Generalized equation of moisture diffusivity and its solution

The generalized equation of moisture diffusivity in capillary-porous bodies is examined, and solutions are given for different boundary conditions.     

On how the moisture diffusivity in hydraulic cement is affected by the type of bond between the moisture and the material

The moisture diffusivitya _m in hydraulic cement is calculated over the entire range of moisture content levels, including the wet and the hygroscopic state. The values obtained here account for the variation of the diffusivity as a function of the temperature and of the moisture content simultaneously.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 4, pp. 694–700, October, 1973.     

An experimental study of heat transfer in water condensation inside vertical tubes

A function is described which satisfactorily generalizes experimental data on heat transfer in water vapor condensation within vertical steel tubes for various hydrodynamic flow modes of the condensate film.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 26, No. 6, pp. 1086–1088, June, 1974.     

A model for non-fickian moisture transfer in wood

A model for non-Fickian moisture transfer in wood is presented. The model considers the transfer of water vapour separate from the transfer of bound water. These two components are linked by an equation describing the sorption on the cell wall level. Hereby, a formulation capable of describing known non-Fickian effects, including the effects of step size, absolute moisture content, and sample length, is achieved. The sorption curves predicted by the model are compared with experimental results and good agreement is found.

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Réssumé Un modèle pour le transfert non-Fickien d'humidité dans le bois est présenté. Le modèle considère le transfert de la vapeur d'au séparé pour le transfert de l'eau liée. Ces deux composants sont liés par une équation décrivant la sorption au niveau de mur de cellules. Par ceci, une formulation capable de décrire des effets non-Fickian connus, comprenant les effets de la taille d'étape, le contenu d'humidité absolu, et la longueur d'échantillon, est réalisée. Les courbes de sorption prévues par le modèle sont comparées aux résultats expérimentaux et une bonne concordance est trouvée.

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Effect of radiation heat transfer on thermal diffusivity measurements

Experimental data on thermal conductivity and thermal diffusivity of a semitransparent material generally include an error due to the radiation heat transfer. This error varies in accordance with the experimental conditions such as the temperature level of the sample and the measuring method. In this paper, research on the influence of radiation heat transfer on thermal diffusivity are reviewed, and as an example, the method to correct the radiation component in the apparent thermal diffusivity measured by the stepwise heating technique is presented. The transient heat transfer by simultaneous thermal conduction and radiation in a semitransparent material is analyzed when the front surface is subjected to stepwise heating. The apparent thermal diffusivity, which includes the radiation component, is calculated for various parameters.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Experimental study on the heat transfer and flow characteristics of nanorefrigerants inside a corrugated tube

The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b.     

Water vapor transfer coefficients for calculating the moisture conditions in walls

Data are given on the computation of surface moisture transfer coefficients and vapor permeability coefficients for the diffusion of water vapor through walls. The theoretical results are compared with the available experimental values.     

Experimental study of turbulent single-phase flow and heat transfer inside a micro-finned tube

Single-phase heat transfer and pressure drop characteristics of a commercially available internally micro-finned tube with a nominal outside diameter of 7.94 mm were studied. Experiments were conducted in a double pipe heat exchanger with water as the cooling as well as the heating fluid for six sets of runs. The pressure drop data were collected under isothermal conditions. Data were taken for turbulent flow with 3300 ≤ Re ≤ 22,500 and 2.9 ≤ Pr ≤ 4.7. The heat transfer data were correlated by a Dittus–Boelter type correlation, while the pressure drop data were correlated by a Blasius type correlation. The correlation predicted values for both the Nusselt number and the friction factors were compared with other studies. It was found that the Nusselt numbers obtained from the present correlation fall in the middle region between the Copetti et al. and the Gnielinski smooth tube correlation predicted Nusselt number values. For pressure drop results, the present correlation predicted friction factors values were nearly double that of the Blasius smooth tube correlation predicted friction factors. It was also found that the rough tube Gnielinski and Haaland correlations can be used as a good approximation to predict the finned tube Nusselt number and ffriction factor, respectively, in the tested Reynolds number range.     

Mesh adaptive finite element formulation for moisture transfer in materials with a critical moisture content

Wetting or drying of most open porous building materials is characterized by a sharp moving waterfront. Due to the high moisture gradients at the waterfront, an accurate finite element simulation requires a very fine mesh. To reduce computational costs a mesh adaptive method based on the Arbitrary Lagrangian Eulerian (ALE) technique is proposed. To continuously relocate the nodes on the computational domain a remesh‐indicator is equally distributed. In problems of water imbibition or drying of open porous building materials specific attention has been paid to the zone of critical moisture content. To this extent the traditional jump‐based indicator, quantifying the jump of a selected state variable, has been modified into an area‐based remesh‐indicator. An error analysis of an academic example shows that the area‐based indicator is superior to the jump‐based one. To illustrate the capabilities of the remeshing method based on an area‐based indicator, one and two‐dimensional examples of water imbibition of ceramic brick and drying of cellulose fibre cement are included. Copyright © 1999 John Wiley & Sons, Ltd.     

A numerical study on heat transfer of the nanofluid flow inside helical tube through the two-phase method

In this study, a new numerical investigation was carried out to study the heat transfer characteristics of nanofluid flow inside a copper helical tube under constant heat flux. A nanofluid with different particle weight concentrations of 0.5%, 1.0%, and 2.0% was used. The effects of different parameters such as Reynolds number, nanofluid particle concentration, and constant heat fluxes (1500 and 3800?W/m²) on heat transfer coefficient were studied. For validation, Nusselt number and convection heat transfer coefficient obtained from the numerical model was compared with the experimental results. Also, to verify the accuracy of the method, grid independency was studied for each heat flux. The observations showed that the heat transfer coefficient increased by using nanofluid instead of base fluid. In addition, the convection heat transfer coefficient performance improved by increasing the nanoparticles’ concentration. The results from the numerical simulation compared with the experimental data showed that this new numerical method has high accuracy and could correctly predict the heat transfer behavior of nanofluids with different weight particle concentrations under constant heat flux.     

