• Energy Research

Performance 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. info:eu-repo/semantics/acceptedVersion

Performance 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. info:eu-repo/semantics/acceptedVersion

Five funnel solar cookers have been tested to investigate the influence of the aperture area on their performance. The largest cooker had an aperture area of 0.5 m(2) and it was tested side by side with two other two smaller cookers. Each cooker was tested with the same amount of glycerine. The linear performance curves relating the efficiency with the specific temperature difference was determined. Then, the determined regressions of the cooker opto-thermal ratio and the reference time on the aperture area were used to predict: i) the influence of the solar irradiance and the aperture area on the maximum temperature achieved by the load, ii) the time duration required for achieving load temperature from 65 to 140 degrees C, and iii) the power of the cooker. It was found that for a solar irradiance range of 600-1100 W m (2), the pasteurization temperature can be achieved even by the smallest cooker, and the efficiency of the largest cooker is close to the efficiency of a cooker with optimum aperture area. Moreover, when using the largest cooker, under an irradiance of 1100 W m (2) and ambient temperature 20 degrees C, the load can achieve 180 degrees C, implying that frying is possible. info:eu-repo/semantics/publishedVersion

Five funnel solar cookers have been tested to investigate the influence of the aperture area on their performance. The largest cooker had an aperture area of 0.5 m(2) and it was tested side by side with two other two smaller cookers. Each cooker was tested with the same amount of glycerine. The linear performance curves relating the efficiency with the specific temperature difference was determined. Then, the determined regressions of the cooker opto-thermal ratio and the reference time on the aperture area were used to predict: i) the influence of the solar irradiance and the aperture area on the maximum temperature achieved by the load, ii) the time duration required for achieving load temperature from 65 to 140 degrees C, and iii) the power of the cooker. It was found that for a solar irradiance range of 600-1100 W m (2), the pasteurization temperature can be achieved even by the smallest cooker, and the efficiency of the largest cooker is close to the efficiency of a cooker with optimum aperture area. Moreover, when using the largest cooker, under an irradiance of 1100 W m (2) and ambient temperature 20 degrees C, the load can achieve 180 degrees C, implying that frying is possible. info:eu-repo/semantics/publishedVersion

Several solar cooker designs have been proposed over the last decades. The funnel cooker is a well-known model, representative of the category of panel-type solar cookers. From the empirical experience of real practice, it is known that the use of partial loads has an impact on the performance of the cooker. However, this effect has not yet been investigated rigorously. This work aims to fill this lack. Extensive experimental work was performed to determine the effect of partial loads on a funnel cooker thermal performance. Tests were conducted on two identical funnel cookers, in Malaga, Spain, with low sun elevation. Cookers were tracked only azimuthally. Experimental protocol was based on ASAE 580.1 Standard for better replicability. Results showed that the standardised power drops by about 15% of the original value when the water volumetric load fraction drops by 25%, for both cooker operations, with and without glass enclosure. This important reduction is explained on how the fill level of the cooking vessel affects its function as a thermal radiation receiver. Results from experimental tests were correlated into a simple formula of practical interest. Finally, a new cooking vessel design, that improves performance at partial loads, i.e., a 25.4% increase in cooker power, was proposed and tested Funding for open access charge: Universidad de Málaga / CBUA

Several solar cooker designs have been proposed over the last decades. The funnel cooker is a well-known model, representative of the category of panel-type solar cookers. From the empirical experience of real practice, it is known that the use of partial loads has an impact on the performance of the cooker. However, this effect has not yet been investigated rigorously. This work aims to fill this lack. Extensive experimental work was performed to determine the effect of partial loads on a funnel cooker thermal performance. Tests were conducted on two identical funnel cookers, in Malaga, Spain, with low sun elevation. Cookers were tracked only azimuthally. Experimental protocol was based on ASAE 580.1 Standard for better replicability. Results showed that the standardised power drops by about 15% of the original value when the water volumetric load fraction drops by 25%, for both cooker operations, with and without glass enclosure. This important reduction is explained on how the fill level of the cooking vessel affects its function as a thermal radiation receiver. Results from experimental tests were correlated into a simple formula of practical interest. Finally, a new cooking vessel design, that improves performance at partial loads, i.e., a 25.4% increase in cooker power, was proposed and tested Funding for open access charge: Universidad de Málaga / CBUA

In 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.

In 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.