International Communications in Heat and Mass Transfer

Published by Elsevier
Print ISSN: 0735-1933
Sudden heating of a fluid in a tube or narrow channel induces localized pressure gradients and transient flow which can significantly affect the heat transfer rate. Experiments with a long, pulse-heated tube containing refrigerant 113 produced induced flow as well as pressure oscillations. This paper presents experimental results, and analyses of the system.
The paper presents comparison in flow characteristics for CFC-12 and HFC-134a in capillary tube. The results revealed that even with minor differences in refrigerant properties between CFC-12 and HFC-134a, the differences in flow characteristics may be significant. Theoretical results predicted that 15% difference or more in critical tube length may be expected.
Condensation heat transfer and pressure drop data of R-134a in annular helical pipes is of significant importance to the effective design and reliable operation of helical pipe heat exchangers for refrigeration, air-conditioning, and many other applications. This paper presents the experimental investigation on condensation heat transfer and pressure drop characteristics of R-134a in an annular helical pipe. The average condensation heat transfer coefficients and pressure drops were experimentally determined for R-134a at three different saturated temperatures (35 °C, 40 °C, and 46 °C). The experimental results are compared with the data available in the literature for helical and straight pipes.
An investigation of turbulent flows occurring in a 180°-bend annular diffuser with an aperture in front of the bend is numerically and experimentally conducted. The blowoff mass flow rate and the inlet pressure have been systematically changed to study their influence on the diffuser performance. Results show that the pressure recovery coefficient increases with increasing blowoff mass flowrate and inlet pressure, but remains nearly constant if the inlet pressure is higher than about 10 bar. The numerical predictions are compared with the experimental data and excellent agreement is achieved. The results provide insight into the characteristics of flow in the diffuser and are useful for diffuser designs of engineering interest.
Analysis of convection flow and heat transfer in a viscous heat-generating fluid near a cone and a wedge is carried out. The effects of free convection and the presence of heat generation or absorption on the flow and heat transfer characteristics are considered. The equations of conservation of mass, momentum, and energy, which govern the flow and heat transfer, are solved numerically by using a variable order, variable step size finite-difference method. The numerical results obtained for the flow and heat transfer characteristics reveal many interesting behaviors. It is observed that the heat source parameter has the dominating effect, on the flow and heat transfer, in setting in the instability.
Here, the homotopy analysis method (HAM), one of the newest analytical methods which is powerful and easy-to-use, is applied to solve heat transfer problems with high nonlinearity order. Also, the results are compared with the perturbation and numerical Runge–Kutta methods and homotopy perturbation method (HPM). Here, homotopy analysis method is used to solve an unsteady nonlinear convective–radiative equation containing two small parameters of ϵ1 and ϵ2. The homotopy analysis method contains the auxiliary parameter h¯, which provides us with a simple way to adjust and control the convergence region of solution series.
Numerical simulations of strongly swirling turbulent flows in a vortex combustor (VC) are conducted. A comprehensive investigation of a three-dimensional isothermal VC flow using three first-order turbulence models: the standard k–ε turbulence model, Renormalized Group (RNG) k–ε model and shear stress transport (SST) k–ω model; and a second-order turbulence model, Reynolds stress model (RSM) together with a second-order numerical differencing scheme is conducted in the present work. The computation indicates that the RSM is superior to the other turbulence models in capturing the swirl flow effect in comparison with measurements. The numerical results for the VC flow provide the characteristics of the flow in terms of relevant parameters for the VC design and operation, composed of axial and tangential velocities, pressure fields, and turbulence kinetic energy.
In the current work, three-dimensional Navier–Stokes equations along with the energy and concentration equations for the fluid coupled with the energy and mass conservation equations for the solid (wood) are solved to study the transient heat and mass transfer during high thermal treatment of wood. The model for wood is based on Luikov's approach and solves a set of coupled heat and mass transfer equations. The model equations are solved numerically by the commercial package FEMLAB for the temperature and moisture content histories under different treatment conditions. The simulation of the proposed conjugate problem allows the assessment of the effect of the heat and mass transfer within wood on the transfer in the adjacent gas, providing good insight on the complexity of the transfer mechanisms.
