Investigation of solar cooker with pcm heat storage

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Investigation of solar cooker with pcm heat storage

  1. 1. INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp. 555-564© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2012): 3.8071 (Calculated by GISI) ©IAEMEwww.jifactor.com INVESTIGATION OF SOLAR COOKER WITH PCM HEAT STORAGE FOR HIGH ALTITUDE PLACES (TAIF CITY) Talal K. Kassem Department of Mechanical Engineering, College of Engineering, Taif University, P.O. Box 888 Zip Code 21974, Taif, Saudi Arabia. Permanent Address: Department of Mechanical Engineering, Faculty of Mechanical and Electrical Engineering, Damascus University, P.O. Box 86, Syria. E-Mail: t.kassem3@yahoo.com Mobile: +966564401827 Abstract In this paper, an experimental investigation is carried on a box solar cooker with heat storage. The cooker is connected to solar water heating system compound of evacuated tubes solar collectors and a storage tank of hot water. The base of this box (the absorber plate) is incorporated by welding with a spiral copper tubes heat exchanger and cylindrical pot inside it filled with paraffin as a PCM. Some parameters affecting on the performance of this system, such the solar radiation, air humidity, orientation of solar cooker and the ambient temperature were investigated. This study highlights the ability of using this system with high performance in the conditions of high altitude (high insulation, partly clouding and moderate temperature) for cooking and heating the food. Keywords: solar cooker, solar heating system, evacuated tubes solar collectors, PCM heat storage 1. Introduction Solar energy is free, environmentally clean, and therefore is recognized as one of the most promising alternative energy resources options. Therefore, solar cooking has proved to be one of the simplest and attractive options for solar energy utilization. Basically there are different types and designs of solar cookers. For each design of them different performance parameters has been used. The available solar cookers are mainly classified into two groups. The first group is solar cookers without storage and the second one is solar cookers with storage. 555
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMESolar cookers without storage are classified into direct and indirect solar cookersaccording to the heat transfer mechanism to the cooking vessel [1]. In direct type solarcookers, solar radiation is used directly in the cooking process, while, in the indirectsolar cookers a heat transfer fluid is used to transfer the heat from the collector to thecooking vessel. Direct type cookers are box and concentrating type cookers. Many designs ofeach type have proposed and tested to investigate the thermal performance parametersfor each type. Among the direct solar cookers, box type solar cookers are more populardue to their simplicity of handling and operation. Different designs of box type solarcookers are available to enhance the thermal performance of solar cooker. Cooker potdesign also helps in improving the thermal performance of the cooker. A solar boxcooker has been designed, constructed and tested by Alozie et al. [2] to investigate itsworkability of cooking food in most tropical regions where the suns radiation isabundant. An experimental study was conducted at Irbid city, Jordan by Al-Azab et al. [3]to investigate the thermal performance of box type solar cooker with two differentcooking pots (finned and un-finned pots).Guar et al. [4] designed and fabricated the pot lid in concave shape and carried outwater heating test and stagnation test with conventional pot lid and concave shaped lid.A comparative experimentally study of a box type solar cooker with two differentcooking vessels has been carried out by Harmim et al. [5]. In most recent review articlefor box type solar cookers, some of the performance parameters and the related testprocedures have been reviewed by Lahkar and Samdarshi [6]. Cooking outdoors and impossibility of cooking food in late evening hours arethe main problems associated with solar cooking systems. There are three methods forstoring thermal energy, namely; latent, sensible, and thermo-chemical heat storage [7].Many Solar Cookers with Latent Heat Storage Materials have been investigated where;the thermal performance of a prototype solar cooker based on an evacuated tube solarcollector with phase change material (PCM) storage unit has been studied by Sharma etal. [8] at Mie, Japan. Buddhi et al. [9] tested acetanilide as a PCM with a melting pointof 118.9 oC for night cooking in a box type cooker with three reflectors.In sensible heat storage, thermal energy is stored by raising the temperature of a solid orliquid. Ramadan et al. [10] designed a simple flat-plate solar cooker with focusingplane mirrors and energy storage capabilities constructed by the locally availablematerials.2. Theoretical model The thermal performance of the box solar cooker can be evaluated according to [11-12] by calculating: The consumed thermal energy on cooking Qh and The efficiency th.The thermal energy used in the cooking process is done by: mw Cw ∆TQh = (1) ∆t 556
