avsdS:nelson (12/17/82)
Thermal expansion of air inside the bag is obviously the reason it inflates. I don't know where you got an "expansion coefficient" for air, but such numbers apply to solids and liquids, not gases. The gas law is PV = nRT, which means that when the temperature doubles so does the volume (or pressure). Undoubtedly both the pressure and volume increase in the tea bag. The water film that covers the bag after it gets wet makes it much less permeable; coarser mesh bags would deflate easier (when you abuse them with a spoon to make them stay down). Glenn Nelson, Ampex, Redwood City
rhm (12/19/82)
The original estimate of thermal expansion of air was correct. At room temperature (300K) it amounts to 1/300 per degree Celsius. Since the pressure does not increase by any measurable amount, the expansion available is limited to a factor of about 370/300, which is inadequate to explain the effect. I think the tea bag question is still open.
lemmon (01/06/83)
Note that the tea bag fills with water (to brew the tea) as well as retaining the original air (now somewhat expanded). The total volume of fluid within the bag therefore increases considerably. I think that this would explain the inflation adequately. Alan Lemmon
tfilm (01/11/83)
It may be of some interest that superheated water will boil in the absence of an external heat source and the presence of nucleation sites. Tea leaves are an excellent source of nucleation sites for the boiling to take place. Having brewed my own tea for over 20 years, I am quite familiar with this phenomena of nucleate boiling which would add additional flavor to the tea bag controversy. A tea lover and material scientist.