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Transient heat transfer through a longitudinal fin of various profiles is studied. The thermal conductivity and heat transfer
coefficients are assumed to be temperature dependent. The resulting partial differential equation is highly nonlinear. Classical
Lie point symmetry methods are employed and some reductions are performed. Since the governing boundary value problem is not
invariant under any Lie point symmetry, we solve the original partial differential equation numerically. The effects of realistic
fin parameters such as the thermogeometric fin parameter and the exponent of the heat transfer coefficient on the temperature
distribution are studied. 相似文献
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This article investigates the thermal performance of convective-radiative annular fins with a step reduction in local cross section (SRC). The thermal conductivity of the fin’s material is assumed to be a linear function of temperature, and heat transfer coefficient is assumed to be a power-law function of surface temperature. Moreover, nonzero convection and radiation sink temperatures are included in the mathematical model of the energy equation. The well-known differential transformation method (DTM) is used to derive the analytical solution. An exact analytical solution for a special case is derived to prove the validity of the obtained results from the DTM. The model provided here is a more realistic representation of SRC annular fins in actual engineering practices. Effects of many parameters such as conduction-convection parameters, conduction-radiation parameter and sink temperature, and also some parameters which deal with step fins such as thickness parameter and dimensionless parameter describing the position of junction in the fin on the temperature distribution of both thin and thick sections of the fin are investigated. It is believed that the obtained results will facilitate the design and performance evaluation of SRC annular fins. 相似文献
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Rabin Y 《Cryo letters》2000,21(3):163-170
The thermal conductivity value of pure water ice is inversely proportional to the temperature and decreases about 5-fold as the temperature increases from the liquid nitrogen boiling temperature (77 K to the freezing point of pure water. The temperature dependency of the thermal conductivity is typically overlooked in bioheat transfer simulations. A closed-form solution of the one-dimensional temperature distribution in frozen water and blood is presented in this study, based on a new thermal conductivity model. Results indicate that temperatures are overestimated up to 38K, and heat fluxes through the frozen region boundaries are underestimated by a factor of 2, when the temperature dependency of the thermal conductivity is neglected. 相似文献
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In this Letter, the homotopy perturbation method (HPM) has been used to evaluate the efficiency of straight fins with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. The fin efficiency of the straight fins with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity. The results reveal that homotopy perturbation method is very effective and simple. The resulting correlation equations can assist thermal design engineers for designing of straight fins with temperature-dependent thermal conductivity. 相似文献
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We study the difference in the maximum stress on a cylinder surface σmax using the measured surface heat transfer coefficient hm instead of its average value ha during quenching. In the quenching temperatures of 200, 300, 400, 500, 600 and 800°C, the maximum surface stress σmmax calculated by hm is always smaller than σamax calculated by ha, except in the case of 800°C; while the time to reach σmax calculated by hm (fmmax) is always earlier than that by ha (famax). It is inconsistent with the traditional view that σmax increases with increasing Biot number and the time to reach σmax decreases with increasing Biot number. Other temperature-dependent properties also have a small effect on the trend of their mutual ratios with quenching temperatures. Such a difference between the two maximum surface stresses is caused by the dramatic variation of hm with temperature, which needs to be considered in engineering analysis. 相似文献
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This Letter shows that the nonlinear equation arising in heat transfer recently investigated in papers [D.D. Ganji, Phys. Lett. A 355 (2006) 337; S. Abbasbandy, Phys. Lett. A 360 (2006) 109; Hafez Tari, D.D. Ganji, H. Babazadeh, Phys. Lett. A 363 (2007) 213] and [M.S.H. Chowdhury, I. Hashim, Phys. Lett. A 372 (2008) 1240] is exactly solvable, analyses the equation fully and, furthermore, gives analytic exact solution in implicit form for each value of parameters of equation. 相似文献
