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TEWL - TransEpidermalWaterLoss

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Welcome to the TransEpidermalWaterLoss Wiki

The wiki aiming to understand water loss through
the epidermis that anyone can edit

STARTED MAY 2008

IntroductionEdit

Trans-Epidermal Water Loss (TEWL) (or TWL) is...

a developing area of science attempting to evaluate water loss from plants or animals. Evaluation is usually confounded by organism controlled water loss*. The focus of this wiki is attempting to understand water loss from areas outside the control of the organism, often known as insensible water loss**. A more accurate but less manageable term could be Insensible Trans-Epidermal Water loss ( ITEWL ). This wiki understands that (with present understanding) it is impossible to define a dividing line with which to separate the organism from its epidermis***, however will attempt to elucidate mechanisms, and ultimately aid quantification in differing environments.

TEWL is a poorly understood topic due to complex factors relating to the epidermis of the plant or animal, and the complex science of evaporation and water vapor in the air. It is relevant to many real world situations affecting people, plants and animals.

Users of this wiki will probably accept that the existing science has its limitations****, and then be prepared engage in the wiki process to hasten understanding

* sweating, transpiration & seasonal epidermis adaptaions etc

** however medical POV defines insensible water loss to include water loss from lungs

*** for further clarity see(new page coming...)

**** thermodynamic fugacity etc


This Wiki is and is not like Wikipedia, anyone can edit here too, but Wikipedia is an encyclopedia, here More detail, Original Research and Community Building are permitted(see Wikia and Wikipedia) The host(Wikia) of this wiki is, at present, Ad-supported.

Not fully understood, yet.Edit

because the mechanisms of TEWL are not fully understood, the problem must first be defined, and this is probably the most major obstacle. The boundary of most(all?) organisms between internal and external is usually the epidermis. If the epidermis is to exist it must have a thickness, no matter how thin, and therefore we must therefore define the edges of the epidermis, and herein lies a problem.

The term Water Vapor Transmission Rate (WVTR) or Moisture Vapor Transmission Rate (MVTR) commonly measured in [Grams per SquareMetre per Day] is analogous with TEWL. However determining macro-conditions either side of a sheet material is far easier than micro-conditions between the inside and outside of an epidermis hour by hour, or even minute by minute.

Defining the scope of this WikiEdit

  • From the perspective of the organism.
  • Due to the interdisciplinary nature of this article it is suggested that complex discipline-specific terms are avoided)
  • Water loss to air (mediums other than air are unlikely to be considered)

Sub-types of TEWLEdit

  • internally heated organisms (eg warm blooded animals)
  • non-heated organisms (eg plants)

Who may be interested in this wikiEdit

Anyone wishing to better understand water loss through the epidermis that is incidental to major paths such as Perspiration and Transpiration. (ie, unregulated, unavoidable water loss)

  • Dermatology
  • Horticulture
  • Climatology (microclimate)

Clarification of definitionsEdit

  • sensible & insensible water loss
  • internal & external
  • humidity (relative, absolute, specific), vapor pressure deficit

Epidermis issuesEdit

Graphic5

water content versus skin depth. From: Electron Probe Analysis of Human Skin: Determination of the Water Concentration Profile. Ronald R Warner, Mark C Myers and Dennis A Taylor. J Invest Dermatol 90: 218-224; 1988. pdf.

Do salts on the epidermis 'harvest' airbourne water ? Wikipedia article on Critical relative humidity

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Air issuesEdit

Sha seasonal humidity

Animated Seasonal progression (Shanghai) if you know the origins of this graphic please edit here

Understanding the Enthalpy of a non-ideal gas (air) in a non-closed (open) system is probably important.

  • meteorologists are probably quite good at it but tend to hesitate the nearer to the ground where most epidermis(s) exist.
  • engineers tend to understand systems that are high energy, usually strong heating or strong cooling, and airbourne water becomes a small component. Energy transfer with steam is high temperature, high pressure.
  • The term 'Non-equilibrium thermodynamics' has produced a interesting article on Wikipedia, something relevent to the non-ideal gas that we mostly call air.

Clusters of water

two water molecules are called a dimer, but very small water droplets contain around a hundred molecules.
So what is between a dimer and an Aerosol?

Average Humidity

Is it possible to determine average Humidity ? - see Average humidity, this leads to deeper questions regarding sample rate and drift and humidity datum and (exposure: intensity or duration ? see Durational analysis )

LinksEdit

Wikipedia article on TEWL

Martin Chaplin (London South Bank University, UK) expansive site about water science

.pdf of lecture slides by Bob Imhof, London Southbank University and a vendor of instruments for skin bioengineering (Biox Systems Ltd) on TEWL and the Skin Barrier

David N. Blauch fundamentals of ideal gases (Java required for interactive learning)

molecular water

About Water Activity

Humidity Formulas

Enthalpy of Moist and Humid Air an engineering perspective

Air Density and Density Altitude Calculations

Learning about weather and climate (see chapters 3 to 7)

royalsociety.org Adaptation of metabolism and evaporative water loss along an aridity gradient (note in this publication TEWL means 'Total Evaporative Water Loss')

Lunar and Planetary Institute (search with http://www.lpi.usra.edu/publications/meetingpubs.shtml) for "Stability of Water and Gully Formation on Mars" - D. W. G. Sears, L. A. Roe, S. Moore. Interesting section on 'Theoretical estimation of evaporation rates on mars'

Alergologia e Inmunologia Clinica JOURNAL:Vol.15,Nº5 OCTOBER 2000 article"Atopic dermatitis" a recomendation of Temperature and Humidity for patients under section 'General hygienic measures' of 18degC@50%rh.Note:this Geographical region is Spain.

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TEWL - TransEpidermalWaterLoss - wiki address > www.tewl.wikia.com









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