近地倾斜轨道航天器在轨热辐射分析

根据航天器轨道动力学和热辐射理论，建立了运行于近地倾斜轨道的圆柱形航天器外热流数学模型；用数值方法对外热流和等效热沉温度进行求解，计算出瞬态工况及周期平均工况下的航天器表面辐射热流及辐射散热器和防辐射涂层表面等效热沉温度的波动。结果表明，航天器受到的辐射热流除了随航天器绕地球公转变化外，还随其轨道面的旋转在更长的周期上产生更大的变化；对柱面上的不同位置受到的辐射作了比较，发现辐射散热器布置在顶部时其等效热沉温度最低。     

含相变材料双层玻璃窗光热分析模型

建立了含相变材料双层玻璃窗的光热传输模型,考虑相变材料和玻璃半透明特性,采用有限差分求解方程。在通过实验数据验证模型准确的基础上,分析了相变材料的融化温度对含相变材料双层玻璃窗光热性能的影响。结果显示:建立的模型可模拟相变材料双层玻璃窗的光热传输过程;随融化温度升高,含相变材料双层玻璃窗温度衰减因子则逐渐增大,相变材料融化时间延后,相变材料呈液态的时间变短,但温度滞后值、热流密度和太阳透射能则呈不规则变化。     

低散热发动机表面传热研究的一种新方法

本文探索了一种低散热发动机陶瓷涂层表面传热的实验研究方法─—表面温度法。通过实测低散热发动机燃烧室陶瓷涂层表面的瞬态温度与平均热流，可较准确地计算低散热发动机陶瓷涂层表面的局部瞬态热流。文中着重介绍了陶瓷涂层表面瞬态热流的具体求解方法。     

低散热发动机表面传热研究的一种新方法

本文探索了一种低散热发动机陶瓷涂层表面传热的实验研究方法－表面温度法。通过实测低散热发动机燃烧室陶瓷涂层表面的瞬态温度与平均热流，可较准确地计算低散热发动机陶瓷涂层表面的局部瞬态热流。文中着重介绍了陶瓷涂层表面瞬态热流的具体求解方法。     

动力电池内部温度梯度反演计算

电池在充放电过程中内部温度的分布特征对于锂离子电池热管理系统的设计十分重要。根据电池的物理结构,将圆柱型电池内部平均分成若干等温层,建立了电池沿径向的产热和传热模型,将测试获得的电池表面温度和热流密度作为边界条件,假设热量从中心向外传递过程中等温层之间的热流密度线性增加,提出了一种计算电池沿径向内部温度分布的方法,并在电池内部中心放置热电偶,验证了该方法的准确性。计算结果表明,电池内部温度并非线性分布,在靠近电池中心位置处相邻等温层之间的温度梯度较小,而在靠近电池表面区域附近相邻等温层之间的温度梯度较大。该计算方法在20～40 ℃环境温度区间内具有较高的精度,而在−10 ℃环境温度下误差会偏大些。     

变热流下透明可燃物热解着火的影响机理分析

着火时间是可燃物热解着火过程的重要特征参数.辐射热流直接影响可燃物的着火时间,为了简化解析求解,前人往往认为辐射热流为恒定常数且不进入样件内部,但火灾发生早期,透明可燃物接收到的辐射热流可能是随着时间上升的变化热流.针对此问题,本文以适用于变化辐射热流的透明可燃物热解数值和解析模型为基础,系统研究了辐射热流上升速度、表面吸收、内部吸收等因素对着火时间的影响,比较了两种模型的结果差异并探讨了环境与物性参数对解析模型准确性的影响.结果表明:在上升热流早期,解析法与数值法求解结果符合较好,随着热流与表面温度增加,表面对流换热、辐射、热解等因素开始作用,导致解析与数值结果出现偏差,需根据此偏差修正给定可燃物着火时间解析预测结果.     