In the present work, we investigate numerically the natural convection flow in 3D cubic enclosure tilted at an angle (γ) with respect to the vertical position. The enclosure is heated and cooled from the two opposite walls while the remaining walls are adiabatic. The numerical procedure adopted in this analysis yield consistent performance over a wide range of parameters. Simulations have been carried out for Rayleigh numbers Ra ranging from 103 to 1.3 × 105, Prandtl number, Pr, (0.71 ≤ Pr ≤ 75) and inclination angle γ (0° ≤ γ ≤ 90°). Particular attention is focused on the three-dimensional steady effects that can arise in such configuration that seem to be unknown in the literature, even for relatively small values of the Rayleigh number. The 3D flow characteristics and thermal fields are analyzed in terms of streamlines, isotherms and Nusselt numbers. A periodic behavior of the 3D flow has been observed at Ra = 8.5 × 104 with a fundamental frequency of 8.27. The Hopf bifurcation is localized. In addition, time-dependent solutions reveal that the flow characteristics depend on the inclination angle γ. The effects of Prandtl number on heat transfer and fluid flow is significant for Pr ≥ 6.
In injection mold, cooling process has important effects on parts quality and production cost. Traditional cooling simulation is conducted in a decoupled way by a cycle-averaged approach plus one-dimensional transient variation for computational efficiency concern. In the present study, fully 3D simulations of mold temperature variation based on FEM and FVM implemented in parallel computation scheme were executed for lens mold embedded with heaters. With the fully 3D simulation, mold temperature and melt temperature are solved in coupled manner and obtained simultaneously. Also the time when mold temperature distribution reaches the cyclic-average steady state can be determined. The simulation results were verified with measured cavity temperatures using infrared thermal image system at interest locations. The numerical results for cyclic, transient with heat source problem show reasonable consistency with measured values. The computing time with multi-CPU and parallel scheme is much less than that of single CPU.
A numerical investigation of laminar periodic flow and heat transfer in a three-dimensional isothermal-wall square channel fitted with 45° inclined baffles on one channel wall is carried out in the present work. The finite volume method is introduced and the SIMPLE algorithm has been implemented for all computations. The fluid flow and heat transfer characteristics are presented for Reynolds numbers ranging from 100 to 1200. The 45° baffle mounted only on the lower channel wall has a height of b and an axial pitch length (L) equal to channel height (H). Effects of flow blockage ratios, BR = b/H = 0.1–0.5, on heat transfer and pressure loss in the square channel are examined and also compared with the typical case of the transverse baffle (or 90° baffle). It is found that apart from the rise of Reynolds number, the increase in the blockage ratio with the attack angle (α) of 45° results in considerable increases in the Nusselt number and friction factor values. The use of the 45° baffle can help to generate a streamwise main vortex flow throughout the channel leading to fast and chaotic mixing of flow between the core and the wall regions. In addition, the computational results reveal that the significant increase in heat transfer rate is due to impingement jets induced by a longitudinal vortex pair (P-vortex) of flow, appearing on the upper, lower and baffle trailing end side walls. The appearance of vortex-induced impingement flows created by the baffles leads to the maximum thermal enhancement factor of about 2.2 at BR = 0.4 and Re = 1200. The enhancement factor of the 45° baffle investigated is found to be higher than that of the 90° baffle for all Reynolds numbers and baffle heights.
Pool boiling heat transfer from nano-porous surface immersed in a saturated FC-72 dielectric fluid has been experimentally studied at atmospheric pressure (101 kPa). The data obtained from nano-porous surface (Anodisc 25) of thickness about 70 μm made from aluminum oxide (Al2O3) obtained from Whatman, were compared to that of a plain surface (aluminum) of thickness about 105 μm. From the experimental data obtained it was evident that there is a reduction of about 30% in the incipient superheat for the applied power for nano-porous surface over plain surface. SEM photographs of the nano-porous coating were taken for determining the size of the pores.
Microwave ablation (MWA) is a process that uses the heat from microwave energy to kill cancer cells. MWA is able to focus radiation on the desired areas without damaging the surrounding tissue, entail a control of heating power for appropriate temperature distribution. Slot coaxial antennas are the most popular antennas in MWA because of their small dimensions and low cost to manufacture. To effectively treat liver cancer, these antennas can be used to produce a highly localized specific absorption rate (SAR) and temperature distribution pattern. In this work, the interstitial MWA in liver by single and double slot antennas is carried out. This paper focuses on the influence of antenna type on microwave power absorbed, SAR and temperature distribution. The results show that the maximum SAR and temperature appears in the liver tissue in case of single slot antenna which are higher than those of double slot antenna. However, no clear difference between these two microwave coaxial antenna (MCA) models has been shown, due to the low microwave power input from the MCA during MWA process.
