共查询到19条相似文献,搜索用时 125 毫秒
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论文中以流函数、涡度和温度为基本变量,建立了铸件凝固时的传热和自然对流的数学模型。控制方程采用半隐式有限差分在固定网格上求解。在模型建立过程中,着重讨论了潜热的处理和固液相区(界面)速度条件。对于潜热处理,采用了基于合金平衡相图的比热焓法;对于固液相区(界面)速度条件,提出了一种新的、基于固相率进行修正的处理方法。另外还探讨了将本文提出的解法应用于复杂几何条件的可能性。最后,通过对一个典型例子进行计算,对自然对流对铸件凝固的影响作了深入的讨论。 相似文献
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运用格子Boltzmann方法研究了底部局部加热多孔介质方腔的自然对流传热.方腔的上壁面为低温热源,下壁面为局部高温热源,左右壁面为绝热条件.重点分析了高温热源位置a及尺寸b对多孔介质方腔自然对流传热性能的影响,提出了平均Nusselt数Nu和位置a及尺寸b的拟合关系式.研究结果表明:高温热源位置及尺寸对多孔介质方腔内自然对流传热性质的影响很大,且存在最佳高温热源位置(a=4/16)和尺寸(b=0.75),以达到最强的对流换热强度(Nu_(max)≈10.35)和最大的对流换热量(Q_(max)≈5.69). 相似文献
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A. Yu. Vasil’ev I. V. Kolesnichenko A. D. Mamykin P. G. Frick R. I. Khalilov S. A. Rogozhkin V. V. Pakholkov 《Technical Physics》2015,60(9):1305-1309
Turbulent free convection of liquid sodium in a straight thermally insulated tube with a length equal to 20 diameters and with end heat exchangers ensuring a fixed temperature drop is investigated experimentally. The experiments are performed for a fixed Rayleigh number Ra = 2.4 × 106 and various angles of inclination of the tube relative to the vertical. A strong dependence of the power transferred along the tube on the angle of inclination is revealed: the Nusselt number in the angular range under investigation changes by an order of magnitude with a maximum at the angle of 65° with the vertical. The characteristics of large-scale circulation and turbulent temperature pulsations show that convective heat transfer is mainly determined by the velocity of large-scale circulation of sodium. Turbulent pulsations are maximal for small angles of inclination (α = 20°–30°) and reduce the heat flux along the channel, although in the limit of small angles (vertical tube), there is no large-scale circulation, and the convective heat flux, which is an order of magnitude larger than the molecular heat flux, is ensured only by small scale (turbulent) flow. 相似文献
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Experiments on thermal visualization of transient natural convection from short vertical rectangular fins were conducted using
the technique of laser holographic interferometry. A sequence of infinite-fringe interferograms recorded for the heating regime
of an aluminum fin demonstrates the effect of fin base heating on local convection coefficients and reveals alternating and
oscillatory buoyancydriven flows similar to those over the top surface of heated horizontal plates. The effect of fin base
heating results in greater uniformity of the local heat transfer coefficient along the fin. It also significantly reduces
the steady-state heat transfer coefficients of short vertical fins compared to their transient values. Hence, the use of steady-state
solutions for the design of short vertical fins operating in transient conditions may not introduce as much error as was previously
thought. 相似文献
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A. S. Filippov 《Journal of Engineering Thermophysics》2011,20(1):64-76
Available experimental data on heat transfer of a melt with volumetric heat generation are analyzed in order to use them for
validating the computer codes that describe a core catcher. The problem for CFD simulation of the experiments on heat transfer
by laminar and turbulent natural convection is described. Information that can be obtained from experiments for verifying
the models of convective heat transfer in a melt is analyzed. The effect of variable viscosity on the integral heat flux is
discussed. Calculation results are represented and compared with experimental data on temperature distribution and integral
heat transfer. The calculations are in good agreement with the experiment. The results are numerically extrapolated to the
range of Rayleigh numbers up to 7 · 1016. It is concluded that the CFD calculations with the κ-ɛ turbulence model can be used in problems concerned with analysis of melt convection in a core catcher. 相似文献
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Turbulent forced convection in a corrugated tube with spring tape is investigated experimentally, for Reynolds numbers from 10,000 to 50,000. The working fluid is air. Experiments are performed for different pitch and spring ratios. Results show that Nusselt numbers can be increased considerably, depending on pitch and spring ratios. An overall assessment, considering the friction losses, is achieved using the thermo-hydraulic performance parameter. The latter is observed to take values larger than unity for all cases, where quite high values around 2.8 occur for cases with smallest pitch and spring ratios. Predictive Nusselt number and friction factor correlations are proposed. 相似文献
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采用F luen软件对封闭腔内Cu-H2O纳米流体强化自然对流换热进行了数值模拟,重点分析Cu纳米粒子添加量和Gr数对换热性能的影响,并解释其换热机理。研究结果表明:在水基液中加入Cu纳米粒子可以显著提高基液的自然对流换热特性。对于一给定的Gr数,随着纳米粒子质量分数的增加,纳米流体的速度组成部分增加,纳米流体质量分数越大,x方向和y方向的速度峰越大,因此加速了流体中能量传输。另一方面,随着Gr数的增加,流线图中旋涡逐渐变大,流线间强度增加,说明换热效果逐渐增强。当Gr数较小时,传热主要是由热壁和冷壁之间的热传导引起的,随着Gr数的增大,换热逐渐变为由对流换热占主导地位。 相似文献
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In this article, studies are made on frost formation and flow over a fin and tube heat exchanger due to natural convection for various conditions of relative humidity, air ambient temperature, and mean refrigerant temperature. The results include frost deposition, steps of frost formation, and its effect on heat transfer rate for different conditions. The results show that frost is formed only on the tip of the fins with higher thickness from top to bottom due to small distance between the fins. Frost causes to trap the air which increases the thermal resistance and reduces heat transfer in the system. 相似文献
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M. A. Sheremet 《Thermophysics and Aeromechanics》2011,18(1):107-121
A numerical analysis of turbulent regimes of the natural convection in a closed rectangular region with heat-conducting walls
of finite thickness was carried out in the presence of a locally concentrated heat source under the conditions of the radiative-convective
heat exchange with the ambient medium on one of the external boundaries. The mathematical model was constructed on the basis
of the Reynolds equations in dimensionless variables stream function — vorticity vector — temperature. Special attention was
paid to the investigation of the influence of the Grashof number er 108≤Gr<1010, of the unsteadiness factor 0< τ <1000, and the thermal conductivity ratio λ
2,1 = 5.7·10−4, 6.8·10−5 on both the local and integral characteristics of the problem. 相似文献
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A new approach is proposed for describing a steady turbulent state formed far from thermodynamic equilibrium in the plasma
column of a tokamak as a result of the development of microinstabilities. A fundamental feature of such a highly nonequilibrium
plasma is its nonquasineutrality, i.e., the plasma properties are largely determined by electric fields localized on a scale
of the order of the Debye radius. It is established that the transverse thermal diffusivity is determined by the expression
where U is the voltage per orbit of the tokamak. The relation n(r)q(r)5=const and the increase in thermal diffusivity at the periphery of the plasma column can be explained on the basis of the
proposed approach.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 640–645 (10 May 1998) 相似文献