Huilin Lu

Numerical study of melted PCM inside a horizontal annulus with threads in a three-dimensional model

This paper presents a numerical investigation of the melting process of a phase change material (PCM) in a tube and shell geometry. Since previous literature mainly focused on the 2-D model, a 3-D model is established in the present work with CFD software to take the velocity and heat transfer along the axial direction into account. In order to enhance the tubes heat transfer performance, two types of threads with different geometry parameters are introduced. The inner cylinder is assumed to be at constant temperature and the outer cylinder insulated. Temperature contours and streamlines are obtained to cast light on the effect of the threads. The predicted result shows all the threads can accelerate the melting process in the top region where natural convection is dominant, and the magnitude of the enhancement is determined by geometry parameters to some extent. However, none of the applied threads has improved the melting rate at the bottom region where heat conduction is dominant.

A numerical study on the gas fluidisation of secondary agglomerates of nanoparticles

Abstract Numerical simulations are performed on the gas fluidization of the secondary agglomerates of SiO2 and SiC nanoparticles. An Eulerian two-fluid approach is used, which models the solids stress modulus with an empirical Jung-Gidaspow relationship and the drag force based on the secondary agglomerates. The results show the behaviour of particulate fluidisation of the secondary agglomerates of nanoparficles. The fluidised bed has a very high expansion ratio but without distinct bubbles. A three-zone distribution of time-averaged particle concentration is observed along the bed height. These are a dense zone in the lower part of the bed, a dilute zone at the top part, and a transitional zone lies in between. The radial distribution of particle concentration is found to be nearly homogeneous in both the dilute and transitional zones. The modelling results are compared with experimental results reported in the literature and reasonably good agreement has been achieved. Supported by National Natural Scie...

Multi-scale study of hydrodynamics in an interconnected fluidized bed for the chemical looping combustion process

During the chemical looping combustion (CLC) process, the gas–solid hydrodynamic behaviors have a direct influence on the stability of the reactor system and the combustion efficiency of the fuel. To gain a better insight into the CLC system, a multi-scale computational fluid dynamic (CFD) simulation is implemented with an integrated drag model considering the impact of bubbles and clusters under the framework of the two-fluid model. A cluster-structure dependent drag model and a bubble-structure dependent drag model are employed to describe the meso-scale effects caused by clusters and bubbles. By comparisons of the gas pressure profile, the model prediction agrees well with experimental results. The distributions of local structural parameters including velocities in the bubble and emulsion, bubble fraction and local velocities in clusters are analyzed.

Experimental and CFD study on the hydrodynamic characters of dense liquid-solid fluidized bed

In a recent study the bed expansion height and liquid phase velocity was measured for liquid-solid fluidized bed with 0.10 m in diameter and 1.037m in height. Liquid flow velocity measurements were performed using the ultrasonic technique. Measurements of the bed expansion height were conducted by a graph paper marked along the length of the column. The Eulerian-Eulerian framework was employed in the CFD simulation of liquid hydrodynamics and solid motion in liquid fluidized bed. The typical flow pattern of the liquid-solid fluidized bed was obtained in the present calculation, i.e., the core annular flow pattern and back mixing near the wall region. Different fluid-particle drag models, virtual mass force and lift force effects were studied in the simulation. Also, comparisons of different restitution coefficients for particle-particle collisions as well as particle-wall interactions have been carried out to study the effect of particle collisions on solid concentration distributions, and a comprehensive...