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A nonlinear differential equation of thermal conductivity is derived phenomenologically from the general principles of construction of functional Q invariant to the inversion operation I(r →–r), and the temperature evolution dynamics is analyzed in the nonstationary case. The proposed method makes it possible to reveal some general regularities in the physical behavior of such systems for describing irreversible phenomena in self-organization processes. It is noted that an analogous situation may take place, for example, in strongly inhomogeneous structures with stochastic internal heat fluxes. 相似文献
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In this paper, we consider the (2+1) nonlinear fractional heat equation with non-local integral terms and investigate two different cases of such non-local integral terms. The first has to do with the time-dependent non-local integral term and the second is the space-dependent non-local integral term. Apart from the nonlinear nature of these formulations, the complexity due to the presence of the non-local integral terms impelled us to use a relatively new analytical technique called q-homotopy analysis method to obtain analytical solutions to both cases in the form of convergent series with easily computable components. Our numerical analysis enables us to show the effects of non-local terms and the fractional-order derivative on the solutions obtained by this method. 相似文献
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Ajay Mishra 《Physics letters. A》2010,374(29):2921-2420
Attempts have been made to look for the exact solutions of certain types of nonlinear diffusion-reaction equations which involve not only the quadratic and quartic nonlinearities but also a time-dependent nonlinear convective flux term. In particular, the solitary wave solutions are found. Such equations arise in a variety of contexts in physical and biological problems. 相似文献
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Rafael Cortell Bataller 《Physics letters. A》2008,372(14):2431-2439
This Letter presents a numerical study of the flow and heat transfer of an incompressible FENE-P fluid over a non-isothermal surface. The governing partial differential equations are converted into ordinary differential equations by a similarity transformation. The effects of the thermal radiation are considered in the energy equation, and the variations of dimensionless surface temperature and dimensionless surface temperature gradient, as well as the heat transfer characteristics with various physical parameters are graphed and tabulated. Two cases are studied, namely, (i) the sheet with prescribed surface temperature (PST case) and (ii) the sheet with prescribed heat flux (PHF case). Moreover, the mechanical characteristics of the corresponding flow are also presented. 相似文献
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A thermal conductivity model for nanofluids including effect of the temperature-dependent interfacial layer 总被引:1,自引:0,他引:1
Chatcharin Sitprasert Pramote Dechaumphai Varangrat Juntasaro 《Journal of nanoparticle research》2009,11(6):1465-1476
The interfacial layer of nanoparticles has been recently shown to have an effect on the thermal conductivity of nanofluids.
There is, however, still no thermal conductivity model that includes the effects of temperature and nanoparticle size variations
on the thickness and consequently on the thermal conductivity of the interfacial layer. In the present work, the stationary
model developed by Leong et al. (J Nanopart Res 8:245–254, 2006) is initially modified to include the thermal dispersion effect due to the Brownian motion of nanoparticles. This model is
called the ‘Leong et al.’s dynamic model’. However, the Leong et al.’s dynamic model over-predicts the thermal conductivity of nanofluids in the case of the flowing
fluid. This suggests that the enhancement in the thermal conductivity of the flowing nanofluids due to the increase in temperature
does not come from the thermal dispersion effect. It is more likely that the enhancement in heat transfer of the flowing nanofluids
comes from the temperature-dependent interfacial layer effect. Therefore, the Leong et al.’s stationary model is again modified
to include the effect of temperature variation on the thermal conductivity of the interfacial layer for different sizes of
nanoparticles. This present model is then evaluated and compared with the other thermal conductivity models for the turbulent convective heat transfer in nanofluids
along a uniformly heated tube. The results show that the present model is more general than the other models in the sense
that it can predict both the temperature and the volume fraction dependence of the thermal conductivity of nanofluids for
both non-flowing and flowing fluids. Also, it is found to be more accurate than the other models due to the inclusion of the
effect of the temperature-dependent interfacial layer. In conclusion, the present model can accurately predict the changes
in thermal conductivity of nanofluids due to the changes in volume fraction and temperature for various nanoparticle sizes. 相似文献
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