@phdthesis{Witter2002,
  author    = {Witter, Ralph},
  title     = {Auswirkungen einer k{\"u}nstlichen Destratifikation auf die thermischen und hydrodynamischen Verh{\"a}ltnisse in der Bleilochtalsperre},
  doi       = {10.25643/bauhaus-universitaet.59},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20040310-629},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  year      = {2002},
  abstract  = {Es werden die Auswirkungen der mit Hilfe eines Blasenschleiers durchgef{\"u}hrten partiellen Destratifikation zur Begrenzung der Algenentwicklung durch Lichtlimitierung auf die thermischen und hydrodynamischen Bedingungen in der Bleilochtalsperre (Th{\"u}ringen) vorgestellt. Ausgangspunkt bilden die theoretischen Betrachtungen zur Dynamik eines Blasenschleiers, aus denen ein Blasenschleiermodell in einer geschichteten Umgebung hervorgeht. Weiterhin werden die dimensionslosen Kennzahlen der Quell- und der Umgebungsschichtungsst{\"a}rke, sowie der entdimensionalisierten Einblastiefe eingef{\"u}hrt, mit denen die Dynamik der voll ausgebildeten Schleierstr{\"o}mung beschreibbar ist. Durch Kopplung des Blasenschleiermodells mit einem Umgebungsschichtungsmodell wird die mechanische Effizienz eines Blasenschleiers auf die Destratifikation einer linearen Umgebungsschichtung f{\"u}r einen großen Bereich der Kennzahlen ermittelt und die Leistungsf{\"a}higkeit des in der Bleilochtalsperre installierten Schleiers theoretisch nachgewiesen. Die Auswirkungen des Betriebs des Blasenschleiers in der Bleilochtalsperre selbst werden anhand von gemessenen Temperaturprofilen diskutiert und {\"u}ber Stabilit{\"a}tsberechnungen quantifiziert. Dabei kam es in den Sommermonaten in der Talsperre zur Ausbildung eines 3-Schichtensystems, {\"u}ber dessen Entstehung im Weiteren eine Ursachenanalyse durchgef{\"u}hrt wird. Es werden Untersuchungen zum Einschichtungsverhalten des Zulaufs, zum zeitlichen Verlauf der Temperaturentwicklung in der Talsperre, Isothermenabsenkungsberechnungen f{\"u}r den Bereich unterhalb des Schleiers, W{\"a}rmehaushaltsberechnungen und in der Talsperre durchgef{\"u}hrte Driftk{\"o}rpermessungen vorgestellt, die das Auftreten des 3-Schichtensystems erkl{\"a}ren. Angaben {\"u}ber die wesentlichen Auswirkungen der k{\"u}nstlichen Destratifikation auf die limnologischen Verh{\"a}ltnisse in der Talsperre runden die Ergebnisse der hydrodynamischen Untersuchungen schließlich ab.},
  subject      = {Bleilochtalsperre},
  language  = {de}
}
@article{AlsaadVoelker,
  author    = {Alsaad, Hayder and V{\"o}lker, Conrad},
  title     = {Could the ductless personalized ventilation be an alternative to the regular ducted personalized ventilation?},
  series = {Indoor Air},
  volume    = {2020},
  journal   = {Indoor Air},
  publisher = {John Wiley \& Sons Ltd},
  doi       = {10.1111/ina.12720},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200805-42072},
  pages     = {13},
  abstract  = {This study investigates the performance of two systems: personalized ventilation (PV) and ductless personalized ventilation (DPV). Even though the literature indicates a compelling performance of PV, it is not often used in practice due to its impracticality. Therefore, the present study assesses the possibility of replacing the inflexible PV with DPV in office rooms equipped with displacement ventilation (DV) in the summer season. Numerical simulations were utilized to evaluate the inhaled concentration of pollutants when PV and DPV are used. The systems were compared in a simulated office with two occupants: a susceptible occupant and a source occupant. Three types of pollution were simulated: exhaled infectious air, dermally emitted contamination, and room contamination from a passive source. Results indicated that PV improved the inhaled air quality regardless of the location of the pollution source; a higher PV supply flow rate positively impacted the inhaled air quality. Contrarily, the performance of DPV was highly sensitive to the source location and the personalized flow rate. A higher DPV flow rate tends to decrease the inhaled air quality due to increased mixing of pollutants in the room. Moreover, both systems achieved better results when the personalized system of the source occupant was switched off.},
