Coupled Flow Phenomena Research Articles

Study of flow boiling in a vertical mini-channel with surface structuring: Heat transfer analysis using inverse method

Using a boiling fluid to cool components is a very efficient process, which is often used in micro/mini channel flows. A proposed application is the direct contact liquid cooling of lithium-ion battery cells, where a dielectric fluid is required and where the effects a cell thermal runaway could be mitigated by a convective boiling flow between the cells. For such applications, better designs require both to understand confined convective boiling with coupled flow phenomena and to quantify the local heat transfer accurately. The present paper introduces new experimental results of flow boiling heat transfer of a dielectric fluid, the HFE-7100, in a vertical rectangular 1 mm deep, 30 mm wide and 120 mm long mini-channel. The test section is an aluminum block instrumented with three lines of five K-type thermocouples located all along the flow. The experiment mainly aims at determining the heat transfer coefficient and CHF and at characterizing both the flow regimes and the dry-out phenomenon. Measurements are carried out from start of boiling to dry-out, at different mass fluxes (140, 390 and 648 kg/(m2.s)) and at a pressure of 1.1 bar. These tests were performed on a reference unmodified surface and compared to two biphilic surfaces including coating techniques. The visualization of the flow is achieved through a glass pane with a high-speed camera to identify different flow patterns. The local heat transfer coefficient is calculated by a resolution of a 2D inverse heat conduction method. This approach uses a numerical Finite Difference Method (FDM) for the spatial discretization and a Tikhonov's method for regularization. The inverse 2D method permits to follow the evolution of the heat transfer coefficient along the channel with the visualized flow pattern. The experimental results show a small sensitivity of the mass flux on the heat transfer coefficient and a predominance of nucleate boiling. On the other hand, there is a significant sensitivity of the mass flux on the dry-out occurrence. Finally, the sensitivity of two techniques of biphilic surface coating on boiling and on the dry-out occurrence is quantified and discussed.

Integrated modeling of multi-scale transport in coal and its application for coalbed methane recovery

Exploitation of coalbed methane (CBM) acts as a synergy between increased natural gas demand and reduced greenhouse gas emissions to the atmosphere. However, substantial CBM resources lie undeveloped because of unfavorable economic conditions. Accurate forecast of production based on a thorough understanding of physical mechanisms is the key to increase and sustain CBM recovery. CBM production involves complex multi-scale phenomena ranging from desorption and diffusion in nanoporous matrix at molecular level to Darcy flow of free gas in cleats at macroscopic level. Current computational modeling built on fracture flow and neglecting multi-scale coupled flow phenomena underestimates long-term production performance. In fact, experimental evidence indicated that matrix experienced a much greater increase in gas deliverability than cleats. In this work, apparent matrix permeability was derived to characterize diffusion rate and directly coupled into current modeling to decipher matrix deliverability and multi-scale flow. The proposed modeling workflow was applied to two field cases in San Juan Fairway with long production history of over 20 years, which assembled adequate forecast to field data. Besides, sensitivity analysis suggested that simulations neglecting matrix flow and solely updating fracture flow were prone to elevated prediction errors for long-term production when diffusive mass flux took the predominant role in overall gas transport. The multi-scale CBM model is convenient for elucidating complex gas transport physics in coal. The outcome of this work implies that a proper diffusion enhancement method can improve overall production rate and elongate total productive lifetime of CBM fields.

Diffusion of stratification based chemically reactive Jeffrey liquid featuring mixed convection

This investigation elaborates simultaneous attributes of chemical reaction and dual stratification in magnetized Jeffrey liquid flow by the vertical cylinder movement. Consideration of mixed convection leads to coupled flow phenomena. Heat sink/source and thermal radiation effect are accounted to scrutinize the heat transport features. The mathematical system is simplified by implementing boundary-layer approach. The process of non-dimensionalization is done by introducing appropriate variables. Computational outcomes are achieved via homotopic criteria. Graphical illustrations are presented to visualize the solution expressions. Rate of heat-mass transfer is noticed higher when stratification variables are augmented however an increment in stratification variables yields lower solutal and thermal fields. It is worth to mention that results for flat surface can be recovered in the absence of curvature parameter.

