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Experimental Characterization and Numerical Modelling of Solar Cooker Prototypes with Thermal Energy Storage

Aquilanti, Alessia (2023)
Experimental Characterization and Numerical Modelling of Solar Cooker Prototypes with Thermal Energy Storage.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00024334
Ph.D. Thesis, Primary publication, Publisher's Version

Abstract

Of all the different renewable energy sources, solar thermal energy, is one of the most promising alternatives to the consumption of highly polluting fossil fuels. Among its applications, solar cooking emerges as one of the most attractive ways to harness this type of energy. In the study presented, different types of solar cookers with and without a storage system were designed and tested: a high-efficiency solar box cooker (SBC), a concentrator cooker (CC), two prototype panel cookers (PSCs), and a medium-efficiency solar box cooker (SBC) equipped with thermal storage based on phase change materials (PCMs). Regarding the latter, an extensive experimental campaign was carried out to characterize the selected PCMs both thermophysically and in terms of their thermal stability. From the analysis, sugar alcohols (SAs) were found to be suitable for use as PCMs in solar furnaces for applications in the low to medium temperature ranges (80-250 °C). The high-efficiency SBC had a concentration ratio of 11.57. It consisted of a cooking chamber, a glazed top cover, and a double row of reflective mirrors. The prototype allowed both azimuthal and zenithal manual alignment. Tests without load were conducted to identify the maximum temperature that the cooker could reach, and load tests were conducted using water and peanut oil in various configurations: with one or two aluminum pots, painted black or unpainted. The cooker was able to bring 1 kg of water to the boiling point in about 11 minutes and get the peanut oil to a temperature of 220 °C in about 41 minutes. The CC, called Heliac, had a concentration ratio of 40.97. It consisted mainly of a wooden lattice structure to which two wooden structures of different sizes were attached: one containing the larger Fresnel lens, and a smaller one containing the reflective surface. Tests with load were carried out using water and silicone oil as test fluids. The cooker was able to make 3 kg of water reach 90 °C in about half an hour and bring 3 kg of silicone oil to 170 °C in less than 1 hour. The two PSCs made are the Newton and the Kimono panel solar cookers, respectively. The former consisted mainly of a prism-shaped glazed cooking chamber and two systems of reflective surfaces, a larger primary one and a smaller secondary one. By changing the inclination of the two reflective surfaces, the device, was able to vary its geometry. No-load tests and tests with load were carried out, using water and glycerin as test fluids. During the experimental campaign, two identical prototypes, one shielded from wind and the other not, were tested to assess how much this environmental parameter affects the final performance. Both devices were able to reach a stagnation temperature of 137 °C. The wind-shielded device was able to bring 2 kg of water to a temperature of 90 °C in about 2 hours and 2 kg of glycerin to a temperature of 110 °C in about 3 hours. These times were slightly longer in the case of the device tested without wind shielding. The Kimono panel solar cooker consisted of acrylic panels connected together and covered with a reflective film. The prototype was tested in parallel with three other panel devices during three different times of the year by conducting no-load and water-load tests. The results showed that the Kimono panel solar cooker is among the best performing prototypes in all the three test periods, with a water heating time to boiling point of 1.74 hours. The medium efficiency SBC had a concentration ratio of 4.08. It was mainly composed of a galvanized steel cooking chamber, a glass cover, and a system of 8 mirrors of two different shapes. Tests without load and tests with load were carried out using water and silicone oil as test fluids. In this case, the contribution to the overall system of the inclusion within the cooking chamber of a storage system based on phase change materials would make was also evaluated. The PCMs selected were erythritol and xylitol. The results showed that the cooling times of 1.5 kg of silicone oil in the chosen temperature range 125-100 °C increased by 350% when tested with the erythritol-based TES compared to when tested alone. In contrast, the cooling time of the same mass of silicone oil in the fluid temperature range 110-80 °C increased by 346% when tested with the xylitol-based TES equipped with a hand stirrer to stimulate nucleation of the material compared with when tested alone. Experimental data from the latter device were used to validate the mathematical model developed specifically to simulate its thermodynamic performance. The model results show a very good fit with reality, managing to simulate the temperature of water and silicone oil in the heating phase of the selected tests with an average deviation from experimental data of 3% and 8%, respectively.

