Browsing by Author "Ruivo, Celestino"
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- Aquecimento ambiente com aquecedores eléctricos com e sem acumulação de calorPublication . Ruivo, Celestino; Mortal, AntónioA manutenção das condições de conforto térmico no interior de muitos dos edifícios residenciais e de serviços durante os meses mais frios é conseguida com recurso a sistemas de aquecimento mais ou menos sofisticados que utilizam quantidades assinaláveis de energia. Para além das condições de conforto térmico é também importante assegurar a manutenção da qualidade do ar. Esta é conseguida em muitos casos com a utilização duma quantidade mínima de ar novo que terá também de ser aquecida.
- 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.
- Corrigendum to “Experimental characterization of a foldable solar cooker with a trapezoidal cooking chamber and adjustable reflectors” [Energy Sustain. Dev. 79 (2024) 101409]Publication . Demissie, Tariku Negash; Tomassetti, Sebastiano; Paciarotti, Claudia; Muccioli, Matteo; Di Nicola, Giovanni; Ruivo, CelestinoThe authors regret that inappropriate references were cited in some sentences of the subsection “Performance parameters for solar cooker testing with load” of the original manuscript. In this Corrigendum, the sentences with the correct references are reported to avoid giving inaccurate information. The authors would like to apologize for any inconvenience caused.
- Experimental characterization of a foldable solar cooker with a trapezoidal cooking chamber and adjustable reflectorsPublication . Demissie, Tariku Negash; Tomassetti, Sebastiano; Paciarotti, Claudia; Muccioli, Matteo; Di Nicola, Giovanni; Ruivo, CelestinoIn this study, a portable and easy-to-construct solar cooker is presented as an alternative to traditional cooking methods to be used in humanitarian contexts in order to face the issue of humanitarian goods transport and storage. The prototype consists of a trapezoidal cooking chamber and adjustable reflector panels made of inexpensive and readily available materials. The solar cooker was designed to be foldable and transportable by using lightweight materials. In fact, the folded prototype is compact, having a mass of 7 kg. The thermal per formance and optical performance of the proposed cooking appliance were evaluated through several experi ments conducted without load and with load. The tests were done by using a black pot enclosed with a glass bowl or a plastic bag. During the tests without load, the highest recorded temperature was 149.38 ◦C. The time needed to bring 1 kg of water from 40 ◦C until 90 ◦C was on average 114 min for the glass enclosure tests and 132 min for the plastic enclosure tests. The prototype loaded with 1 kg of glycerin took the same average time of 121 min to reach 105 ◦C from 40 ◦C for both glass and plastic enclosure tests. The average values of cooking power, derived using Hottel-Whillier-Bliss formulation with a reference global normal solar irradiance for the clear sky condi tion, are estimated as 26.0 W for the water tests using the glass enclosure and 31.8 W for the glycerin tests with the glass enclosure. Finally, the cooking performance of the prototype was evaluated by cooking common foods (i.e., tomatoes, rice, potatoes). The average cooking times for tomatoes, rice, and potatoes were always lower than two hours, a value consistent with the cooking times of different box solar cookers.
- 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.
- 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.
- 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.
- Experimental evaluation of the performance of new copenhagen solar cooker configurations as a function of solar altitude anglePublication . Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Jiménez-Navarro, Juan-Pablo; Ruivo, CelestinoThe 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 degrees), medium (66 degrees) and high (75 degrees). 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.
- Experimental thermal performance evaluation of different configurations of Copenhagen solar cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo Andres, Antonio; Ruivo, CelestinoIn 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 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.
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