Bayesian Estimation of Temperature-Dependent Thermophysical Properties and Transient Boundary Heat Flux

In this article, we apply a Bayesian approach for the simultaneous identification of volumetric heat capacity, thermal conductivity, and boundary heat flux, in a one-dimensional nonlinear heat conduction problem. The Markov chain Monte Carlo sampling approach, implemented in the form of the Metropolis–Hastings algorithm, was used for the solution of the inverse problem. Simulated temperature measurements were used in the inverse analysis in order to examine the accuracy and stability of the overall approach. Independent measurement data were used to construct the prior model for the coefficients to be estimated. The approach is also applied to experiments involving the heating of a reference material with an oxyacetylene torch.     

Transient Heat Transfer from an Offshore Buried Pipeline during Start-up Working Conditions

The 2D heat transfer from offshore, completely buried pipelines is studied with reference to transient working conditions. In particular, the start-up case is considered (i.e., the case of a pipeline initially at equilibrium with the surrounding soil). Two different start-up cases are investigated: the step-rising case and the smooth-rising case. (In the latter, the steady-state wall temperature is reached in a finite time.) The energy balance equation is written in a dimensionless form and solved numerically by means of a finite element method. The dimensionless temperature field in the soil and the thermal power exchanged per unit length by the pipeline with the soil are determined. A comparison with a simpler one-dimensional model of the phenomenon (“extra-soil layer” approximation) is performed.     

Heat Transfer Analysis of Functionally Graded Hollow Cylinders Subjected to an Axisymmetric Moving Boundary Heat Flux

The transient heat transfer analysis of functionally graded (FG) hollow cylinders subjected to a distributed heat flux with a moving front boundary on its inner surface is presented. The heat flux is assumed to be axisymmetric, and its front boundary moves along the axis of the cylinder. A method composed of the finite element and differential quadrature methods is employed to discretize the governing equations in the spatial domain. After demonstrating the convergence and accuracy of the method, the effects of different parameters on the temperature distribution and time history of the temperature at different points of FG cylinder are investigated.     

用于电子元件散热的集成热管换热特性研究

本文对应用于电子元件散热的热管换热器在不同的加热功率、不同风量情况下的传热特性进行了实验研究，从而得出换热量、总热阻、翅片表面阻力系数、换热系数、总热阻与加热功率及风道内空气肫数的关系，并与市场上的SP-94型热管散热器及传统纯铜散热器进行了比较，发现该热管换热器无论是散热量、平均换热系数还是总热阻都有明显的优势。因此，这种散热器在实际工程应用中必将有着广泛的潜力。     

粘土多孔砖瞬态传热数值分析

利用自然对流和热传导的物理耦合模型,控制方程采用有限容积法,求解算法使用SIMPLE算法,研究了粘土多孔砖在周期性条件下的瞬态传热规律.通过计算得到粘土多孔砖壁温特性,同时也研究了通过粘土多孔砖的热流变化规律,并与相同尺寸实心砖的传热过程比较.发现实心砖和粘土多孔砖的内壁面温度的延迟相差不大.而粘土多孔砖与实心砖平均热流相差很大.实心砖的平均热流约比粘土多孔砖平均热流大64%,说明粘土多孔砖节能效果显著.     

Transient Analysis of Slip Flow and Heat Transfer in Microchannels

Hybrid analytical-numerical solutions for transient flow and transient convective heat transfer within microchannels are presented. Analytical solutions for flow transients in microchannels are obtained by making use of the integral transform approach. The proposed model involves the transient fully developed flow equation for laminar regime and incompressible flow with slip at the walls in simple channel geometries. The solution is constructed so as to account for any general functional form of the time variation of the pressure gradient along the duct. Then, the transient-state convection heat transfer is solved for laminar slip flow inside microchannels formed by parallel-plates, making use of the generalized integral transform technique (GITT) and the exact analytical solution of the corresponding eigenvalue problem in terms of confluent hypergeometric functions so as to eliminate the transversal coordinate. The resulting system of transformed partial differential equations in the longitudinal coordinate is numerically solved by the Method of Lines as implemented in the routine NDSolve of the Mathematica system. Mixed symbolic-numerical algorithms are developed under the Mathematica platform.     

Nanofluid Flow and Heat Transfer in Boundary Layers: The Influence of Concentration Diffusion on Heat Transfer Enhancement

ABSTRACT

The present work uses a perturbation procedure to deduce the small perturbation differential equations for velocity, temperature, and the diffusion equation for nanoparticle volume concentration. Thermophysical variables are obtained from conventional means (e.g., mixture and field theory estimates) for nanofluids consisting of alumina nanoparticles dispersed in water (alumina–water nanofluid) and gold nanoparticles dispersed in water (gold–water nanofluid), and, in the case of gold–water nanofluid, molecular dynamics results are used to estimate such properties, including the transport coefficients. The very thin diffusion layer, at large Schmidt numbers, is found to have a great impact on the velocity and temperature profiles, owing to the transport property dependency and has a profound influence on surface conduction heat transfer rate enhancement and skin friction suppression for the case of nanofluid concentration withdrawal at the wall. In this case, the diffusional heat transfer rate is negligible, again, owing to the large Schmidt numbers encountered. Possible experiments directed at this interesting phenomenon are discussed.     

