Forced convection heat transfer in narrow passages

A simple analysis of heat transfer in narrow ducts is derived, with application to a fluid in laminar flow through an elliptical duct of high aspect ratio. A solution to the latter problem for aspect ratios in the range 1.0 to 100 is also presented.     

Laminar heat transfer to Newtonian and non-Newtonian fluids in tubes

A theoretical treatment is presented which allows radial temperature and velocity profiles and the axial pressure profile to be predicted whenThe theoretical predictions have been confirmed by comparing them with experimental temperature and velocity profiles obtained for a Newtonian oil andThe experimental Nusselt numbers were also compared with the theoretical predictions and with those calculated from the generally accepted design correEmpirical methods for predicting the overall pressure drop can also give rise to large errors.     

Forced convection heat transfer to a power-law fluid in arbitrary cross-section ducts

A numerical method is developed to predict the three-dimensional forced convection laminar incompressible flow of a power law fluid in arbitrary cross-section straight ducts. The continuity equation and boundary layer forms of the energy and momentum equations in rectangular coordinates are transformed into new orthogonal coordinates with boundaries coinciding with the coordinate surfaces. The resulting equations are solved using the finite difference technique. The numerical scheme is capable of handling different hydrodynamic and thermal entry boundary conditions but results are only presented for uniform inlet velocity and temperature profiles and isothermal wall. To demonstrate the wider applicability of the method local heat transfer coefficients and pressure drop in square, trapezoidal and regular pentagonal ducts are computed as functions of pertinent thermal and hydrodynamic parameters.     

Forced convection heat transfer in tube banks in cross flow

The forced convection heat transfer characteristics for an incompressible, steady and Newtonian fluid flow over a bundle of circular cylinders has been investigated numerically. The inter-cylinder hydrodynamic interactions have been approximated by employing a simple cell model. The momentum and energy equations have been solved by using a finite difference based numerical solution procedure for a range of physical and kinematic conditions. Furthermore, the role of the type of thermal boundary condition, namely, a constant temperature or a constant heat flux, imposed on the surface of the cylinder has also been elucidated. Extensive results on the temperature fields, and on the variation of the Nusselt number on the surface of a typical cylinder in the assemblage have been obtained for two values of the Prandtl number (corresponding to air and water). The Reynolds number of flow was varied in the range 1-500 and the voidage of the assemblage ranged from 0.4 to 0.99 thereby covering the entire range of interest as encountered in tubular heat exchangers and in fibrous beds. The paper is concluded by presenting extensive comparisons with the limited analytical/numerical and/or experimental results available in the literature for the case of a single cylinder as well as that for tube bundles.     

Forced convection heat or mass transfer with rapidly varying surface boundary conditions

An asymptotic solution to the problem of forced convection of mass transfer with rapidly varying boundary conditions is derived. This solution, which has an especially useful and convenient form, is shown to be applicable under appropriate conditions to a large class of problems. In particular, the results are valid for situations involving either laminar or turbulent flows in both boundary layers and ducts; fluid properties maybe variable, and moderate transverse surface velocities and dissipative effects may be present. For special conditions, the present solution is shown to reduced to certain known results. The new results are applied to certain problems involving neither a specified surface temperature or heat flux, such as convection—radiation and catalytic surface recombination. The relationship of the new solution to other asymptotic forced convection results is discussed.     

低熔点熔盐圆管内强迫对流换热

熔融盐具有使用温度高、热稳定性和传热性能好等优点,被认为是太阳能热发电系统中最有前途的传热、蓄热介质之一。通过搭建槽式太阳能熔盐集热传热实验台,进行了低熔点熔盐管内受迫对流换热实验,获得了不同熔盐流速下套管式熔盐-水传热单元的总传热系数;通过最小二乘法获得了低熔点熔盐管内充分发展紊流段对流换热Nusselt数随Reynolds数的变化曲线和实验关联式,并与经典关联式进行了对比,结果表明,实验数据和Dittus-Boelter方程、Colburn方程、Seider-Tate方程以及Gnielinski方程最大偏差分别为+23%、+13%、-10%和-20%,实验数据和经典公式符合较好。     

Mass transfer from spheres submerged in Newtonian and non-Newtonian fluids

Mass transfer from spheres immersed in Newtonian and power-law fluid flows in the high Reynolds number region is discussed using a modified penetration model. By defining appropriate characteristic velocity and length, the proposed model in which a velocity gradient at the transfer surface is taken account of can be used to evaluate the rate of mass transfer from a sphere in complicated practical flow situations. The proposed model compares reasonably well with previously reported experimental data and correlations for mass transfer from a sphere in a fluid flowing at uniform approach velocity, in a fixed or fluidised bed, and in a stirred tank. Futhermore, good agreement is found between the model and the available experimental data and correlation for mass transfer from a rotating sphere.     

