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Design, construction and operation of spherical solar cooker with automatic sun tracking system Riyad Abu-Malouh, Salah Abdallah, Iyad M. Muslih Department of Mechanical and Industrial Engineering, Applied Science University, Amman 11931, Jordan a r t i c l ei n f o Article history: Received 15 March 2009 Received in revised form 2 December 2009 Accepted 21 July 2010 Available online 6 September 2010 Keywords: Solar cooking Sun tracking PLC control Frequency control a b s t r a c t In this work, the effect of two axes tracking on a solar cooking system was studied. A dish was built to concentrate solar radiation on a pan that is fi xed at the focus of the dish. The dish tracks the sun using a two axes sun tracking system. This system was built and tested. Experimental results obtained show that the temperature inside the pan reached more than 93 ?C in a day where the maximum ambient tem- perature was 32 ?C. This temperature is suitable for cooking purposes and this was achieved by using the two axes sun tracking system. ? 2010 Elsevier Ltd. All rights reserved. 1. Introduction The energy section in Jordan depends heavily on the imported oil and gas products. This energy policy put the country in tough economic situations and slowed down the economical growth in the last years. This situation is worsening by the dramatic increase in the crude oil prices worldwide and in the increased demand on energy consumption. Jordan lies in high solar insolation band, where the average insolation intensity on horizontal surface is approximately 57 kW h/m2/day, which is one of the highest in the world 1. Biermann et al. 2 conducted a 1 year comparative fi eld test of different types of cooking appliances including seven brands of solar cookers. The test took place in three study areas in South Afri- ca and involved 66 families, who expressed their preferences for certain cooker types. Solar and wood (stoves and open fi res) cook- ers were the most used cooking appliances. The families used solar cookers for about 38% of overall test days and for 35% of overall cooked meals and used wood cooking appliances for 42% of overall test days. Fuel consumption measurements showed overall fuel savings of 38% resulting in estimated payback periods (through monetary fuel savings) from 8 months onwards, depending on the cooker type and region. Solar cooking in boarding schools and communal centers in iso- lated areas demands heating of large quantities of food. Franco et al. 3 presented three different kinds of absorbers, optimized to fulfi ll different functions in a concentrator of an area of 2 m2. These alternatives allowed the possibility of satisfying the needs of a communal dining center, cooking for up to 30 children, once each concentrator has been installed. The policy formulation for substituting cooking energy by renewable energy is addressed in multi-criteria context. In this re- gard, a survey was conducted to evaluate the perceptions of differ- ent decision making groups on present dissemination of various cooking energy alternatives in India 4,5. Nine cooking energy alternatives were evaluated based on 30 different criteria, among which were technical, economic, environmental, social, behavioral and commercial issues. It was found that liquefi ed petroleum gas stove is the most preferred device, followed by kerosene stove, box type solar cooker (BSC) and parabolic solar cooker (PSC). PSC were investigated by many researchers. Ozturk 6 con- structed and designed a low cost PSC and experimentally evaluated its energy and exergy effi ciencies. The energy output of the PSC varied between 20.9 and 78.1 W, whereas its exergy output was in the range of 2.96.6 W. It was found that the energy and exergy effi ciencies of the PSC were in the range of 2.815.7 and 0.41.25 respectively. Petela 7 analyzed a PSC of cylindrical trough shape from exergy point of view. Equations for heat transfer between three surfaces: (i) cooking pot, (ii) refl ector, and (iii) imagined sur- face making up the system were derived. The exergy effi ciency of the PSC was found to be relatively very low (equals approximately 1%), and about 10 times smaller than the respective energy effi - ciency which was in agreement with experimental data. Sonune and Philip 8 designed a Fresnel type domestic concentrating coo- ker, which has an aperture area of 1.5 m2and a focal length of 0196-8904/$ - see front matter ? 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2010.07.037 Corresponding author. Tel.: +962 5 3740026. * Corresponding author. E-mail addresses: (R. Abu-Malouh), Salahabdalah_1964 (S. Abdallah). Energy Conversion and Management 52 (2011) 615620 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: /locate/enconman 0.75 m and was found to provide an adequate temperature needed for cooking, frying and preparation of chapattis and capable of cooking food for a family of 45 persons. The BSC has also been a subject of investigations conducted by many researchers. El-Sebaii and Aboul-Enein 9 presented a tran- sient mathematical model for a BSC with one step outer refl ector hinged at the top of the cooker. The model was validated by com- paring the temperature distribution obtained by computer simula- tionwithexperimentalresults.Goodagreementbetween experimental and theoretical results was observed. The perfor- mance of a BSC with auxiliary heating was studied and analyzed with the aid of (i) a built-in heating coil inside the cooker and (ii) a retrofi t electric bulb in a black painted cylinder 10. The re- sults showed that with the use of auxiliary energy, when neces- sary, a solar cooker may be used throughout the year in areas where electricity is available. The study also recommended (i) to place electric heating elements below the absorber tray in solar cookers which are to be built and (ii) to place a retrofi t electric bulb