM filled aluminium pots are suitable for day time cooking. It is observed from full load test that the water temperature in PCM filled steel pots are maintained above 950C for more than 3 hours than PCM filled aluminium pots in off sunshine conditions. Keywords: Box Type solar cooker, Latent heat energy storage, cooking vessel. Cite this Article: Ajeet Kumar Rai and Sanjay Kumar Srivastava, Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking, International Journal of Mechanical Engineering and Technology, 10(3), 2019, pp. 1931-1938. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 1. INTRODUCTION Energy is essential to sustain life on the earth. Energy is available in various forms on the earth. A major amount of total available energy is utilized for cooking. Heat energy is the most suitable form of energy to cook food. Heat generation by burning of fossil fuels is common practice for cooking applications in developing countries. But fast depletion of resources and environmental problems associated with use of fossil fuels has restricted its use. Utilization of renewable energy based technologies is the most promising options for cooking applications. Since cooking requires 36% of total primary energy consumptions in India [1]. In present days 14% of total world energy demand is supplied by renewable energy sources [2]. Therefore, there is a rising attention concerning the renewable energy options to meet the cooking requirements of people in developing countries. Since it is free of cost and environment friendly, the solar energy is recognized as one of the most promising choice among other clean http://www.iaeme.com/IJMET/index.asp 1931 editor@iaeme.com
Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking energy technologies. The earth receives 3.85 million EJ of solar energy each year [3]. It is well known that most of the thickly populated countries from the developing part of the world are blessed with abundant solar radiation with mean daily illumination in the range of 5-7 kW h/m2 and have more than 275 sunny days in a year [4]. From this point of view, it can be easily said that solar cookers have a big potential in these countries in order to meet the energy demand especially in the domestic sector. In addition, utilization of solar cookers provides many advantageous like no recurring costs, high nutritional value of food, potential to reduce drudgery and high durability [5]. Since solar energy is not continuously available with same maximum intensity. Thermal energy storage mediums may be used to make solar cookers working for longer periods. Thermal energy can be stored as sensible heat, latent heat or combination of these two. Materials that can store latent heat during the phase transition are known as phase change materials. Latent heat of phase change material is many orders higher than the specific heat of materials. Therefore PCM can share 2-3 times more heat or cold per volume or per mass as can be stored as sensible heat in water in a temperature interval of 20 0C. Rai et al have reviewed work on PCMs and their wide range of applications [6]. They have also suggested a wide range of PCMs that can be selected as a storage media. In order to select the most suitable PCM as a storage media some criteria are also mentioned. Abhat, Dincer and Rosen have given a detailed classification of PCMs with their properties [7,8]. Shukla et al have used PCM as a energy storage medium to study the performance of a solar still [9]. Rai et al constructed novel continuous single stage solar still with PCM. They reported that the productivity of a solar still can be greatly enhanced by the use of a PCM integrated to the still [10]. Paraffin are chemically known as hydrocarbons which are generally found to be as wax at room temperature. Paraffin consists of a mixture of mostly straight chain n-alkanes CH3–(CH2)–CH3. The crystallization of the (CH3)- chain release a large amount of latent heat. Both, the melting point and latent heat of fusion, increase with chain length. Paraffin qualifies as heat of fusion storage materials due to their availability in a large temperature range. System-using paraffin usually has very long freeze–melt cycle. Apart from some several favorable characteristic of paraffin, such as congruent melting and good nucleating properties, they show some undesirable properties such as low thermal conductivity, non-compatible with the plastic container and moderately flammable. All these undesirable effects can be partly eliminated by slightly modifying the wax and the storage unit. In this present experimental work, the attention is mainly focused on the exploring possibility of use of solar cooker for evening cooking. PCM are used for latent heat energy storage in sun shine hours which can later be used during off-sunshine hours. Sensible energy storage is ensured with the use of cooking pots of Steel. Steel pots with PCM are tested and its performance is compared with the Aluminium cooking pots integrated with PCM. 2. THERMAL TEST PROCEDURE FOR BOX TYPE SOLAR COOKERS The energy balance for the horizontally placed empty solar cooker at stagnation (quasi-steady state) is given as [11,12] o H s  U L Tps  Tas  (1) Where o is the optical efficiency, T ps is the plate stagnation temperature, H s and Tas are, respectively, the insolation on a horizontal surface and the ambient temperature at the time stagnation temperature is reached. The first figure of merit, F1, is defined as http://www.iaeme.com/IJMET/index.asp 1932 editor@iaeme.com