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEThe efficiency of the cooker is defined by the ratio of heat uses for cooking to theinsolation of solar energy incident on the base of cooker: m w C p ∆T ηth = t (2) A c ∫ G t dt 0The efficiency of evaporation can be defined by the ratio of the thermal energy used inthe evaporation process ( m w .e . h fg ) to the insolation of solar energy incident on thebase of cooker: m w .e h fg Q solar − Q lostηe = = (3) t Q solar Ac ∫ G t dt 0Heat lost from the cooker to the surrounding can be done by:Qsolar = U system (T100 − Tamb ) (kJ) (4)By knowing the experimental value of ηe , the total coefficient of heat transfer Usystemcan be calculate by: (1 − ηe ) A c G tUsystem = (5) T100 − TambThe maximum temperature can be reached when ηe = 0. This means that the gainedthermal energy from the solar radiation was dissipated in two ways: - Evaporation of water from the pot inside the cooker. - Heat loses to the surrounding.3. Experimental Work: Figure 1 . Outlines the experimental system which composed of the solar heatingsystem (evacuated tubes solar collectors with a storage tank of hot water) and the solarcooker. The solar cooker consists of two boxes designed in the form of parallelrectangles join between them a layer of thermal insulation (wool thermal) thickness of 5mm. The reflector support, made of iron, has been used for making the reflector rigidand adjusting the reflector in an angle calculated according to the place, date and time.One layer of glass (mm) as transparent cover.The internal box of the cooker was made of galvanized iron of dimensions (45 x 60 x 40cm). The base of this box is connected by welding on the one hand with a spiral coppertubes heat exchanger, and on the other hand with a cylindrical pot, where the heatexchanger includes inside the cylindrical pot which filled with paraffin of density of0.75 kg/l (in the case of fluid).Paraffin melts at 27 ⁰C and it can store a lots of heat energy. In this system, the storagetank of the solar heating system feeds hot water to the heat exchanger, where thethermal energy will be stored in paraffin which heats the cooking pot and accelerates thecooking process, and then hot water returns to the storage tank. 557
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Fig. 1: A schematic diagram showing the arrangement of the cooker-collectorsystems.All edges and corners of the box solar cooker were well filled with silicon to prevent anyleakage of heat or air infiltration.The south faced solar water heating system is installed on the roof of the Fluid MechanicsLaboratory, Mechanical Engineering Department, College of Engineering, Taif University, Taifcity, Saudi Arabia.The total intensity of solar radiation has been measured by using Pyranometer - LP 02 withAmplifier - AC 420 and Hand held readout unit- LI 18, which mounted in parallel manner to thetransparent cover of the cooker. The inner box of the cooker receives the total solar radiation(beam and diffuse) and the reflected radiation from the mirror of reflector which fixed on aniron framework in the east-west and north sides of the cooker. The cooker box is kepthorizontal.Reflector was oriented southwards with a tilt angle of 60 to 105 degrees. This angle depends onthe solar altitude angle and the hour angle as shown in Fig. 2. 120 100 Reflector tilt angle 80 60 40 0 10 20 30 40 solar angle 80 90 100 Altitude 50 60 70 Fig. 2: Variation of reflector tilt angle with altitude solar angle.The thermal performance of the solar cooker was evaluated under Taif weather conditions (1450 m abovesea level). So, a series of experiments were performed with and without connection of the solar cooker tothe solar heating system (with and without heat storage).In this study absorber plate temperature, internal temperature of the solar cooker and the temperature ofwater in the cooking vessel were measured as shown in table (1) by using K-type thermocouples, whilst,the ambient temperature and the relative humidity were measured by a hygrometer. 558