叶片热障涂层结构内的非定常传热效应

在热冲击与脉动热流边界条件下,应用数值方法求解一维非傅立叶导热方程,分析双层结构热障涂层内的一维非定常传热特性。计算模型引入壁面曲率修正,考虑了涡轮叶片表面的型线曲率影响。分析结果表明:涂层材料热松弛时间的长短是瞬态传热特性的决定因素。边界受瞬态冲击热流条件下,涂层内的温度分布在10倍的松弛时间后达到平衡分布。边界热流脉动周期与松弛时间相当时,涂层内热流出现了波状传输,热障涂层内的温度呈波状分布。非傅立叶导热方程预测的温度交变厚度大于抛物型方程预测的厚度,显示了高频热流作用下,涂层材料可能发生疲劳破坏。叶片表面的的凸形曲率以指数率形式,增强了涂层内温度波幅度,解释了叶片前缘等处涂层易出现裂纹的现象。     

110 kV单芯电缆缆芯暂态温度径向感知模型研究

为了实现基于电缆表面温度测量的电缆缆芯暂态温度实时反演,本文首先分析电缆内部径向热流扩散路径特点,建立了电缆各层结构的热阻热容集中参数等效模型,并分析热路等效模型的误差影响因素。其次开展110 kV单芯电缆本体暂态温度场有限元仿真计算,分析了交联聚乙烯绝缘层分层建模的必要性,并确定分层数量。最后分析了材料参数的分散性对径向感知模型反演精度的影响。研究表明,本文提出的暂态温度径向感知模型具有较高的反演精度,可应用于各种工况下缆芯温度的实时监测。     

研究柴油机传热的表面温度法

本文介绍了一种柴油机燃烧室瞬态传热的实验研究方法——表面温度法。通过实测柴油机燃烧室表面的瞬态温度与平均热流,较准确地确定柴油机燃烧室局部表面的瞬态热流。文中从理论和实测两个方面分析了作者研制的表面瞬态温度传感器——薄膜热电偶的动态特性,介绍了柴油机燃烧室表面瞬态温度与传热的研究工作。     

一体式再生燃料电池温度和热流密度非原位同步测量

一体式再生燃料电池的热流密度和温度分布的研究对电池热管理具有重要的意义。本文将自制的薄膜传感器植入一体式再生燃料电池中,进行非原位实验研究。在给定不同气体预热温度下,测量了一体式再生燃料电池内部热流密度和局部温度,并根据已得到的温度和热流密度计算出局部表面传热系数。结果表明,在不同的气体预热温度下,流道内气体的温度和气体扩散层表面的温差维持在3℃左右。气体扩散层表面的热流密度整体呈现出下降的趋势。靠近加热棒处的温度最高,但热流密度最低。相同的气体预热温度下,流道内气体和气体扩散层表面的温差对换热量的影响要大于温度梯度的影响;气体预热温度的上升对表面传热系数h的影响不大。30℃时,表面传热系数h值在450 ~ 750 W/(m²?K) 之间。40℃时,表面传热系数h在450 ~ 650 W/(m²?K)之间。     

NUMERICAL STUDY ON 3-D LIGHT AND HEAT TRANSPORT IN BIOLOGICAL TISSUES EMBEDDED WITH LARGE BLOOD VESSELS DURING LASER-INDUCED THERMOTHERAPY

Tissue vasculature plays an important role in the temperature responses of biological bodies subject to laser heating. For example, interfaces between blood vessel and its surrounding tissues may lead to reflection or absorption of the coming laser light. However, most of the previous efforts just treat this by considering a collective model. To date, little attention has been paid to the effect of a single blood vessel on tissue temperature prediction during laser-induced thermotherapy. To resolve this important issue in clinics, we propose to simultaneously solve the three-dimensional (3-D) light and heat transport in several typical tissue domains with either one single blood vessel or two countercurrent blood vessels running through. Both surface and intervenient laser irradiations are considered in these studies. The 3-D heat transfer and blood flow models are established to characterize the temperature transients over the whole area. Coupled equations for heat and blood flow in multiple regions are solved using the blocking-off method. In particular, the Monte Carlo method is introduced to calculate the light transport inside the tissues as well as the blood vessel. Theoretical algorithms to deal with the complex interfaces between the tissues and vessels, and the tissue–air interface, are given. The heat generation pattern due to absorption of laser light is thus obtained by Monte Carlo simulation and then adopted into the heat and flow transport equations to predict the 3-D temperature transients over the whole domain. It is demonstrated that without considering large-size blood vessels inside the tissues, a very different temperature response is induced when subject to the same laser heating. Detailed temperature developments for the aforementioned vessel configurations are comprehensively analyzed. Implementation of the laser irradiation pattern to the clinical practices is discussed. We also test the effects of the buoyancy-driven blood flow due to laser heating on the tissue temperature response. This study may raise new issues to evaluate the contribution of a single blood vessel in modeling laser–tissue interaction. Such information is expected to be critical for accurate treatment planning in clinics.     

