Wen-Qiang Lu

A new numerical method to simulate the non-Fourier heat conduction in a single-phase medium

Abstract Many non-equilibrium heat conduction processes can be described by the macroscopic dual-phase lag model (DPL model). In this paper, a numerical method, which combines the dual reciprocity boundary element method (DRBEM) with Laplace transforms, is constructed to solve such mathematical equation. It is used to simulate the non-Fourier phenomenon of heat conduction in a single-phase medium, then numerically predict the differences between the thermal diffusion, the thermal wave and the non-Fourier heat conduction under different boundary conditions including pulse for one- and two-dimensional problems. In order to check this numerical methods reliability, the numerical solutions are still compared with two known analytical solutions.

GENERALIZED TIME DELAY BIOHEAT EQUATION AND PRELIMINARY ANALYSIS ON ITS WAVE NATURE

As a new developing field, the science of bioheat transfer is making its fundamental propositions and theories much more complete and thus postulates new concepts based on the new discovery and knowledge. In this note, an important improvement on the previously developed thermal wave models of bioheat transfer (TWMBT) is given.

Shear-rate dependent effective thermal conductivity of H2O+SiO2 nanofluids

Effective thermal conductivity (ETC) of water-based silicon dioxide nanofluids in shear flow fields (flow shear rate range was 0–820 1/s) was measured using a rotating Couette apparatus. The results show that the ETC of the nanofluids in shear flow fields is significantly higher than that in static states. For the flow shear rates lower than a critical value (infinite-shear rate), the ETC asymptotically increases with increasing the flow shear rate; for the flow shear rates higher than the critical value, the ETC displays a plateau value (infinite-shear thermal conductivity). The increase of the ETC with shear rate is more obvious as increase the nanoparticle diameter and the nanoparticle volume fraction. For 16 different measured nanofluids, the infinite-shear rates vary from 445.0 to 712.1 1/s, while the infinite-shear thermal conductivities increase by 9%–17% comparing with the zero-shear thermal conductivities. The conventional ETC prediction correlation proposed for the suspensions containing micro-sized particles is not suitable for the nanofluids qualitatively and quantitatively. Finally, an exponential correlation is proposed based on our measured data to predict the ETC of nanofluids considering the effects of flow shear rate, nanoparticle diameter, and nanoparticle volume fraction.

Boundary element analysis of thermocapillary convection with a free surface in a rectangular cavity

Abstract A boundary element method for analysing thermocapillary convection with a free surface has been developed. The divergence theorem is applied to the non-linear convective volume integral in the boundary element formulation with the pressure penalty function. Consequently, velocity and temperature gradients are eliminated and the complete formulation is written in terms of velocity and temperature. This provides considerable reduction in storage and computational requirements while improving accuracy. Employing this method, a simulation of surface tension driven convective flow in a rectangular cavity with differential heated isothermal lateral walls in a microgravity environment has been demonstrated. The influence of different Marangoni numbers, Reynolds numbers and Prandtl numbers on the shape of the free surface, the temperature distribution and the flow fields has also been studied.

The Effect of Beam Intensity on Temperature Distribution in ADS Windowless Lead-Bismuth Eutectic Spallation Target

The spallation target is the component coupling the accelerator and the reactor and is regarded as the “heart” of the accelerator driven system (ADS). Heavy liquid metal lead-bismuth eutectic (LBE) is served as core coolant and spallation material to carry away heat deposition of spallation reaction and produce high flux neutron. So it is very important to study the heat transfer process in the target. In this paper, the steady-state flow pattern has been numerically obtained and taken as the input for the nuclear physics calculation, and then the distribution of the extreme large power density of the heat load is imported back to the computational fluid dynamics as the source term in the energy equation. Through the coupling, the transient and steady-state temperature distribution in the windowless spallation target is obtained and analyzed based on the flow process and heat transfer. Comparison of the temperature distribution with the different beam intensity shows that its shape is the same as broken wing of the butterfly. Nevertheless, the maximum temperature as well as the temperature gradient is different. The results play an important role and can be applied to the further design and optimization of the ADS windowless spallation target.