非牛顿流体中气泡群传质的研究

CO2气泡群在液相中的传质在化工过程中广泛存在.对CO2气泡群在3种不同流体(牛顿流体、非弹性剪切变稀流体和黏弹性剪切变稀流体)中的气液传质过程进行了研究.利用CO2探针测定了不同操作条件下CO2的体积传质系数,考察了液相浓度,气体流量以及流变性质对体积传质系数的影响.结果表明:在3种流体中,体积传质系数均随气体流量的...     

Forced convection mass deposition and heat transfer onto a cylinder sheathed by protective garments

In chemical, biological, radiological, and nuclear protective clothing, a layer of activated carbon material in between two textile layers provides protection against hazardous gases. A cylinder in cross flow, sheathed by such material, is generally used to experimentally test the garment properties. This is, however, complicated and predictive models are needed. We present a computational fluid dynamics model for the initial phase in which the carbon filter material is not yet saturated. The textiles are modeled as chemically inactive porous layers, the carbon filter particles have been resolved explicitly. The model has been validated against experimental data. We demonstrate that (1) computational fluid dynamics simulations can be used for the efficient design and optimization of protective garments, and (2) the addition of a highly porous active carbon layer highly increases the chemical protection capabilities, while having relatively little negative impact on the thermal comfort of protective garments. © 2013 American Institute of Chemical Engineers AIChE J, 60: 353–361, 2014     

Heat transfer in laminar flow of non-Newtonian fluids

The main objective of this work is the consideration of local heat transfer coefficients for non-Newtonian power-law pseudoplastic liquid in laminar flow in circular conduits. The wall boundary conditions chosen are cases involving uniformly constant heat flux and step change in heat flux.Analytical solutions are developed for the wall temperature profile and compared with experimental data. Additionally, the experimental data have been correlated for comparison with existing relationships, hitherto not verified adequately. The limits of experimental data are:

     

Forced convection heat transfer in low prandtl number turbulent flows: Influence of axial conduction

The effect of axial conduction was investigated for turbulent heat transfer in a round pipe with uniform wall temperature. Exact solutions were obtained by using the method of separation of variables for the two cases with and without the axial conduction term. The solutions show that the effect of axial conduction is important at low Peclet numbers, say Pe < 100, but negligible in the thermally fully-developed region. Also, the fully developed Nusselt numbers depend only on Reynolds number at low Peclet numbers and the interpolation formula is proposed: which fits the calculated data well in the liquid metal range 0.001 < Pr < 0.022 for Pe < 100.     

Laminar natural heat transfer from an isothermal sphere to non-newtonian fluids

An experimental study of natural convection heat transfer conducted with water and thirteen aqueous polymer solutions obeying the power-law model, varying in flow behavior index from 0.3 to 0.99, and consistency index between 10 and 5 × 10³, showed that the behavior of these solutions justifies the theoretical treatment of this phenomenon proposed by Acrivos⁽¹⁰⁾. The heat source was an internally electrically heated copper sphere, 5 inches in diameter, and designed to provide an isothermal surface.     

Momentum transfer to Newtonian and non-Newtonian fluids flowing through packed and fluidized beds

This paper deals with the flow behaviour of Newtonian and non-Newtonian fluids flowing through packed and expanded beds. With the help of tube-bundle theory a generalized average shear-stress—shear-rate relationship is derived and found to predict the flow behaviour of power law as well as non-power law fluids. Polyvinyl alcohol solutions in water, a representative of power law fluids, and grease in kerosene, a representative of nonpower law fluids, are studied. The present investigation covers the range of Reynolds number from 10^?3 to 10³. An expression for average shear-stress at minimum fluidization velocity is derived and found to agree with that of our experiment. The generalized frictional Reynolds number is defined and a design chart is also presented for the evaluation of fluidizing velocities.     

Laminar natural convection heat transfer to a viscoelastic fluid

A theoretical analysis of laminar natural convection heat transfer to a viscoelastic fluid has been done by the approximate integral method. It has bee