Analytical solution of the parabolic and hyperbolic heat transfer equations with constant and transient heat flux conditions on skin tissue

In this article, the parabolic (Pennes bioheat equation) and hyperbolic (thermal wave) bioheat transfer models for constant, periodic and pulse train heat flux boundary conditions are solved analytically by applying the Laplace transform method for skin as a semi-infinite and finite domain. The bioheat transfer analysis with transient heat flux on skin tissue has only been studied by Pennes equation for a semi-infinite domain. For modeling heat transfer in short duration of an initial transient, or when the propagation speed of the thermal wave is finite, there are major differences between the results of parabolic and hyperbolic heat transfer equations. The non-Fourier bioheat transfer equation describes the thermal behavior in the biological tissues better than Fourier equation. The outcome of transient heat flux condition shows that by penetrating into the depths beneath the skin subjected to heat, the amplitude of temperature response decreases significantly. The blood perfusion rate can be predicted using the phase shift between the surface temperature and transient surface heat flux. The thermal damage of the skin is studied by applying both the parabolic and hyperbolic bioheat transfer equations.     

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.     

SOLVING A THERMAL REGENERATOR MODEL USING IMPLICIT NEWTON-KRYLOV METHODS

Laser tissue welding and soldering with use of short laser pulses are proposed. The transient radiation heat transfer in the picosecond time scale is numerically investigated for the first time using the discrete ordinate method for cylindrical geometries. The numerical method developed incorporates the propagation of radiation with the speed of light. The temporal radiation fields of tissue cylinders under the irradiation of short laser pulses are obtained. The use of short laser pulses for tissue welding and soldering is found to have reduced thermal damage to the healthy tissue and improves the uniformity of heating in the tissue closure region in both the depth and radial directions. The addition of absorbing solders in tissue soldering results in a well-confined radiation energy deposition field in the proximity of the solder-stained region and lessens the outgoing radiative heat flux at the laser incident surface. Comparisons of radiation heat transfer are made between the spatially square-variance and Gaussian-variance laser inputs and between the temporally Gaussian-profile and skewed-profile pulses, respectively.     

Estimation of exhaust gas temperature of the rocket nozzle using hybrid approach

In this paper the theoretical model is built for ZEpHyR (ZARM Experimental Hybrid Rocket) main engine which is being developed at ZARM institute, Bremen, Germany. The theoretical model is used to estimate the temperature of exhaust gas. The Conjugate Gradient Method (CGM) with Adjoint Problem for Function Estimation iterative technique is used to solve the Inverse Heat Conduction Problem (IHCP) to estimate the heat flux and internal wall temperature at the throat section of the nozzle. Bartz equation is used to calculate the convective heat transfer coefficient. The exhaust gas temperature is determined using the estimated heat flux, the wall temperature at internal surface of nozzle and the heat transfer coefficient. The accuracy of CGM iterative scheme to solve the IHCP is also investigated and its results are presented.     

Boiling heat transfer in vertical minichannels. Liquid crystal experiments and numerical investigations

The paper presents the results of experimental and numerical studies of boiling heat transfer in the flow of refrigerants R123 and R11 through vertical, rectangular minichannels, with one wall heated. An application of liquid crystal thermography has helped detect two-dimensional temperature distribution on the heating surface, allowing determination of boiling heat fluxes and experimental boiling curves. The main objectives of the paper included the development of two-dimensional approach to solve the inverse heat conduction boundary problem for determining local values of internal heating surface temperature, boiling heat flux and heat transfer coefficient, and the improvement of the applied numerical method making use of the equalizing calculus and heating surface temperature measurement errors. A detailed discussion of temperature, heat flux and heat transfer coefficient errors is also provided.     

