Density based topology optimization of turbulent flow heat transfer systems

The focus of this article is on topology optimization of heat sinks with turbulent forced convection. The goal is to demonstrate the extendibility, and the scalability of a previously developed fluid solver to coupled multi-physics and large 3D problems. The gradients of the objective and the constraints are obtained with the help of automatic differentiation applied on the discrete system without any simplifying assumptions. Thus, as demonstrated in earlier works of the authors, the sensitivities are exact to machine precision. The framework is applied to the optimization of 2D and 3D problems. Comparison between the simplified 2D setup and the full 3D optimized results is provided. A comparative study is also provided between designs optimized for laminar and turbulent flows. The comparisons highlight the importance and the benefits of full 3D optimization and including turbulence modeling in the optimization process, while also demonstrating extension of the methodology to include coupling of heat transfer with turbulent flows.     

Computational simulation of gas flow and heat transfer near an immersed object in fluidized beds

To improve the understanding of the heat transfer mechanism and to find a reliable and simple heat-transfer model, the gas flow and heat transfer between fluidized beds and the surfaces of an immersed object is numerically simulated based on a double particle-layer and porous medium model. The velocity field and temperature distribution of the gas and particles are analysed during the heat transfer process. The simulation shows that the change of gas velocity with the distance from immersed surface is consistent with the variation of bed voidage, and is used to validate approximately dimensional analysing result that the gas velocity between immersed surface and particles is 4.6U_mf/ε_mf. The effects of particle size and particle residence time on the thermal penetration depth and the heat-transfer coefficients are also discussed.     

Three-dimensional fluid topology optimization for heat transfer

Structural and Multidisciplinary Optimization - In this work, an in house topology optimization (TO) solver is developed to optimize a conjugate heat transfer problem: realizing more complex and...     

Concurrent shape and topology optimization for steady conjugate heat transfer

Structural and Multidisciplinary Optimization - Topology optimization is typically used to discover an optimized material distribution which implicitly defines the external shape of a body. The...     

Transient heat transfer and gas flow in a MEMS-based thruster

Time-dependent performance of a high-temperature MEMS-based thruster is studied in detail by a coupled thermal-fluid analysis. The material thermal response governed by the transient heat conduction equation is obtained using the finite element method. The low-Reynolds number gas flow in the microthruster is modeled by the direct simulation Monte Carlo (DSMC) approach. The temporal variation of the thruster material temperature and gas flowfields are obtained as well as the thruster operational time limits for thermally insulated and convectively cooled thrusters. The predicted thrust and mass discharge coefficient of both two-dimensional (2-D) and three-dimensional (3-D) micronozzles decreases in time as the viscous losses increase for higher wall temperatures.     

Industrial application of topology optimization for combined conductive and convective heat transfer problems

This paper presents an industrial application of topology optimization for combined conductive and convective heat transfer problems. The solution is based on a synergy of computer aided design and engineering software tools from Dassault Systèmes. The considered physical problem of steady-state heat transfer under convection is simulated using SIMULIA-Abaqus. A corresponding topology optimization feature is provided by SIMULIA-Tosca. By following a standard workflow of design optimization, the proposed solution is able to accommodate practical design scenarios and results in efficient conceptual design proposals. Several design examples with verification results are presented to demonstrate the applicability.     

Measurements and modeling of two-phase flow in microchannels withnearly constant heat flux boundary conditions

Two-phase forced convective flow in microchannels is promising for the cooling of integrated circuits. There has been limited research on boiling flow in channels with dimensions below 100 μm, in which bubble formation and flow regimes can differ from those in larger channels. This work develops single and multi-channel experimental structures using plasma-etched silicon with pyrex glass cover, which allow uniform heating and spatially-resolved thermometry and provide optical access for visualization of boiling regimes. Boiling was observed with less than 5°C of super-heating in rectangular channels with hydraulic diameters between 25 and 60 μm. The channel wall widths are below 350 μm, which minimizes solid conduction and reduces variations in the heat flux boundary condition. Pressure drop and wall temperature distribution data are consistent with predictions accounting for solid conduction and homogeneous two-phase convection     

Numerical simulation of flow and heat transfer in radially rotating microchannels

