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1.
A numerical investigation of the mixed convection heat transfer from vertical helically coiled tubes in a cylindrical shell at various Reynolds and Rayleigh numbers, various coil‐to‐tube diameter ratios and non‐dimensional coil pitches was carried out. The particular difference in this study compared with other similar studies is the boundary conditions for the helical coil. Most studies focus on constant wall temperature or constant heat flux, whereas in this study it was a fluid‐to‐fluid heat exchanger. The purpose of this article is to assess the influence of the tube diameter, coil pitch and shell‐side mass flow rate on shell‐side heat transfer coefficient of the heat exchanger. Different characteristic lengths were used in the Nusselt number calculations to determine which length best fits the data and finally it has been shown that the normalized length of the shell‐side of the heat exchanger reasonably demonstrates the desired relation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs. 相似文献
3.
《International Journal of Solids and Structures》2006,43(2):295-306
This paper is concerned with steady-state heat conduction in rigid shell-like interphase regions. By analogy this work may provide insight into related problems of electric, dielectric and magnetic behavior. Although the field equations for three-dimensional linear Fourier heat condition are rather simple, the solution of problems in shell regions is significantly complicated when the shell has a general geometry and variable thickness. Here, the problem of heat conduction between confocal elliptical surfaces is solved within the context of the theory of a Cosserat shell. This problem is of particular interest because the Cosserat solution can be compared with an exact solution and the influences of variable shell thickness and strong variations of the temperature field through the shell’s thickness can be explored independently. The results show that the Cosserat approach is reasonably accurate even for moderately thick shells, moderate ellipticity, and moderately strong variation of the temperature through the shell’s thickness. 相似文献
4.
The heat transfer through an infinite flat plate is studied when the temperatures of the two free streams surrounding it are
varying harmonically with time and out of phase, with a delay period τd. The configuration is a simplified model for the heat transfer through the separating wall in the isochoric counter-current
heat exchanger. The results show that apart from the τd effect, the perturbation parameters depend mainly on the cavity passing frequency f. At the thick plate solution, the combined passing frequency–delay time influences are significant only when the dimensionless
frequency is smaller than 10. Within this range τd affects seriously not only the temperature perturbation amplitudes (which determine the thermal stresses) but also the heat
fluxes and the accumulated energy ones. When f ≥ 10, the plate behaves as two separate semi-infinite slabs. Heat penetration delays greater than one cavity passing period
may be possible. 相似文献
5.
岩土介质非稳态热固结耦合问题的热源函数法 总被引:9,自引:1,他引:9
考虑耦合效应的饱和土体热固结问题控制方程,利用Fourier变换、Laplace变换给出其在变换域上的解,将初始温度场分布视为虚拟的热源或者将热源等价为特定的初始温度分布,利用热源函数法给出瞬时线热源非稳态温度场、应力场和位移场的解析求解方法,通过在时间域和空间域上进行积分,给出有初始温度场分布以及有分布内热源存在且热源强度随时间变化条件下的热固结问题计算方法。对一无限大物体内存在有平面矩形域热源情况下周围介质的温度、孔隙水压力以及位移等的变化特征进行分析。研究表明,热源函数法可有效地求解一系列复杂情况下的热固结问题。 相似文献
6.
基于应力平衡条件、渗流连续方程、能量守恒方程,考虑土颗粒和孔隙水热膨胀系数的不同,建立考虑热水力耦合的饱和土体三维热固结控制方程。利用傅里叶变换和拉普拉斯变换导出变换域上的控制方程,解得点热源在变换域和实数域上的解析解,再利用区域积分给出两平行圆柱形热源热固结土体温度、孔压、位移的解析解,并对其进行分析,发现径距比增大会导致两热源温度相互影响程度减弱,热固结系数减小会导致孔压和位移的峰值增大。 相似文献
7.
N. K. Talukder 《Heat and Mass Transfer》2000,36(2):143-146
Due to radioactivity of spent nuclear fuel, a repository is expected to act as a heat source of exponentially decreasing
intensity over hundreds of years. In case of underground emplacement of such a heat source, the temperature changes in the
soil layers surrounding the heat source may have important implications such as evaporation of the water contained in the
soil and its subsequent condensation. Assuming a uniformly distributed power generation over a horizontal, relatively thin,
circular zone of several thousand meters diameter located several hundred meters below the ground surface, the temperature
variations along the vertical centerline of the heating zone was estimated analytically under simplifying assumptions. Unsteady
one-dimensional heat conduction in a semi-infinite solid with an exponentially decreasing heat flux at the proximal end was
considered. The corresponding solution of the Fourier equation for heat conduction contains Error Functions of complex arguments.
