Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Micropolar nanofluid flow with MHD and viscous dissipation effects towards a stretching sheet with multimedia feature

To promote radiation electrical MHD activation energy thermal extrusion manufacturing system efficiency by using Carreau-Nanofluid with parameters control method

Latent heat storage (LHS) is considered as the most promising technique for thermal energy storage, due to its high energy storage density and nearly constant working temperature. However, the lower thermal conductivity of the phase change material (PCM) used in LHS system seriously weakens thermal energy charging and discharging rates. In order to improve the thermal performance of LHS system, a lot of research on performance enhancement have been carried out. This review paper will concern on the development of PCMs and performance enhancement methods for LHS system in the last decade. The available enhancement methods can be classified into three categories: using high thermal conductivity additives and porous media to enhance PCM thermal conductivity, using finned tubes and encapsulated PCMs to extend heat transfer surface, using multistage or cascaded LHS technique and thermodynamic optimization to improving the heat transfer uniformity. The comparative reviews on PCMs, corresponding performance enhancement methods and their characteristics are presented in present paper. That will help in selecting reliable PCMs and matching suitable performance enhancement method to achieve the best thermal performance for PCM based LHS system. In addition, the research gaps in performance enhancement techniques for LHS systems are also discussed and some recommendations for future research are proposed.

A review of phase change material and performance enhancement method for latent heat storage system

In order to saving thermal energy, latent heat thermal energy storage systems (LHTESS) can be utilized. Common phase change material (PCM) has low thermal conductivity. In this paper, CuO nanoparticles have been used to enhance the performance of LHTESS. CuO–water nanofluid properties are estimated by means of KKL. This unsteady process has been simulated by Finite element method. Results prove that solidification process is accelerated by adding CuO nanoparticles in to pure PCM. As number of undulations increases average temperature and total energy profiles reduce while solid fraction profile increases. Also, it can be concluded that highest rate of solidification is obtained for dp = 40 nm.

Numerical simulation for solidification in a LHTESS by means of nano-enhanced PCM

Experimental and numerical investigations of force analysis acted on single circular cylinder in the T pipe junction with the effect of vanes are reported in this paper. Experiments are carried on in a small wind tunnel at five different velocity ratios (R) from 0.117 to 0.614. The mean pressure data acted on the cylinder are obtained and in turn the drag and lift. Vanes are installed at the junction to change the secondary flow in the branch duct and the angle is in the range of 90° ≤ φ ≤ 130°. Numerical studies which are validated by the experimental data help understand the flow structure for the analysis. It is found that in the T shape junction without vanes, the cylinder presents different surface mean pressure distributions at the different positions in the suction duct. As the increase of the distance from the junction to the cylinder center, the surface mean pressure distributions recover to the benchmark gradually which performs in the straight duct beforehand. Four feature points including the front/rear stagnation points and the separation points and the corresponding three divisions of flow region are analyzed in detail with the auxiliary numerical simulation of flow structure. Effect of the vanes with different angle is also discussed. Finally, the drag and lift coefficients acted on the cylinder with or without vanes are performed.

Force Analysis of a Circular Cylinder at Ununiformed Flow in a T Pipe Junction

Numerical simulation on turbulent fluid flow and heat transfer enhancement of a tube bank fin heat exchanger with mounted vortex generators on the fins

Compact heat exchangers are characterized by high heat duties per unit volume and high heat transfer coefficients. The heat enhancement of wing-type vortex generators (WVGs) with different heights, attack angles and distances between the fins were studied in this report. The staggered circular tube bank fin surface was investigated in detail by changing the angle of attack with &#952; &#61; 25&deg;,35&deg;,45&deg;, the height of wing-type vortex generators with H&#61;6mm, 7mm, 8mm, the distance between the fins with Tp&#61;6mm, 8mm, 10mm, the diameter of tube is 40mm. The result shows that the friction factor and Nusselt number increased with the increasing of attack angle, height of WVGs and distance of fins, but the Nusselt number does not change much with the attack angle. The WVGs have little heat enhancement to the tube surface; the WVGs have the influence to the other surface forming the channel. In the local mass/heat transfer study, the results show that the heat transfer reverse on the fin behind the tube can be avoided through WVGs. 

The experimental study of heat transfer enhancement and pressure drop characteristics with wing-type vortex generators for staggered circular tube bank fin compact heat exchanger

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Thermal and flow characteristics of a channel formed by circular tube bank fins stamped with convex/concave pyramids were numerically investigated by ANSYS Fluent software, and the parametric studies on the thermal performance of the pyramid fin are examined for varying pyramid height (Hp), pyramid length (Lp), and pyramid width (Wp) as Reynolds number (Re) ranged from 1297 to 4541. The pyramid fin provides superior thermal performance to the counterpart plain fin, which is ascribed to the punched pyramids effectively expanding heat transfer area and inducing the secondary flow to better fluid mixing, and the action of the convex/concave pyramids lead to the area of undesirable heat transfer dead zone behind the circular tube being significantly reduced. Under identical pumping power constraint, the thermal performance factor of 1.41 is achieved for Hp = 1 mm, Lp = 5.74 mm, and Wp = 3 mm at Re = 3892, and the optimal pyramid height and width fin respectively are Hp = 1 mm and Wp = 3 mm for studied cases, while the optimal pyramid length is associated closely with Re. The correlations of average Nusselt number and friction factor are proposed to estimate thermal performance of the pyramid fin used in a finned circular tube heat exchanger. 

Liang-Bi Wang

Papers

Force Analysis of a Circular Cylinder at Ununiformed Flow in a T Pipe Junction

Numerical simulation on turbulent fluid flow and heat transfer enhancement of a tube bank fin heat exchanger with mounted vortex generators on the fins

The experimental study of heat transfer enhancement and pressure drop characteristics with wing-type vortex generators for staggered circular tube bank fin compact heat exchanger

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Secondary Flow and Heat Transfer Enhancement Characteristics of a Channel Formed by Circular Tube Bank Fins Stamped with Convex/Concave Pyramids