Transition-to-turbulence in partially filled pipes

Description

The safe disposal of nuclear waste in post operation and decommissioning activities represents one of the greatest challenges facing the nuclear industry, and improving waste treatment strategies is critical. The waste to be removed usually takes on the form of solids suspended in solution (often called “slurries” which can potentially be non-Newtonian). The advantage of suspending solid waste in solution is that they can be pumped, transported and stored with reduced manual handling. During transportation, a balance must be struck between clogging of the pipe network due to particulate deposition and unnecessary diluteness which leads to the generation of more waste product that requires storage. Due to the toxic nature of this material, there is an emphasis on passive flow transport (gravity driven flows), this leads to the prevalence of the partially filled pipe regime. In current operations, particle deposition is unavoidable and thus, to unclog the pipes, the particulates need to be resuspended and “flushed out”. Resuspension necessitates high flow rates leading to generation of additional waste product. We hypothesize that (1) there exists an optimal set of flow parameters that will minimize particulate deposition and thus minimize the number of “flush outs” required and (2) there is a minimum flow rate required to initiate resuspension thus minimizing generation of additional waste in the “flush out” operation of the transport process. To better understand particulate deposition and resuspension in partially filled pipes, we need to better understand the flow physics of partially filled pipe flow.

This project leverages physical infrastructure and domain expertise unique to Liverpool where detailed characterisation of the flow in both laminar and turbulent partially filled pipes was previously conducted [1,2]. It also enhances existing links between the University of Liverpool (UoL) and the United Kingdom National Nuclear Laboratory (UKNNL) [1,3,4].  Building upon this foundation, new experiments will be conducted to determine the minimum Reynolds number, , (or Froude number,) that signals the onset of transition for given fill heights and the minimum (or) where turbulence becomes self-sustaining. Identifying the critical points at which transition to turbulence starts (1) and ends (2) is key as it marks the onset of significant fluctuations (1) and sustained mean secondary flows (2) and constitutes the first step in outlining our optimal parameter set for minimizing particle deposition. Velocity field measurements will be conducted in the very-large-scale pipe flow facility at UoL using advanced laser diagnostic techniques. These data will reveal the phenomenological pathway to turbulence in partially filled pipe flow. In parallel, the successful candidate will utilise the slurry transport rig (STR) at UKNNL Workington to test our hypotheses of an optimal parameter set on a non-active test material analogous to waste product encountered in the nuclear industry. Together, this new knowledge will inform modelling and prediction efforts. 

Background

Transition to turbulence in full pipe flow first observed by Osborne Reynolds in the late 19th century [5] remains an active area of research [6,7]. Pipes running partially full, however, have received far less attention, yet this type of flow also has many important engineering applications within the nuclear, petro(chemical) and wastewater industries. In the context of nuclear waste transported in partially filled pipe networks (where the waste product is often solids in suspension), two key questions arise: (1) how to avoid solid particulate deposition (which leads to clogging) and, perhaps more importantly, (2) how to initiate re-suspension of the particles to reverse clogging and avoid overpressure.

Particle resuspension is typically associated with high values of boundary shear stress generally resulting in undesirably high flow rates. Thus, to facilitate the optimisation of this waste transport process we require better understanding of the boundary shear stress and the flow field velocity distribution in partially filled pipes. The velocity distribution for laminar partially filled pipe flow was determined analytically [8] and has since been confirmed both experimentally [1] and using numerical simulations [9]. Turbulent flow in partially filled pipes has been reported in several experimental [1,2,4,10-12] and numerical studies [13-15]. Still, compared to full pipe flow, studies conducted on partially filled pipes are very limited and amongst those studies there are yet to be any studies of transition to turbulence.   As such, this project will elucidate fundamental flow physics whilst at the same time generate new knowledge with clear industrial relevance and impact. 

Aims

1.      Experimentally establish the threshold for transition to turbulence in partially filled pipe flow for Re, Fr, and fill height and determine the nature of transition i.e. sub- or super-critical (UoL)

2.   Establish a minimum viable and combination to (1) minimize particle deposition and (2) initiate resuspension of model particulate suspensions (UoL/UKNNL). 

3.   Test and validate this minimum viable Re and Fr number combination for model particulate suspensions in the STR (UKNNL).

Key Accountabilities

Working within an interdisciplinary team, the successful candidate will be responsible for

·      Establishing the working limits of the flow rigs at both UoL and UKNNL for sustaining laminar and turbulent partially filled pipe flow

·      Conducting relevant experiments (using laser-diagnostic and flow visualisation techniques) to elucidate the flow physics and determine the start and end of transition to turbulence in partially filled pipe flow

·      Analysing the test data and contributing to the development of empirical models

·      Disseminating findings through preparation of high-quality journal articles and participation at leading international conferences

Eligibility

Applicants should have, or expect to achieve, at least a 2.1 honours degree or a master’s (or equivalent) in a relevant science or engineering related discipline.

Equality, diversity and inclusion

Equality, diversity and inclusion is fundamental to the success of The University of Manchester, and is at the heart of all of our activities. We know that diversity strengthens our research community, leading to enhanced research creativity, productivity and quality, and societal and economic impact.

We actively encourage applicants from diverse career paths and backgrounds and from all sections of the community.

We also support applications from those returning from a career break. We consider offering flexible study arrangements (including part-time: 50%, 60% or 80%, depending on the project/funder).

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