Defect and Diffusion Forum Vols. 297-301

Abstract: The heat transfer performance of heat exchanger plate decreases as time goes by. The main reason for this phenomenon is the fouling of the heat exchanger plates. To remove the fouling, we have usually cleaned the plate of heat exchanger using chemicals or polishing brush or cloth with hand after stopping the equipment and disassembling the heat exchanger. However, to clean the plate using these methods, the heat exchanger equipment needs to be stopped and disjointed. In addition, it must be re-jointed after cleaning. Especially, the concern of environmental pollution happens in case of using chemicals. Therefore, we need to develop an automatic fouling removal equipment which can continuously keep high heat transfer efficiency and solve the problem of environmental pollution. So, in this paper, we developed and tested the equipment which can clean the fouling on heat exchanger plates automatically per constant period and interval using air bubbles. The total heat transfer coefficient decreased with a slower tendency when using air bubbles compared to the existing methods. There was 10% higher heat transfer effect air bubbles every 10 minutes for 2 hours to remove the fouling ingredients on the heat transfer surface area concerned to the case without air bubbles after 192 hours.

Abstract: The heat and water vapour transmitting properties of fibrous materials are important factors that affect the clothing's comfort as well as the quality of special functional clothing that is worn in extreme environmental conditions. The paper introduces advanced system for the simulation of physiological processes that appear next to the human skin. Its use enables the measurement of heat and vapour transfer trough fibrous structures, as well as determination of vapour permeability and permeability index. The experiments reported here refer to the measurement of a number of fibrous materials used for the next-to-skin wear. For the measurement have been produced materials that differ either in their structure or raw material in order to observe the influences of different parameters to the transfer properties. The transfer trough fibrous materials is mainly affected by its structure that comprises of a repeat units with cellular geometry containing air pores, yarns that form basic structure and intersection points of two or more yarns. Therefore, the structure of materials is also investigated and described by means of fabric moduli. Dynamics of heat and vapour transfer is observed through the experimentally obtained data and the influence of a number of structural parameters is discussed. The statistical methods are used to qualify the effects of investigated variables on the heat and vapour resistance.

Abstract: This paper investigates the thermal properties of metallic open-cell and closed-cell foam structures in space filling and non-space filling configurations. In both, i.e. open-cell and closed-cell structures, a linear trend depending on the relative density has been reported. However the closed-cell structures compared to open-cell ones have a higher thermal conductivity for the same relative density.

Abstract: First discovered by the late Dr John Manning, the vacancy-wind effect is a subtle phenomenon that occurs when two or more atomic species compete for vacancies in a net vacancy flux. The vacancy-wind effect is incorporated in (for example) the vacancy-wind or Manning factor that appears in the Darken-Manning Equation relating the interdiffusivity, the tracer diffusivities and the thermodynamic factor. The mechanism of the vacancy-wind phenomenon has long been very poorly understood. Recently, a moving reference frame Monte Carlo method was used to illustrate graphically how the vacancy-wind effect operates in both ionic conductivity in an ionic solid with a dilute solute and chemical interdiffusion in concentrated alloys and ionic compounds. That strategy is extended in this paper to show graphically how the vacancy-wind effect operates in interdiffusion in a stoichiometric intermetallic taking the B2 structure. A simple 4-frequency vacancy diffusion model is used. In previous work, it was shown that depending on composition and temperature, this model can exhibit the six-jump-cycle mechanism. It is shown that in the limit of perfect order that there is no vacancy-wind effect associated with this mechanism when both types of cycle operate equally (zero net vacancy flux). The non-unity value of the vacancy-wind factor found for this mechanism under zero vacancy flux conditions is purely a consequence of a particular geometric mix of tracer and collective atom displacements. The concept that a non-zero off-diagonal phenomenological coefficient provides the vacancy-wind effect is verified.