土壤源热泵U型埋管换热器传热的非稳态数值模拟

本文基于能量平衡方程,建立了土壤源热泵U型埋管换热器周围土壤的非稳态传热模型,用所建立的传热模型对土壤源热泵冬季取热过程进行了动态模拟.研究了不同物性土壤温度及U型埋管出口流体温度的变化规律,分析了土壤物性对换热器换热性能的影响,采用间歇运行方式提高了换热器换热能力.通过建立数学模型得出的结果,可供设计参考.     

Estimation of the Boundary Heat Flux in Grinding via the Conjugate Gradient Method

The unknown boundary surface heat flux in workpieces during grinding is estimated by the application of inverse heat transfer analysis. The conjugate gradient method of function estimation is used for the minimization procedure. Simulated temperature measurements are used in the inverse analysis for typical practical cases, in order to show that results more accurate than those available in the literature are obtained with the present solution approach. Actual experimental data are also used in the computations to estimate the surface heat flux.     

磁场作用下纳米磁流体热管传热速率的研究

提出了一种利用外加磁场来强化纳米磁流体真空热管传热的实验研究方法,设计和建立了纳米磁流体真空热管传热测试实验台,并在不同种类、不同强度的外加磁场作用下分别对纳米磁流体真空热管的传热速率进行了实验研究.结果表明：纳米磁流体热管在各种外界条件下都优于磁流体热管和水工质热管;各种磁场都能强化纳米磁流体热管的传热,其中静态直流磁场作用下纳米磁流体真空热管的传热速率提高最大.     

泡沫铝通道内瞬态流动的平均换热系数

针对泡沫铝金属填充矩形通道内的对流换热开展了瞬态实验研究,分析了泡沫铝孔径(孔隙率)、流体流量(流速)等关键参数的影响。为了有效地处理实验数据,重新定义并推导了平均换热系数的计算公式,得到了泡沫铝通道内流动的平均换热系数,并引入了基于渗透率的雷诺数和达西数,确定了相关换热、流动准则数关系。实验研究表明,流速的增大有利于对流换热的强化:而平均换热系数对泡沫金属孔径较敏感;对于低孔隙率泡沫金属,渗透率成为影响换热强度的主要因素,相同或接近的孔隙率下,孔径越大,渗透率和达西数越大,越有利于换热,且压损减小。     

Input Estimation Method in the Use of Electronic Device Temperature Prediction and Heat Flux Inverse Estimation

The input estimation method (IEM) is proposed in this research to estimate the real-time time-variant core heat flux of electronic components. The IEM is an on-line real-time estimation method, which combines the Kalman filter mechanism and recursive least-square estimation (RLSE). On the premise that there exists both system processing error and measurement error, using temperature measurements measured from the exterior of the device package, the core time-variant heat flux of the device can be precisely estimated inversely.     

Temperature-Invariant Scaling for Compressible Turbulent Boundary Layers with Wall Heat Transfer

In a recent paper by Zhang et al. in 2012, a Mach number-invariant scaling was proposed to account for the effect of variation of free-stream Mach number in supersonic turbulent boundary layers. The present work focuses on the effect of variation of wall temperature with strong heating and cooling at the wall. Direct numerical simulation is used to study scaling and turbulence structure of a spatially evolving Mach 2 supersonic boundary layer at a friction Reynolds number of 500. A new scaling law is proposed to account for temperature-dependent fluid-property variations. This universal scaling appears superior to the existing models with the novelty that it applies not only for the mean-velocity profile but also extends to the turbulent transport, production, and dissipation terms in the budget of the turbulent kinetic energy.     

燃烧室部件耦合系统过渡工况传热全仿真模拟研究

内燃机的起动、停车、加载等运行工况发生急剧变化（过渡工况）过程中,其燃烧室部位外于强烈地被加热或被冷却状态。这种热冲击增加了部件的动态疲劳热应力,给内燃机的可靠性带来严重恶果,是导致燃烧室部位破裂的主要原因之一。燃烧室部件的传热研究是热负荷计算和评定的基础,对内燃机的可靠性设计具有重要意义。作对燃烧室部件活塞组气缸套耦合系统在过渡工况下的耦合传热关系进行了较深入的研究,建立了描述这一传热过程的数学模型;并利用该模型,模拟了125风冷柴油机在各种过渡工况下的传热情况。     

