马蹄形火焰玻璃熔窑燃烧空间流动与传热的数值模拟

对马蹄形火焰玻璃窑炉燃烧空间内的流动、燃烧及辐射传热等过程进行了数值模拟研究,得到了炉内燃烧空间的速度场、温度场、组分浓度分布及燃烧空间向玻璃液面传递的热流分布。探讨了燃烧空间入口的进气角度对炉内温度场和向玻璃面传递的热流的影响,模拟结果表明,当入口的进气角度在5°～10°之间时,传热效果较好。     

Thermal quadrupoles approach for two-dimensional heat flux estimation using infrared and thermocouple measurements on the JET tokamak

This paper presents several 2D heat flux calculation methods applied to temperature data of one of the most exposed plasma facing components of the JET tokamak. We have two temperature diagnostics: a high time resolution infrared system is used to measure the surface temperature and two embedded thermocouples to measure the temperature in the bulk at 1 cm depth from the surface. A direct calculation is possible using the surface temperature but the presence of thin carbon layers disturb the measurements and leads us to make an inverse computation of the heat flux using the thermocouple data.     

Determination of thermal contact resistance from transient temperature measurements

The temperature distribution in combustion engine components is highly influenced by thermal contact resistance. For the prediction and optimisation of the thermal behaviour of modern combustion engines knowledge about the contact heat transfer is crucial.Available correlations to predict the contact resistance are simplifications of the real geometric conditions and only tested for moderate pressures up to 7 MPa. Typical combustion engine applications include contact pressures up to 250 MPa.The experimental approach presented here to derive the thermal contact resistance in terms of contact heat transfer coefficients for high temperature and high pressure conditions is based on transient infrared temperature measurements. Two bodies initially at two different temperatures are brought in contact and the surface temperature histories are recorded with a high-speed infrared camera. The contact heat flux is calculated by solving the related inverse problem. From the contact heat flux and from the measured temperature jump at the interface the contact heat transfer coefficient is calculated.The inverse method used for the calculation of the heat flux is based on the analytical solution for a semi-infinite body and a step response to a Neumann boundary condition. This method provides an algorithm that is used in a sequential manner. The use of “future” temperature data greatly improve the stability of the governing equations and reduce the sensitivity to measurement errors.     

Local Heat Flux Investigation During Pool Boiling Single Bubble Cycles Under Reduced Gravity

In the present work the bubble diameter, heater surface temperature distribution, and local heat flux during different stages of single bubble cycles during pool boiling of PF-5060 at a pressure of p = 600 mbar have been investigated in several stable low g levels during the 1st Joint European Partial-g Parabolic Flight (JEPPF) Campaign. In previous parabolic flight campaigns, microgravity conditions were achieved by following a parabolic trajectory with the specially equipped A-300-Zero-G Aircraft. In this recent JEPPF campaign, the parabolic trajectories were slightly shifted, to establish—apart from microgravity conditions—also stable gravity levels of 0.16 g (lunar gravity) and 0.38 g (Martian gravity). High-resolution measurements of the heater surface temperature were performed using high-speed infrared thermography. An infrared (IR)-transparent sputtered heater design was employed in order to allow temperature measurements by IR thermography at a distance of approximately 800 nm to the heater/fluid interface. From the acquired temperature data, the local heat flux distribution was calculated numerically. Bubble shape and interaction were recorded with a high-speed black-and-white camera. In contrast to previous investigations, the stable low gravity levels enabled performance of measurements during single bubble (ebullition) cycles without the influence of residual flows induced by boiling under a different gravity level, as is the case in the beginning of a regular microgravity parabola. The accuracy of the measurement technique could be drastically enhanced compared to earlier publications. A local temperature drop and corresponding heat flux peak have been observed close to the three-phase contact line.     

