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- 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.
- 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.
- Study on thermal comfort by using an atmospheric pressure dependent predicted mean vote indexPublication . Ruivo, Celestino; Gameiro da Silva, Manuel; Broday, Evandro EduardoThe thermal environment index Predicted Mean Vote is a descriptor largely applied to evaluate the comfort sensation of people in moderate environments. Software tools based on the Fanger's method have been created and used, which application is limited for the sea level atmospheric pressure. A procedure for estimating the index of thermal comfort of individuals in environments at air pressure different from barometric pressure 0 m of altitude was recently introduced. In present study, indoor air state associated with neutral thermal comfort conditions of individuals in seating activity are predicted for atmospheric pressure values in the range between 65.0 kPa and 101.3 kPa. It was observed that neutral temperature diminishes with the decrease of barometric pressure. Dependencies of index PMV on the activity level, the clothing insulation, relative, air velocity and on relative humidity for two atmospheric pressure values are investigated. It is concluded that the impact of pressure of the environment on the index of thermal comfort must be also considered when sizing an air-conditioning system.
- Simplified model of finned-tube heat exchangers based on the effectiveness method and calibrated with manufacturer and experimental dataPublication . Ruivo, Celestino; Dominguez-Munoz, Fernando; Costa, Jose J.A simplified model for predicting the overall thermal performance of finned-tube heat exchangers considering water and air as hot and cold fluids, respectively, is investigated. The model is based on the classical epsilon-NTU method and the thermal convective resistance in each fluid is estimated after conventional type (Nusselt number) empirical correlations. The model is calibrated with catalogue data of a heating coil. Calibrations of six families of model versions are performed by using different numbers of operating cases ranging from 2 to 320, some of them taking into account the influence of varying properties. The calibrated versions are tested for operating cases listed in the catalogue and the best performing versions are identified, such as the one calibrated with 24 cases and taking into account the effect of the fluid properties, which provided better accuracy than the versions calibrated in previous works. A test of the method robustness is conducted regarding the influence of the initial guessed values of the thermal resistances on the calibration procedure. The validity of the component model is further investigated by using a set of published experimental data for an automotive radiator covering ranges of practical interest of the mass flow rates of both air and water streams, and some versions providing excellent results are identified. The model based on a suitable version previously calibrated and tested is a promising procedure for the modular component simulation of finned-tube heat exchangers, when used as air conditioning heating coils or in other particular applications. (C) 2016 Elsevier Ltd. All rights reserved.
- Qualidade térmica em salas de aulasPublication . Ruivo, Celestino; Inverno, Armando; Lamarão, António Hugo Tavares da SilvaA qualidade ambiental nos espaços interiores dos edificios de serviços é hoje em dia um factor determinante na qualidade do serviço prestado que é indispensável garantir. O conforto humano associado ao bem estar num determinado espaço interior é influenciado pela iluminação, decoração, espaço disponível por ocupante, nível de ruído, pureza do ar e pelos factores ambientais de conforto térmico tais como: a temperatura do ar, as tempe- raturas das superficies envolventes, a humidade relativa e a distribuição do ar. O presente trabalho consiste simplesmente na apresentação de alguns valores de medições experimentais dos factores associados ao conforto térmico em salas de aula e na averiguação da sensação térmica dos ocupantes em vários pontos da zona ocupada.
- 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.
- Methodology for calculating an atmospheric pressure-sensitive thermal comfort index PMVapsPublication . Ruivo, Celestino; da Silva, Manuel Gameiro; Broday, Evandro EduardoSeveral software tools have been created to calculate the indices Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) by following Fanger's method, which is valid only for atmospheric pressures close to 1 atm. The main objective of this work is to propose a formulation named PMV-PS for predicting an atmospheric pressure-sensitive thermal comfort index (PMVaps). The effort conducted by the authors was focused on the identification of the variables and expressions used in the calculation of thermal comfort index that may be affected by the change of the atmospheric pressure. The best known formulations for each individual aspect were introduced in the new model. It has been calibrated with data at sea level and tested for a set of cases considering different values of metabolic activity rate, thermal resistance of clothing and environmental parameters. At sea level there are negligible differences between PMV and PMVaps. However, when atmospheric pressure deviates from 1 atm, large differences between PMV and PMVaps are observed. PMV-PS model is a good starting point for further investigations into the influence of atmospheric pressure on thermal comfort perception and assessment, under real conditions, or using hypobaric chambers. Moreover, due to the subsisting doubts resulting from the analysis of published studies, it is crucial to perform further experimental work with high statistical significance i) to test the validity of the adopted correlations for the relationship between metabolic rate and atmospheric pressure and ii) to investigate in deep thermal comfort sensation of individuals used to live at altitude and of individuals with short-term exposure to an environment different from what they are used to live. Based upon the main findings of the present work, not considering the atmospheric pressure effect in PMV index may lead to significant errors. (C) 2021 Elsevier B.V. All rights reserved.
- 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.
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