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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。 相似文献
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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。 相似文献
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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。 相似文献
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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. 相似文献
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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。 相似文献
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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。 相似文献
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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. 相似文献
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Analytical solution of the parabolic and hyperbolic heat transfer equations with constant and transient heat flux conditions on skin tissue 总被引:1,自引:0,他引:1
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. 相似文献
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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. 相似文献
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J. W. Howse G. A. Hansen D. J. Cagliostro K. R. Muske 《Numerical Heat Transfer, Part A: Applications》2013,63(1):23-44
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. 相似文献
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Sylwia Hozejowska Magdalena Piasecka Mieczyslaw E. Poniewski 《International Journal of Thermal Sciences》2009,48(6):1049-1059
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. 相似文献
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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. 相似文献
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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. 相似文献
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Nazia Afrin Yuwen Zhang J.K. Chen 《International Journal of Heat and Mass Transfer》2011,54(11-12):2419-2426
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. 相似文献
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A. Belmiloudi 《Journal of Dynamical and Control Systems》2007,13(2):217-254
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.
相似文献
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《International Communications in Heat and Mass Transfer》1997,24(2):161-170
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. 相似文献