Condensation Corrosion: A Theoretical Approach

Abstract

Condensation of water from warm, humid air to cold rock walls in caves is regarded to play a significant role in speleogenesis. The water condensing to the cave walls quickly attains equilibrium with the carbon dioxide in the surrounding air, and consequently dissolves limestone or gypsum forming various types of macro-,meso-, and micromorphologies. In this paper we present the basic physical principles of condensation and give equations, which allow a satisfactory estimation of condensation rates. Water condensing to a cooler wall releases heat of condensation, which raises the temperature of the wall thus reducing the temperature difference ΔT between the warm air and the cave wall. Furthermore one has to take into account the heat flux from the air to the cave wall. This defines the boundary conditions for the equation of heat conduction. For a constant temperature of the air initial condensation rates are high but then drop down rapidly by orders of magnitude during the first few days. Finally constant condensation rates are attained, when the heat flux into the rock is fully transmitted to the surface of the karst plateau. For spherical and cylindrical conduits these can be obtained as a function of the depth Z below the surface. When diurnal or seasonal variations of the air temperature are active as is the case close to cave entrances, condensation rates can become quite significant, up to about 10 -6 m/year. The theoretical results are applied also to corrosion of speleothems and the formation of »röhrenkarren« as described by Simms (2003). To convert condensation rates into retreat of bedrock the saturation state of the solution must be known. In the appendix we present experiments, which prove that in any case the solution flowing off the rock is saturated with respect to limestone or gypsum, respectively.. O speleogenetskem pomenu vode, ki iz toplega vlažnega zraka kondenzira na hladne jamske stene je napisanega veliko. Kondenzirana voda se hitro uravnoteži z ogljikovem dioksidom v jamski atmosferi, zato raztaplja apnenec in pri tem tvori različne skalne oblike. V članku predstavimo fizikalne osnove in podamo enačbe, ki omogočajo približno oceno hitrosti kondenzacije v različnih pogojih. Zaradi kondenzacijske toplote in prenosa toplote iz zraka na steno, se temperatura stene viša, pri čemer se zmanjšuje razlika temperature med zrakom in steno. To predstavlja robni pogoj za prevajanje toplote iz jame. Pri konstantni temperaturi zraka, hitrost kondenzacije v nekaj dneh pade za več velikostnih redov, dokler ne doseže končne vrednosti, pri kateri se ves toplotni tok prenese na površje. Slednjo za primer krogelnih in valjastih prostorov opišemo kot funkcijo globine rova Z. Pri dnevnih in sezonskih spemembah temperature, značilnih v bližini jamskih vhodov, je hitrost kondenzacije in posledično korozije do 1μm na leto. Teoretične rezultate uporabimo tudi za izračun korozije kapnikov in tipa škrapelj (röhrenkarren), ki jih opisuje Simms (2003). Za pretvorbo hitrosti kondenzacije v hitrost korozije, potrebujemo...

Consider a cylindrical cave: A physicist's view of cave and karst science

“…Cigna 1993;Hoyos et al 1998), and the formation and evolution of caves over time (e.g. Dreybrodt et al 2005b;Covington et al 2013). Fig.…”

“…Meteorology also affects the formation of caves through condensation. The amount of con densed water can be significant (Dublyansky & Dublyansky 2000), and as it initially contains dissolved carbon dioxide but no minerals it is typically fairly aggressive (Dreybrodt et al 2005b). Condensation corrosion has been proposed to explain the formation of large cupolas (Audra et al 2002).…”

“…Steady state condensation requires a source of water that is warmer than the surroundings (Sarbu & Lascu 1997), and its rate is limited by heat conduction through the bulk of the rock away from the cave wall. The geometry of the cave and the surrounding rock has a strong influence on the rate (Dreybrodt et al 2005b). In the case of periodic condensation, temperature variations cause heat to be stored in a layer of rock surrounding the cave and dispersed back during colder periods.…”

Morphological and mineralogical evidence for ancient bat presence in Cova des Pas de Vallgornera (Llucmajor, Mallorca, Western Mediterranean)

“…The existence of bat-derived features (bat claws and thumb marks) caused by biomechanical erosion on walls and ceilings, could possibly be explained because their surfaces were already affected by deep weathering processes which would be related to condensation-corrosion processes. The latter happening when the temperature of the cave walls is below the dew point of the cave air; water condensates and reaches an equilibrium with the partial pressure of CO 2 of the cave atmosphere, provoking an aggressive solution that is able to dissolve limestone (Dreybrodt et al, 2005). During the period the cave entrances remained opened and bats inhabited in there, the already mentioned air movements (cold winter air from the surface) would have increased the condensation-corrosion rate causing a strong and faster weathering that affected walls and ceilings, allowing bat biomechanical erosion.…”

Modeling microfracture geometry to the asses the function of a karst system (Vízfő spring catchment area, Western Mecsek Mountains, Hungary)

“…In the early 1990s, karst system modelling was mainly used to reconstruct individual fracture developments (e.g., PALMEr, 1991;DrEybroDT & GA-broVšEK, 2000b;bAUEr et al, 2000). From the mid-1990s, technology enabled 2D models to also be used (KAuF MANN & brAUN, 1999bAUEr et al, 2002bAUEr et al, , 2003KAUFMANN, 2003a,b;DrEybroDT et al, 2005). We can now construct 3D numeric models, even though this is a complex, multi-step process.…”