Abstract: Recently, the transition point between the Harrison Type-A and Type-B kinetics regimes as well as the emerging intermediate AB transition regime have been analysed in detail by making use of Lattice Monte Carlo (LMC) simulations of tracer depth concentration profiles as a function of diffusion time and distance between grain boundaries e.g. [1-3]. In the present study, we analyse Harrison Type-B to Type-C kinetics regimes in the transient grain boundary diffusion problem using the parallel slabs model and LMC numerical simulation. The transition point where the Harrison Type-B kinetics regime last occurs (transition point between the Harrison Type-B kinetics and the Type-BC kinetics) is estimated at  (= 0.5δ(Dlt)-1/2) = 0.1. The Harrison Type-C grain boundary diffusion kinetics regime is also analysed using LMC simulated concentration depth profiles. The transition point where the Harrison Type-C kinetics regime first occurs (transition point between the Type-BC kinetics and the Harrison Type-C kinetics) is estimated at  = 5.0. Therefore an intermediate Type-BC regime can be expected to occur between 0.1 <  < 5.0. Preliminary results for the cubic grain model show that the interval for the intermediate Type-BC regime is somewhat narrower for this model and occurs at 0.5 <  < 5.0.

Abstract: This work presents experimental values of Moisture Buffer Value (MBV) obtained with three different samples of building materials, using a non-stationary process of moisture absorption. The tests carried out at the laboratory tried to explore the importance of some of the variables that can interfere in the final results, such as materials themselves, temperature level and the use of finishing coatings. The experimental data obtained at 15°C and 23°C were then analyzed using the second order sorption kinetic model. The application of kinetics models to the experimental results was explored and several parameters were retrieved. A proposal for the use of these parameters is presented and its practical use is discussed.

Abstract: The present work describes the mass transfer process between a moving fluid and a slightly soluble flat surface buried in a packed bed of small inert particles with uniform voidage, by both advection and diffusion/dispersion. Numerical solutions of the differential equations describing solute mass conservation were undertaken to obtain the concentration profiles, for each concentration level. A simple mathematical expression that relates the dependence between concentration and axial distance is proposed to describe the approximate size of the diffusion wake downstream of the reactive solid mass.

Abstract: This paper describes a simple experimental technique, easy to set-up in a laboratory, for the measurement of solute solubility in liquids (or gases). Experimental values of solubility were determined for the dissolution of benzoic acid in water and salicylic acid in water, at temperatures between 5°C and 70°C. The solubility experimental values obtained are in good agreement with the theoretical values of solubility and the empirical correlations presented in literature. The results show that it is possible to obtain good results for solubility values, using a simple and inexpensive experimental technique.

Abstract: This work present a model for prediction of moisture gain over storage time for individually packaged, which considered both the moisture transfer through the polymeric film to the headspace and from the headspace to the product. The transport of moisture between the headspace and each product was assumed to be controlled by external resistance. No interaction between the packaged components was considered. Moisture content within the product was assumed to be uniform for a given time and to relate to the headspace humidity by the GAB sorption isotherm. The isotherm parameters were determined by equilibrating samples at different relative humidity. The transient period of these experiments was used to estimate the mass transfer coefficients. The model was validated by monitoring the moisture take up by breakfast cereal and chocolate powder packed individually in different materials, oriented polypropylene (OPP) and low density polythelene (LDPE), during storage at 25°C and 75% RH (relative humidity). The model provided very good fits for the products packaged individually (with r2 above 0.99).

Abstract: In this paper a mathematical model for prediction of moisture gain over storage time for binary mixtures of moisture sensitive products was developed, which considered both the moisture transfer through the polymeric film to the headspace and from the headspace to the product. Moisture content within the product was assumed to be uniform for a given time and to relate to the headspace humidity by the GAB sorption isotherm. The transient period of these experiments was used to estimate the mass transfer coefficients. The model was validated by monitoring the moisture take up by breakfast cereal and chocolate powder mixture in different materials, oriented polypropylene (OPP) and low density polythelene (LDPE), during storage at 25°C and 75% relative humidity (RH). The model showed that for mixes some bias was clear, particularly for the cereal, probably owing to interactions between the products. If the resistance of the product to moisture uptake were not taken into consideration, the model would over-predict the experimental results by up to 20%.