The effect of magnetic field dependent (MFD) viscosity on the onset of ferroconvection in a ferrofluid saturated horizontal porous layer is investigated theoretically. The bounding surfaces of the porous medium are considered to be either rigid-ferromagnetic or stress free with constant heat flux conditions. The resulting eigenvalue problem is solved numerically using the Galerkin technique and also analytically by regular perturbation technique. It is found that increase in porous parameter, MFD viscosity parameter and decrease in the magnetic number is to delay the onset of ferroconvection, while the nonlinearity of fluid magnetization has no influence on the stability of the system.
When boiling or bubbling occurs in a liquid pool, droplets are ejected from the surface by bursting of bubbles or splashing. In function of their size, the droplets are partly carried away by a streaming gas and partly returned to the bubbling surface by gravity force. It is measured simultaneously the size and velocity of droplets at several distances from the bubbling surface. It is used a Phase-Doppler Anemometry (PDA: Particle Dynamic Analyzer) in order to measure simultaneously the size based upon the phase of the scattering light of first order refraction (P=1) and the velocity droplets. It is utilized a log-normal distribution function in order to describe the high droplet-size polydispersity distribution.
This paper presents an analytical, variable-conductivity, thermal model for single-point diamond precision machining of semi conductors. The model is used to calculate the temperature development during the simulated machining of silicon and germanium wafers. The heat generated at a tool-work piece contact is taken as the product of the coefficient of friction, the relative sliding speed, and the contact stress. Whereas, heat partition between the diamond abrasive and the work piece is obtained through a modified Jaeger-Blok analysis that incorporates the coupling of the thermal properties of the tool-work piece system. The results indicate that: for the ranges of nominal loads, cutting speeds and, feeds encountered, the work piece surface temperature rise is well below the thermal softening temperatures for these materials. This, has direct implications to the ductile removal mechanisms. The low values calculated for the work surface are shown to be consistent with several calculations based on the analysis of conventional machining.
It is well known that the weldline reduces the mechanical performance of the conventional injection molded parts. Yet, systematic researches and reports on weldline strength of thin-wall molded parts are still insufficient. This study investigates the influence of processing conditions on the weldline strength of thin-wall Acrylonitrile Butadiene Styrene Copolymer (ABS) parts. The relevant parameters include melt temperature, mold temperature, injection speed and packing pressure. Tensile tests on specimens of different thickness (1.0, 1.2 and 2.5 mm) are conducted. Comparisons on tensile strength for single-gate molded specimens (without weldline) with those of double-gate molded specimens (with weldline) are presented. From the experimental results, it was found that weldline specimens molded at higher melt temperature, higher mold temperature, faster injection speed and lower packing pressure would result in better mechanical strengths. Higher melt and mold temperatures not only lower the residual stress but also help the diffusion of molecular chains leading to a higher degree of surface bonding at the weldline interface. On the other hand, high packing pressure leads to higher residual stress formation and reduces the molecular bonding rate. In addition, part thickness also exhibits significant effect on weldline strength. A regression analysis combined with fitting model seems to correlate process conditions and weldline strength reduction quite well.
Mathematical equations are developed to study thermal processes in a CPC collector with a flat one-sided absorber. An expression for the temperature of the heat transfer fluid as a function of the space-co-ordinate in the flow direction and the time dependent solar intensity is developed. The effects of various parameters on the thermal performance of such a CPC are studied. The selectively coated CPC with flat one-sided collector is more efficient than the black painted one with the same condition. The predicted results were also compared with the experimental results reported in the literature.
This study investigates the free convective flow of heat generating/absorbing fluid between vertical parallel porous plates due to periodic heating of the porous plates. The analysis is performed by considering fully developed flow and steady-periodic regime. The momentum and energy equations, which arise from the definition of velocity and temperature, are written in dimensionless form. Separating the temperature and velocity fields into steady and periodic parts, the resulting second order differential equations are solved to obtain the expressions for velocity, temperature, skin friction and the rate of heat transfer. The effects of various flow parameters such as the suction/injection (s), heat source/sink (δ), Strouhal (St) and Prandtl (Pr) numbers on the skin friction coefficient, rate of heat transfer, velocity and temperature profiles are discussed with the aid of line graphs and contour maps.
