共查询到20条相似文献,搜索用时 0 毫秒
1.
Jerry G. Myers Sam W. Hussey Jungho Kim 《International Journal of Heat and Mass Transfer》2005,48(12):2429-2442
The lack of time and space resolved measurements under nucleating bubbles has complicated efforts to fully explain pool-boiling phenomena. In this work, time and space resolved temperature and heat flux distributions under nucleating bubbles on a constant heat flux surface were obtained using a 10 × 10 microheater array with 100 μm resolution along with high-speed images. A numerical simulation was used to compute the substrate conduction, which was then subtracted from the heater power to obtain the wall-to-liquid heat transfer. The data indicated that most of the energy required for bubble growth came from the superheated layer around the bubble. Microlayer evaporation and contact line heat transfer accounted for not more than 23% of the total heat transferred from the surface. The dominant heat transfer mechanism was transient conduction into the liquid during bubble departure. Bubble coalescence was not observed to transfer a significant amount of heat. 相似文献
2.
M. Mohammadiun A.B. Rahimi I. Khazaee 《International Journal of Thermal Sciences》2011,50(12):2443-2450
In this paper, the conjugate gradient method coupled with adjoint problem is used in order to solve the inverse heat conduction problem and estimation of the time-dependent heat flux using the temperature distribution at a point. Also, the effects of noisy data and position of measured temperature on final solution are studied. The numerical solution of the governing equations is obtained by employing a finite-difference technique. For solving this problem the general coordinate method is used. We solve the inverse heat conduction problem of estimating the transient heat flux, applied on part of the boundary of an irregular region. The irregular region in the physical domain (r,z) is transformed into a rectangle in the computational domain (ξ,η). The present formulation is general and can be applied to the solution of boundary inverse heat conduction problems over any region that can be mapped into a rectangle. The obtained results for few selected examples show the good accuracy of the presented method. Also the solutions have good stability even if the input data includes noise and that the results are nearly independent of sensor position. 相似文献
3.
Patricia L. Ricketts Ashvinikumar V. Mudaliar Brent E. Ellis Clay A. Pullins Leah A. Meyers Otto I. Lanz Elaine P. Scott Thomas E. Diller 《International Journal of Heat and Mass Transfer》2008,51(23-24):5740-5748
Non-invasive blood perfusion measurement systems have been developed and tested in a phantom tissue and an animal model. The probes use a small sensor with a laminated flat thermocouple to measure the heat transfer and temperature response to an arbitrary thermal event (convective or conductive) imposed on the tissue surface. Blood perfusion and thermal contact resistance are estimated by comparing heat flux data with a mathematical model of the tissue. The perfusion probes were evaluated for repeatability and sensitivity using both a phantom tissue test stand and exposed rat liver tests. Perfusion in the phantom tissue tests was varied by controlling the flow of water into the phantom tissue test section, and the perfusion in the exposed liver tests was varied by temporarily occluding blood flow through the portal vein. The phantom tissue tests indicated that the probes can be used to detect small changes in perfusion (0.005 ml/ml/s). The probes qualitatively tracked the changes in the perfusion of the liver model due to occlusion of the portal vein. 相似文献
4.
Daniel Weisz-Patrault Alain Ehrlacher Nicolas Legrand 《International Journal of Heat and Mass Transfer》2012,55(4):629-641
Knowledge of the temperature field in the roll is a critical factor of modern, high-speed rolling mills. In this paper, an inverse analytical method is developed to determine the temperature field and especially the temperature (and heat flux) at the surface of the roll by measuring the temperature with a thermocouple (fully embedded) at only one point inside the roll. Iterative methods are not studied because short computation times are desired. Some assumptions are done to resolve analytically the unsteady heat equation, taking into account the restrictions of the measurement system (e.g., measurement according to successive times). The solution is validated by comparing the outputs of the method and prescribed analytical temperature fields. Good agreement is obtained. Noise sensitivity is estimated by adding artificial random numbers to the inputs. Good accuracy is observed. A 10% error of the temperature sensor depth is also considered and does not compromise the method. On the other hand, the computation time (around 0.05 s by cycle) is studied to rapidly optimise the industrial parameters during the rolling process. 相似文献
5.
