Structural Drying >> Ceiling Leak Mold From Pipe Break

However, this relationship could not be proven by experimental investigations on other materials. Scheffler (2008)showed measurement results for a calcium silicate insulation material and a ceramic brick. Both materials have a distinct first drying phase. All results indicated a linear relationship between first drying phase duration Ceiling Leak Mold From Pipe Break and sample height. 

Onechart of these results is shown in Figure 2 at the right. The studywas performed with samples of different diameter and heightand for different vapor transfer conditions to study these influences as well. All results showed a perfectly linear relationship.These discrepancies stipulated an additional study toinvestigate how these differences can occur Ceiling Leak Mold From Pipe Break and understand what influence on the drying process might have caused them. 

ANALYSIS OF THE INFLUENCES ON THE DRYINGThe analyses compared measurement against simulationresults, one-dimensional models against three-dimensionalreality, Ceiling Leak Mold From Pipe Break and different materials with different sample heights.From this, a set of possible influences to investigate wascompiled:1. Influence of heat and vapor transfer coefficients.

Influence of the applied material Ceiling Leak Mold From Pipe Break and simulation model 3. Influence of accounting for or neglecting the threedimensional heat transport 4. Influence of the initial moisture content 5. Influence of the investigated sample heights Investigating these would shed light not only on theparticular discrepancy between measurement and simulation,but also on the influences of the drying experiment in general.

Heat and Vapor Transfer (1)The heat and vapor transfer conditions significantly influence the slope of the drying curve during the first drying phase, Ceiling Leak Mold From Pipe Break and by that also the first drying phase duration. This becomesclear when looking at the left chart of Figure 3, where simulation results of a ceramic brick drying are shown. 

The only changed parameter is the vapor transfer coefficient ß. Not only the first drying phase duration, Ceiling Leak Mold From Pipe Break but also the moisture content at its end are influenced by the transfer conditions at the material surface.

(1)where LE = Lewis number for water vapor given with LE = 0.87 m = dimensionless parameter, Ceiling Leak Mold From Pipe Break according to Baer and Stephan (2003), m = 1/3 = heat transfer coefficient= gas constant for water vapor= Kelvin temperature= specific heat capacity (isobaric condition)= density of air.

The simulation study of Krus et al. (2007) used the analogy between heat and vapor transfer coefficient, Ceiling Leak Mold From Pipe Break also known asthe LEWIS-relation (Equation 1). Evaluation of dryingmeasurements indicated that this relation does not always hold for experiments with higher airflow velocities. However, this is only important if experiment and simulation are compared.

For a simulation study using the same heat and vapor transfercoefficients in all cases, Ceiling Leak Mold From Pipe Break this does not lead to different results.Material and Moisture Transport Model (2)The quality of the applied material functions is an often disputed problem whenever numerical simulations are carriedout. The approximation quality of the material functions iscrucial for any calculation where the results need to be correct.

To exclude any such influences from the discussion, Ceiling Leak Mold From Pipe Break drying simulations were performed with two different material andtransport models according to Krus and Holm (1999) andScheffler and Plagge (2010).The material functions were adjusted according to thesemodels to measured brick data. 

Drying simulations wereperformed while the liquid transport function was slightlyvaried (for both the whole function Ceiling Leak Mold From Pipe Break or only in the lower moisture content range). These calculations produced different but very similar results. All of them showed a linear dependencebetween first drying phase duration and sample height. 

Therefore, the applied model and the approximation quality do notexplain the differences and are of minor importance here.Three-Dimensional Heat Transport (3)Due to the cooling effect of evaporation, Ceiling Leak Mold From Pipe Break the drying surface of a material sample is significantly colder than thesurrounding air. 

As the sample has a finite dimension, heat isnot only transferred from the top (air) and bottom (materialsample) surfaces, but also from the lateral sides of the sample.This leads to a distinct temperature distribution at the drying surface, Ceiling Leak Mold From Pipe Break which in turn causes a vapor pressure distribution there. Consequently, the evaporation rate is not the sameeverywhere at the drying surface.

As the lateral heat flow increases the temperature, thiseffect increases the evaporation rate and, hence, Ceiling Leak Mold From Pipe Break the dryingspeed. This becomes visible in the right-side chart of Figure 3.Here, radial-symmetric three-dimensional simulation resultsfor a ceramic brick drying are displayed. The only variedparameter is the sample diameter, where one-dimensionalcorresponds with an infinite sample diameter.

The influence is clearly visible. This effect is particularlyimportant when comparing experimental data with simulationresults, Ceiling Leak Mold From Pipe Break and the main reason why cylindrical samples should beused for drying experiments (Scheffler and Plagge 2005). The simulation results according to Krus et al. (2007)were done one-dimensionally. 

This might lead to deviationsbetween measured Ceiling Leak Mold From Pipe Break and calculated drying curves, but it doesnot change the relationship between first drying phase duration and sample height from linear to square root. The influence of three-dimensional heat transport is therefore not thereason for the observed deviations. Initial Moisture Content (4)The initial moisture content has a significant influence onthe first drying phase duration. 

The more water needs to beevaporated through a certain surface, the longer it takes.Figure 4 illustrates this with simulation results of a ceramicbrick drying starting from different initial moisture contents.As the initial moisture content is very important for thefirst drying phase duration, Ceiling Leak Mold From Pipe Break it should receive special attention.In order to make results comparable, all investigations shoulduse the same initial moisture content. 

For a simulation, any moisture content can be adjusted and assigned in an even distribution. For an experiment, Ceiling Leak Mold From Pipe Break this is not easily possible. The experimental drying normally starts after a completed water absorption experiment. 

This means that the mean moisture Ceiling Leak Mold From Pipe Break content that is established inside the sample will rangebetween capillary and effective saturation. A drying simulation should therefore start from the moisture content reachedafter a water absorption experiment.

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