This work is focused on the study of combined heat and mass transfer on double-diffusive convection near a vertical truncated cone in a fluid-saturated porous medium in the presence of a first-order chemical reaction and heat generation or absorption with variable viscosity. The viscosity of the fluid is assumed to be an inverse linear function of the temperature. A boundary layer analysis is employed to derive the non-dimensional non-similar governing equations. The governing equations for this investigation are formulated and solved numerically using the fourth-order Runge–Kutta integration scheme with Newton–Raphson shooting technique. Comparisons with previously published work on special cases of the problem are performed and found to be in excellent agreement. A parametric study illustrating the influence of chemical reaction parameter, heat generation or absorption parameter, viscosity-variation parameter, buoyancy ratio and Lewis number on the fluid velocity, temperature, concentration as well as Nusselt number and Sherwood number is conducted. The results of this parametric study are shown graphically and the physical aspects of the problem are highlighted and discussed.
A theoretical analysis of the process of gas absorption to a thin liquid film on a horizontal rotating disk is presented. The film is formed by the impingement of a confined liquid jet at the center of the disk and subsequent radial spreading of liquid along the surface of the disk. The chemical reaction between the gas and the liquid film is expressed as a zero-order homogeneous reaction. The process is modeled by establishing equations for the conservation of mass, momentum, and species concentration and solving them analytically. The final solution is expressed using confluent hypergeometric functions. Results for gas concentration and Sherwood number are presented using Reynolds number, Ekman number, and chemical reaction rate as parameters.
This paper is focused on the study of coupled heat and mass transfer by boundary-layer free convection over a vertical flat plate embedded in a fluid-saturated porous medium in the presence of thermophoretic particle deposition and heat generation or absorption effects. The governing partial differential equations are transformed into ordinary differential equations by using special transformations. The resulting similarity equations are solved numerically by an efficient implicit tri-diagonal finite-difference method. Comparisons with previously published work are performed and the results are found to be in excellent agreement. Many results are obtained and a representative set is displayed graphically to illustrate the influence of the heat generation or absorption coefficient, buoyancy ratio and the Lewis number on the temperature and concentration profiles and the wall thermophoretic deposition velocity.
Transient heat and mass transfer associated with a moving liquid during absorption was numerically studied in this work. The roles played by the internal circulation inside the droplet and the exorthermic heat effect were demonstrated. The numerical results reveal that the significant absorption enhancement by internal circulation becomes neglible with the increase of exothermic absorption heat. The highly exotermic system of , which is used as a typical refrigerant/absorbent combination in commercial absorption heat pump (AHP), was selected as an example to illustrate this point.
This paper proposes a numerical study to simulate the effects of dielectric shield on the specific absorption rate (SAR) and the temperature increase in the human body exposed to leakage microwave energy. In this study, the effects of shield dielectric properties on distributions of SAR and temperature increase within the human body at various operating frequency are systematically investigated. Based on the obtained results, the installed dielectric shield strongly affects the SAR and the temperature increase in human body. The SAR and the temperature increase in human body can be reduced simultaneously by setting the appropriate dielectric properties of the dielectric shield. The appropriate dielectric properties of the dielectric shield greatly depend on the operating frequencies. These fundamental data for the implementations of the radiation protection shielding materials, with focusing on the human organism, are provided as well.
We formulate the problem of free convection from a vertical wavy surface embedded in a uniform porous medium in the presence of an external magnetic field and internal heat generation or absorption effects. Using the appropriate transformations, the boundary layer equations are reduced to non-linear partial differential equations. The transformed boundary layer equations are solved numerically using Runge–Kutta integration scheme with the shooting technique. We have focused our attention on the evaluation of the local Nusselt number Nux, dimensionless velocity, f′, and temperature, θ. The governing parameters are the amplitude of the waviness of the surface, a, ranging from 0.0 (flat plate) to 0.3, and the heat generation absorption parameter Q ranging from − 0.25 to 0.25, and magnetic parameter Mn, ranging from 0.0 to 2.0. The effect of all these parameters are discussed and plotted.
The effect of a uniform transverse magnetic field on the free convection flow of an electrically conducting fluid past an infinite vertical plate for both the classes of impulsive as well as uniformly accelerated motion of the plate is discussed. In this analysis, the magnetic lines of force are assumed to be fixed relative to the plate. Laplace transform technique has been used to obtain the expressions for the velocity field and skin-friction for both cases. It is found that the effect of the magnetic field is to increase the velocity field in both cases.
