Experimental thermal performance evaluation of different configurations of Copenhagen solar cooker

In this work, four different configurations of Copenhagen solar cookers were tested experimentally at the same time under the same weather conditions. First tests were carried out using pots without water load. Secondly, tests were performed with the equal amount of water in each pot. Thirdly, tests were carried out with different amounts of water for one of the configurations. From the results of the first set of tests, it was found that the performance of one of the configurations depends more significantly on the solar altitude angle than the others. A large number of experiments for each set of tests were conducted covering a wide range of solar altitude angles. A thermal performance analysis based on the ASAE S580.1 standard was performed with the measured data of the second and third sets of tests. The obtained plots with the observation points of each configuration evidence that the linear trend of the standardised power is not universal. The observed trends are very dependent on the solar altitude angle. Thus, the procedure for evaluating standardised power recommended by the standard for cooker performance comparison should be improved

Influence of the aperture area on the performance of a solar funnel cooker operating at high sun elevations using glycerine as load

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/publishedVersio

Proposal of a non-linear curve for reporting the performance of solar cookers

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/publishedVersio

La refrigeración solar de los edificios

La climatización, además de afectar al confort de una vivienda, es importante en secotres como la economía. De esta depende, por ejemplo, la productividad de un invernadero. Por ello, la innovación en este campo pasa por estudiar sistemas más eficientes que aprovechen enrgías limpias como el so

The effect of partial loads on the performance of a funnel solar cooker

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.info:eu-repo/semantics/publishedVersio

Optical performance analysis of the Copenhagen solar cooker with COMSOL Multiphysics

The Copenhagen solar cooker is a compact, panel-type design with four flexible reflective panels to redirect solar radiation onto a cooking pot. The geometric configuration of the panels is adjustable, depending on the sun elevation angle. Despite the simplicity of the concept, the resulting curved reflector geometries do not align with any analytical surface, posing a modeling challenge. This work introduces an innovative approach: COMSOL Multiphysics structural mechanics simulation is used to emulate the manual folding process of the reflector panels, in order to create accurate geometric models of the two most used configurations: Ninety and Flower. Then, the COMSOL ray optics module is used to characterize the optical performance of the generated Copenhagen solar cooker models. A large number of studies are presented, of interest both to the practical user who wants to optimize the use of their Copenhagen cooker and to the designer looking for future optimizations. This is the first work in scientific literature that analyzes the optical system of the Copenhagen solar cooker

Numerical Evaluation in a Scaled Rotor-Less Nozzle Vaned Radial Turbine Model under Variable Geometry Conditions

[EN] The widespread trend of pursuing higher efficiencies in radial turbochargers led to the prompting of this work. A 3D-printed model of the static parts of a radial variable geometry turbine, the vaned nozzle, and the volute, was developed. This model was up-scaled from the actual reference turbine to place sensors and characterize the flow around the nozzle vanes, including the tip gap. In this study, a computational model of the scaled-up turbine was carried out to verify the results in two ways. For this model, firstly compared with an already validated CFD turbine model of the real device (which includes a rotor), its operating range was extended to different nozzle positions, and we checked the issues with rotor-stator interactions as well as the influence of elements such as the screws of the turbine stator. After showing results for different nozzle openings, another purpose of the study was to check the effect of varying the clearance over the tip of the stator vanes on the tip leakage flow since the 3D-printed model has variable gap height configurations.This research work was supported by Grant PDC2021-120821-I00, funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGeneration EI/PRTR.Serrano, J.; Tiseira, A.; López-Carrillo, JA.; Hervás-Gómez, N. (2022). Numerical Evaluation in a Scaled Rotor-Less Nozzle Vaned Radial Turbine Model under Variable Geometry Conditions. Applied Sciences. 12(14):1-17. https://doi.org/10.3390/app12147254117121

The effect of partial loads on the performance of a funnel solar cooker

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 testedFunding for open access charge: Universidad de Málaga / CBU

Experimental evaluation of the performance of new Copenhagen solar cooker configurations as a function of solar altitude angle

The Copenhagen cooker is a panel-type solar cooker that uses four flexible reflective panels to redirect solar radiation to a cooking vessel. Its concept design allows adjustment of the four panels to create new geometries that can adapt to the solar altitude angle. Originally, three geometrical configurations were presented by its creators. In this work, building upon these originals, new configurations are proposed to improve performances. To quantify performance improvement, experimental tests are performed. First, stagnation tests are carried out to identify the best configuration for different solar altitude angles. Then, the most promising new configurations and the original ones are tested, side-by-side, heating a water load and for different ranges of altitude angle: low (35 ), medium (66 ◦ ) and high (75 ◦ ). Results show that performance significantly improves. Results across the entire solar altitude angle range help general users to set the most effective configuration based on their specific conditions. Last, our experimental study suggests that tests without load can be a good predictor of the behaviour of solar cookers with load. This qualitative conclusion would allow solar cookers to be tested in shorter periods for all ranges of solar altitude angle, which is of great value for general users.Funding for open access charge: Universidad de Málaga / CBU