for heating on the absorber tray for year-round cooking for cookers which have been already built. El-Sebaii 11 presented a simple mathematical model for a BSC with outerinner refl ectors based on analytical solution of the energy-balance equations for different elements of the cooker. The cooker performance was investigated by computer simulation in terms of the cooker effi - ciency as well as characteristic and specifi c boiling times. Numerical calculations were carried out for different tilt angles of the outer refl ector on a typical winter day in Tanta/Egypt. It was shown that at the optimum tilt angle of the outer refl ector, which equals 60 ?C, the specifi c and characteristic boiling times are de- creased by 50% and 35%, respectively, compared to the case with- out the outer refl ector. The overall utilization effi ciency of the cooker was found to be 31%. A hot BSC was designed, manufac- tured and tested in Istanbul Technical University 12. In the theo- retical analysis, the differential equations have been solved numerically by the fourth-order RungeKutta method. The obtained theoretical results were compared with the exper- imental ones and showed a good match. A model to predict the cooking power of a solar cooker based on three controlled param- eters (solar intercept area, overall heat loss coeffi cient and absor- ber plate thermal conductivity) and three uncontrolled variables (solar insolation, temperature difference and load distribution) was presented 13. The model was validated for commercially available solar cookers of both the box and concentrating types. The model basis was a fundamental energy-balance equation. Coeffi cients for each term in the model were determined by regres- sion analysis of experimental data. The valid range of model appli- cation included most of the feasible design space for family-sized solar cookers. The model was found to be applicable for estimating the cooking capacity of existing box type and concentrating type solar cookers and for determining the combinations of intercept area and heat loss coeffi cient required to cook a given quantity of food in a given climate. A simple wooden, hot box, with one refl ec- tor solar cooker was designed and several demonstration units were fabricated by El-Ghetany and Abdel Dayem 14. The units were fi eld tested and showed acceptable performance. Maximum inner temperature of the units reached 160 ?C under fi eld condi- tions of Giza, Egypt (30?N). Different foods were cooked successfully such as rice, meat, fi sh, and beans. The time of cooking ranged from 1 to 2.5 h. A series of tests were carried out during nine days to compare the Sudanese BSC with some similar Indian designs 15. Sudanese BSC showed better thermal performance. Using inter- nal, external refl ectors and sloping of the top cover enhanced sig- nifi cantly the thermal performance. This was revealed by the amount of heat absorbed and hence the achieved plate tempera- ture. Algifri and Al-Towaie 16 outlined a method to determine a refl ectors performance and its orientation factors that depend upon the elevation angle of the sun, the solar surface azimuth an- gle and the refl ector tilt angle. The analysis was applied to a cooker placed in the city of Aden in Yemen. The results indicated with proper cooker orientation improvement in the performance of the cooker due to the refl ector. It reached during the winter sea- son more than 100% at lower elevation angles and more than 60% at high elevation angles. Factors governing the operation of three BSC models (HS7534, HS7033 and HS5521) were described 17. The results showed that HS552I is cheaper, and its volume is only 35% compared to HS7033. Comparing the performance of HS7033 and HS5521 was also per- formed based on the data collected during testing with and with- out load. The results showed that the HS5521 has the same heat collection rate and is able to cook as fast as HS7033. Ekechukwu and Ugwuoke 18 presented the design philosophy, construction and measured performance of a plane refl ector augmented BSC. The experimental solar cooker consisted of aluminum plate absor- ber painted with black matt and a double glazed lid. Predicted water boiling time using the two fi gures of merit compared favor- ably with the measured values. The performance of the cooker with the plane refl ector was im- proved tremendously compared to the cooker performance with- out the refl ector. A hot BSC with used engine oil as a storage material was designed, fabricated and tested to enable cooking even in the late evening 19. The performance and testing of the cooker was investigated by measuring the stagnation temperatures and conducting cooking trials. The effi ciency of the hot box storage solar cooker was found to be 27.5%. Kumar investigated the top heat losses, constituting the major losses in the BSC and affecting its thermal performance 20. The investigation revealed that the pot water required less time to reach a certain temperature with an increase in solar radiation level while, as expected, it took longer time with higher values of load of water in the pots. Reddy and Rao 21 showed that the per- formance of conventional BSC can be improved by better designs of cooking vessels with proper understanding of the heat fl ow to the material to be cooked. An attempt was made to arrive at a mathe- matical model to understand the heat fl ow process to the cooking vessel and thereby to the food to be cooked. The mathematical model considered a double glazed hot BSC loaded with two different types of vessels, kept either on the fl oor of the cooker or on lugs. It was found experimentally and by modeling that the cook- ing vessel with a central cylindrical cavity lugs results in higher temperature of the thermal fl uid than that of a conventional vessel on the fl oor or on lugs. El-Sebaii and Ibrahim constructed and tested a BSC with one or four cooking