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMETable. 1. Variation of the absorber plate temperature, pot water temperature andambient temperature with solar radiation intensity on 30/06/2012. Solar radiation Temperatures (◦C) intensity on Time (h) horizontal surface Ambient Absorbent (W. m-2) water Temperature plate 11:00 968 31 112 52 11:30 1011 31.5 119 58 12:00 1026 32.5 127 62 12:30 1037 33 133 72 13:00 1046 33 135 79 13:30 1025 33.5 136 83 14:00 998 32.5 137 88 14:30 936 32 139 97 15:00 846 31.5 136 98 15:30 763 31 134 98 16:00 605 31 131 98 16:30 469 30 127 95 17:00 358 29.5 123 924. Results and Discussion The incident solar radiation variation on a horizontal surface for Taif city during daytime on Sunday 16/09/2012 is shown in Fig. 3. Fig. 3: Variation of the incident solar radiation on Taif city during day time on Sunday (16/ 09/2012). 559
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEa- Investigation of solar cooker without heat storage: The solar cooker was not connected to the solar heating system. So, the absorberplate of the cooker will be heated only by the total solar radiation (beam and diffuse)which is affected by the climatic conditions especially in the cloudy and partly cloudydays and in the cold climate.I- The solar cooker has one position The solar cooker was oriented southwards while the tilt angle of the reflectorwas 85 degrees. The cooking pot was loaded by 2 liter water. Measurements were takenat intervals of 1 hour during the period of effective sunshine from 09:00 am to 17:00pm. (15 – 19 /09/ 2012), and the pot water temperature inside the cooker cannot exceed90 ◦C. The results were plotted in Fig. 4 on Sunday (16/09/2012) where, the maximumvalue of the solar radiation intensity decreases to below 820 W.m-2. Temperature of theabsorbed plate increases during the day until it achieves its maximum value (82 ◦C) at13:30 pm, where the cooking process cannot be started. Fig. 4: Variation of the absorber plate temperature, the pot water temperature and the ambient temperature with time of day for one position (16 /09/ 2012).For the same case where, the solar cooker has one position from 09:00 am to 18:00 pmand its reflector facing the south. The solar cooker was investigated for a few typicaldays (12- 17/05/2012). The variation of temperature of the absorber plate of cooker, potwater temperature and ambient temperature are given in Fig. 5 on Wednesday(16/05/2012) when the solar radiation intensity was about 910 W/m2. It is seen that themaximum attainable temperature of the absorber plate of the cooker is about 125 ◦C at14:00 pm. 560
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 140 120 Temperature (°C) 100 80 Absorber 60 plate 40 20 0 8 10 12 14 Time (hr) 16 18 Fig. 5: Variation of the absorber plate temperature, the pot water temperature and the ambient temperature with time of day for one position (16/05/2012).II- The solar cooker has two positions The solar cooker was investigated during two periods (from 09:00 am to 12:00 pm) and(from 12:00 pm to 17:00 pm) for the period of (09 – 13/06/2012). On Monday (11/06/2012) themaximum value of the solar radiation exceeded 1050 W.m-2. The solar azimuth angle will bevaried between ßs = 25◦ north- east for the first period (09:00 – 12:00) and ßs = 24◦ north- westfor the second period (09:00 – 12:00). The reflector tilt angle was 85◦ for the two periods. Fig. 6: Variation of the absorber plate temperature, the pot water temperature and the ambient temperature with time of day for two positions (11/06/2012).Figure 6 shows that the temperature of the absorber plate has two tops at 11:00 am and 15:00pm (131 and 134.2◦C) respectively, while the temperature of water in the cooking pot reaches itsmaximum value (97.4 ◦C) at 15:00 pm and continues to be constant approximately. 561
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME III- The solar cooker has a permanent setting (ßs= 0): In this case the reflector tilt angle (δ) of the solar cooker can be defined by rapport tothe altitude solar angle (h) by the relation 3δ – 2h = 180◦ during the period between 08:00 am to16 pm (26 – 30/08/2012), with approximately the same maximum daily average value of thesolar radiation intensity (986 W.m-2) for the period of (09 – 13/06/2012). The variations of theabsorber plate temperature, the pot water temperature, and the ambient temperature on Tuesday(28/08/2012) with solar radiation of (1032 W. m-2) were plotted in the Fig. 7. The absorber platetemperature increases rapidly to the maximum value on 15 PM.Fig. 7: Variation of the absorber plate temperature, the pot water temperature and the ambient temperature with time of day for permanent setting (28/08/2012).b- Investigation of solar cooker with heat storage: The solar cooker was connected to the solar heating system, where the hot water flows fromthe storage tank to the heat exchanger where it loses some of its thermal energy to heat theparaffin in the cylindrical pot, and the absorber plate temperature increases rapidly to reach itsmaximum value (about 140 ◦C) on Monday (15/10/2012) where, the maximum value of thesolar radiation intensity was in the order of 790 W.m-2. In this case the cooking process can bestarted at 13:00 pm as shown in the Fig. 8. 150 100 Temperature (°C) Absorber plate 50 0 11 13 Time (hr)15 17 Fig. 8: Variation of the absorber plate temperature, the pot water temperature and the ambient temperature with time of day (15/10/2012). 562
