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- Proposal of a non-linear curve for reporting the performance of solar cookersPublication . Ruivo, Celestino; Apaolaza-Pagoaga, Xabier; Coccia, Gianluca; Carrillo-Andrés, AntonioPerformance parameters of solar cookers have conventionally been determined by assuming a linear trend between the cooker power and the difference between load temperature and ambient air temperature. This approach may not be convenient for some solar cooker designs. In the present work, the suitability of a non-linear regression derived from fitting the measured load temperature to a second order exponential polynomial was investigated and compared with the linear regression. Both regressions were compared with the corresponding experimental curves of a panel cooker and a box cooker. In the case of the panel cooker, the linear trend of the experimental plot was confirmed over a large period of the conducted test. Minor deviations from the experimental data were observed only at the beginning and at the end of the test. On the contrary, in the box solar cooker, significant deviations between the linear regression plot and the experimental points were observed, while smaller deviations were obtained using the non-linear regression. Thus, the proposed method can be seen as a promising approach that should be considered when updating the existing procedures for testing and reporting the performance of solar cookers.
- Concentrating solar cookers in urban areas: establishing usefulness through realistic intermediate temperature rating and gradingPublication . Sagade, Atul A.; Apaolaza-Pagoaga, Xabier; Ruivo, Celestino; Carrillo-Andrés, AntonioConcentrating Solar Cookers (CSCs) are well-known for fast cooking and can significantly contribute to attaining the United Nation's sustainable development goals. CSCs attain intermediate temperatures (120-240 degrees C) and are suitable for several cooking applications. The realistic rating and grading of CSCs is inevitable for establishing their usefulness in urban areas, which is the main objective of the present work. This paper reveals the experimental results of two existing concentrating solar cookers with different geometries and aperture areas. The first cooker is a shallow satellite antenna parabolic dish, and the other is a small deep parabola. Cooker Opto-thermal Ratio (COR) acts as a thermal performance parameter, and glycerin as a test load for their performance evaluation.The mean values of COR for the cookers, CSC1, and CSC3, are 0.180 and 0.092, respectively. The typical theoretical values of maximum achievable fluid temperature are 192.9 and 113.9 degrees C, respectively, and that for reference time are 23.8 and 60.5 min for CSC1 and CSC3, respectively. COR identifies the variation in the performance of CSCs based on a design change. The objective parameters enable realistic intra-cooker performance comparison of the CSCs at intermediate temperatures. The results depict that the existing designs of CSCs can be graded appropriately using COR and provide new insights into their performance at intermediate temperatures realistically. TPP-based realistic rating and grading of existing designs of solar cookers enable their effortless selection as per end-user requirements and help in the faster propagation of solar cooking technology in urban and semi-urban areas.
- Standardised power of solar cookers with a linear performance curve following the Hottel-Whillier-Bliss formulationPublication . Ruivo, Celestino; Coccia, Gianluca; Di Nicola, Giovanni; Carrillo-Andrés, Antonio; Apaolaza-Pagoaga, XabierIn the present work, an improvement of protocol widely used for reporting the thermal behaviour of solar cookers is communicated to the scientific community. The linear regression used to represent the standardised cooking power is based on the well-known Hottel-Whillier-Bliss equation written in dimensionless format. The authors’ new formulation procedure for estimating the standardised power includes a correction for the difference between the load temperature and the ambient air temperature of the procedure of ASAE S580.1 Standard. It is derived from a simple theoretical deduction, similar to the ones usually applied to solar thermal flat collectors. The correction factor relates itself with the ratio between the measured solar irradiance and the solar irradiance chosen as a standard value. As one example, test results of a funnel cooker loaded with water are used to show the impact of the improvement of the procedure for reporting performance of a solar cooker. The procedure is valid only for solar cookers evidencing a clear linear performance curve.
- Experimental determination of effective concentration ratio for two different designs of concentrating solar cookersPublication . Sagade, Atul A.; Apaolaza-Pagoaga, Xabier; Ruivo, Celestino; Carrillo-Andrés, AntonioThe concentration ratio is most influential characteristic of the solar concentrators, impacting on its opto-thermal performance. Hence, concentration ratio's, realistic and quantificable measurement is essential. Therefore, this paper reveals the usefulness of the determination of an effective concentration ratio (Ceff) for a satellite antenna dish and Parvati concentrating solar cookers. Open and closed reflector open sun cooling tests were performed to determine the cooker opto-thermal ratio (COR). A thin black cloth used over each reflector neutralizes the effect of the reflection of solar radiation in the closed reflector tests. Subsequently, the COR values for these two types of tests enables the determination of the Ceff. Some corrective actions are suggested to eliminate the errors occurring during open reflector open sun cooling tests. Results show that the values of the Ceff for the satellite dish and Parvati cookers are 7.34 and 3.61, respectively. The determination of Ceff values enables commenting on its effective and realistic value, the role of the concentrator's reflecting surface in the concentration effect, and the degradation of the reflector surface. Thus, the Ceff is a practical indicator for assessing the impact of optical characteristics of the reflecting surface of the CSCs.