pots under the weather con- ditions of Tanta city in Egypt 22. Experiments were performed during July 2002 using the cooker with and without load. The coo- ker was able to cook most food kinds with an overall utilization effi ciency of 26.7%. Amer introduced a novel design of solar cooker, in which the absorber is exposed to solar radiation from top and bottom sides 23. A set of plane diffuse refl ectors were used to direct the radiation onto lower side of the absorber plate. The performance of the new cooker and the conventional BSC was investigated under same operating conditions. The obtained results show that the absorbers of the BSC and the double exposure cooker attain 140 ?C and 165 ?C respectively. Sharma et al. investigated the thermal performance of a prototype solar cooker based on an evacuated tube solar collector with phase change material (PCM) storage unit with commercial grade erythritol as a latent heat storage material 24. Solar energy was stored in the PCM storage unit during sunshine hours and was utilized for cooking in late evening/night time. Noon and evening cooking experiments were conducted with different loads and 616R. Abu-Malouh et al./Energy Conversion and Management 52 (2011) 615620 loading times. Cooking experiments and PCM storage processes were carried out simultaneously. The system was found capable to cook successfully twice (noon and evening) in a single day during Japanese summer months. Noon cooking did not affect evening cooking, and the evening cooking using the PCM heat storage was found to be faster than noon cooking. It was noticed that the PCM did not melt in January (winter) in Japan. In summer, PCM temperatures reached more than 110 ?C at the time of evening cooking. Hence, erythritol was found to be a promising PCM for solar cooking. Sharaf 25 revealed the concept of conical focus and explained the design of a solar cooker on its basis. The conical cooker was practically tested for grilling both white and red meat in a record time and a method for obtaining real boiling temperature of water (100 ?C) using a so- lar heater was reported. The results showed that the conical cooker has advantages regarding ease of manufacture, low price, light- weight and effi ciency. It also demonstrated its ability and suitabil- ity for cooking different kinds of meat and legumes. Narasimha Rao and Subramanyam investigated the role of the vessel inside the so- lar cooker 26. It was found that raising the vessel by providing few lugs made the bottom of the vessel a heat transfer surface. This change improved the systems performance by improving the heat transfer rates in both heating and cooling modes. Despite their ability to provide adequate temperatures needed for cooking, frying and preparation of chapattis, all the aforemen- tioned types of concentrating solar cookers, suffer like all concen- trating solar cookers with manual tracking from their low effi ciency. This low effi ciency is due to the fact that the solar rays are not perpendicular to the cookers surface most of the day. Accordingly, it is expected that the effi ciency can be considerably improved by keeping the solar rays perpendicular to the cookers surface by using an automatic sun tracking system 8,27 with the solar cooker. In this context, this paper presents the design, construction and operation of a solar cooker with automatic two axes sun tracking programmable logic controller (PLC) system, characterized by a fairly simple electromechanical setup which re- duces cost, maintenance and the possibility of failure. 2. The automatic sun tracking system design and control The amount of power produced by solar system depends on the amount of sunlight to which it is exposed. As the suns position changes throughout the day, the solar system must be adjusted so that it is always aimed precisely at the sun and, as a result, pro- duces the maximum possible power. Single axis tracking systems are considerably cheaper and easier to construct, but their effi - ciency is lower than that of two axes sun tracking systems. On the other hand, some solar systems require only two axes tracking, such as point focus concentrators. Two axes sun tracking systems can be applied in all types of so- lar systems to increase their effi ciency. A large number of investi- gations have been performed to design and employ two axes sun tracking systems, however, only a few were cited in the literature that investigated the effect of using two axes sun tracking systems controlled by a modern computerized control system, such as a programmable logic controller (PLC) control system. Barakat et al. 28 designed a two axes sun tracking system with closed loop system and with complicated typical electronic control cir- cuits. They found that the energy available to the two axes tracker is higher by 20%. Neville 29 presented a theoretical comparative study between the energy available to a two axes tracker, an eastwest tracker and a fi xed surface. It was found that the energy available to the ideal tracker is higher by 510% and 50% than the eastwest track- er and the fi xed surface, respectively. Khalifa 30 performed an experimental study to investigate the effect of using a two axes sun tracking system on the thermal performance of compound par- abolic concentrators (CPC). The tracking CPC collector showed a better performance with an increase in the collected energy of up to 75% compared with an identical fi xed collector. Hession and Bonwick 31 introduced a sun tracking system for use with various collectors or platforms. The system used both analog and digital techniques with sun sens- ing phototransistors that enabled the suns position to be resolved to a precision of better than 0.1?. Baltas et al. 32 made a compar- ative study between continuous and stepwise tracking. They showed that unlike concentrating systems, fl at plate photovoltaic (FPPV) arrays yielded almost t