Ajeet Kumar Rai and Sanjay Kumar Srivastava Tps  Tas F1  (2) Hs And can be obtained from the simple stagnation test without load. Lower permissible limit of the value of F1 may be specified to ensure a minimum level of thermal performance. It is stipulated that F1 should equal or exceed 0.12. The second figure of merit F2 is therefore obtained from sensible heating test. The proposed figure of merit is based on following analysis.   ( MC ) w Tw Tw 2  1        AF '0CR Tw1  H  1 T w T  F1 a    (3) Where, Tw is the average water temperature over an interval. Insolation may be assumed constant and equal to average value ( H ) over the time interval.   ( MC ) w Tw 2  1  F2  CR F '0  Tw    A Tw1 H   1 F1  T w  Ta    (4) The temperature interval ∆Tw can be gradually reduced until the computed values of F2 attain the desired degree of convergence. 3. DESIGNING OF THE STORAGE UNIT FOR COOKING POT Mass of the latent heat storage material may be calculated using the following equation and the assumptions taken are as given by Sharma et al [14] as Mf CW (Tf – Tm) + MPCM CPCM (TPCM – Tm) + MPCML = ULA (Tf –Ta) ∆t (5) Considering 1. Average solar radiation (9 AM to 3 PM) - 640 W/m2. 2. Average ambient temperature - 200C 3. PCM temperature at 3 PM (before evening loading) - 1200C 4. Food temperature at 3 PM (before loading) - 200C 5. Evening food is loaded at 3 PM 6. Solar cooker is closed to the solar radiation at 4 PM 7. PCM temperature at 4 PM - 970C 8. Food temperature at 4 PM - 970C 9. PCM temperature at 6.00 PM - 850C 10. Food temperature at 6.00 PM - 850C It may be assumed that PCM initially is at ambient temperature, and the specific heat will be the same for both the solid and liquid phases. The thermo-physical properties of PCM and various cooker parameters are used. To have the food temperature at the solidifying point of the PCM at 6.00 PM, the energy released by the PCM and food should be equal to the energy loss from the cooker. http://www.iaeme.com/IJMET/index.asp 1933 editor@iaeme.com
Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking 4. EXPERIMENTAL SETUP The standard size box type solar cooker is used in the present experiment with aluminium and steel pots integrated with latent heat energy storage material. Paraffin Wax is used as latent heat energy storage material. Figure 1 shows the photograph of box type solar cooker used in experiments. PCM filled cooking pots of aluminium and steel are designed and assembled with the available cooking pots in the solar cooker. Box type solar cooker is constructed using GI sheet and insulated by a layer of styro-foam insulating material of thermal conductivity = 0.033 W/m-K. For the box type solar cooker, the absorber plate consists of GI sheet painted black of a surface area (47.5cm × 47.5cm) with 8.75 cm height and outer surface area (57.5cm× 57.5cm) with 17.5 cm height. Figure 1 photograph of the PCM filled cooking vessel and box type solar cooker Aluminium pots of two different sizes, one of 1.5 liter capacity and another of 0.75 liter capacity are taken. Small pot of diameter of 157 mm is kept inside the bigger pot of diameter 212 mm concentrically. Height of small pot is 40 mm and that of the bigger pot is 55 mm. Thickness of the pots material is 1 mm. PCM storage unit in aluminium pot is made by filling paraffin Wax in the annulus space between the two concentric pots of different sizes. Similarly energy storage unit in Steel pots are also made. Holes at the top cover are made to insert the thermocouple wire to measure the PCM and water (when loaded) temperatures. Pots are blackened from outside to absorb maximum insolation. Experiments were conducted in the Solar Energy Laboratory of Mechanical Engineering Department of the SHUATS Prayagraj U.P. India in the month of June 2018. Experiments were started at 6:00 AM and continued till 7:00 AM next morning. During all the experiments solar radiation intensity on the horizontal surface was measured using Solarimeter with least count of 20 (W/m²). Digital temperature recorder with copper-constantan thermocouples is used to measure the temperature of different locations on the box type solar cooker for example, absorber plate, cooking pots, cooking fluid, PCM temperature, ambient temperature. 5. RESULTS AND DISCUSSION Experimental studies are carried out on box type solar cooker with two different types of pot materials, one is steel and other is aluminum. Fig 2 shows the variation of solar intensity with http://www.iaeme.com/IJMET/index.asp 1934 editor@iaeme.com
Ajeet Kumar Rai and Sanjay Kumar Srivastava respect to the time of the day. Solar intensity starts increasing at steady rate before noon till it reaches the maximum, and then rate of decrease is fast. Maximum value of 840 W/m2 is obtained at around 2.00 P.M. 900 800 700 Solar Intensity(W/m2) 600 500 400 300 200 100 0 Time of the day (hr) Figure 2 Variation of solar intensity with time of the day To obtain the value of F1, the first figure of merit, stagnation tests were performed as per international test procedures. Cooker was placed in the sun with covered reflector. Experiments were conducted in the Solar Energy Laboratory of SHUATS Prayagraj, U.P. India. Maximum stagnation temperature of absorber plate was obtained as 142 0C at around 1 PM. At this time ambient temperature was 360C. The value of F1 is obtained as 0.13. According to Mullick et al, 1987 the first figure of merit F1 varies between 0.12 and 0.16. Value of F1 indicates good optical efficiency and low heat loss factor. Box type solar cooker is of grade A as per BIS standard. Before tests for second figure of merit, temperature variation of pots of aluminium and steel were