In order to analyze the effects of the spray activation on the behavior of steam and hydrogen which are produced in the reactor vessel and released into the containment of the APR1400 nuclear power plant during hypothetical severe loss-of-coolant accidents (LOCA), the 3-dimensional CFD code GASFLOW was used. For the two-phase flow with a gas mixture and spray droplets, GASFLOW solves a homogeneous two-phase model which was validated in this study by simulating one of the TOSQAN experiments. The results of the GASFLOW analyses for the LOCAs in the APR1400 show that the spray system can affect the hydrogen distributions in the containment by condensing the steam and it is important to control the spray system carefully during an accident from a hydrogen safety aspect.
The usage of pulsed cooling for mold temperature to improve the molding process has been gaining increasing attention. In this study, Blu-ray Disc substrates, adapted for the commercial format media, were injection molded by combining pulsed-cooling technology. When applying pulsed cooling, coolant circulation is usually stopped during the melt-filling process and the mold opening and closing period. This leads to the additional cavity surface temperature increase and may vary part qualities. The correlations of mold temperature, cycle time, and pulse cooling duration with microgroove duplication accuracy and substrate qualities such as warpage in different directions were investigated in details. Measured results were also compared with those of injection-compression molded Blu-ray Disc using conventional cooling. The experiments showed that by using pulsed cooling in a proper manner one may manufacture Blu-ray Discs with lower warpage, higher accuracy in microgroove replication meanwhile reducing coolant temperature by 8 °C and shortening the cycle time by10% as compared to the conventional-cooling process. The usefulness of pulsed cooling and its potential in improving part quality and reducing cycle time during injection molding have been successfully demonstrated.
A major source of uncertainty in contact heat transfer experiments is the heat loss from the specimens to the surroundings by convection, conduction and radiation. A detailed analysis is presented comparing the resistance to heat transfer across the joint to the resistance to heat flow from the specimens to the surroundings. It is shown that the heat losses may be reduced by the provision of a shield. It is also shown that, unless the contact pressures are very low or there is large flatness deviation in the contacting surfaces, the vacuums of the order obtained by means of a rotary vane pump may be adequate; otherwise, a diffusion pump may also be necessary.
The periodic hot-wire method is an appropriate means for the determination of the thermal diffusivity a and thermal conductivity λ. A thin platinum wire in a sample is heated by a sinusoidal alternating current. The resulting thermal waves penetrate into the surrounding sample. The thermal diffusivity a and the thermal conductivity λ of the sample can be calculated by analysing the amplitudes and the phase-lags of the waves and applying the Fourier equation. In order to derive the evaluation procedure for a and λ the temperature field in the sample is calculated analytically under the assumption, that the platinum wire represents a perfect, infinitly extended line heat source. This assumption can only be approached and thus measurements must deviate from theory. These deviations were determined by numerical calculations of the temperature field considering the real geometry of the platinum wire. The measurement accuracy and the optimum frequency range of the periodic hot-wire method has been obtained by comparing the numerically and analytically calculated temperature fields.
This paper describes the application of the finite difference method to the simulation of three-dimensional natural convection in a box. The velocity–vorticity formulation is employed to represent the mass, momentum, and energy conservations of the fluid medium. We employ a fractional time marching technique for solving seven field variables involving three velocity, three vorticity and one temperature components. By using the fast Fourier transform (FFT) and a tridiagonal matrix algorithm (TDMA), the velocity Poisson equations are advanced in space along with the continuity equation, thus solving efficiently and easily the diagonally dominant tridiagonal matrix equations. Both vorticity and energy equations are discretized through an explicit method (Adams–Bashforth central difference scheme) as a simplified numerical scheme for solving 3D problems, which otherwise requires enormous computational effort. A natural convection in a box for the Rayleigh number equal to 104, 105, 106 and 107 as well as As = Lx / Lz aspect ratios varying from 0.25 to 4 is investigated. It is shown that the benchmark results for temperature and flow fields could be obtained using the present algorithm.
The present study was conducted to numerically investigate the steady laminar buoyancy-driven and convection heat transfer characteristics within three different across-shape concave enclosures for the Prandtl number of 0.71 and 4, the Grashof number range 104 ≤ Gr ≤ 2 × 105, and the gap range 0 ≤ H1/H2 ≤ 0.25. The steady Navier–Stokes equations, governing the flow under Boussinesq approximation, are solved with the dimensionless stream function-vorticity formulation in terms of curvilinear coordinates using the finite difference method. The results show that the effects of various shapes, the strength of the vortex is relatively bigger in the rectangular–rectangular concave enclosure than in the rectangular–circular concave enclosure at the same Grashof number. Heat transfer from the different across-shape concave enclosures is evaluated, and flow and heat transfer characteristics are discussed.