  subject      = {Str{\"o}mungsmechanik},
  language  = {en}
}
@article{AlsaadVoelker,
  author    = {Alsaad, Hayder and V{\"o}lker, Conrad},
  title     = {Qualitative evaluation of the flow supplied by personalized ventilation using schlieren imaging and thermography},
  series = {Building and Environment},
  volume    = {2020},
  journal   = {Building and Environment},
  number    = {Volume 167, article 106450},
  publisher = {Elsevier},
  address   = {New York},
  doi       = {10.25643/bauhaus-universitaet.4511},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211008-45117},
  pages     = {11},
  abstract  = {Personalized ventilation (PV) is a mean of delivering conditioned outdoor air into the breathing zone of the occupants. This study aims to qualitatively investigate the personalized flows using two methods of visualization: (1) schlieren imaging using a large schlieren mirror and (2) thermography using an infrared camera. While the schlieren imaging was used to render the velocity and mass transport of the supplied flow, thermography was implemented to visualize the air temperature distribution induced by the PV. Both studies were conducted using a thermal manikin to simulate an occupant facing a PV outlet. As a reference, the flow supplied by an axial fan and a cased axial fan was visualized with the schlieren system as well and compared to the flow supplied by PV. Schlieren visualization results indicate that the steady, low-turbulence flow supplied by PV was able to penetrate the thermal convective boundary layer encasing the manikin's body, providing clean air for inhalation. Contrarily, the axial fan diffused the supplied air over a large target area with high turbulence intensity; it only disturbed the convective boundary layer rather than destroying it. The cased fan supplied a flow with a reduced target area which allowed supplying more air into the breathing zone compared to the fan. The results of thermography visualization showed that the supplied cool air from PV penetrated the corona-shaped thermal boundary layer. Furthermore, the supplied air cooled the surface temperature of the face, which indicates the large impact of PV on local thermal sensation and comfort.},
  subject      = {Bildverarbeitung},
  language  = {en}
}
@inproceedings{AlsaadVoelker,
  author    = {Alsaad, Hayder and V{\"o}lker, Conrad},
  title     = {Measuring and visualizing the flow supplied by personalized ventilation},
  series = {Proceedings Book Roomvent 2020},
  booktitle = {Proceedings Book Roomvent 2020},
  address   = {Turin, Italy},
  doi       = {10.25643/bauhaus-universitaet.4657},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46573},
  abstract  = {This study investigates the flow supplied by personalized ventilation (PV) by means of anemometer measurements and schlieren visualization. The study was conducted using a thermal manikin to simulate a seated occupant facing a PV outlet. Air velocity was measured at multiple points in the flow field; the collected velocity values were used to calculate the turbulence intensity. Results indicated that PV was supplying air with low turbulence intensity that was able to penetrate the convective boundary layer of the manikin to supply clean air for inhalation. The convective boundary layer, however, obstructed the supplied flow and reduced its velocity by a total of 0.26 m/s. The PV flow preserved its value until about 10 cm from the face where velocity started to drop. Further investigations were conducted to test a PV diffuser with a relatively large outlet diameter (18 cm). This diffuser was developed using 3d-modelling and 3d-printing. The diffuser successfully distributed the flow over the larger outlet area. However, the supplied velocity and turbulence fields were not uniform across the section.},
  subject      = {Bel{\"u}ftung},
  language  = {en}
}