Structural Drying >> Storm Damage Roof Leak

Hygrothermal building component simulation requires a complete set of storage and transport functions. Such functions are typically determined by the aid of material models defining a set of functions that are adjusted to basic material data. Basic material data consists of either single parameters or measured functional courses of, Storm Damage Roof Leak for example, water uptake or drying. 

For parameter adjustment during material modeling, functional courses are most reliable. For a simple comparison of material properties,though, single number material parameters are more appropriate.The drying behavior of building materials is rather complex, Storm Damage Roof Leak which is the reason why a single-number drying coefficient does not yet exist. 

Some first attempts to standardize drying data have been made. However, these did not yet result in a consistent drying coefficient definition.The paper briefly introduces the different dependencies of the drying process. Data from experimental Storm Damage Roof Leak and numerical investigations is provided and discussed. On this basis, a new drying coefficient for building materials is defined. 

This coefficient isultimately discussed with regard to its meaning as well as its additional information content compared to other moisture transportcoefficients. The moisture transport properties significantly influencethe application, durability, Storm Damage Roof Leak and particular structural behaviorof building materials. 

Investigations of such behavior areeither done experimentally or by numerical simulation (Pedersen 1989; Künzel 1994; Janssen et al. 2007; Nicolai et al.2010). The moisture transport behavior is important in bothcases and can be derived for the different moisture contentranges from vapor diffusion, water absorption, Storm Damage Roof Leak and drying experiments.

The water absorption experiment provides information about the Storm Damage Roof Leak material’s transport properties for liquid water. The measurement conditions comprise water contents close tosaturation. The vapor diffusion experiment provides informationabout the material’s moisture transport properties in the hygroscopic moisture range. 

It comprises mainly vapor transport.Measurements at higher relative humidities include unsaturated liquid transport as well. The drying experiment provides information about liquid Storm Damage Roof Leak and vapor transport properties. It comprises the whole range from saturated liquid to only vapor transport and, hence, marks the link between the two other experiments.

This is the reason why the drying experiment is considered to be very important for the hygric material characterization (Krus and Holm 1999; Storm Damage Roof Leak Scheffler 2008). It reveals moisturetransport information within the largest range of moisture stages. Drying is an integral transport experiment that does notrequire expensive equipment to be performed. 

However, thedrying is much more dependent on the boundary and transfer conditions than the other two experiments. Therefore, all ofthese conditions have to be known for a proper data analysis. At present, the drying experiment is not standardized, and Storm Damage Roof Leak a simple material parameter to be derived does not exist. 

Therefore, this paper first investigates the drying process andits governing influences and then reviews some first attemptsto derive a simple material coefficient. On that basis, Storm Damage Roof Leak theauthors propose a new drying coefficient for building materials and discuss its meaning and its correlation to the othertransport parameters.

Basics of the Drying Process In general, Storm Damage Roof Leak drying is a three-dimensional heat and moisture transport phenomenon that includes evaporation cooling,which leads to a temperature and also to a moisture profile.The drying behavior of porous materials depends on thefollowing: material properties (moisture storage and transport) 

Climatic conditions (temperature and relative humidity) transfer conditions for heat Storm Damage Roof Leak and vapor (air velocity andsurface roughness [Worch 2004])The material properties influence how quickly moisturecan be transported inside the material. The combination ofclimatic and transfer condition.

The boundary conditions—defines the speed Storm Damage Roof Leak and quantity of moisture that can betransported to the surrounding atmosphere. Figure 1, left side,illustrates these influences. This also becomes visible in amaterial’s drying curve (Figure 1, right side). Two distinctphases, called first and second drying phase (Krischer andKast 1992), can be distinguished. 

The first drying phase is characterized by an almost linear weight loss in time. During this phase, Storm Damage Roof Leak the material transports moisture faster to the evaporation surface than what can evaporate. During the first drying phase, the drying is limited by the boundary conditions.In the second drying phase, this physical phenomenon reverses. 

The moisture transport becomes slower Storm Damage Roof Leak and the boundary conditions allow more moisture movement towardthe surrounding air than actually arrives at the surface. The process is slowed and a distinct moisture content profile develops inside the material. During the second drying phase, thedrying is limited by the material properties. 

When performing these drying experiments, this is theinteresting part of the results because it reflects the materialbehavior. Adjustment and approximation procedures, Storm Damage Roof Leak as introduced by Krus and Holm (1999), Scheffler (2008) and Scheffler and Plagge (2010) can interpret the physics of the seconddrying phase. 

For a more detailed analysis of the dryingprocess and how to measure and interpret such data, Storm Damage Roof Leak see Scheffler and Plagge (2005).Since the drying is influenced by many conditions, it isimportant to conduct drying experiments under standardizedconditions or measure all influencing parameters—i.e., relative humidity and temperature of the environment and surfacetemperature of the evaporation surface. 

Until now, a standardfor drying experiments does not exist. Moreover, it is verydifficult to maintain constant and reproducible conditions during the drying. Therefore, Storm Damage Roof Leak it is recommended that all conditions be measured Problems in Drying Coefficient Derivation

The different dependencies of the drying experiment ongeometrical, initial, and boundary conditions, as well as on thematerial properties, Storm Damage Roof Leak make the derivation of a simple singlevalue material parameter very difficult. Within the German national research project MASEA, aimed at developing amaterial database for old existing building materials (see also,BINE 2007), discussions on a drying coefficient were started. 

It quickly became clear that time Storm Damage Roof Leak and sample height play an important role and must be combined. Krus et al. (2007) published their first considerations and proposed to plot the duration of the first drying phase versus sample height. 

Based on a simulation study with constant climatic conditions, they had obtained a square root of sample height relationship. Similarly to the water absorption coefficient, Storm Damage Roof Leak the drying coefficient was proposed to be the slope of this curve in a square root ofsample height scale.

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