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WIRC/WISE Colloquium: PhD student seminar by David Birt and Bert Swart

In this seminar, PhD students from across the University of Bath present their research projects on a variety of water-related topics.

  • 12 Dec 2019, 1.15pm to 12 Dec 2019, 2.05pm GMT
  • 6 East, 2.2, University of Bath
  • This event is free

In this Water Innovation & Research Centre (WIRC) seminar, we will hear from two students: David Birt and Bert Swart, whose expertise ranges from wave energy to reservoir resiliency to novel water treatment.

Please register via Eventbrite to hear more about these fascinating projects.

Application of models in investigating stratification

David Birt

David Birt is a WISE CDT student within the Department of Architecture and Civil Engineering, supervised by Dr Jun Zang and Dr Lee Bryant. David's PhD project focuses on drinking water reservoir resiliency in a changing climate particularly looking at artificial destratification.

Abstract: Thermal stratification suppresses mixing preventing recharge of oxygen to the hypolimnion, which can negatively impact water quality. Evidence suggests that climate change will increase the intensity and length of thermal stratification, exacerbating water quality issues such as low dissolved oxygen concentrations. A case study example is presented for Blagdon Lake, during the June 2017 heatwave, when thermal stratification developed. To investigate this period of stratification, and possible future events, AME3D (a 3D hydrodynamic model) was used. Observations from two temperature chains were used for calibration. A 25 m grid bathymetry was used with forcing data gathered from proximal weather stations. Inflows from feeder streams were derived from abstraction and reservoir volume data. Despite indirect forcing, results represented Blagdon’s physics. The calibrated model had a RMSE of 0.51°C and successfully captured aspects of stratification and the mass balance, although over-mixing occurs. Moreover, a better understanding of spatial and temporal characteristics of thermal stratification can be obtained. Subsequently, the model could be a useful tool in reservoir planning and management. With sufficient future forcing data it can help predict physics in future climates.

In situ characterisation of size distribution and rise velocity of microbubbles under controlled conditions by using high-speed photography

Bert Swart

Bert Swart is a WISE CDT student within the Department of Chemical Engineering, supervised by Dr Jannis Wenk and Dr John Chew. His project investigates the effectiveness of a new method of microbubble production for Dissolved Air Flotation (DAF) in water treatment.

Abstract: Microbubbles have been gaining importance for a variety of applications in industry and research. Characterisation of microbubble populations is critical to understand their behaviour in suspension including multiphase interactions, but remains challenging, particularly at high bubble densities, typically used in practical applications. We have developed an automated method based on image analysis to measure bubble size and size distributions for microbubbles, including bubble rise velocity at bubble densities within a cross section of up to 6.8 bubbles / mm2. The method was tested using air bubbles in water at diameters between 50 and 150 µm produced by a regenerative turbine pump with a water flowrate of 16 l/min and an air flowrate of 1.5 l/min. Series of bubble suspension images were collected from a side-stream viewing slit and processed through image analysis code that converted, filtered and statistically evaluated the initial images to yield both position and diameter of a subset of focussed bubbles within each image. A maximum error of ± 10 μm for mean bubble diameter was estimated through sensitivity analysis of image analysis factors. Manual image analysis was done to validate the results of the MATLAB image analysis and showed an error in mean diameter determination no larger than 2.3 µm.To show the ability of the method to detect small shifts in bubble size distribution, experiments were carried out over a range of operating conditions including pump pressure variation, water temperature variation and surfactant addition. Decreases in pump outlet from 0.4 MPa to 0.2 MPa pressure led to increasing mean bubble sizes from 86 µm to 129 µm. Temperature increase from 10 ºC to 60 ºC at an operating pressure of 0.3 MPa resulted in mean diameters increasing from 88 µm to 102 µm. Ionic surfactants reduced bubble size by 56%, in contrast to non-ionic surfactants, which had no significant effect on bubble size. Rise velocity analysis showed bubbles obeying Stokes’ law for solid spheres moving through viscous fluid under creeping flow conditions irrespective of surfactant addition. The developed system enables fast, simple and accurate size determination for microbubbles, including continuous sampling and observation.

Location

University of Bath, Claverton Down Campus


6 East, 2.2 University of Bath Claverton Down Bath BA2 7AY United Kingdom

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