Axial temperature distributions of a thermal energy storage (TES) system under variable electrical heating have been investigated. An electrical hot plate in thermal contact with a hollow copper spiral coil through which the oil flows simulates a solar collector/concentrator system. The hot plate heats up the oil which flows through the storage thus charging the TES system at a constant controlled temperature. The Schumann model and the modified Schumann model for the dynamic temperature distributions in the TES system are implemented in Simulink. The simulated results are compared with experimental results during the charging and discharging of the TES system. The Schumann model is in close agreement with experiment at lower TES temperatures during the early stages of the charging process. However, larger deviations between experiment and simulation are seen at later stages of the charging process and this is due to heat losses that are unaccounted for. The modified Schumann model is in closer agreement with experiment at later stages of the charging process. The discrepancies between experiment and simulation are also discussed. Discharging simulation results using both models are comparable to the experimental results. 相似文献
6.
《International Journal of Heat and Mass Transfer》2007,50(11-12):2060-2068
In this paper, we present an inverse method, an input estimation method, to recursively estimate both the time varied heat flux and the inner wall temperature in the chamber. The algorithm includes the use of the Kalman filter to derive a regression model between the biased residual innovation and the heat flux through a given heat conduction state space model. Based on this regression model, the Recursive Least Squares Estimator (RLSE) is proposed to extract the time-varying heat flux on-line as the input. Computational results show that the proposed method exhibits a good estimation performance and highly facilitates practical implementation. 相似文献
7.
Tsung-Chien Chen Chiun-Chien Liu 《International Journal of Heat and Mass Transfer》2008,51(13-14):3571-3581
During the missile flight, the jet flow with high temperature comes from the heat flux of propellant burning. An enormous heat flux from the nozzle throat-insert inner contour conducted into the nozzle shell will degrade the material strength of nozzle shell and reduce the nozzle thrust efficiency. In this paper, an on-line inverse method based on the input estimation method combined with the finite-element scheme is proposed to inversely estimate the unknown heat flux on the nozzle throat-insert inner contour and the inner wall temperature by applying the temperature measurements of the nozzle throat-insert. The finite-element scheme can easily define the irregularly shaped boundary. The superior capability of the proposed method is demonstrated in two major time-varying estimation cases. The computational results show that the proposed method has good estimation performance and highly facilitates the practical implementation. An effective analytical method can be offered to increase the operation reliability and thermal-resistance layer design in the solid rocket motor. 相似文献
8.
9.
Eric Forrest Erik Williamson Jacopo Buongiorno Lin-Wen Hu Michael Rubner Robert Cohen 《International Journal of Heat and Mass Transfer》2010,53(1-3):58-67
Nanoparticle thin-film coatings applied to boiling surfaces using a layer-by-layer (LbL) assembly method demonstrated significant enhancement in the pool boiling critical heat flux (CHF) and nucleate boiling heat transfer coefficient. Up to 100% enhancement of the critical heat flux and over 100% enhancement of the heat transfer coefficient were observed for pool boiling of nickel wires coated with different thin-films of silica nanoparticles. Surface characterization revealed that the surface wettability changed drastically with the application of these coatings, while causing virtually no change in the surface roughness. It is concluded that the nanoporous structure coupled with the chemical constituency of these coatings leads to the enhanced boiling behavior. 相似文献
10.
11.
