Topology of advective-diffusive scalar transport in laminar flows

The present study proposes a unified Lagrangian transport template for topological description of advective fluid transport and advective-diffusive scalar transport in laminar flows. The key to this unified description is the expression of scalar transport as purely advective transport by the total scalar flux. This admits generalization of the concept of transport topologies known from laminar mixing studies to scalar transport. The study is restricted to two-dimensional systems and the fluid and scalar transport topologies, as a consequence, prove to be Hamiltonian. The unified Lagrangian transport template is demonstrated and investigated for a heat-transfer problem with nonadiabatic boundaries, representing generic scalar transport with permeable boundaries. The fluid and thermal transport topologies under steady conditions both accommodate islands (constituting isolated flow and thermal regions) that undergo Hamiltonian disintegration into chaotic seas upon introducing time periodicity. The thermal transport topology invariably comprises transport conduits that connect the nonadiabatic boundaries and facilitate wall-wall and wall-fluid heat transfer. For steady conditions these transport conduits are regular; for time-periodic conditions these conduits may, depending on degree of diffusion, be regular or chaotic. Regular conduits connect nonadiabatic walls only with specific flow regions; chaotic heat conduits establish connection (and thus heat exchange) of the nonadiabatic walls with the entire flow domain

A way to visualise heat transfer in 3D unsteady flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Heat transfer in fluid flows traditionally is examined in terms of temperature field and heat-transfer coefficients. However, heat transfer may alternatively be considered as the transport of thermal energy by the total convective-conductive heat flux in a way analogous to the transport of fluid by the flow field. The paths followed by the total heat flux are the thermal counterpart to fluid trajectories and facilitate heat-transfer visualisation in a similar manner as flow visualisation. This has great potential for applications in which insight into the heat fluxes throughout the entire configuration is essential (e.g. cooling systems, heat exchangers). To date this concept has been restricted to 2D steady flows. The present study proposes its generalisation to 3D unsteady flows by representing heat transfer as the 3D unsteady motion of a virtual fluid subject to continuity. The heat transfer visualisation is provided with a physical framework and demonstrated by way of representative examples. Furthermore, a fundamental analogy between fluid motion and heat transfer is addressed that may pave the way to future heat-transfer studies by well-established geometrical methods from laminar-mixing studies

Lagrangian flow structures in 3D AC electro-osmotic microflows

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Flow forcing by AC electro-osmosis (ACEO) is a promising technique for actuation and manipulation of microflows. Utilisation to date mainly concerns pumping and mixing. However, emerging micro-fluidics applications demand further functionalities. The present study explores first ways by which to systematically realise this in three-dimensional (3D) microflows using ACEO. This exploits the fact that continuity “organises” Lagrangian fluid trajectories into coherent structures that geometrically determine the transport properties. 3D Lagrangian flow structures typically comprise families of concentric (closed) streamtubes, acting both as transport barriers and transport conduits, embedded in chaotic regions. Representative case studies demonstrate that ACEO, possibly in combination with other forcing mechanisms, has the potential to tailor these features into multi-functional Lagrangian flow structures for various transport purposes. This may pave the way to “labs-within-a-channel” that offer the wide functionality of labs-on-a-chip yet within one microflow instead of within an integrated system

An efficient approach for eigenmode analysis of transient distributive mixing by the mapping method

The mapping method is an efficient tool to investigate distributive mixing induced by periodic flows. Computed only once, the mapping matrix can be applied a number of times to determine the distribution of concentration inside the flow domain. Spectral analysis of the mapping matrix reveals detailed properties of the distributive mixing as all relevant information is stored in its eigenmodes. Any vector that describes a distribution of concentration can be expanded in the complete system of linearly independent eigenvectors of the mapping matrix. The rapid decay of the contribution of each mode in the eigenmode decomposition allows for a truncation of the eigenmode expansion from the whole spectrum to only the dominant eigenmodes (characterized by a decay rate significantly lower than the duration of the mixing process). This truncated decomposition adequately represents the distribution of concentration inside the flow domain already after a low number of periods, because contributions of all non-dominant eigenmodes rapidly become insignificant. The truncation is determined independently of the initial distribution of concentration and based on the decay rates of the eigenmodes, which are inversely proportional to the corresponding eigenvalues. Only modes with eigenvalues above a certain threshold are retained. The key advantage of the proposed compact eigenmode representation of the mapping method is that it includes practically relevant transient states and not just the asymptotic one. As such the method enables an eigenmode analysis of realistic problems yet with a substantial reduction in computational effort compared to the conventional approach

Observer design for a nonlinear two-dimensional pool boiling system

Abstract onl

Boiling Heat Transfer in Battery Electric vehicles

In this paper the feedback stabilisation of a boiling-based cooling scheme is discussed. Application of such cooling schemes in practical setups is greatly limited by the formation of a thermally insulating vapour film on the to-be-cooled device, called burn-out. In this study a first step is made, to check the viability of such cooling systems, already used in high performance electronics, applied to Electric Vehicles (EVs). It can be used for instance for the cooling of high heat flux transistors and for the thermal homogenisation of battery packs. Thereto, the unstable transition to burn-out is stabilised by controlling the pressure inside the boiling chamber, with which boiling (and thus creation of the thermally insulating vapour film) can be stimulated or suppressed. The feedback law used to do this is based on the dominant modes of the temperature field of the thermally conducting element, i.e. the heater, between the device and the boiling liquid. As not all states used in this feedback law can be measured, an observer or "state-estimator" must be implemented in the control strategy. The observer is a copy of the nonlinear boiling model with an additional term to assure convergence of observer to system state. Simulations are performed to demonstrate controller efficiency on the nonlinear cooling device. This puts forth the boiling-based cooling scheme as viable for application in EVs, enabling increased cooling and thermal-homogenisation capacities compared to conventional thermal management methods. The nextstep should be experiments to proof the principle on battery cells/packs and high heat flux transistors

Magneto-optic contact for application in an amplifying waveguide optical isolator

We present the development of a metal-semiconductor contact for a TM-mode amplijying waveguide optical isolator and show that it is a compromise between good (magneto-)optical performance and good electrical behavior

Anti-colorectal cancer immunity : control ‘the force’!

This dissertation reports on the relation between the immune system, colorectal cancer and immunotherapy. In the first part, expression of HLA class I and expression of CXCL5 in colocectal cancer was studied. Low expression of HLA class I in rectal tumors was associated with poor survival of rectal cancer patients. Low expression of CXCL5 in cancer cells was significantly associated with poor prognosis in a population of colorectal cancer patients and correlated with presence of intra-tumoral CD8+ T-cell infiltration. In the second part of this thesis we focused on induction of tumor specific T-cells. For immunotherapeutic purposes distinction should be made between microsatellite instable (MSI-H) and microsatellite stable (MSS) colorectal tumors, as MSI-H tumors express neo-antigens __foreign__ to the immune system while immunotherapy against MSS tumors depends on tumor associated __self__-antigens. We developed a methodology predicting immunogenic behavior of frameshift-mutated antigens present in MSI-H tumors that was based on accumulation and MHC class I presentation. This method can be used to develop cancer immunotherapy of patients at risk for MSI-H tumors. In the last two chapters we described safety and immunogenicity of a p53 synthetic long peptides vaccine combined with and without Interferon-alpha. Addition of IFN-_ to the p53-SLP_ vaccine significantly improved p53-specific after vaccination. Altogether this dissertation reports on the relation between the immune system, colorectal cancer and immunotherapy. This knowledge can be used to further optimize immunotherapeutic strategies to treat cancer patients.UBL - phd migration 201