Eismann, Ralph

Profilbild
E-Mail-Adresse
Geburtsdatum
Projekt
Organisationseinheiten
Berufsbeschreibung
Nachname
Eismann
Vorname
Ralph
Name
Eismann, Ralph

Filter

2018 - 201912020 - 20211
Filter zurücksetzen

Einstellungen

Dateien dazu vorhanden?: Ja × Typ: 01A - Beitrag in wissenschaftlicher Zeitschrift ×

Suchergebnisse

Gerade angezeigt 1 - 2 von 2
  • Vorschaubild
    Publikation
    A thermal-hydraulic model for the stagnation of solar thermal systems with flat-plate collector arrays
    (MDPI, 30.01.2021) Eismann, Ralph; Hummel, Sebastian; Giovanetti, Federico [in: Energies]
    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.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    An Explicit and Continuous Friction Factor Correlation for Helical Tubes with Arbitrary Roughness
    (Global Digital Central, 11.04.2018) Eismann, Ralph; Adams, Robert [in: Frontiers in Heat and Mass Transfer]
    Convergence of numerical schemes for pipe network analysis requires continuous modelling of pressure losses in the transition region between laminar and turbulent regions. Several existing correlations for the friction factor of straight pipes and helical tubes are presented. Based on these correlations a new explicit correlation for helical tubes with arbitrary surface roughness is derived. The friction factor is expressed as a continuous function of the Reynolds number covering laminar, transitional, and turbulent flow regions. Potential sources of error are also discussed, including the effects of tube deformation caused by the bending process.
    01A - Beitrag in wissenschaftlicher Zeitschrift