A physical model is formulated to evaluate the radiative heat transfer across transparent honeycomb insulation materials. The model takes into account the refraction, reflection, absorption and scattering characteristics of cell walls and enables the computation of elemental transmittance, integral transmittance and the geometrical shape factor. The predicted results of heat loss across a honeycomb array exhibit by far the best agreement with the result of an earlier experiment. The model is used to investigate the effect of wall thickness, aspect ratio, and absorptivity of the wall on radiative heat transfer. The results are presented in the form helpful for engineering design of TIM.
Artificial Neural Network (ANN) and Adaptive-Network-Based Fuzzy Inference System (ANFIS) were used to predict the natural convection thermal and flow variables in a triangular enclosure which is heated from below and cooled from sloping wall while vertical wall is maintained adiabatic. Governing equations of natural convection were solved using finite difference technique by writing a FORTRAN code to generate database for ANN and ANFIS in the range of Rayleigh number from Ra = 104 to Ra = 106 and aspect ratio of triangle AR = 0.5 and AR = 1. Thus, the results obtained from numerical solutions were used for training and testing the ANN and ANFIS. A comparison was performed among the soft programming and Computational Fluid Dynamic (CFD) codes. It is observed that although both ANN and ANFIS soft programming codes can be used to predict natural convection flow field in a triangular enclosure, ANFIS method gives more significant value to actual value than ANN.
Numerical and experimental works are conducted to develop a visualization technique for the phase distribution in a two-phase system by electrical impedance tomography technique, which reconstructs the resistivity distribution with the electrical responses that are determined by corresponding excitations. In conventional Newton–Raphson method, the flow field is discretized into pixels, each of which has an unknown resistivity value to be determined by the image reconstruction algorithm. The pixels are usually fixed in a predetermined way. In practical cases, such as the impedance imaging of two-phase flow, this model might not be useful. For the two-phase flow system, the impedance of each phase does not change but instead the phase boundary depends on the distribution of dispersed phase. In the present study, a new image reconstruction algorithm employing adaptive mesh regeneration technique is developed for the detection of phase boundary. Numerical works show that the proposed method can treat two-phase systems reasonably even with some errors in measurement data. Also, with an apparatus developed for impedance imaging this study attempts to reconstruct the images of the simulated bubble distributions and the reconstructed images imply the potential possibility of the electrical impedance tomography for the two-phase flow visualization.
The Additive Correction Multigrid strategy [B.R. Hutchinson and G.D. Raithby, Num. Heat Tranfer, 9, pp 511--537, 1986] is shown to be identical to a cell-centred multigrid algorithm using both restriction and prolongation operators based on piecewise constant interpolation. It is demonstrated that the method therefore cannot be expected to give true multigrid performance (i.e. grid-independent rate of convergence) for diffusion dominated problems. 1. Introduction The Additive Correction Multigrid (ACM) method introduced by Hutchinson and Raithby [1] has been used to some extent by practitioners of numerical computation of heat transfer and fluid flow [2, 3, 4]. The method is a cell-based multilevel method that is a generalisation of the additive correction methods described by Settari and Aziz [5], and it has been used to solve the linear set of equations obtained by discretisation of conservation equations of advection-diffusion type that govern fluid flow and heat transfer. In this ...
This is an investigation of non isothermal and non-Newtonian laminar flow in the entrance region of short tubes. The flow is steady, incompressible and tube wall has constant temperature with heating and cooling. Experimental work was conducted using water solutions of Xanthan and Guar gums which exhibited pseudoplastic behavior. Experiments lie in the ranges: 2×10−04 < Gz−1 < 10−02, 300 < Pr < 1000, 30 < Re < 400 and 30.9 < L/D < 135.8. Results were reported as non-dimensional correlations allows practical calculations of Nusselt, Graetz and Stanton. The Stanton number was modified in this work for the potency of Reynolds and one demonstrated a good correlation to distinguish the heating and cooling conditions. The results for the Nusselt number are compatible with the literature.
Schematic diagram of motor-assisted viral transport between the cell membrane and cell nucleus. 