A General Boundary Condition Treatment in Immersed Boundary Methods for Incompressible Navier-Stokes Equations with Heat Transfer

A general boundary condition scheme for incompressible flows over immersed bodies on Cartesian grids is developed to treat Dirichlet, Neumann, and Robin boundary conditions on the immersed surfaces. Various forced and natural convection problems over a circular cylinder and the nature convection between two concentric cylinders are computed to validate the proposed scheme. Results show that the method is second-order in L ₁ and L ₂ norms for velocity, pressure, and temperature for all three boundary conditions. The method is also second-order in L_∞ norm for Dirichlet boundary condition, while it is of the order of 1.4 in L_∞ norm when Neumann or Robin condition is applied.     

空气侧换热器结霜时传热与阻力特性研究

在质量、动量和能量守恒的基础上,采用分布参数法建立了空气侧换热器结霜时的动态数学模型,该模型耦合了结霜子模型和热交换子模型。利用该模型分析了不同温度和相对湿度下霜的厚度随时间的变化及结霜对空气侧换热器传热与阻力的影响。结果表明：在不同的工况下,空气侧换热器结霜情况不同;空气温度一定时,相对湿度越大,结霜越严重,融霜的时间间隔越短;随着结霜量的增加,换热器的换热量减小,风量也就逐渐减少,阻力却迅速增加。计算出了不同工况下融霜的时间间隔。     

Enhanced Transient Heat Transfer From Arrays of Jets Impinging on a Moving Plate

This article addresses the numerical analysis of single and multiple circular jets impinging perpendicularly on a flat plate for heating and cooling purposes. Computational fluid dynamics (CFD) is used to evaluate heat transfer calculations for different configurations and different flow boundary conditions. The commercial CFD package FLUENT is employed with various turbulence models. Results for a single jet are validated against experimental data. The SST k ? ω turbulence model is compared with the elliptic V2F model, and both were validated against experimental data. Results were obtained for a range of jet Reynolds numbers and jet-to-target distances. Optimization results for the single jet case are validated against experimental data. The SST k ? ω and V2F turbulence models succeeded with a reasonable accuracy (within 20% error) in reproducing experimental results. The heat transfer rates from the use of multijet configurations are discussed in the article. Transient heat transfer between multiple jets and a moving plate is more difficult to study due to the changing boundaries but is also very relevant in engineering applications. This article presents full CFD calculations of the transient heat transfer between a bank of circular jets and a moving plate. Design optimization has also been achieved for the single- and multiple-jet configurations.     

Numerical Investigation of Boundary Grid Effect on Heat Transfer Computation of RP-3 at Supercritical Temperature of Helical Tube Wall

To get reliable computational results,the RNG k-εturbulence model with enhanced wall treatment was validated to solve the heat transfer of supercritical RP-3 in a helically coiled tube,and models of the thermo-physical properties of RP-3 were optimally chosen.Most significantly,the grid independence was validated by two-step procedure,and the effect of boundary grids of the supercritical-temperature wall on the computational accuracy was well studied.Through adjusting boundary-layer girds’size,four regions (increased,pseudo-convergence,decreased and convergence) of the outlet temperature T_(out) were obtained and analyzed.The results showed that the maximum computation errors of T_(out) and the pressure differential between the inlet and outletΔP reached 20.65%and 98.15%,respectively,indicating that boundary grids have a significant influence on computation of flow and heat transfer.Based on this,a dimensionless distance from the wall-adjacent cell to the wall y~+=Pr_w~(-1/1.78)(Pr_w denotes Wall Prandtl number) was recommended as a convergence point.The variation laws of viscous length scale y~*were discussed under different structural parameters,operation parameters,and helical lengths.An explicit model of y~*was proposed to calculate the height (y) of the first boundary layer grids and refine boundary grids efficiently.A modified model for coefficient of friction factor C_(f )was proposed based on Rogers’s,and Nusselt number Nu was proposed based on an analogy of momentum and heat transfer.The above models about y~*,C_f and Nu could apply to both the entrance region and the whole tube length,and showed good performance when Reynolds number was extended to above 70 000,or whenever the outlet temperature is below or above the critical point.     

基于差分方法的边界延长形式对热传导实现过程的影响

针对200MW汽轮机转子的热传导实现过程,比较差分方法在两种不同外延边界的情况下,两种方法热传导的实现过程对转子一维径向上温度分布结果的影响。     

内燃机缸内积炭及进气涡流强度对局部瞬态传热的影响

通过实验研究了内燃机缸内积炭及进气涡流强度对局部瞬态传热的影响，并测量了气缸盖鼻梁区和活塞燃烧室表面的瞬态热流，结果表明燃烧室受热表面积炭层的存在对工质与燃烧室各零件间的瞬态传热表现出强的闭塞作用。