Yoshimichi Hagiwara Daichi Yamamoto 《International Journal of Heat and Mass Transfer》2012,55(9-10):2384-2393
Experiments have been conducted on the unidirectional freezing of dilute aqueous solutions of winter flounder antifreeze protein, which are 0.02 mm thick, between two cover glasses on the stage of a microscope. The instantaneous temperature field has been obtained by measuring the intensity of near-infrared light with a near-infrared camera. In addition, the local protein concentration has been measured separately using the brightness of fluorescence emitted from molecules tagged to the protein. It is found that the temperature distribution in the ice region near the ice/water interface is similar to that predicted from the modified Neumann solution. Furthermore, the temperature measurement made using the near-infrared light with a specific wavelength is verified. In addition to this, in the case of antifreeze protein solutions, serrated interfaces are observed. The sum of the conduction heat flux of a protein solution near the front edge of the serrated interface and the heat flux for solidification is lower than the conduction heat flux of ice. On the other hand, the sum of the conduction heat flux of protein solution near the bottom edge of the serrated interface and the heat flux for solidification is higher than the conduction heat flux of ice. The balance of heat flux is obtained by taking account of heat convection due to high-concentration regions of protein. These regions move to the deepest parts of the interface and form narrow liquid regions inside the ice. The convection is maintained by the heat conduction in a direction perpendicular to the direction of ice growth. Not only protein adsorption to the interface but also the heat conduction/convection contributes to the modification of ice growth in the non-equilibrium state. 相似文献
12.
Mohammad M. Mansoor Kok-Cheong Wong Mansoor Siddique 《International Communications in Heat and Mass Transfer》2012
A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing single-phase flows. The numerical code was validated by comparison with previous experimental and numerical results for the same micro-channel dimensions and classical correlations based on conventional sized channels. High heat fluxes up to 130 W/cm2 were applied to investigate micro-channel thermal characteristics. The entire computational domain was discretized using a 120 × 160 × 100 grid for the micro-channel with an aspect ratio of (α = 4.56) and examined for Reynolds numbers in the laminar range (Re 500–2000) using FLUENT. De-ionized water served as the cooling fluid while the micro-channel substrate used was made of copper. Validation results were found to be in good agreement with previous experimental and numerical data [1] with an average deviation of less than 4.2%. As the applied heat flux increased, an increase in heat transfer coefficient values was observed. Also, the Reynolds number required for transition from single-phase fluid to two-phase was found to increase. A correlation is proposed for the results of average Nusselt numbers for the heat transfer characteristics in micro-channels with simultaneously developing, single-phase flows. 相似文献
13.
Yu-Ching Yang Shao-Shu ChuWin-Jin Chang Tser-Son Wu 《International Communications in Heat and Mass Transfer》2010
In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat flux and temperature distributions for the system composed of a multi-layer composite strip and semi-infinite foundation, from the knowledge of temperature measurements taken within the strip. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. Results show that an excellent estimation on the time-dependent heat flux can be obtained for the test case considered in this study. 相似文献
14.
Peter Vadasz 《International Journal of Heat and Mass Transfer》2005,48(14):2822-2828
This study shows that the physical conditions necessary for thermal waves to materialize in Dual-Phase-Lagging porous media conduction are not attainable in a porous slab subject to a combination of constant heat flux and temperature (Neumann and Dirichlet) boundary conditions. It is demonstrated that the approximate equivalence between Dual-Phase-Lagging (DuPhlag) heat conduction model and the Fourier heat conduction in porous media subject to Lack of Local Thermal Equilibrium (La Lotheq) that suggested the possibility of thermal oscillations and resonance reveals a condition that cannot be fulfilled because of physical constraints. 相似文献
15.
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
16.
The heat transfer due to the flow over two porous blocks situated in a square cavity is investigated and the effects of heat flux and the porosity on the flow structure and the heat transfer in the cavity are examined. In the simulations, four heat fluxes and three porosities are accommodated while air is used as the working fluid. The flow conditions at the cavity inlet are kept the same for all the cases simulated. The equilibrium equations pertinent to the flow over porous blocks in the cavity are used to predict the velocity and temperature fields. It is found that increasing porosity of the blocks modifies the flow field in the cavity, which is more pronounced as the heat flux increases. The Nusselt number enhances with the increasing porosity and heat flux. 相似文献
17.
This study describes the transient temperature distributions in a cooling apparatus for high-power semiconductor devices used in electric-railcar drive systems. The cooling apparatus is composed of heat pipes, air-cooled fin arrays, and a metal block which is used for attaching several semiconductor packages, In our numerical simulation model, we substituted solid elements for the heat pipes, and determined their thermal properties by experiment. As a result, we could obtain transient temperature distributions for the cooling apparatus through a heat conduction analysis. Calculated results showed that when the amount of heat generated in the devices changes, the temperature of the cooling apparatus changes more slowly than that of the devices. A comparison between the transient-temperature distribution calculations and the experiments confirmed the accuracy of the modeling and prediction method. Thus, these calculations can be used to provide data for packaging design, especially concerning thermal stress and fatigue in the packages. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 107–115, 1997 相似文献
18.
