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Efficient Numerical Modeling of Moving Contact Lines under Non-isothermal Conditions

Periodic Reporting for period 1 - ENMMCL (Efficient Numerical Modeling of Moving Contact Lines under Non-isothermal Conditions)

Reporting period: 2015-10-06 to 2017-10-05

Flows with moving contact lines (MCLs) are the heart of numerous industrial applications, such as surface coating, mould filling, displacement of oil by CO2, spray cooling, condensing, microreactors etc. Although moving contact line is only a small part of the flow even in small systems, in fact the speed of the contact line and the dynamic contact angle largely control the flow. Improved understanding of MCL dynamics and capability of predictive analysis of flows involving MCLs will therefore greatly benefit the design and optimization of numerous industrial applications. In many practical systems, contact lines move under non-isothermal conditions, for example, in fire flooding, in condensers, in droplet impact on a hot substrate in spray cooling, etc. Despite considerable attention and decades of development, the understanding for dynamics of moving contact lines is still far from enough. In our project, we will develop a non-isothermal combined theory for MCL dynamics and will use it to build a novel macroscale computational model, which can simulate non-isothermal MCL flows efficiently and accurately. The specific research objectives are:
(1) to investigate the dependency of the dynamic contact angle on the contact line speed and other system parameters using systematic experiments, and to develop fundamental understandings of the results
(2) to develop a non-isothermal theory to predict the interface shape close to the MCL
(3) to develop a novel macroscale computational model for efficient simulations of non-isothermal MCL flows and to validate the model
All three research objectives have been achieved during the fellowship period.
During this project, the fellow has carried out both experimental and numerical studies on the dynamics of moving contact line under non-isothermal conditions, the main results are as follows:
(1)The fellow studied the theories of MCL (Molecular Kinetic Theory, Hydrodynamic Theory, Combined Theory) under non-isothermal conditions, and revealed the dependency of the dynamic contact angle on the contact line speed and other system parameters.
(2) The fellow carried out the experiment on droplet spreading on hot substrate and revealed the effect of substrate temperature on the droplet spreading. The thermal effect on droplet spreading regimes (first-stage pinch-off, second-stage pinch-off, no pinch-off) is revealed.
(3) Based on the theories of MCL, the macro-scale computational model was built up to describe accurately the droplet spreading under non-isothermal conditions after validation with experimental results.
(4) The evaporation model was built up for droplet evaporation on hot substrate, which agreed quite well with the theoretical solutions.

The results from the project are currently being summarized into six journal papers. During the project, the fellow attended the 2nd International Heat Transfer Symposium in 2016 to disseminate the research results, which have received wide attention from the international peers.
In this project a novel macroscopic model for moving contact line is built up under non-isothermal condition, and it is important from both fundamental and application point of view. It leads to a step change in the modeling of MCLs in non-isothermal systems, by delivering a novel macroscale model with unprecedented efficiency. The related dynamic wetting is directly relevant to several Key Enabling Technologies, identified by the EU as being strategically important: Nanotechnologies, Advanced Materials, Advanced Manufacturing and Biotechnologies. The project will benefit researchers in wide disciplines, and the simulation tool can help companies in various sectors such as manufacturing, materials, oil & gas, healthcare in design and optimization of their products.
Schematic diagram of a macroscale model for moving contact lines