Item Type: Ph.D. Thesis
Erschienen: 2023
Creators: Aquilanti, Alessia
Type of entry: Primary publication
Title: Experimental Characterization and Numerical Modelling of Solar Cooker Prototypes with Thermal Energy Storage
Language: English
Referees: Koenders, Prof. Dr. Eduardus ; Di Nicola, Prof. Dr. Giovanni
Date: 29 September 2023
Place of Publication: Darmstadt
Collation: xxxv, 218 Seiten
Refereed: 12 June 2023
DOI: 10.26083/tuprints-00024334
URL / URN: https://tuprints.ulb.tu-darmstadt.de/24334
Abstract:

Of all the different renewable energy sources, solar thermal energy, is one of the most promising alternatives to the consumption of highly polluting fossil fuels. Among its applications, solar cooking emerges as one of the most attractive ways to harness this type of energy. In the study presented, different types of solar cookers with and without a storage system were designed and tested: a high-efficiency solar box cooker (SBC), a concentrator cooker (CC), two prototype panel cookers (PSCs), and a medium-efficiency solar box cooker (SBC) equipped with thermal storage based on phase change materials (PCMs). Regarding the latter, an extensive experimental campaign was carried out to characterize the selected PCMs both thermophysically and in terms of their thermal stability. From the analysis, sugar alcohols (SAs) were found to be suitable for use as PCMs in solar furnaces for applications in the low to medium temperature ranges (80-250 °C). The high-efficiency SBC had a concentration ratio of 11.57. It consisted of a cooking chamber, a glazed top cover, and a double row of reflective mirrors. The prototype allowed both azimuthal and zenithal manual alignment. Tests without load were conducted to identify the maximum temperature that the cooker could reach, and load tests were conducted using water and peanut oil in various configurations: with one or two aluminum pots, painted black or unpainted. The cooker was able to bring 1 kg of water to the boiling point in about 11 minutes and get the peanut oil to a temperature of 220 °C in about 41 minutes. The CC, called Heliac, had a concentration ratio of 40.97. It consisted mainly of a wooden lattice structure to which two wooden structures of different sizes were attached: one containing the larger Fresnel lens, and a smaller one containing the reflective surface. Tests with load were carried out using water and silicone oil as test fluids. The cooker was able to make 3 kg of water reach 90 °C in about half an hour and bring 3 kg of silicone oil to 170 °C in less than 1 hour. The two PSCs made are the Newton and the Kimono panel solar cookers, respectively. The former consisted mainly of a prism-shaped glazed cooking chamber and two systems of reflective surfaces, a larger primary one and a smaller secondary one. By changing the inclination of the two reflective surfaces, the device, was able to vary its geometry. No-load tests and tests with load were carried out, using water and glycerin as test fluids. During the experimental campaign, two identical prototypes, one shielded from wind and the other not, were tested to assess how much this environmental parameter affects the final performance. Both devices were able to reach a stagnation temperature of 137 °C. The wind-shielded device was able to bring 2 kg of water to a temperature of 90 °C in about 2 hours and 2 kg of glycerin to a temperature of 110 °C in about 3 hours. These times were slightly longer in the case of the device tested without wind shielding. The Kimono panel solar cooker consisted of acrylic panels connected together and covered with a reflective film. The prototype was tested in parallel with three other panel devices during three different times of the year by conducting no-load and water-load tests. The results showed that the Kimono panel solar cooker is among the best performing prototypes in all the three test periods, with a water heating time to boiling point of 1.74 hours. The medium efficiency SBC had a concentration ratio of 4.08. It was mainly composed of a galvanized steel cooking chamber, a glass cover, and a system of 8 mirrors of two different shapes. Tests without load and tests with load were carried out using water and silicone oil as test fluids. In this case, the contribution to the overall system of the inclusion within the cooking chamber of a storage system based on phase change materials would make was also evaluated. The PCMs selected were erythritol and xylitol. The results showed that the cooling times of 1.5 kg of silicone oil in the chosen temperature range 125-100 °C increased by 350% when tested with the erythritol-based TES compared to when tested alone. In contrast, the cooling time of the same mass of silicone oil in the fluid temperature range 110-80 °C increased by 346% when tested with the xylitol-based TES equipped with a hand stirrer to stimulate nucleation of the material compared with when tested alone. Experimental data from the latter device were used to validate the mathematical model developed specifically to simulate its thermodynamic performance. The model results show a very good fit with reality, managing to simulate the temperature of water and silicone oil in the heating phase of the selected tests with an average deviation from experimental data of 3% and 8%, respectively.

