@inproceedings{Schiebler2020,
title = {Improved flat plate collector with heat pipesfor overheating prevention in solar thermal systems},
author = {B Schiebler and F Weiland and F Giovannetti and O Kastner and S Jack},
doi = {10.18086/swc.2019.01.08},
year = {2020},
date = {2020-06-10},
booktitle = {Proceedings ISES Solar World Congress 2019 / IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019},
pages = {61-72},
abstract = {Heat pipes in solar thermal collectors can reduce thermal loads in the solar circuit by using the physical effect of dry-out limitation. By avoiding high temperatures and vapor formation, simplified, more reliable and cost effective solar thermal systems can be designed. This paper presents a theoretical study ondifferentheat pipe andmanifoldconfigurationsfor flat plate collectors. The focus is ona highthermal efficiency in the operating rangeand a significant temperature limitation in stagnation mode. Several prototype collectorsaremanufactured and experimentallyinvestigated by means of indoor performance measurements. Thereby,a conversion factor of 73%isreported, whichrepresents an increase of 4percentage pointscompared to a previous prototype. Duringstagnationeventswe localizea maximum fluid temperature about130°C within the manifold, whichdecreases to values below 100°C towardsthe collector connections.Finally, we evaluate the system performance of the prototypewithanexemplary solar DHW-systemby means of dynamic TRNSYS-simulations. The results show that the calculated annual yield ispredictedonly 5% lower than the one of a comparabledirect flow collectorand critical stagnation eventscan be fully avoided.},
keywords = {Flat plate collector, heat pipe, overheating prevention, stagnation temperature},
pubstate = {published},
tppubtype = {inproceedings}
}

@article{Schiebler2018d,
title = {Experimental and theoretical investigations on temperature limitation in solar thermal collectors with heat pipes: Effect of superheating on the maximum temperature},
author = {B Schiebler and S Jack and H Dieckmann and F Giovannetti},
doi = {10.1016/j.solener.2018.06.036},
issn = {0038-092X},
year = {2018},
date = {2018-09-01},
journal = {Solar Energy},
volume = {171},
pages = {271-278},
abstract = {Heat pipes in solar thermal collectors enable to reduce the temperature loads in the solar circuit during stagnation periods by exploiting their dry-out limit. With this approach vapour formation in the solar circuit can be completely avoided, which is essential to reduce costs of solar thermal systems by simplified and more reliable solar circuits. The design of “deactivating” collector heat pipes with a desired maximum temperature requires a comprehensive understanding of the heat transfer processes in the heat pipe, in particular when dry-out takes place. We developed a model, which allows calculating the maximum fluid temperature in the collector for various working fluids. Compared to existing approaches, the effect of superheated vapour in the heat pipe during stagnation is additionally considered. The paper describes the theoretical model in detail and its extensive experimental validation. The results show that the model is able to predict the maximum fluid temperature with an accuracy better than 5 K. Based on parametric studies with different working fluids, we analyse and discuss the temperature limitation and its effect on the collector performance.},
keywords = {cost reduction, evacuated tube collector, Flat plate collector, heat pipe, stagnation temperature, Superheated vapour},
pubstate = {published},
tppubtype = {article}
}

@article{Föste2016b,
title = {Butane Heat Pipes for Stagnation Temperature Reduction of Solar Thermal Collectors},
author = {S Föste and B Schiebler and F Giovannetti and G Rockendorf and S Jack},
doi = {10.1016/j.egypro.2016.06.168},
issn = {1876-6102},
year = {2016},
date = {2016-06-01},
journal = {Energy Procedia},
volume = {91},
pages = {35-41},
abstract = {Heat pipes in solar thermal collectors enable to reduce the temperature loads in the solar circuit during stagnation periods by exploiting their dry out limit. Typically water, pentane or acetone are used as heat transfer media in collector heat pipes. Butane is very suitable to reach a high temperature gradient of the dry out even if the maximum temperature in the fluid circuit should be designed to 120 ̊C or below. The paper presents experimental results with butane heat pipes that operate up to a maximum temperature of 120 ̊C with a high temperature gradient in the dry-out region. This ensures that the collector performance in the operating range (typically up to 100 ̊C) is not affected negatively by the dry-out. Different approaches to increase the thermal conductance of butane heat pipes by enhancing the inner surface of the condenser or of both, the condenser and the evaporator are experimentally assessed and discussed. Measurement results report an increase of the heat pipes’ thermal conductance from 3 W/K (standard geometry) to 23 W/K.},
note = {Proceedings of the 4th International Conference on Solar Heating and Cooling for Buildings and Industry (SHC 2015)},
keywords = {butane, cost reduction, evacuated tube collector, Flat plate collector, heat pipe, stagnation temperature},
pubstate = {published},
tppubtype = {article}
}

@inproceedings{Föste2014bb,
title = {Heat Pipe Collectors for Cost Reduction of Solar Installations},
author = {S Föste and S Jack and B Schiebler and F Giovannetti and G Rockendorf },
editor = {ISES},
doi = {10.18086/eurosun.2014.16.06},
year = {2014},
date = {2014-09-19},
booktitle = {Conference Proceedings EuroSun 2014},
address = {Aix-les-Bains, France},
abstract = {Heat pipes in solar thermal collectors offer the advantage of a simpler hydraulic interconnection of the solar circuit while reducing the system load during stagnation compared to direct flow collectors. Within a research project, we basically analyzed heat pipe solutions for collectors, developed design methods and optimization potential and investigated the integration of heat pipes in flat plate collectors. Novel flat plate collector prototypes with an inherent overheating protection have been built and tested successfully. The maximum fluid temperature was limited to 140 °C, thus compared to a direct flow collector, a temperature decrease of more than 40 K is achieved. This paper presents the developed technology and explains, that the transfer of complexity from the system to the collector by the use of heat pipes can lead to a reduction of system costs of more than 25 %.},
keywords = {Aluminum heat pipe, cost reduction, Flat plate collector, heat pipe, stagnation temperature},
pubstate = {published},
tppubtype = {inproceedings}
}

@article{Jack2014b,
title = {Flat Plate Aluminum Heat Pipe Collector with Inherently Limited Stagnation Temperature},
author = {S Jack and J Parzefall and T Luttmann and P Janßen and F Giovannetti},
doi = {10.1016/j.egypro.2014.02.013},
issn = {1876-6102},
year = {2014},
date = {2014-04-01},
journal = {Energy Procedia},
volume = {48},
pages = {105-113},
note = {Proceedings of the 2nd International Conference on Solar Heating and Cooling for Buildings and Industry (SHC 2013)},
keywords = {Aluminum, copper substitution, Flat plate collector, heat pipe, stagnation},
pubstate = {published},
tppubtype = {article}
}