This paper presents an analytical solution of one-dimensional transient molecular-motor-assisted transport equations that describe transport of adenoviruses in a spherical cell. The model of intracellular trafficking of adenoviruses is based on molecular-motor-assisted transport equations suggested by Smith and Simmons [D.A. Smith, R.M. Simmons, Models of motor-assisted transport of intracellular particles, Biophysical Journal 80 (2001) 45–68.]. These equations are presented in spherical coordinates and extended by accounting for the random component of motion of viral particles bound to filaments. This random component is associated with the stochastic nature of molecular motors responsible for the locomotion of viral particles bound to filaments. Utilizing the method of separation of variables, a generalized Fourier series solution for this problem is obtained. The solution uses two different orthogonal sets of eigenfunctions to represent the concentration of free viral particles transported by diffusion and the concentration of microtubule-bound viral particles transported by kinesin-family molecular motors away from the cell nucleus. Binding/detachment kinetic processes between the viral particles and microtubules are specified by first rate reaction constants; these lead to coupling between the two viral concentrations. The obtained solution simulates viral transport between the cell membrane and cell nucleus during initial stages of viral infection.
The present study proposes an improved model for the single-blow technique which is commonly used to measure the thermal performance of a cryocooler's regenerator matrix. The improvements in the present model include the heat flux from the fluid into the side wall and the axial conduction of the wire-screen matrix and side wall as a suddenly heated fluid passes through the wire-screen matrix. Numerical results obtained from the present model are compared with both the analytic results that exclude the axial conduction and the predicted results of a prior study that neglect the heat flux into the side wall. Results are also presented to illustrate the effect of the heat capacity of the side wall, the heat flux into the side wall, and the axial conduction on both the exit fluid temperature response and the NTU value.
The heat and mass transfer characteristics of free convection about a permeable horizontal cylinder embedded in porous media under the coupled effects of thermal and mass diffusion are numerically analyzed. The surface of the horizontal cylinder is maintained at a uniform wall temperature and uniform wall concentration. The transformed governing equations are obtained and solved by Keller box method. Numerical results for the dimensionless temperature profiles, the dimensionless concentration profiles, the Nusselt number and the Sherwood number are presented. Increasing the buoyancy ratio N and the transpiration parameter fw increases the Nusselt number and the Sherwood number. For thermally assisting flow, when Lewis number Le increases, the Nusselt (Sherwood) number decreases (increases). Whereas, for thermally opposing flow, both the Nusselt number and the Sherwood number increase with increasing the Lewis number.
A numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ = 10− 5). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ = 10− 5). The present study is performed for Γ values from 10− 5 to 1 and G value from 1 to 100.
Thermal management of packages consists of external cooling mechanisms, heat dissipaters, and thermal interfaces. While keeping cooling condition constant, junction temperature of LEDs with higher thermal resistance increases more rapidly; hence the luminous efficiency decreases more obviously. This paper includes the discussion about the calculation methods of the lighting's heat transfer. The calculation process has been demonstrated by an example of cooling of LEDs lighting in this paper. In particular, the operation package heat transfer enhancement is required by most package manufacturers with a decrease of 20% ~ 30% of the thermal resistance over conventional package geometries.
The Reynolds-stress model, as with most other models, has been calibrated for “simple” shear flow i.e. zero pressure gradient boundary layer. Such calibration of the empirical constants does not provide universality because these constants are structural parameters which may change as flow structure changes. It is widely (drown that in adverse pressure gradient calculation, the near-wall length scale is overpredicted. By correlating the empirical constants in the ε-equation into a form analogous to length scale proportional to distance from the wall, it is found that the non-uniform near-wall shear stress profile is translated via the empirical constants into a larger than expected length scale. To overcome the problem a length-scale-limiting model was formulated to inhibit this increase in length scale by increasing the production of ε.
This paper presents a simulation study of oxygen mass transfer in subsurface aeration systems using two models proposed in the literature. A modification in one of the models was introduced, resulting in significant differences in oxygen concentration in the gas phase for small airflow rate values. Simulation results show that the oxygen equilibrium concentration decreases with increases in temperature, and that the time required for attaining steady state conditions decreases significantly as the airflow rate increases. The modified model was also applied to evaluate the performance of an aeration system in auquaculture.
Heat transfer and pressure drop measurements from an aerofoil in cross-flow, arranged in single, six-row aligned and staggered positions, have been reported in the Reynolds number range of 50,000 to 135,000. Comparison of the measured values of Stanton number and pressure loss factors with the available data on circular and some stream-lined shapes, show a good promise for the use of aerofoil elements in cross-flow exchangers.