《International Journal of Heat and Mass Transfer》2007,50(19-20):3820-3831
This paper presents a systematic approach to determine temperature wall functions for high Rayleigh number flows using asymptotics. An asymptotic analysis of the flow and heat transfer in the near wall region forms the basis for the development of the wall functions. Appropriate normalization of the variables followed by asymptotic matching of the temperature gradients of the inner and outer layers in the overlap region leads to a logarithmic temperature profile as a wall function that has undetermined constants. A key classification that has been made in the present study is the introduction of (1) The direct problem and (2) The inverse problem. The former means that temperature profiles, either from experiments or Direct Numerical Simulations (DNS), are available and the wall function problem finally reduces to one of determining certain constants in a general wall function formula. More radical and of more interest, is the inverse problem. The idea behind this it is that when a temperature profile can be recast into a Nusselt–Rayleigh correlation, it should be perfectly possible for one to start from a Nusselt–Rayleigh correlation and end up with a wall function for temperature. This approach again will have undetermined constants that can be calibrated from either experimental or DNS data. The main advantage of using the inverse problem is the dispensation of the need to measure temperatures accurately within the boundary layer. For both the direct and inverse problems, a graded treatment to determine the constants is presented. The treatment at its highest level will result in a parameter estimation problem that can be posed as an optimization problem. The optimization problem is then solved by state of the art techniques like Levenberg–Marquardt algorithm and Genetic algorithms (GA) and the solutions are compared. While for the direct problem, the approach is illustrated for the infinite channel problem (a simple flow), for the inverse problem, the approach is elucidated for the Rayleigh–Bénard problem (a complex flow). Finally, a blending procedure to arrive at a universal temperature profile that is valid in the viscous sublayer, buffer and the overlap layers is suggested. The key ideas of (1) using optimization techniques for determining the constants in the wall function and (2) obtaining wall functions from the Nusselt numbers by the inverse approach are expected to be useful for a wide class of problems involving natural convection. 相似文献
19.
A simple methodology for numerical modelling of total heat transfer in an axisymmetric, cylindrical pulverized coal-fired furnace is introduced. The solution for the flow field and energy equations are coupled with the solution of the radiative transfer equation. The SIMPLER code is employed to solve all the equations numerically. The radiation part is modelled using the first-order spherical harmonics approximation. The radiative properties of the gases and particulates such as soot, coal/char and fly-ash are obtained locally to account for the temperature and concentration distribution effects. Using a k - ε model, the turbulence closure is obtained. Parametric studies are performed and are presented graphically to demonstrate the effects of particulate concentrations on the distributions of medium radiative and physical properties, temperature, and the wall total and radiative heat fluxes. 相似文献
20.
V.A.F. Costa M.L. Mendonça A.R. Figueiredo 《International Journal of Heat and Mass Transfer》2008,51(13-14):3342-3354
Porous media with high water content can be successfully used as thermal barriers to operate under high exposure temperatures and/or high heat fluxes. Modeling and simulation of such systems presents difficulties and challenges, which are pointed and worked out in this work. Liquid water and water vapor transfers are considered, including the capillary effects for the liquid phase, as well as the air transfer inside the porous medium. Heat transfer model includes conduction, radiation, enthalpy convection, sensible heating and phase change. A realistic model is considered at the exposed boundary in what concerns mass transfer: the outflow mass transfer is dictated by the water effusion and not by the convection transfer mechanism between the exposed surface and the environment. A set of numerical aspects is detailed, concerning both the numerical modeling and the solution of the discretization equations, which are crucial to obtain successful simulations. Some illustrative results are presented, showing the potential of the wetted porous media when used as thermal barriers, as well as the capabilities of the presented physical and numerical models to deal with such systems. 相似文献