Analytical Transport Network Theory for Onsager, Coupled Flows: Part 1—Channel-Scale Modeling of Linear, Electrokinetic Flow

AbstractThe analytical transport network (ATN) model for flow through microstructural networks is extended to linearly coupled flows subject to Onsager reciprocity. Electrokinetic flow is used as an example system. Through the extension, we gain an improved understanding of if, and how, morphology and topology influence coupled flow systems differently than un-coupled flows. In Part 1, a channel-scale model is developed to describe electrokinetic flow through a channel of arbitrary morphology. The analytical model agrees well with finite element analysis (FEA), but is significantly less expensive in terms of computational resources, and, furthermore, offers general insight into morphology's additional influence on coupled flows relative to uncoupled flows. In Part 2, we exploit these savings to develop a computationally economical, network-scale model and associated algorithm for its implementation to voxel-based three-dimensional images. Included in the algorithm is a means for rapidly calculating a structure's tortuosity factor. This modeling effort represents an important initial step in extending the ATN approach to coupled flow phenomena relevant to emerging technologies that rely on heterogeneous, hierarchical materials.

Analytical Transport Network Theory for Onsager, Coupled Flows: Part 2—Network-Scale Modeling of Linear, Electrokinetic Flow

Abstract The analytical transport network (ATN) model was developed to study transport through heterogeneous and hierarchical microstructural networks. Here, ATN is extended to electrokinetic flow, a linear, coupled flow that satisfies Onsager’s reciprocity relations. In Part 1, a channel-scale model was developed to describe electrokinetic flow through a channel of arbitrary morphology. In Part 2, we exploit the computational economy of the channel-scale model to develop an efficient network-scale model of electrokinetic flow in large, geometrically complex material structures. The corresponding algorithm for applying the theory to voxel-based, three-dimensional (3D) images is automated and computationally efficient. In addition, it provides a means for rapidly obtaining a structure’s tortuosity factor from a 3D image. We outline the manner in which morphology and topology exerts an additional influence on electrokinetic flow relative to pure conduction and viscous fluid flow. The effort represents an important initial step in extending the ATN approach to a broader range of linear and eventually nonlinear coupled flow phenomena. The extension is relevant to a number of technological fields, including emerging energy conversion and storage technologies.

High performance parallel computing of flows in complex geometries: II. Applications

Present regulations in terms of pollutant emissions, noise and economical constraints, require new approaches and designs in the fields of energy supply and transportation. It is now well established that the next breakthrough will come from a better understanding of unsteady flow effects and by considering the entire system and not only isolated components. However, these aspects are still not well taken into account by the numerical approaches or understood whatever the design stage considered. The main challenge is essentially due to the computational requirements inferred by such complex systems if it is to be simulated by use of supercomputers. This paper shows how new challenges can be addressed by using parallel computing platforms for distinct elements of a more complex systems as encountered in aeronautical applications. Based on numerical simulations performed with modern aerodynamic and reactive flow solvers, this work underlines the interest of high-performance computing for solving flow in complex industrial configurations such as aircrafts, combustion chambers and turbomachines. Performance indicators related to parallel computing efficiency are presented, showing that establishing fair criterions is a difficult task for complex industrial applications. Examples of numerical simulations performed in industrial systems are also described with a particular interest for the computational time and the potential design improvements obtained with high-fidelity and multi-physics computing methods. These simulations use either unsteady Reynolds-averaged Navier–Stokes methods or large eddy simulation and deal with turbulent unsteady flows, such as coupled flow phenomena (thermo-acoustic instabilities, buffet, etc). Some examples of the difficulties with grid generation and data analysis are also presented when dealing with these complex industrial applications.

Thermal constraints on disposal of heat-emitting waste in argillaceous rocks

Although the post-closure thermal phase of a repository containing heat-emitting radioactive wastes is likely to be of comparatively short duration when judged against performance assessment time-scales, the effects of temperature increase and associated thermal gradients within an argillaceous host-rock are likely to be wide-ranging and include: (a) geomechanical effects on the rock-mass and engineered structures (linings, emplacement boreholes, etc.), (b) perturbation of groundwater pressures and flow by ‘aquathermal mechanisms’, (c) possible near-field effects on mass transport properties and mechanisms (e.g. coupled flow phenomena), and (d) effects on the chemical evolution of the near-field environment. Maximum allowable temperature in a repository is likely to be constrained by host-rock and/or clay buffer/backfill thermal behaviour. Given the diverse range of the thermal responses, the identification of a primary constraint on near-field temperature and the specification of a maximum allowable temperature remains problematic.

Coupled flow phenomena in thin free-surface films

The flow of aqueous salt solutions in thin free-surface films is analyzed with a simple physico-chemical model. In addition to gravity, gradients in temperature, solute concentration and electric potential act as forces on the film. Through surface-tension gradients, electro-kinetic effects and thermal diffusion, a non-equilibrium thermodynamic coupling between the four forces and their respective fluxes is established. A global treatment of the Onsager thermodynamics is used to describe the cross-coupling, the physicochemical model used is shown to satisfy the Onsager reciprocal theorem and the relative importance of the various surface phenomena occurring in the film is acessed.