Two-Way Coupling Simulation of Heat Transfer in ADS Windowless Spallation Target

The steady-state phase distribution and the structural parameters have been taken as the input for the nuclear physics calculation in the ADS windowless spallation target. The distribution of the extreme large power density of the heat load is imported back as the source term in the energy equation. Then temperature distribution is obtained based on the flow process and heat transfer. The preliminary results show that the temperature distribution reaches the steady-state and its shape is like the broken wings of the butterfly. This is very important for the further design and optimization of the ADS windowless spallation target. So the two-way coupling simulation of the heat transfer process is successfully performed between the computational fluid dynamics and the nuclear physics simulation.Copyright

Some non-Fourier heat conduction characters under pulsed inlet conditions

Through simulating one- and two-dimensional non-Fourier heat conduction problems under different pulsed inlet conditions, this paper numerically predicts some different non-Fourier heat conduction characters arose from different pulse types and different pulse frequencies. Meanwhile, the differences among thermal wave, non-Fourier and Fourier heat conduction are also showed.

Development of Anodic Alumina Membranes for Hemodialysis

In this paper, a novel large size (50x50mm2) anodic porous alumina membrane specially used in hemodialysis process is developed. By using a two-step anodization fabrication method, a semi-permeable membrane with nano-sized pores is produced. Comparing with spongy style pores located on polymer membranes, this membrane has straight channel pores. And these pores are uniform in size. Experimental results in this paper also show that the relationship between membrane pore size and anodization voltage follows linear rule on the scale of several nano-meters. These intrinsic properties of the alumina membrane are highly desired in the process of hemodialysis since: 1) with straight channel pores, the adsorption amount of small molecules inside the membrane is much lower than that of spongy style pores; 2) the uniform pore size provides us a chance to avoid occurrence of protein leaking problem when using polymer membranes with spontaneous pore size; 3) the linearity property tells that the membrane pore size is controllable during quantitive fabrication.

Molecular Dynamics Simulation of Fluid Transport in Nanoscale Pore of Porous Medium

In this paper, the Poiseuille water flow inside a nanosized channel style pore formed by two solid parallel walls is studied using molecular dynamics (MD) simulation. Alumina has been chosen as the material of the wall. The flow is initiated by applying a uniform external force on each water molecule inside the channel. Periodic boundary conditions are imposed for the simulation. 12–6 L–J potentials are chosen in the simulation to describe H2O‐H2O molecule interactions as well as H2O‐Al2O3 molecule interactions. The present work aims at finding that, in the process of hemodialysis, how the filtration velocity and slip boundaries inside the pore of a filtration membrane are affected by the magnitude of the applied external force and how the results are different from that of the simplified Kedem‐Ketchalsky (1958) equations employing the present physical parameters.In this paper, the Poiseuille water flow inside a nanosized channel style pore formed by two solid parallel walls is studied using molecular dynamics (MD) simulation. Alumina has been chosen as the material of the wall. The flow is initiated by applying a uniform external force on each water molecule inside the channel. Periodic boundary conditions are imposed for the simulation. 12–6 L–J potentials are chosen in the simulation to describe H2O‐H2O molecule interactions as well as H2O‐Al2O3 molecule interactions. The present work aims at finding that, in the process of hemodialysis, how the filtration velocity and slip boundaries inside the pore of a filtration membrane are affected by the magnitude of the applied external force and how the results are different from that of the simplified Kedem‐Ketchalsky (1958) equations employing the present physical parameters.

Thermal Transport in Sheared Nanoparticle Suspensions: Effect of Temperature

ABSTRACT Nanoparticle suspensions, known as nanofluids, exhibit many potential applications in thermal and chemical engineering, of which the thermal transport characteristics have a great dependence with the corresponding flow process and heat transfer process. Recently, a shear flow-induced enhancement of the thermal transport in the nanoparticle suspensions was previously reported. Here, the effective thermal conductivity (ETC) of deionized water based silicon oxide nanoparticle suspensions in the shear flows at different temperatures were experimentally measured to elucidate the effect of temperature on the thermal transport in sheared nanoparticle suspensions. The results show that the ETC enhancement induced by shear flows is more obvious at lower temperatures, which can be attributed to the easily formed nanoparticle agglomerates for the lower mobilities of nanoparticles. Meanwhile, a correlation for quantitatively predicting the ETC enhancements, i.e., the ratios of infinite-shear thermal conductivity to zero-shear thermal conductivity, is proposed with considering the effect of temperature. In summary, the thermal transport in sheared nanoparticle suspensions demonstrates distinctive characteristics at different temperatures for the distinguishing nanoparticle structures.