Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- 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.
- 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.
- Influence of the aperture area on the performance of a solar funnel cooker operating at high sun elevations using glycerine as loadPublication . Ruivo, Celestino; Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Coccia, GianlucaFive 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.