Aspects of the study of moisture transfer in composite materials with the help of x-ray computational tomography

Questions associated with the assumptions employed in x-ray computational tomography, the choice of data processing regime, and the thickness of the scanned layer are studied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 6, pp. 924–929, December, 1988.     

垂直管内沸腾传热实验研究

重点介绍垂直管内低过热度下沸腾传热性能的测试装置和方法、数据处理及相关计算方法。实验装置采用套管换热器模型,以蒸汽为热源,整体构成一逆流换热空间。通过测取蒸发速度、温度等相关参数,得到在不同蒸汽压力、温度下的总传热系数、沸腾传热系数与热流密度、蒸汽侧压力的关系曲线,从而得出单管在何种状态下沸腾传热性能,并对两试件(光管和高通量管)进行性能对比实验研究,比较其传热性能。     

Determination of the thermal and the moisture diffusivity in a porous body from the kinetic characteristics of the drying process

A method is proposed for simultaneously determining the thermal and the moisture diffusivity in a porous body during drying. The results of such a determination are presented, together with the Lykov number for drying cellulose.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 4, pp. 635–639, April, 1972.     

Transient hygrothermal stresses in composites: Coupling of moisture and heat with temperature varying diffusivity

In this paper, the influence of coupled diffusion of heat and moisture on the transient stresses in a composite is investigated analytically where the moisture diffusion coefficient is taken to be temperature dependent while the thermal diffusion coefficient is kept constant. There is no a priori reason why moisture and temperature should be uncoupled such that each will obey the simple diffusion theory, particularly without reference made to the initial and boundary conditions of a particular situation. A study of the coupled diffusion equations were made by a finite-difference scheme allowing for time-dependent changes in the humidity and temperature of the environment. The appropriate transient boundary conditions are specified on the surfaces of an infinite plate. Numerical calculations were carried out for the T300/5208 graphite fiber-reinforced epoxy matrix composite in which the nonuniformity of moisture and temperature is evaluated for sudden changes in the surface moisture and/or temperature. The coupling effect between temperature and moisture is found to be most significant when the plate undergoes a sudden change in surface temperature while the surface moisture concentration is held constant. The present findings indicate that the stresses due to coupling can deviate from the uncoupled results anywhere from 20 to 80% depending on the surface temperature gradient. This suggests the need to perform additional experiments for evaluating the coupled diffusion phenomenon and its influence on the mechanical behavior of epoxy-resin-composites.     

Thermo/moisture responsive shape-memory polymer for possible surgery/operation inside living cells in future

The recoverable strain of shape-memory polymers (SMPs) is an order higher than their metal counterpart, i.e., shape-memory alloys. The recent finding of the influence of moisture on the glass transition temperature of a polyurethane SMP, which is traditionally known for its thermo-responsive nature, enables us to realize not only water-driven for shape recovery, but also recovery following a pre-determined sequence. Utilizing these features of this SMP, we propose the concept of delivering a tiny device which is made of this material into a pore through a very small hole. The feasibility of the concept is demonstrated experimentally. This concept could eventually be used to deliver a micro/nano device into living cells for surgery or operation inside of them.     

Moisture transfer of certain bodies with volumetric moisture absorption

An analytical solution is given to a boundary problem of the third kind, that of moisture transfer for bodies in the form of an infinite plate and an infinite cylinder, based on the generalized equation of moisture conduction, suggested by A. V. Luikov [1].     

R32/R134a水平内螺纹管内流动沸腾强化换热实验研究

对非共沸混合制冷剂R32／R134a(25％Wt／75％Wt)在水平内螺纹强化管中的流动沸腾换热特性进行了研究。实验结果表明：在内螺纹强化管中的流动沸腾换热性能比在光管中有较明显的提高,强化管强化系数变化的大致范围为1．5～2．2。根据活化穴、二次流和毛细提升三者之间的相互作用,探讨了内螺纹强化管的强化机理;并从重力影响、非共沸混合工质组分差与二次流影响的角度上,对在环状流下混合工质剂2／R134a在内螺纹强化管和光管中流动沸腾换热时管子周向壁温的变化特征作出了分析。     

Study of mass transfer in the extraction of moisture from capillary-porous materials

Processes of extraction of water from moist clay minerals by an organic solvent, dioxane, are examined. It is shown that these processes conform to the fundamental laws of mass transfer.     

Numerical solution of an inverse diffusion problem for the moisture transfer coefficient in a porous material

On the basis of the solution of a nonlinear diffusion equation with initial and boundary conditions, a transfer coefficient of moisture in a sample of a porous material is found by minimization of a functional, which expresses error of the calculated profile of moisture concentration in well defined time moments from their experimental values for the defined moisture transfer coefficient. In this case the transfer coefficient as opposed to previous studies is found as a sum of a power function and an exponential function of the moisture concentration. The exponent of the power function depends on time. Thus, a more accurate coincidence of the calculated profiles of the moisture concentration to their experimental profiles is gained in comparison to the investigations performed by other authors. The exponential term provides a good coincidence of the mentioned profiles for big times nearby the boundary of the sample, where the moisture evaporation to the atmosphere takes place.