Thermohydraulische Dimensionierung von Solaranlagen

Eismann, Ralph

doi:10.1007/978-3-658-07125-7

Cited by 3 publications

(9 citation statements)

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“…Due to the imbalance caused by the opening pressure of the check valves, the steam generally flows downwards driving the residual liquid towards the lower regions. As a result, the total steam range is lower compared to situations where the check valves are open, which corresponds to the results of dedicated experiments on a solar system with the same hydraulic design [3]. This is the reason why the steam ranges for collectors with thermochromic absorbers and operational check valves, datasets 07−24 to 07−27, are generally overestimated by the model, as displayed in Figure 10 (red circles).…”

Section: Thermochromic Absorbers-active Check Valvessupporting

confidence: 56%

“…The model is implemented into the open-source simulation tool THD, dedicated to the thermal-hydraulic dimensioning of solar systems up to about 100 m 2 collector area [17,36]. The actual size is limited mainly by the validity of the assumption that pressure losses during stagnation are negligible.…”

Section: Discussionmentioning

confidence: 99%

“…The main objective of these studies was to understand and characterize the stagnation process qualitatively and to derive practical rules for the design of collectors and solar thermal systems. Eismann and von Felten [3] conducted experiments on a real system with 52 m 2 flat-plate collectors. Stagnation was triggered by manually switching off the pump.…”

Section: Introductionmentioning

confidence: 99%

“…This allows displacement of liquid from the collector field in both the supply and return lines. Based on the measurement data from experiments on a real system with two 22 m 2 flat-plate collectors, Hausner and Fink [4] described stagnation as a sequence of five successive phases as (1) liquid expansion, (2) displacement of liquid by steam (3) emptying by boiling (phase with saturated steam), (4) emptying by boiling (phase with saturated and superheated steam) and ( 5) refilling of the collectors. From experimental data and qualitative considerations, they classified the hydraulic designs of collectors and their connections by external pipes according to their emptying behavior.…”

Section: Introductionmentioning

confidence: 99%

“…This residual quantity was calculated beforehand by a drift-flux model. This model was incorporated in the first version of the open source tool THD [17]. However, experimental validation of the model was not possible at the time.…”

Section: Introductionmentioning

confidence: 99%

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A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

2021

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Stagnation is the transient state of a solar thermal system under high solar irradiation where the useful solar gain is zero. Both flat-plate collectors with selective absorber coatings and vacuum-tube collectors exhibit stagnation temperatures far above the saturation temperature of the glycol-based heat carriers within the range of typical system pressures. Therefore, stagnation is always associated with vaporization and propagation of vapor into the pipes of the solar circuit. It is therefore essential to design the system in such a way that vapor never reaches components that cannot withstand high temperatures. In this article, a thermal-hydraulic model based on the integral form of a two-phase mixture model and a drift-flux correlation is presented. The model is applicable to solar thermal flat-plate collectors with meander-shaped absorber tubes and selective absorber coatings. Experimental data from stagnation experiments on two systems, which are identical except for the optical properties of the absorber coating, allowed comparison with simulations carried out under the same boundary conditions. The absorber of one system features a conventional highly selective coating, while the absorber of the other system features a thermochromic coating, which exhibits a significantly lower stagnation temperature. Comparison of simulation results and experimental data shows good conformity. This model is implemented into an open-source software tool called THD for the thermal-hydraulic dimensioning of solar systems. The latest version of THD, updated by the results of this article, enables planners to achieve cost-optimal design of solar thermal systems and to ensure failsafe operation by predicting the steam range under the initial and boundary conditions of worst-case scenarios.

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Section: Thermochromic Absorbers-active Check Valvessupporting

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

2021

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Thermal and hydraulic investigation of large-scale solar collector field

et al. 2018

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A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

Eismann¹,

Hummel²,

Giovannetti³

2020

Preprint

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Stagnation is the transient state of a solar thermal system under high solar irradiation where the useful solar gain is zero. Both flat-plate collectors with selective absorber coatings and vacuum-tube collectors exhibit stagnation temperatures far above the saturation temperature of the glycol-based heat carriers within the range of typical system pressures. Therefore, stagnation is always associated with vaporization and propagation of vapor into the pipes of the solar circuit. It is therefore essential to design the system in such a way that vapor never reaches components that cannot withstand high temperatures. In this article, a thermal-hydraulic model based on the integral form of a two-phase mixture model and a drift-flux correlation is presented. The model is applicable to solar thermal flat-plate collectors with meander-shaped absorber tubes and selective absorber coatings. Experimental data from stagnation experiments on two systems, which are identical except for the optical properties of the absorber coating, allowed comparison with simulations carried out under the same boundary conditions. The absorber of one system features a conventional highly selective coating, while the absorber of the other system features a thermochromic coating, which exhibits a significantly lower stagnation temperature. Comparison of simulation results and experimental data show good conformity. This model is implemented into an open-source software tool called “THD” for the thermal-hydraulic dimensioning of solar systems. The latest version of THD, updated by the results of this article, enables planners to achieve cost-optimal design of solar thermal systems and to ensure failsafe operation by predicting the steam range under the initial and boundary conditions of worst-case scenarios.

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Thermohydraulische Dimensionierung von Solaranlagen

Cited by 3 publications

References 0 publications

A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

Thermal and hydraulic investigation of large-scale solar collector field

A Thermal-Hydraulic Model for the Stagnation of Solar Thermal Systems with Flat-Plate Collector Arrays

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