The evaluation of the Error Functions for discrete space and time parameters was performed applying analytical procedures
and using standard tables. The results show temperature distributions in the soil at various time points over thousands of
years after underground emplacement of spent nuclear fuel.
Received on 19 July 1999 相似文献
8.
A performance model for counter flow arrangement in concentric tube recuperator that can be used to utilize the waste heat
in the temperature range of 900–1,400°C is presented. The arrangement consists of metallic tubular inner and outer concentric
shell with a small annular gap between two concentric shells. Flue gases pass through the inner shell while air passes through
the annular gap in the reverse direction (counter flow arrangement). The height of the recuperator is divided into elements
and an energy balance is performed on each elemental height. Results give necessary information about surface, gas and air
temperature distribution, and the influence of operating conditions on recuperator performance. The recuperative effectiveness
is found to be increased with increasing inlet gas temperature and decreased with increasing fuel flow rate. The present model
accounts for all heat transfer processes pertinent to a counterflow radiation recuperator and provide a valuable tool for
performance considerations. 相似文献
9.
The paper considers the flow of a power-law fluid past a vertical stretching sheet. Effects of variable thermal conductivity and non-uniform heat source/sink on the heat transfer are addressed. The thermal conductivity is assumed to vary linearly with temperature. Similarity transformation is used to convert the governing partial differential equations into a set of coupled, non-linear ordinary differential equations. Two different types of boundary heating are considered, namely Prescribed power-law Surface Temperature (PST) and Prescribed power-law Heat Flux (PHF). Shooting method is used to obtain the numerical solution for the resulting boundary value problems. The effects of Chandrasekhar number, Grashof number, Prandtl number, non-uniform heat source/sink parameters, wall temperature parameter and variable thermal conductivity parameter on the dynamics are shown graphically in several plots. The skin friction and heat transfer coefficients are tabulated for a range of values of the parameters. Present study reveals that in a gravity affected flow buoyancy effect has a significant say in the control of flow and heat transfer. 相似文献
10.
Time-dependent natural convective heat transfer in a closed rectangular domain with heat-conducting boundaries of finite thickness is investigated numerically in the case of local heating on the inner side of the vertical wall. Convection-radiation heat transfer takes place on one of the outer boundaries of the solution domain. The inhomogeneous temperature distribution in the gas cavity is clearly manifested when the Grashof number Gr > 106. Circulation flows can be distinguished in various zones of the solution domain on the basis of the numerical investigations carried out. These flows are due to the effect of the heat-release source, the propagation of perturbations induced by elements of the rigid wall, and the dynamics of conductive heat transfer in the solid material. The scales of the effect of the Grashof number on the hydrodynamic and thermal characteristics are indicated. 相似文献
11.
Results of a numerical solution of the boundary-value problem of radiative-conductive heat transfer in a flat layer of a selectively
absorbing and radiating medium are presented. The effect of the optical properties of the medium and the walls, the temperature
of the source of radiation, and the relationship between the absorption spectra of the medium and the source of radiation
on temperature distribution is studied.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 124–129, March–April, 2000. 相似文献
12.
G. V. Kuznetsov M. A. Sheremet 《Journal of Applied Mechanics and Technical Physics》2008,49(6):946-956
Conjugate convective-conductive heat transfer in a rectangular region with forced flow and a heat source is simulated numerically.
Distributions of the thermal and hydrodynamic characteristics of the flow regimes studied are obtained. The evolution of the
process analyzed is shown.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 69–81, November–December, 2008 相似文献
13.
14.
V. V. Mel’nikov 《Journal of Applied Mechanics and Technical Physics》2009,50(1):66-71
This paper presents a solution of the problem of unsteady heat transfer in a three-layer hollow sphere in a central-symmetric
formulation with various time-dependent boundary conditions on the inner and outer surfaces. In each layer of the sphere there
is heat release of known intensity which depends on the radial coordinate and time. The solution is obtained by a finite integral
transform on the radial coordinate. A numerical solution is presented for one version of the boundary conditions.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 78–84, January–February, 2009. 相似文献
15.