Investigation of fluid flow and heat transfer in rotating microchannels is important for centrifugal microfluidics, which has emerged as an advanced technique in biomedical applications and chemical separations. The centrifugal force and Coriolis force, arising as a consequence of the microchannel rotation, change the flow pattern significantly from the symmetric profile of a non-rotating channel. Successful design of microfluidic devices in centrifugal microfluidics depends on effectively regulating these forces in rotating microchannels. In this work, we have numerically investigated the flow and heat transfer in rotating rectangular microchannel with continuum assumption. A pressure-based finite-volume technique with a staggered grid was applied to solve the steady incompressible Navier–Stokes and energy equations. It was observed that the effect of Coriolis force was determined by the value of the non-dimensional rotational Reynolds number (Re _ω ). By comparing the root mean square deviation of the axial velocity profiles with the approximate analytical results of purely centrifugal flow for different aspect ratios (AR = width/height), a critical rotational Reynolds number (Re _ω,cr) was computed. Above this value of (Re _ω,cr), the effect of secondary flow becomes dominant. For aspect ratios of 0.25, 0.5, 1.0, 2.0, 4.0 and 9.09, this critical rotational Reynolds number (Re _ω,cr) was found to be 14.0, 5.5, 3.8, 4.7, 6.5 and 10.0, respectively.     

Fluid flow and heat transfer in the evaporating thin film region

The evaporating thin film region is an extended meniscus beyond the apparent contact line at a liquid/solid interface. Thin film evaporation plays a key role in a highly efficient heat pipe. A detailed mathematical model predicting fluid flow and heat transfer through the thin film region is developed. The model considers the effects of inertial force, disjoining pressure, surface tension, and curvature. Utilizing the order analysis, the model is simplified and can be numerically solved for the thin film profile, interfacial temperature, meniscus radius, heat flux distribution, velocity distribution, and mass flow rate in the evaporating thin film region. The prediction shows that while the inertial force can affect the thin film profile, interfacial temperature, meniscus radius, heat flux distribution, velocity distribution, and mass flow rate, in particular, near the non-evaporating region, the effect can be neglected. It is found that a maximum velocity, a maximum heat flux, and a maximum curvature exist for a given superheat, but the locations for these maximum values are different.     

Mobile robot path planning algorithm by equivalent conduction heat flow topology optimization

This paper addresses the path planning problem for a point robot moving in a planar environment filled with obstacles. Our approach is based on the principles of thermal conduction and structural topology optimization and rests on the observation that, by identifying the starting and ending configurations of a point robot as the heat source and sink of a conducting plate, respectively, the path planning problem can be formulated as a topology optimization problem that minimizes thermal compliance. Obstacles are modeled as regions of zero thermal conductivity; in fact, regions can be assigned varying levels of non-uniform conductivity depending on the application. We describe the details of our path planning algorithm, including the use of artificial mass constraints (particularly limits on the plate mass) to ensure convergence, and the choice of penalty exponents. The feasibility and practicality of our approach is validated through numerical experiments performed with several benchmarks, with intriguing possibilities for extension to more complex environments and real terrains. The benchmark problems of this paper mainly consist of obstacle-free path planning problems in two-dimensional space with maze-typed, symmetric, and spiral-type obstacles. We also address planning problems involving user-specified checkpoints, and also finding shortest paths on real three-dimensional terrain. To the authors’ knowledge, the path planning going through a stopover is considered for the first time.     

气固两相流中颗粒间碰撞传热进展

稠密气固两相流中,颗粒间的碰撞成为流动、传热过程的重要作用机理,它们对热交换过程有重要的贡献。文章概述了气固两相流中,颗粒间碰撞传热机理的研究现状;评述了欧拉-拉格朗日和欧拉-欧拉模型框架下,颗粒间碰撞传热研究的进展。基于颗粒动力学理论和随机碰撞频率的概念,建立了适用于欧拉-欧拉方法的颗粒间碰撞传热的数学模型。     

The heat transfer from a sphere in free convective flow

We consider the free convective flow over the surface of a sphere whose temperature is suddenly raised to a value greater than that of its surroundings. Numerical solutions of the Navier-Stokes equations are obtained for finite values of the Prandtl and Grashof numbers. The heat-transfer characteristics are examined, and where possible compared with earlier results obtained from boundary-layer theory in the high Grashof number limit.     

Projection-based two-phase minimum and maximum length scale control in topology optimization

The objective of this paper is a tradeoff between changing design and controlling sampling uncertainty in reliability-based design optimization (RBDO). The former is referred to as ‘living with uncertainty’, while the latter is called ‘shaping uncertainty’. In RBDO, a conservative estimate of the failure probability is defined using the mean and the upper confidence limit, which are obtained from samples and from the normality assumption. Then, the sensitivity of the conservative probability of failure is derived with respect to design variables as well as the number of samples. It is shown that the proposed sensitivity is much more accurate than that of the finite difference method and close to the analytical sensitivity. A simple RBDO example showed that once the design variables reach near the optimum point, the number of samples is adjusted to satisfy the conservative reliability constraints. This example showed that not only shifting design but also shaping uncertainty plays a critical role in the optimization process.     