Evaporation heat transfer of liquid nitrogen on microstructured surface at high superheat level

Liquid nitrogen, as a coolant, is generally applied in cell vitrification cryopreservation. It takes heat from the carrier with cell samples through its violent evaporation on the carrier surface. As a result, the temperature of the carrier plunges dramatically. This article focuses on the unsteady evaporation heat transfer characteristics of liquid nitrogen on a microstructured surface etched into the frozen carrier surface at a high superheat level. The heat flux and evaporation heat transfer coefficient of liquid nitrogen were investigated using a lumped capacitance method. The experimental results showed that the cooling rate of the thin film evaporation on the microstructured surface is obviously higher than that of pool boiling, which is currently being used for cell cryopreservation. The heat flux and the evaporation heat transfer coefficient work together to present a parabolic trend with the superheat decreasing during this heat transfer process. Besides, the microstructure of the surface has an important effect on the evaporation heat transfer of liquid nitrogen. The larger the thin film evaporation zone is, the higher the heat transfer coefficient is. The current investigation results in a cell cryopreservation method through vitrification with relatively low concentrations of cryoprotectants.     

Thermal lagging in living biological tissue based on nonequilibrium heat transfer between tissue,arterial and venous bloods

Arterial, venous blood and solid tissue are the three energy carriers that contribute to heat transfer in the living biological tissues. A generalized dual-phase lag mode for living biological tissues based on nonequilibrium heat transfer between tissue, arterial and venous bloods is presented in this paper. The phase lag times for heat flux and temperature gradient only depend on properties of artery, vein and tissue, blood perfusion rate and convective heat transfer rate and are estimated using the available properties from the literature. It is found that the phase lag times for heat flux and temperature gradient are the identical for the case that the tissue and blood have the same properties. However, the phase lag times are different for the case that the properties of tissue and bloods are different. The phase lag times for brain and muscles are also discussed.     

Determination of temperature distributions on the rake face of cutting tools using a remote method

Cutting temperature is a major factor in controlling the tool wear, surface quality, and chip formation mechanics. To understand the exact temperature rise in the tool-chip interface has been recognized as an important study in achieving the best cutting performance. For the above reason, an inverse estimation of the heating history on the rake face of cutting tool is presented in this paper. The first stage of the analysis is to solve a heat transfer model of cutting tool with three-dimensional boundary element method. This is a direct heat transfer problem. Furthermore, the inverse heat transfer technique of sequential estimation is employed to simulate the time histories of heat fluxes at the rake face based on the measured temperature responses on the tool measuring point. The present model can be used not only to determine the part of heat flux conducting into the cutting tool but also the temperature contours on the tool-chip interface.     

Analysis of the Impact of Nonlinear Heat Transfer Laws on Temperature Distribution in Irradiated Biological Tissues: Mathematical Models and Optimal Controls

In this paper, we consider nonlinear control problems governed by some generalized transient bioheat transfer-type models with the nonlinear Robin boundary conditions. The control estimates the blood perfusion rate, the heat transfer parameter, the distributed energy source terms, and the heat flux due to the evaporation, which affect the effects of thermal physical properties on the transient temperature of biological tissues. The result can be very beneficial for thermal diagnostics in medical practices, for example, for laser surgery, photo and thermotherapy for regional hyperthermia often used in treatment of cancer. First, the mathematical models are introduced and the existence, uniqueness, and regularity of a solution of the state equation are proved as well as the stability and maximum principle under extra assumptions. Afterwards, the optimal control problem is formulated in order to control the online temperature given by radiometric measurement. We prove that an optimal solution exists and obtain necessary optimality conditions. Some strategy for numerical realization based on the adjoint variables are provided.