This paper aims to provide an exact solution to the problem of sensible heat transfer and storage in fluid-solid systems. Periodically fluctuating operating conditions are considered in detail, and a simple solution procedure is proposed in order to obtain the fluid and solid temperature distributions for any periodic thermal energy supply. Some significant examples are solved explicitly, and the relevant results are reported and briefly discussed in order to examine directly the storage unit's capability of smoothing out time fluctuations of the power source. 相似文献
16.
AbstractEnlightened by the Caputo fractional derivative, the present study deals with a novel mathematical model of generalized thermoelasticity to investigate the transient phenomena due to the influence of magnetic field and moving heat source in a rod in the context of three-phase lag (TPL) theory of thermoelasticity. Both ends of the rod are fixed and heat insulated. Employing Laplace transform as a tool, the problem has been transformed into the space-domain and solved analytically. Finally, solutions in the real-time domain are obtained by applying the inverse Laplace transform. Numerical calculation for stress, displacement, and temperature within the rod is carried out and displayed graphically. The effect of moving heat source speed on temperature, stress, and temperature is studied. It is found from the distributions that the temperature, thermally induced displacement and stress of the rod are found to decrease at large source speed. For the better understanding of the effect of moving heat source on all the distributions, three animations are added. 相似文献
17.
In this paper the influence of temperature on velocity signal in hot-wire measurement of turbulence is analysed. It is pointed
out that when the temperature influence is small, the temperature influence on measured intensity of velocity fluctuations
is second order small and negligible. However, the temperature influence on measuring longitudinal heat flux is of first order
quantity, and must be corrected, or large error will occur. The method to correct the temperature influence on measuring ρ
θu
and the procedure to decide experimentally temperature influence coefficient have been given. 相似文献
18.
Analytically solving a three-dimensional (3-D) bioheat transfer problem with phase change during a freezing process is extremely difficult but theoretically important. The moving heat source model and the Green function method are introduced to deal with the cryopreservation process of in vitro biomaterials. Exact solutions for the 3-D temperature transients of tissues under various boundary conditions, such as totally convective cooling, totally fixed temperature cooling and a hybrid between them on tissue surfaces, are obtained. Furthermore, the cryosurgical process in living tissues subject to freezing by a single or multiple cryoprobes is also analytically solved. A closed-form analytical solution to the bioheat phase change process is derived by considering contributions from blood perfusion heat transfer, metabolic heat generation, and heat sink of a cryoprobe. The present method is expected to have significant value for analytically solving complex bioheat transfer problems with phase change. 相似文献
19.
Condensing of a sugar–water solution is a widely used production process, especially in food industry. In this study, boiling
temperature and heat transfer of different concentration levels of sugar/water solution is experimentally studied. In the
experiment, the pool boiling with constant temperature difference between surface and boiling temperature is investigated.
Boiling point of sugar/water solution depends on sugar mass concentration and on vapor phase pressure. A function is suggested
to calculation the boiling temperature. The experimental data and the calculated values of boiling temperature are compared.
The results are verified with previous investigations. It is determined that the heat flux between surface and sugar/water
solution while pool boiling displays a linear relation with water mass concentration in the solution. Heat transfer coefficient
could be determined in dependency of surface temperature and sugar mass concentration. Furthermore a function is suggested
to predict the heat flux for engineering purpose, which is already used in similar form for pure substances. 相似文献
20.
This paper is devoted to transient heat transfer involving radiation and conduction. Considering a non-gray purely absorbing
media, the radiative heat transfer equation (RTE) is solved iteratively with the Discrete Ordinates Method (DOM) using an
exponential differencing scheme. The energy balance equation is used to compute temperature at each time step with the Crank–Nicholson
technique. Energy equation is coupled to the RTE through the radiative source term. Both equations are discretized with finite
differencing schemes. The energy conservation leads to the sparse system of linear equations A× T=B which is solved with a bi-conjugate stabilized gradient technique (BCSG). Validation of the model with different test cases
is achieved and application to transient heating of glass is also studied. 相似文献