A Lifting Relation from Macroscopic Variables to Mesoscopic Variables in Lattice Boltzmann Method: Derivation, Numerical Assessments and Coupling Computations Validation

In this paper, analytic relations between the macroscopic variables and the mesoscopic variables are derived for lattice Boltzmann methods (LBM). The analytic relations are achieved by two different methods for the exchange from velocity fields of finite-type methods to the single particle distribution functions of LBM. The numerical errors of reconstructing the single particle distribution functions and the non-equilibrium distribution function by macroscopic fields are investigated. Results show that their accuracy is better than the existing ones. The proposed reconstruction operator has been used to implement the coupling computations of LBM and macro-numerical methods of FVM. The lid-driven cavity flow is chosen to carry out the coupling computations based on the numerical strategies of domain decomposition methods (DDM). The numerical results show that the proposed lifting relations are accurate and robust

Numerical study on heat transfer enhancement for laminar flow in a tube with mesh conical frustum inserts

Enhanced heat transfer tubes (EHTT) with segmented mesh-conical frustums are considered. Tube diameter and frustum apex angle are fixed as 20 mm and 60o, respectively. The height ratio of frustum and sliced part are set as a golden ratio (1.618). Laminar thermal-hydraulic performance and effects of some parameters, e.g., bottom frustum diameter and pitch, are numerically simulated. The equal equivalent diameter and total flow area criteria are adopted to simplify 3D mesh pores to 2D ones. Flow and temperature fields show large velocities and gradients close to the wall and smaller velocities in the bulk region. This enhances heat transfer with a limited pressure drop. EHTTs obtain 1.4 - 3.3 times higher heat transfer than bare tubes and the performance evaluation criterion (PEC) varies from 1.3 to 1.8. Nusselt number (Nu) and friction factor (f) correlations are proposed. New insights into heat transfer enhancement and tube configuration are provided

Numerical study on heat transfer in a tube with conical-mesh frustums inserted

In this work, an innovative enhanced heat transfer tube (EHTT) is proposed, inserted with segmented conical-mesh frustums. The diameter of the bottom surface and the pitch between conical frustums were investigated while the diameter of the tube and apex angle are fixed at 20 mm and 60o, respectively. The ratio between the height of the frustum and that of the sliced part was set as a golden ratio (1.618), which is regarded as the optimal in nature. Numerical simulations were employed to study the performance of the enhanced heat transfer tube in the laminar flow region and the effects of the parameters on performance were compared. To save the workload and time of simulation, the equal equivalent diameter and total flow area criteria were adopted to simplify the 3-Dimensional mesh pores to 2-Dimensional mesh pores. Besides a multiscale grid system was built to link the micron scale of the mesh pores and macroscale of the tube and periodic boundary conditions were used. The results demonstrated that the flow and temperature fields were modeled effectively, with larger velocity and velocity gradient in the vicinity of the wall as well as smaller velocity in the bulk flow region, which produced better performance of heat transfer with a relatively low friction penalty. The EHTT could obtain 3.3 times higher performance than bare tube, based on the cases studied. It was also shown that Nusselt number increased as the Reynolds number increased, and the EHTT performed better with a larger bottom diameter and smaller pitch of the conical frustums. Surprisingly, for the frustums in which the ratio between the bottom diameter and tube diameter was 0.8, it was indicated that the Nusselt number increased significantly with a slight friction decrease when the ratio between the pitch and tube diameter decreased from 3 to 2.5. This study provides a new insight into heat transfer enhancement and tube configuration, which has a wide engineering application potential.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016