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- Optical characterization of a funnel solar cooker with azimuthal sun tracking through ray-tracing simulationPublication . Carrillo-Andrés, Antonio; Apaolaza-Pagoaga, Xabier; Ruivo, Celestino; Rodríguez-García, Eduardo; Fernández-Hernández, FranciscoFunnel type solar cookers are simple and effective. Most of them rely on a multifaceted reflector to concentrate solar radiation on a cooking pot that is placed inside a transparent enclosure to create a greenhouse effect. The analysis of the resulting optical system is a complex task, as multiple reflections occur. The overall performance of funnel solar cookers is strongly affected by their optical efficiency. There is a lack of information in academic literature about this important research topic. This work aims to fill this gap presenting an optical performance analysis of a funnel solar cooker with only azimuthal sun tracking. Open-source numerical ray-tracing software Soltrace is used to investigate relevant characteristics such as the intercept factor, optical efficiency, dependency on incidence angle, performance of each reflecting surface and irradiation density flux distribution on different surfaces of the cooking pot. Some important results for beam radiation at normal incidence are the intercept factor, determined to be 0.664, and the optical efficiency with realistic optical properties, that turned out to be 0.370. When the incidence of solar beam radiation is not normal, optical efficiency remains above 90% of its normal incidence value, if the alignment errors are less than 10 degrees.
- 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 the thermal performance of the Haines 2 solar cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Ruivo, CelestinoThis work presents the most exhaustive experimental characterization of the thermal performance of the Haines 2 solar cooker available to date. Two Haines 2 solar cookers were tested side-by-side in Malaga, Spain, 36.7 N, between May 2021 and December 2021. A novel test procedure using empty pots and a tilted plane with variable inclination gave useful information about the influence of the solar altitude angle on cooker performance, and allowed identification of the best range for each of the two available reflector configurations for this cooker. Some suggestions are given to improve the cooker design for low solar altitude angles. In addition, a large number of water heating tests partly based on the ASAE S580.1 standard protocol were conducted to i) determine the standardised power, ii) examine the influence of the solar altitude angle, and iii) investigate the impact of using partial loads. All these results provide a complete characterization of the performance of this cooker in a wide range of operating conditions of practical interest. It is recommended that future versions of ASAE S580.1 standard consider the influence of both solar altitude angle and partial loads.
- 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.
- Performance of solar funnel cookers using intermediate temperature test load under low sun elevationPublication . Apaolaza-Pagoaga, Xabier; Sagade, Atul A.; Ruivo, Celestino; Carrillo-Andrés, AntonioSolar funnel cookers can be designed as attractive and affordable low-cost devices accessible to people in all continents of the world regardless of their walk-in life. The present work is aimed to investigate the applicability of funnel cookers to attain the temperature in excess of the boiling point of water. It widens their acceptability for cooking and opens new opportunities for technological developments in such designs of solar cookers. Two identical designs of funnel cookers, FC1 and FC2, have been tested with appropriately sized identical cooking pots and glass enclosure to serve the purpose. Cooker FC2 is tested with a glass enclosure only, while a glass enclosure is not used in FC1. Glycerine is used as a test load. Cooker Opto-thermal Ratio (COR) as a thermal performance parameter and overall cooking efficiency are used to compare the performance of the two funnel cookers. It is shown that the temperature of the test load in the cooker FC2 can reach 140 to 150 degrees C. So, this funnel cooker design can be preferred for cooking food at a relatively high temperature over the boiling point of water. The experimental results show that: i) the mean values of the Cooker Opto-thermal Ratio for cookers FC2 and FC1 are estimated to be 0.157 and 0.110 (m2 degrees C)/W, respectively, and ii) the values of the overall cooking efficiency for cookers FC2 and FC1 are estimated to be 11.8% and 10.2%, respectively.
- 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 the standardised power of a solar funnel cooker for low sun elevationsPublication . Ruivo, Celestino; Carrillo-Andres, Antonio; Apaolaza-Pagoaga, XabierOver the past few decades, many efficient solar cooker designs have evolved. It is important to measure their performance and communicate this information to researchers, manufacturers and users around the world. Funnel type solar cookers are simple, effective and have multiple advantages in practical use, but there is limited experimental data about them in the academic literature. This work provides performance data for a well-known design of funnel cooker. When possible, the experimental protocol was based on the ASAE S580.1 Standard. The following procedures were added to improve the quality and reliability of the measured data: i) two identical funnel cookers were tested simultaneously, side by side, to control for weather variables, ii) a large number of observations were made iii) confidence and prediction intervals were calculated for the main figures of merit iv) cooled water was used to extend the range of valid observations. Tests were conducted in Malaga, Spain, at latitude 36.9 degrees N, between November 2019, and February 2020, a period with low sun elevation. Azimuthal solar tracking was applied. Two different pot lids were compared to investigate their influence on the standardised cooker power obtained. (C) 2021 Elsevier Ltd. All rights reserved.
- New approach for analysing the effect of minor and major solar cooker design changes: influence of height trivet on the power of a funnel cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Ruivo, CelestinoIn present work, the power values of two funnel cookers were determined by following the standard ASAE S580.1 procedure and also a novel improved approach for better analysing the effect of minor design changes. This new approach is based on experimental side by side tests of the two cookers and it adopts a shorter time interval and a curve fitting based on the LOESS adjustment is adopted for the evaluation of the difference in power values of the different designs tested. The two funnel cookers were tested experimentally with a load ratio of 4 kg m-2. The influence of the height of a trivet, from 0 to 100 mm, on the cooker power was evaluated. The estimated changes in power values due to the design changes were low but not negligible. As example, the power standardised increases 6 W when a height trivet of 25 mm is used respecting cooking operation without trivet. The novel approach is promising because it enables to determine the impact of minor design changes on the power of the cooker. The same analysis is not possible to be performed with the standard ASAE S580.1 procedure due to the uncontrollability of the weather conditions.