Characterisation of the spray cooling heat transfer involved in a high pressure die casting process

A systematic experimental study was conducted to examine the heat transfer characteristics from the hot die surface to the water spray involved in high pressure die casting processes. Temperature and heat flux measurements were made locally in the spray field using a heater made from die material H-13 steel and with a surface diameter of 10 mm. The spray cooling curve was determined in the nucleate boiling, critical heat flux, as well as the transition boiling regimes. The hydrodynamic parameters of the spray such as droplet diameters, droplet velocities, and volumetric spray flux were also measured at the position in the spray field identical to that of the test piece. Droplet size and velocity distribution were measured using a PDA system. A new empirical correlation was developed to relate the spray cooling heat flux to the spray hydrodynamic parameters such as liquid volumetric flux, droplet size, and droplet velocity in all heat transfer regimes. The agreement between experimental data and predicted results is satisfactorily good.     

Simulation and validation of radiative transfers in urbanised areas

The energy balance at the soil-atmosphere interface is the fundamental equation to simulate the microclimate of urban areas. It implies the equilibrium of several energetic terms, such as: radiation (in the solar and infrared wavelengths), conduction (soil heat flux), convection (sensible heat flux) and evapotranspiration (latent heat flux). This article deals with the 3D-numeric simulation of heat transfers in an urban canyon and the validation of the appropriate algorithms and results. The simulation procedure and parameterisation of the surface elements are briefly described. All the heat transfer algorithms are taken from the existing literature. Among the mechanisms, the terrestrial infrared radiation is the most difficult term to be simulated, because realistic surface temperatures must be obtained. For this reason, at each time step, a special iterative treatment is applied to solve the energy balance equation until complete stabilisation of the surface temperatures. As a result, the simulation model is able to give all the components of the energy balance equation for every mesh. The aim of the paper is to demonstrate the validity of this approach by comparing the simulation results with the experimentation. The reliability of the simulated radiative fluxes is judged against a data set specially acquired during a dedicated experimental campaign that took place in an urban canyon of a French city (Strasbourg) during summer 2002.     

用不同模型研究炉壁黑度对炉膛内热交换的影响

给出了加热炉和锅炉炉膛内炉气分别为灰体和非灰体的零维段法模型,并用这些模型分别研究了加热炉和锅炉内炉壁黑度变化对炉内热交换的影响。结果表明,当假设加热炉内的炉气为灰体时,无论炉壁是否为辐射绝热面,金属所得的热流都不随炉壁黑度的变化而变,但当加热炉内的炉气为非灰气体时,金属所得的热流随炉壁黑度的增大而增加,这与高辐射率涂料在加热炉上的应用实践是一致的。当炉气温度为定值时,锅炉内的炉壁温度随壁炉黑度的增大而升高,而炉壁吸热量不随炉壁黑度的变化而变。图5参7     

循环流化床锅炉水冷壁的热流密度分布

超临界循环流化床锅炉的一个主要技术关键是炉膛受热面的横向热流分布.在管内工质温度不同、容量不同的3台循环流化床锅炉上,测量了不同高度上膜式水冷壁的金属壁温.将有限元算法用于水冷壁的换热分析,得到了循环流化床锅炉炉膛内烟气向水冷壁的换热系数分布.该结果为超临界CFB锅炉的设计提供了依据.     

The Inverse Reconstruction of the Heat Transfer Coefficient for the Free Surface Water Jet

This article presents an application of inverse algorithm for reconstruction of heat transfer coefficient (HTC) for a water jet impinging a flat surface. Such an approach, allows for decoupling complex fluid flow from heat conduction in a solid impinged by jet. The approach starts with parameterization of a functional form of unknown boundary temperature and heat flux occurring at the fluid–solid interface. Later, Newton's law of cooling is used to force temporal invariability of HTC. Unknown coefficients of HTC distribution are determined from a least square fit between measured and computed temperatures. Temperatures entering the objective function are recorded by an infrared camera at the surface opposite to impinged one.     

