Xin Liu, Ph.D candidate

161 Louis Pasteur, CBY A030

Ottawa, Ontario, Canada, K1N 6N5

Tel: (613) 562-5800-ext 6875

Email: liuxin429go@gmail.com

Department: Environmental Engineering, University of Ottawa

Research Interests:

Computational Hydrodynamics

Numerical modeling of Shallow water system

Hyperbolic system governing sediment transport and bed evolution

Gas-particle two phase flow in equipment

Renewable energy: Biomass gasification; Solar energy transportation, Heat exchange piles

Selected Publications:

1. X. Liu, A. Mohammadian, A. Kurganov, J.A. Infante Sedano. Well-balanced fully coupled central-upwind scheme for shallow water flows over erodible bed. (Submitted in 2014)

2. X. Liu, A. Mohammadian, J.A. Infante Sedano. A robust well-balanced and fully coupled 2-D model for dam break flow over erodible bed. (Submitted in 2014)

3. X. Liu, A. Mohammadian, J.A. Infante Sedano. A well-balanced 2-D model for dam break flow with wetting and drying. (Submitted in 2013)

4. X. Liu, J.A. Infante Sedano, A. Mohammadian. One dimensional numerical simulation of bed changes in irrigation channel using finite volume method. Irrigat Drainage Sys Eng. (2012)

5. X. Liu, W. Chen, et al. 3D numerical simulation of flow structure in miniature biomass circulating fluidized bed gasifier. Transact of the Chin Society for Agricultural Machinery. (2011)

6. X. Liu, W. Chen, et al. Various Circulating Fluidized Beds biomass gasifiers. Boiler Technology. (2011)

7. W. Chen, X. Liu. Three-Dimensional Simulation of Gas-Solid Flow in the Biomass Circulating Fluidized Bed Gasifier’s Riser. Advanced Materials Research. (2010)

Numerical modeling of shallow water system

The shallow water equations are a set of hyperbolic partial differential equations derived from depth-integrating the Navier-Stokes equations, in the case where the horizontal length scale is much greater than the vertical length scale. Shallow water equations have been widely used in various engineering fields, e.g. river flow modeling, dam-break and flood prediction, coastal engineering, harbor engineering, tidal waves simulation, tsunami prediction, simulation of atmospheric circulation, etc.

In my research, the shallow water system is applied to simulate the dam-break flow, wave propagation and flood process based on Finite volume method. In the model, the second order accuracy both in time and space is achieved, the well-balanced property is preserved and technique for tracking wetting and drying fronts is adopted. For high-energetic flow like dam-break process, non-negative water depth reconstruction and implicit splitting treatment for friction term are applied to maintain the stability. Thus a robust 2-D model for shallow water system which can deal various flows over irregular topography is built.

Sediment transport and Bed erosion

Rapid morphological evolution and intense sediment exchange with relative high sediment concentration frequently occurred in high-energetic flows over erodible bed. In my research, the conventional shallow water equations for clear water needs additional terms considering the interaction, momentum exchange and overall mass conservation between water and sediment and thus represents the system of water-sediment mixture. Moreover, to simulate the strongly coupled simultaneous physical processes consists of water flow, sediment transport and bed erosion, a fully coupled strategy is applied by building a truly hyperbolic system.

Gas-particle two-phases flow in equipment

Gas-solids fluidization is widely applied in industry, including petroleum, chemical, metallurgical and energy industries. In my past work, the fluidized bed is used for biomass gasification to produce combustible gas. Using the Gidaspow model for calculating the momentum exchange coefficient, and taking mutual influence of different mechanic parts in consideration, simulation of a full-loop miniature circulating fluidized bed gasifier (CFBG) is taken and it focuses on the gas-solid flow structure in the riser. The heterogeneous behavior in the CFBG riser and the radial profiles of solid volume fraction under different solid inventories are investigated as a replenishment of certain data those are difficult to measure in experiments. The results showed it can’t form an obvious core-annulus flow because of the riser’s high height-diameter ratio and the big re-feed pipe diameter. There are clusters growing and dissipation in a short time. A turning point of pressure drop may be seemed as a separation of dense area and dilute area. The three-dimensional (3D) simulation revealed the solid flux and the pressure drop agree with the experimental data.

The gas-solid injector could be used to add raw material to reactor. A 3-D simulation case of gas-solid injector conducted in 2009 by Xin Liu is presented.

Renewable energy projects

Biomass gasification means incomplete combustion of biomass resulting in production of combustible gases consisting of Carbon monoxide (CO), Hydrogen (H₂) and traces of Methane (CH₄). This mixture is called producer gas. Producer gas can be used to run internal combustion engines (both compression and spark ignition), can be used as substitute for furnace oil in direct heat applications and can be used to produce, in an economically viable way, methanol – an extremely attractive chemical which is useful both as fuel for heat engines as well as chemical feedstock for industries5. Since any biomass material can undergo gasification, this process is much more attractive than ethanol production or biogas where only selected biomass materials can produce the fuel. Circulating fluidized bed gasifier is a kind of advanced gasification plant which has high heating rate, high reaction speed and high gas calorific value. It could apply to gasification generating, liquefaction and so on well. It has a high intensity of gasification and no moving components in it. So the gasification facility is suited to be large-scaled and industrialized.

Storage of solar energy for the use at night is a challenging issue. One of the methods used in practice is to use latent heat and store energy in reservoirs of molten salt. The objective is this project is optimal design of phase-change heat storage systems and estimation and minimization of heat loss in such systems. The heating loss of transporting pipe and reservoir are predicted for facility optimizing and design.

Ground heating requires exchange piles are buried in the underground. However, the moisture transfer in unsaturated soil will affect the heating efficiency and waste extra energy. Using dry hot wind to remove the moisture around piles in soil is one of the feasible methods. An experimental study and numerical prediction of moisture removing is conducted.