Experimental Validation of the Heat and Mass Transfer Model for Convective Drying

Kowalski, Stefan Jan; Musielak, Grzegorz; Banaszak, J.

doi:10.1080/07373930601160940

Cited by 24 publications

(12 citation statements)

References 19 publications

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“…30°C ± 0.1°C). A similar intermediate plateau in the temperature distribution during the falling rate period was also noticed by Kowalski et al during their drying experiments, in which they have studied the convective drying of a cylindrical sample made of kaolin (radius 0.03m and height 0.06m) [27]. The temperature distribution was determined by temperature probes inside the sample, drying curves were determined by weighing of the sample.…”

Section: Measurement Resultsmentioning

confidence: 88%

Drying behaviour of calcium silicate

Belleghem

Steeman

Janssens

et al. 2014

Construction and Building Materials

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Nowadays, the hygrothermal performance of the building envelope is often evaluated using HAM (heat, air and moisture) models. These models can be used to predict the hygrothermal response of the building envelope and can assist in reducing the risk of any moisture-related damage (e.g. decrease of thermal insulation value due to wetting, interstitial condensation etc.). At the same time it is important to understand the physical mechanisms of wetting and drying of building materials. Experimental research can contribute to a better understanding of these mechanisms. In this paper the focus lies on the wetting and drying phenomena occurring in building materials. One specific material is highlighted: calcium silicate. Calcium silicate is an inorganic, hygroscopic and capillary active insulation material, which is often used in interior thermal insulations systems. The paper describes a drying experiment in which a calcium silicate sample dries out starting from saturation. The experiments showed that calcium silicate has an atypical drying behaviour: during the second drying phase an intermediate plateau was observed in the temperature course. Numerical simulations performed with a recently developed CFD-HAM model were compared with the experimental results and were used to explain the experimental observations. Nomenclature IntroductionDuring the last decades, the requirements for buildings have increased tremendously: a comfortable indoor climate and a healthy environment are desired for the building occupants, in combination with a sustainable and energy efficient design and a low energy use. Although the quality of building envelopes has grown during the last decades, moisture-related problems may still arise. Moisture-damage can be the result of rising damp, surface condensation (as a result of thermal bridges) or interstitial condensation (for instance caused by interior insulation systems). The presence of a high moisture content in building envelopes during service life should be avoided: an increased moisture content may lead to serious structural as well as to aesthetic problems: corrosion, loss of thermal insulation quality [1,2], mould and mildew [3], salt efflorescence [4,5] etc. Avoiding the risk of damage to the building envelope is related to the hygrothermal performance of building materials and building envelope systems. HAM (heat, air and moisture) models are widely used to predict heat and mass transfer in building envelope systems and allow building designers to evaluate the performance of the building and its envelope in advance or to suggest alternative solutions in case of deficiencies. The knowledge of the wetting and drying behaviour of building materials is an important aspect in this matter. In the past a lot of research has been done on the drying and wetting kinetics of porous materials in general and on building materials in particular. A wide range of textbooks can be found that describe the combined heat and moisture transport in porous materials [6,7]. Based on this knowl...

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Section: Measurement Resultsmentioning

confidence: 88%

Drying behaviour of calcium silicate

Belleghem

Steeman

Janssens

et al. 2014

Construction and Building Materials

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“…Although the theoretical analysis of the thermohygro-mechanical state of the kaolin plate under drying presented in this article was much simplified with respect, for example, to that in Kowalski et al, [21] it enabled drawing quite relevant and of practical importance conclusions. The first conclusion is that the volumetric (microwave) heating raises significantly the drying rate because of expulsion of the moisture due to both the thermal expansion and the thermodiffusional effect.…”

Section: Final Remarksmentioning

confidence: 97%

“…Substituting in formula (41) the temperature distribution given by (21) and the moisture distribution given by (28a) and integrating and rearranging slightly will yield the final form of the stress distribution in an elastic plate dried convectively in the constant drying rate period for the asymmetric problem:…”

Section: Stresses Induced In Convective Dryingmentioning

confidence: 99%

Analysis of Effectiveness and Stress Development during Convective and Microwave Drying

Kowalski

Mielniczuk

2007

Drying Technology

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The aim of the article is to study the effectiveness of convective and microwave drying with respect to drying time and stress generation in clay-like dried bodies. The theoretical analysis of stresses was confined to the constant drying rate period because clay shrinks and the stresses are generated mainly in this period. The theoretical prediction of stress development was validated using an acoustic emission method by monitoring the micro-and macrocracks formation caused by the stresses. Apart from the stress analysis, the combined convective-microwave drying was examined experimentally during whole process in order to show that the volumetric heat supply due to microwave heating enhances convective drying and, apart from this, such a combined drying process develops less stress in dried material. The theoretical and experimental studies were performed on a kaolin sample in the form of a thin plate. INTRODUCTIONThe negative feature of drying processes of capillaryporous materials is the problem of drying-induced stresses responsible for the material destruction. The tendency to stress generation increases with the rate of drying and the size of the drying body. Therefore, the efforts are made to find methods of stress minimizing and thus avoiding the drying body destruction when the drying rate increases.The main aim of this article is to prove the hypothesis that a combined convective-microwave drying shortens the drying time and also diminishes the tendency to stress generation. The hypothesis is based on the statement that the volumetric heat supply, as it takes place in microwave heating, increases the temperature inside the body and thus causes a coincidence of the thermodiffusional and the diffusional moisture fluxes. Such a flux coincidence raises the moisture outflow and moderates its distribution

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“…Diffusion is a slow mass transfer process in comparison with evaporation happened at the second period, and the water transfer rate is correspondingly decreased to form a non-linear drying result until reaching the final moisture content at o. A typical fabric drying curve shows the three drying periods Kowalski et al (2007) has employed partial differentiation and numerical analysis tools to present thermo-mechanical properties of a drying process for porous materials. However, the modeling process is computational intensive and time consuming.…”

Section: Three Periods Of a Fabric Drying Cyclementioning

confidence: 99%