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- On the use of experimental measured data to derive the linear regression usually adopted for determining the performance parameters of a solar cookerPublication . Ruivo, Celestino; Apaolaza-Pagoaga, Xabier; Di Nicola, Giovanni; Carrillo-Andrés, AntonioIn the present work, the results of testing panel and box solar cookers are used to investigate the suitability of using the linear regression for estimation of the performance parameters of a solar cooker. The panel cooker and the box cooker were experimentally tested with glycerine and peanut oil, respectively. An exponential fitting to the plot of measured load temperature versus time is used to derive the linear regression between the instantaneous efficiency and the specific difference of temperature. The linear regression curve is compared with the corresponding experimental curve. Minor deviations are observed in the case of the panel cooker, but only in the middle part of the test. In the case of the box cooker, the deviations are very significant during the whole test. The present work presents the simplified formu-lation associated with the physical problem. It points out the importance of performing further research to develop a more accurate procedure. The determination of parameters based on the linear regression cannot be seen as a universal procedure applicable to all types of cookers. The opto-thermal ratio and the maximum achievable load temperature are overestimated.
- Experimental characterization of a foldable solar cooker with a trapezoidal cooking chamber and adjustable reflectorsPublication . Demissie, Tariku Negash; Tomassetti, Sebastiano; Paciarotti, Claudia; Muccioli, Matteo; Di Nicola, Giovanni; Ruivo, CelestinoIn this study, a portable and easy-to-construct solar cooker is presented as an alternative to traditional cooking methods to be used in humanitarian contexts in order to face the issue of humanitarian goods transport and storage. The prototype consists of a trapezoidal cooking chamber and adjustable reflector panels made of inexpensive and readily available materials. The solar cooker was designed to be foldable and transportable by using lightweight materials. In fact, the folded prototype is compact, having a mass of 7 kg. The thermal per formance and optical performance of the proposed cooking appliance were evaluated through several experi ments conducted without load and with load. The tests were done by using a black pot enclosed with a glass bowl or a plastic bag. During the tests without load, the highest recorded temperature was 149.38 ◦C. The time needed to bring 1 kg of water from 40 ◦C until 90 ◦C was on average 114 min for the glass enclosure tests and 132 min for the plastic enclosure tests. The prototype loaded with 1 kg of glycerin took the same average time of 121 min to reach 105 ◦C from 40 ◦C for both glass and plastic enclosure tests. The average values of cooking power, derived using Hottel-Whillier-Bliss formulation with a reference global normal solar irradiance for the clear sky condi tion, are estimated as 26.0 W for the water tests using the glass enclosure and 31.8 W for the glycerin tests with the glass enclosure. Finally, the cooking performance of the prototype was evaluated by cooking common foods (i.e., tomatoes, rice, potatoes). The average cooking times for tomatoes, rice, and potatoes were always lower than two hours, a value consistent with the cooking times of different box solar cookers.