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。     

Thermal response of a flat heat pipe sandwich structure to a localized heat flux

The temperature distribution across a flat heat pipe sandwich structure, subjected to an intense localized thermal flux has been investigated both experimentally and computationally. The aluminum sandwich structure consisted of a pair of aluminum alloy face sheets, a truncated square honeycomb (cruciform) core, a nickel metal foam wick and distilled water as the working fluid. Heat was applied via a propane torch to the evaporator side of the flat heat pipe, while the condenser side was cooled via natural convective and radiative heat transfer. A novel method was developed to estimate experimentally, the heat flux distribution of the torch on the evaporator side. This heat flux distribution was modeled using a probability function and validated against the experimental data. Applying the estimated heat flux distribution as the surface boundary condition, a finite volume analysis was performed for the wall, wick and vapor core regions of the flat heat pipe to obtain the field variables in these domains. The results were found to agree well with the experimental data indicating the thermal spreading effect of the flat heat pipe.     

Flow and heat transfer during a single drop impact on a liquid film

ABSTRACT

A two-dimensional incompressible laminar computational model was established to analyze flow and heat transfer characteristics during a single liquid drop impinging onto a liquid film, with an underneath surface of relatively low temperature. Using the coupled level set and volume of fluid method, the gas–liquid interface at different time sequences can be obtained clearly. Concerning the heat transfer process, three different factors including impact velocity, film thickness, and drop diameter were discussed. Results indicate that liquid inside the film can be classified as three zones: the impact zone, the transition zone, and the static zone, specifically according to different heat flux. Average surface heat flux can be increased by increasing impact velocity, while effects of film thickness and drop diameter are minor. Corresponding mechanisms were interpreted as well. For heat flux distribution in the impact and transition zones, both film thickness and drop diameter influence the distribution greatly. With an increment in film thickness and drop diameter, heat flux in the impact zone decreases, while heat flux in the transition zone appears to be an opposite trend. Also in the transition zone, the fluctuation amplitude of the heat flux rises as the two factors are reduced.     

Turbulent film condensation in the presence of non-condensable gases over a horizontal tube

A numerical model is presented for studying turbulent film condensation in the presence of non-condensable gases over a horizontal tube. Inertia, pressure gradient are included in this analysis, and the influence of turbulence in the proposed two-phase model is considered. The numerical results demonstrate that a very small bulk concentration of non-condensable gas reduces the heat transfer coefficient and film thickness considerably. The local heat flux and film thickness increase as tube surface temperature decreases at any bulk concentration of non-condensable gas. Moreover, inlet velocity increases as film thickness decreases and heat flux increases, a numerical result in agreement with that obtained by Nusselt. Numerical results indicate that average dimensionless heat transfer coefficients are in good agreement with theoretical and experimental data.     

Validated Numerical Analysis of CaSO4 Fouling

In scaling experiments, the formation of fouling layers on heat transfer surfaces usually proceeds in a non-uniform manner. The result is a non-uniform layer, and hence a varying thermal resistance over the area covered with scale. Consequently, a non-uniform heat flux distribution results over the heat transfer surface. To evaluate the changes in the heat flow distribution resulting from a non-uniform scale layer, numerical calculations have been performed using a case where CaSO₄ scales form on a heated copper plate subjected to a shear flow. The calculated heat flux is used to calculate fouling resistances from measured temperatures. The results of the numerical calculations confirm that a non-uniform heat flux distribution occurs over the surface when the plate is partially covered with scale. Further, it is seen that the heat flux, the surface temperature, and the driving force all decrease with increase in scale accumulation.     

Experimental and theoretical investigation of surface temperature non-uniformity of spray cooling

In this study, a test system for spray cooling, in which the heating surface temperatures were simultaneously measured by thermocouples and an infrared imager, was set up. A mathematical model of spray cooling heat transfer characteristics was presented based on the fundamentals of dynamics and heat transfer. The temperature distribution on the heating surface was investigated by the experimental and theoretical methods, the surface temperature non-uniformity and its influencing factors were analyzed. The predictions by the model coincided with the experimental results well, and a comparison was demonstrated with a deviation below 10%. It can be concluded that the surface temperature non-uniformity is influenced by the spray characteristics, nozzle-to-surface distance, inlet pressure, heat flux, spray angle and the system pressure. In the case of the same heat flux, the surface temperature non-uniformity can be reduced by the small spray angle, low system pressure, low nozzle-to-surface distance, and the high inlet pressure.     