recorded. It was observed that once the steel pot crosses the aluminium pot temperature during day time heating, temperature of steel pot remains at higher value than the aluminium pot temperature. This is due to higher thermal conductivity of aluminium which cools it fast, and thermal inertial effect and lower thermal conductivity of steel pot which keep it hot for longer duration. For evening cooking using box type solar cooker, steel pots are of good choice Varshney et al [23]. Figure 3 shows the variation of temperature of PCM filled steel and aluminium pots with cavity temperature and ambient temperature. Trend of cavity temperature during the day time is similar to that of the solar intensity variation as expected. After sunset aluminium pot cools down faster than the steel pot. The maximum temperature in unloaded condition of PCM filled aluminium pot was about 9% higher than PCM filled steel pot. In unloaded condition temperature of steel pot is maintained above 800C after 8 hours of sunset. It is concluded that the PCM Filled steel pots are most suitable for boiling type of cooking. http://www.iaeme.com/IJMET/index.asp 1935 editor@iaeme.com
Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking Figure 3 Variation of temperature of cooker components without load with PCM filled aluminium and steel pots AMBIENT TEMPERATURE (⁰C) CAVITY TEMPERATURE (⁰C) STEEL POT TEMPERATURE (⁰C) ALUMINIUM POT TEMPERATURE (⁰C) 140 120 100 Temperature (0C) 80 60 40 20 0 Time of the day (hr) Figure 4 Variation of temperature of cooker components with load with PCM filled aluminium and steel pots The second figure of merit F2 is calculated for PCM filled aluminium and steel pots using load test. It is observed that F2 of PCM filled steel pot is 5% more than that of PCM filled aluminium pot. Finally, the results obtained using the international cooking power test procedure clearly show that the present cooker satisfies the standard. Figure 4 obtained from load test shows that the maximum temperature obtained is higher in case of loaded aluminium pot than that of the loaded steel pot. For the day time cooking, aluminium pots will be preferred choice. After the maximum temperature is reached, the temperature of steel pot is observed to http://www.iaeme.com/IJMET/index.asp 1936 editor@iaeme.com
Ajeet Kumar Rai and Sanjay Kumar Srivastava be higher than the aluminium pot temperature, which is sustained throughout the night, makes the steel pot of preferred choice for the evening solar cooking. It is also observed from full load test that the temperature of water in PCM filled steel pot is maintained above 950C till 9 PM. However, the temperature of water in PCM filled aluminium pot is maintained at 950C till 6 PM only. Means PCM filled steel pot is most suitable for evening cooking. 6. CONCLUSION Energy storage materials are used in the cooking pots of box type solar cooker for evening cooking. In the present work, Paraffin wax is used as energy storage material (PCM) in the box type solar cooker to improve the performance of the system in off sunshine conditions. Pots of aluminium and steel are used to encapsulate PCM and their performance in terms of evening cooking is tested. PCM filled aluminium pots and are suitable for day time cooking. PCM filled steel pots are found more suitable for evening cooking. On the basis of present study, the following points may be highlighted  The first figures of merit F1 is found as 0.13 for the box-type solar cooker used in the present study.  The maximum temperature in unloaded condition of PCM filled aluminium pot was about 9% higher than PCM filled steel pot.  In unloaded condition temperature of steel pot is maintained above 800C after 8 hours of sunset.  The second figure of merit F2 for box type solar cooker in full load condition with PCM filled steel pot is 5% higher than that of PCM filled aluminium pot.  It is observed from full load test that the temperature of water in PCM filled steel pot is maintained above 950C till 9 PM. However, the temperature of water in PCM filled aluminium pot is maintained at 950C till 6 PM only. So, PCM filled steel pot is most suitable for evening cooking REFERENCES [1] Pohekar SD, Kumar D, Ramachandran M. Dissemination of cooking energy alternatives in India: a review. Renewable and Sustainable energy Reviews, 2005; 9: 379-93. [2] Panwar NL, Kaushik SC, Kothari S. Role of renewable energy sources in environmental protection: a review. Renew Sust Energy Rev 2011;15: 1513-24. [3] Johansson TB, Kelly H, Reddy AKN, Williams RH, and Burnham L. Renewable Energy sources for fuels and electricity. Earth Scan Publication Ltd. and Island Press; 1993. [4] Nahar N M. Performance and testing of a hot box storage solar cooker. Energy conversion and Management; 2003; 44: 1323–1331. [5] Cuce Erdem, Cuce Pinar Mert. A comprehensive review on solar cookers. Applied Energy (102) 2013; 1399-1421. [6] Ajeet Kumar Rai and Ashish Kumar, A review on phase change materials and their applications. International journal of Advanced Research in Engineering and Technology (IJARET), 2012: 3(2), pp 214-225. [7] Abhat, Low temperature latent heat thermal energy storage: heat storage materials, Solar Energy, 1983; 30: 313-332. [8] Dincer I., Rosen M.A., Thermal energy storage, Systems and Applications John Willey and Sons Chichester (England), 2002. [9] Al-Hamadani A.A.F. and Shukla S.K., Modeling of solar distillation system with phase change material (PCM) storage medium, thermal science, 2011. http://www.iaeme.com/IJMET/index.asp 1937 editor@iaeme.com
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