Alternative Abstract:
Alternative abstract Language

Die thermische Solarenergie ist unter den erneuerbaren Energiequellen eine der vielversprechendsten Alternativen zum Verbrauch stark umweltbelastender fossiler Brennstoffe. Unter den Anwendungen erweist sich das solare Kochen als eine der attraktivsten Möglichkeiten, diese Art von Energie zu nutzen. In der vorliegenden Studie wurden verschiedene Arten von Solarkochern mit und ohne Speichersystem entworfen und getestet: ein hocheffizienter Solarkasten-Kocher (SBC), ein Konzentratorkocher (CC), zwei Prototyp-Panelkocher (PSC) und ein Solarkasten-Kocher (SBC) mit mittlerem Wirkungsgrad, der mit einem thermischen Speicher auf der Basis von Phasenwechselmaterialien (PCM) ausgestattet ist. Für letzteren wurde eine umfangreiche Versuchskampagne durchgeführt, um die ausgewählten PCMs thermophysikalisch und hinsichtlich ihrer thermischen Stabilität zu charakterisieren. Die Analyse ergab, dass die Zuckeralkohole (SA) für den Einsatz als PCM in Solaröfen für Anwendungen im niedrigen bis mittleren Temperaturbereich (80-250 °C) geeignet sind. Der hocheffiziente SBC hat ein Konzentrationsverhältnis von 11.57. Er besteht aus einer Kochkammer, einer verglasten oberen Abdeckung und einer doppelten Reihe von reflektierenden Spiegeln. Der Prototyp ermöglicht sowohl eine azimutale als auch eine zenithale manuelle Ausrichtung. Es wurden Tests ohne Belastung durchgeführt, um die Höchsttemperatur zu ermitteln, die der Kocher erreichen kann, und es wurden Belastungstests mit Wasser und Erdnussöl in verschiedenen Konfigurationen durchgeführt: mit einem oder zwei Aluminiumtöpfen, schwarz lackiert oder unlackiert. Der Kocher war in der Lage, 1 kg Wasser in etwa 11 Minuten zum Sieden zu bringen und das Erdnussöl in etwa 41 Minuten auf eine Temperatur von 220 °C zu bringen. Der CC, genannt Heliac, hat ein Konzentrationsverhältnis von 40.97. Er besteht im Wesentlichen aus einer Holzgitterstruktur, an der zwei unterschiedlich große Holzkonstruktionen befestigt sind: eine mit der größeren Fresnellinse und eine kleinere mit der reflektierenden Oberfläche. Die Belastungstests wurden mit Wasser und Silikonöl als Testflüssigkeit durchgeführt. Der Kocher war in der Lage, 3 kg Wasser in etwa einer halben Stunde auf 90 °C zu erhitzen und 3 kg Silikonöl in weniger als einer Stunde auf 170 °C zu bringen. Bei den beiden hergestellten PSC handelt es sich um den Newton bzw. den Kimono. Ersterer besteht im Wesentlichen aus einer prismenförmigen, verglasten Kochkammer und zwei Systemen von Reflexionsflächen, einer größeren primären und einer kleineren sekundären. Durch Änderung der Neigung der beiden reflektierenden Flächen kann die Geometrie des Geräts variiert werden. Es wurden Tests ohne Last und mit Last durchgeführt, wobei Wasser und Glyzerin als Testflüssigkeiten verwendet wurden. Während der Versuchskampagne wurden zwei identische Prototypen getestet, von denen der eine windgeschützt und der andere nicht windgeschützt war, um festzustellen, wie stark dieser Umweltparameter die endgültige