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME5- Conclusion An experimental investigation on the performance of box solar cookerg has beencarried out. Therefore, to enhance the efficiency of the proposed solar cooker system, aseries of experiments have been implemented during two periods with and without heatstorage to evaluate the performance of the solar cooker under outdoor weatherconditions of Taif city. This experimental study and the different obtainedmeasurements lead to the following conclusions: - The performance of the solar cooker with heat storage is much better than that of without heat storage ones in all climate conditions, where the thermal energy storage is essentially needed to increase the utility and reliability of the solar cookers. - The solar heating system coupled with the solar cooker can maintain the stability of the absorber plate temperature of the cooker in the cloudy and partly cloudy days. - The solar cooker without heat storage can’t be used for cooking in the cold and cloudy days. - Using the heat storage can accelerate the cooking process which can be started at 12:00 PM. At the same time, the solar heating system decreases the falling of the internal temperature of the cooker. - The results show that the best time to cook with the solar box cooker is between the hours of 11.00 am and 4:00 pm (K.S.A. locale time) on sunny days and is not possible to cook on cloudy or rainy days or at night unless effective solar storage devices are incorporated.Nomenclaturemw mass of heated water in the pot of cooking (kg)Cp thermal capacity of water (KJ. kg-1 K-1) o∆T water Temperature Difference (35 – 95) ( C) t period of time of heating (sec)Gt intensity of solar energy (W. m-2)Ac area of solar collectors (m2)m w.e mass of the measured evaporated water (kg)h fg evaporation latent heat of water (kJ. kg-1)References [1] Muthusivagami .R.M., et. al. (2010), “Solar cookers with and without thermal storage: A review”, Renewable and Sustainable Energy Reviews, Vol. 14, No. 2, pp. 691-701. [2] Alozie .G.A., et. al. (2010), “Design and construction of a solar box cooker as an alternative in Nigerian kitchens”, ISESCO Science and Technology Vision, Vol. 6, No. 9, pp. 57- 62. 563
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME[3] Al-Azab .T.A., et. al. (2009), “Experimental investigation of a box-type solar cooker with finned pot thermal performance in Jordan”, GCREEDER, Amman, Jordan, March 31st –April 2nd.[4] Gaur .A, et. al. (1999), “Performance study of solar cooker with modified utensil”, Renewable Energy, journal, Vol. 18, No. 12, pp. 121-129.[5] Harmim .A, et. al. (2008), “Experimental study of a double exposure solar cooker with finned cooking vessel”, Solar Energy, journal, Vol. 82, No. 4 pp. 287-289.[6] Lahkar .P. J., and Samdarshi .S.K. (2010), “A review of the performance parameters of box type solar cookers and identification of their correlations”, Renewable and Sustainable Energy Reviews, journal, Vol. 14, No. 6, pp. 1615- 1621.[7] Sharma .A, et. al. (2009), “Solar cooker with latent heat storage systems: a review”, Renewable and Sustainable Energy Reviews, journal, Vol. 13, No 6-7, pp. 1599-1605.[8] Sharma .S.D., et. al. (2005), “Thermal performance of a solar cooker based on an evacuated tube solar collector with a PCM storage unit”, Solar Energy, journal, Vol. 78, No 3, pp. 416-426.[9] Buddhi .D, et. al. (2003), “Thermal performance evaluation of a latent heat storage unit for late evening cooking in a solar cooker having three reflectors”, Energy Conversion and Management, journal, Vol. 44, No 6, pp. 809-817.[10] Ramadan .M.R.I., et. al. (1998), “A model of an improved low cost indoor solar cooker in Tanta”, Solar and Wind Technology, journal, Vol. 5, No 4, pp. 387- 393.[11] Pejak .E.R. (1991), “Mathematical model of the thermal performance of box type solar cookers”, Renewable Energy, journal, Vol. 1, No 5-6, pp. 609 – 615.[12] Klemens .S (2003), “Solar cooking system with or without heat storage for families and institutions”, Solar Energy, journal, Vol. 75, No 1, pp. 35 – 41. 564

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