Estimation of front surface temperature and heat flux of a locally heated plate from distributed sensor data on the back surface

We present a new method of solving the three-dimensional inverse heat conduction (3D IHC) problem with the special geometry of a thin sheet. The 3D heat equation is first simplified to a 1D equation through modal expansions. Through a Laplace transform, algebraic relationships are obtained that express the front surface temperature and heat flux in terms of those same thermal quantities on the back surface. We expand the transfer functions as infinite products of simple polynomials using the Hadamard Factorization Theorem. The straightforward inverse Laplace transforms of these simple polynomials lead to relationships for each mode in the time domain. The time domain operations are implemented through iterative procedures to calculate the front surface quantities from the data on the back surface. The iterative procedures require numerical differentiation of noisy sensor data, which is accomplished by the Savitzky–Golay method. To handle the case when part of the back surface is not accessible to sensors, we used the least squares fit to obtain the modal temperature from the sensor data. The results from the proposed method are compared with an analytical solution and with the numerical solution of a 3D heat conduction problem with a constant net heat flux distribution on the front surface.     

Effect of gas radiation on radiative heat transfer in urban street canyon model

In this paper, we describe the results of numerical simulation of radiative heat transfer between the human body and an urban street canyon (building walls, pavement, and the sky) in the presence of participating non‐gray gas mixtures consisting of H₂O and CO₂. The ambient temperature in typical summer conditions and the concentration of gas mixtures during summer in Tokyo were assumed. Further, the parallel infinite plane model and simple urban street canyon model were used. The results show that the participating gas significantly affects the infrared radiation field in an urban street canyon. The radiation flux emitted by the participating gas is approximately 35% of the total radiation flux incident on the human body surface. This causes a homogenization of the infrared radiation field surrounding the human body. Gas radiation plays an important role in the heat transfer between the human body and the environment under hot and humid summer conditions. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20258     

Two‐phase flow convective condensation of refrigerant mixtures under gas/liquid injection

The influence of gas/liquid injection on two‐phase flow condensation heat transfer characteristics of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow condensation inside enhanced surface tubing. The data also revealed that gas, liquid and gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the condensation point of the refrigerant mixtures in question. It was also evident that the proposed condensation correlations and the experimental data were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ± 10, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

10 mm钢化玻璃全尺寸火灾实验

在ISO 9705标准燃烧室内,位于室中央,采用不同规模的油池火,对常用的厚10mm钢化玻璃窗的火灾特性进行了全尺寸火灾实验研究,完成了8组实验.给出了包括热释放速率、热辐射通量、室内和玻璃附近气体温度分布、玻璃暴露表面温度、玻璃遮蔽表面温度、玻璃首次破裂时间和破裂模式等实验数据.分析了玻璃破裂与其表面温度分布等参数的关系,研究结果可为性能化防火设计中评估钢化玻璃发生破裂和失效提供参考.     

Duhamel integral form for the interface heat flux between bubble and liquid

The solution of heat equation inside oscillating gas bubble with moving boundary was obtained by Fourier’s method. The integral formula for interface heat flux, containing theta-function in the integrand was derived. The kernel of the integral is represented by a series of exponential functions, and a simple analytic approximation obtained earlier is used for it with high accuracy. The asymptotic expression for the interface heat flux in the Duhamel integral form with rooted kernel was derived.The vapor bubbles were also considered. In this case the major problem is external heat problem in liquid. It is shown that the asymptotic expression for the heat flux at the interface in the case of gas bubbles has the similar structure as the heat flux from the vapor bubble surface to the liquid. In both cases it is Duhamel integral with rooted kernel.