Leistung beeinflusst. Beide Geräte waren in der Lage, eine Stagnationstemperatur von 137 °C zu erreichen. Das windgeschützte Gerät war in der Lage, 2 kg Wasser in etwa 2 Stunden auf eine Temperatur von 90 °C und 2 kg Glyzerin in etwa 3 Stunden auf eine Temperatur von 110 °C zu bringen. Diese Zeiten waren bei dem ohne Windschutz getesteten Gerät etwas länger. Der Kimono besteht aus Acrylplatten, die miteinander verbunden und mit einer reflektierenden Folie überzogen sind. Der Prototyp wurde parallel zu drei anderen Paneelgeräten zu drei verschiedenen Jahreszeiten in Leerlauf- und Wasserlasttests getestet. Die Ergebnisse zeigen, dass der Kimono in allen drei Testperioden zu den leistungsfähigsten Prototypen gehört, mit einer Wassererwärmungszeit bis zum Siedepunkt von 1.74 Stunden. Der SBC mit mittlerem Wirkungsgrad hat ein Konzentrationsverhältnis von 4.08. Er besteht hauptsächlich aus einer Kochkammer aus verzinktem Stahl, einer Glasabdeckung und einem System aus 8 Spiegeln in zwei verschiedenen Formen. Es wurden Tests ohne Last und Tests mit Last mit Wasser und Silikonöl als Testflüssigkeiten durchgeführt. In diesem Fall wurde auch der Beitrag bewertet, den der Einbau eines auf Phasenwechselmaterialien basierenden Speichersystems in die Kochkammer zum Gesamtsystem leisten würde. Als PCMs wurden Erythritol und Xylitol ausgewählt. Die Ergebnisse zeigten, dass sich die Abkühlzeiten von 1.5 kg Silikonöl in dem gewählten Temperaturbereich von 125 bis 100 °C um 350% erhöhten, wenn sie mit dem TES auf Erythritol-Basis getestet wurden, als wenn sie allein getestet wurden. Im Gegensatz dazu verlängerte sich die Abkühlzeit der gleichen Masse Silikonöl im flüssigen Temperaturbereich von 110-80 °C um 346%, wenn sie mit dem TES auf Xylitol-Basis getestet wurde, das mit einem Handrührer ausgestattet war, um die Keimbildung des Materials zu stimulieren, als wenn sie allein getestet wurde. Die experimentellen Daten des letztgenannten Geräts wurden zur Validierung des mathematischen Modells verwendet, das speziell zur Simulation der thermodynamischen Leistung des Geräts entwickelt wurde. Die Ergebnisse des Modells stimmen sehr gut mit der Realität überein, da es die Temperatur von Wasser und Silikonöl in der Erhitzungsphase der ausgewählten Tests mit einer durchschnittlichen Abweichung von den experimentellen Daten von 3% bzw. 8% simuliert.

German
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-243343
Classification DDC: 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering
600 Technology, medicine, applied sciences > 624 Civil engineering and environmental protection engineering
Divisions: 13 Department of Civil and Environmental Engineering Sciences
13 Department of Civil and Environmental Engineering Sciences > Institute of Construction and Building Materials
Date Deposited: 29 Sep 2023 12:05
Last Modified: 02 Oct 2023 05:07
PPN:
Referees: Koenders, Prof. Dr. Eduardus ; Di Nicola, Prof. Dr. Giovanni
Refereed / Verteidigung / mdl. Prüfung: 12 June 2023
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