Fluid flow and heat transfer past two spheres in a cylindrical tube

The fluid flow and the heat transfer for a row of spheres in a cylindrical tube is modelled by considering the flow past two spheres in a long tube. The problem is solved numerically by a finite element method, using a velocity-pressure formulation for the Navier-Stokes equations.Results are obtained for Reynolds number up to 200, with Prandtl numbers of 0.72 and 7.0, for a range of sphere sizes and sphere separations. It was found that as the distance between the spheres was decreased a circulatory region of flow appeared between the spheres for a given Reynolds number. This eddy led to poor heat transfer in this region. Increasing the Reynolds number was found not to improve the situation as the eddy grew in size and caused poorer heat transfer. This was found to be true with even the widest gap sizes considered.     

Diffuse interface method for fluid flow and heat transfer in cellular solids

This work presents a contribution on the numerical modelling capabilities for the simulation of fluid flow and heat transfer in cellular solids – in particular we focus on open cell aluminium foams. Rather than applying one of the classical academical or commercial numerical finite volume (FV), finite difference (FD) or finite element (FE) interface tracking methods, we base our models on an interface capturing phase field method (Nestler, 2005). A coupled diffuse interface lattice Boltzmann fluid flow solver (Ettrich, 2014) and a diffuse interface heat transfer approach (Ettrich et al., 2014) are combined in view of dealing with even more convoluted geometries, incorporating the dynamics of interfaces and complex multiphysics applications. Numerical results for the combined fluid flow and heat transfer simulations in open cell metal foams are in very good agreement with experimental data (Ettrich and Martens, 2012; Ettrich et al., 2012).     

Non-coaxial rotating flow of viscous fluid with heat and mass transfer

Heat and mass transfer in unsteady non-coaxial rotating flow of viscous fluid over an infinite vertical disk is investigated. The motion in the fluid is induced due to two sources. Firstly, due to the buoyancy force which is caused because of temperature and concentration gradients. Secondly, because of non-coaxial rotation of a disk such that the disk executes cosine or since oscillation in its plane and the fluid is at infinity. The problem is modeled in terms of coupled partial differential equations with some physical boundary and initial conditions. The dimensionless form of the problem is solved via Laplace transform method for exact solutions. Expressions for velocity field, temperature and concentration distributions are obtained, satisfying all the initial and boundary conditions. Skin friction, Nusselt number and Sherwood number are also evaluated. The physical significance of the mathematical results is shown in various plots and is discussed for several embedded parameters. It is found that magnitude of primary velocity is less than secondary velocity. In limiting sense, the present solutions are found identical with published results.

     

Teaching computer-aided design of fluid flow and heat transfer engineering equipment

A teaching programme for fluid mechanics and heat transfer is described which contains a computer-aided learning (CAL) component and a computer-aided design (CAD) component. The first centres on a final-year lecture course on the fundamentals of the subject and is heavily supported by computer-based tutorial exercises, while the second consists of a CAD course and separate project work in which the students apply the knowledge acquired in the ‘fundamentals’ course to selected design probems. It is argued that the understanding of the physical and numerical modelling taught in the CAL course is essential to the proper implementation of CAD.     

Near-wall effects in micro scale Couette flow and heat transfer in the Maxwell-slip regimes

The effects of modified transport characteristics within an extremely thin layer adjacent to the fluid–solid interfaces are investigated for fully developed laminar micro-scale Couette flows with slip boundary conditions. The wall-adjacent layer effects are incorporated into the continuum-based mathematical model by imposing variable viscosity and thermal conductivity values close to the channel walls, for solving the momentum and energy conservation equations. Analytical expressions for the velocity profiles are derived and are subsequently utilized to obtain the temperature variations within the parallel plate channel, as a function of the significant system parameters. It is revealed that the variations in effective viscosity and thermal conductivity values within the wall-adjacent layer have profound influences on the fluid flow and the heat transfer characteristics within the channel, with an interesting interplay with the wall slip boundary conditions. These effects cannot otherwise be accurately captured by employing classical continuum based models for microscale Couette flows that do not take into account the alterations in effective transport properties within the wall adjacent layers.