A simple approach for evaluating the effect of wall suction and thermophoresis on aerosol particle deposition from a laminar flow over a flat plate is proposed. The plate considered is a cold surface. The procedure is based on the concept of high-mass transfer with a blowing parameter. The thermophoresis is treated with two parts that include a suction-like convection term and a first-order reaction-like term. The results are easily calculated and have a very good agreement with the numerical solutions for self-similar boundary flow.
The present study was conducted to numerically investigate the transport mechanism of laminar combined convection in a shear- and buoyancy-driven cavity. The focus was on the interaction of the forced convection induced by the moving wall with the natural convection induced by the buoyancy. Two orientations of thermal boundary conditions at the cavity walls are considered in order to simulate the aiding and opposing buoyancy mechanisms. Velocity and temperature distributions of the flow are carried out through a stream function-vorticity transformation with a finite difference scheme. Parametric studies of the effect of the mixed convection parameter, Gr/Re2, on the fluid flow and heat transfer have been performed. Calculations cover Re=100, Pr=0.71 and Gr/Re2 the range of 0.01–100. Three different regimes are observed with increasing Forced convection (with Gr/Re2 negligible natural convection), mixed convection (comparable forced and natural convection) and natural convection (with negligible forced convection). The code developed was carefully tested for the two limiting cases, the pure forced convection and the pure natural convection, for which experimental and numerical data are available.
This paper briefly describes laboratory experiments performed to investigate the ability of air curtain arrangements to prevent heat propagation in case of fire in a corridor-like geometry. The arrangement considered in this study is a system based on two twin plane jets. Simultaneous measurements of temperature and velocity were performed with fine thermocouples and a Laser Doppler Anemometer (LDA), respectively. The jet Reynolds number based on the average discharge velocity U0 and the total width 2e of the investigated twin-jet was about 1000. Information about the spatial distributions of the one-point correlations and is provided. Results show that it is the longitudinal turbulent heat flux that predominantly contributes to turbulent transfers. Transfer rates increase on approaching the impingement region. The jet can be split into three regions: for x/2e < 5 one can still distinguish the separate influence of the two initial jets composing the curtain: for 5 < x/2e < 8.5, a transition zone exists where the two initial jets merge. In this region, transfers are not necessarily much higher. They are expected to intensify closer to the wall due to strong mixing in the impingement region.
Convection/diffusion experiment in the DMPC: example shows bottom outlet flow restricted to force convection across sample, which opposes diffusion flux.
Apparent flow resistance of seven fabrics as a function of relative humidity. 
Test Fabric Transport Properties
Model geometry to simulate convection/diffusion processes in the DMPC. 
A set of partial differential equations describing time-dependent heat and mass transfer through porous hygroscopic materials was developed. Water in a hygroscopic porous solid may exist in vapor or liquid form in the pore spaces or in bound form when it has been absorbed by the solid, which is typically some kind of hydrophilic polymer. Factors such as the swelling of the solid due to water imbibition, and the heat of sorption evolved when the water is absorbed by the polymeric matrix, were incorporated into the appropriate conservation and transport equations. A numerical code to solve the set of nonlinear coupled equations was developed, and applied to an experimental apparatus designed to simulate transient and steady-state convection/diffusion conditions for textile materials. Experimental measurements of air permeability and diffusion properties as a function of relative humidity provided fundamental data on the changes in transport properties as hygroscopic textiles fibers swell and decrease the free gas phase volume within the porous structure. When these relations were incorporated into the numerical model, it was possible to directly compare the predictions of the numerical code with results generated in the experimental apparatus. Results are shown for hygroscopic porous textiles under several conditions. Under pure diffusion, with no convective flows across the sample, the temperature changes of hygroscopic textiles subjected to step changes in environmental relative humidity are shown to agree with the numerical predictions. These temperature changes are due to sorption of water vapor from the flows on the two sides of the material, and relate to textile fiber equilibrium sorption isotherms and sorption kinetics, as well as the physical structure and thermal properties of the textile. Under conditions of both a concentration gradient and a pressure gradient across the fabric, which results in combined diffusion and convection, it is shown that the effect of fiber swelling, which results in significant changes in the resistance to convective flow, also has an effect on the resulting total mass flux across the textile layer.
Top-cited authors
Smith Eiamsa-Ard
  • Mahanakorn University of Technology
Pongjet Promvonge
  • King Mongkut's Institute of Technology Ladkrabang
Somchai Wongwises
  • King Mongkut's University of Technology Thonburi
Hakan Fehmi Öztop
  • Firat University
Masoud Afrand
  • Islamic Azad University, Najafabad Branch