8/1/2023 0 Comments Quicktrim isoburnIf the air conditioning ducts can push out air with this dewpoint, one can choose to have a low temperature with a high RH, or any other combination along the path of the curve. This particular dewpoint is shown because it is the practical limit for orthodox air conditioning with water cooling. The Isoburn and Conservation Heatingįigure 1 also shows the line marking the 4☌ dew point*. It is similar to figure 1, but the lines are for constant durability rather than constant reaction rate. Don Sebera (reference on page 1) gave the name 'Isoperms' to a set of curves which were similar in shape but defined lines of constant durability, which is the reciprocal of the rate. Lines of equal degradation rate, 'Isoburns', with the line of constant 4☌ dewpoint superimposed.Īs one slides a finger upwards along one of these curves, every combination of temperature and relative humidity will give the same degradation rate for materials susceptible to hydrolysis. Unlike the PI, there is no absolute value, expressed as degree of degradation per year, or lifetime in years.įigure 1. The rates are expressed relative to the rate at 20☌ and 50% RH, and are valid only for a reaction with activation energy 100kJ/mol. The curves are computed from the mass-action/Arrhenius equation derived on page 1. The array of pale curves in figure 1 shows combinations of temperature and relative humidity which give the same rate of hydrolysis. It is better to quote a rate of reaction and leave it to the conservator to decide how much degradation corresponds to the end of useful life as an archive or museum object. If the same base material is used for a child's toy, much more degradation can happen before the toy becomes unrecognisable and ineffective in a museum display. For a roll of film in an archive a small degree of degradation is enough to alter the spacing of the sprocket holes so the film tears in the projector and cannot be shown. Lifetime can be accurately defined, though seldom predicted. For us mortals the definition is appropriate: the heart is either pumping or stopped. Expressing the durability of materials as a lifetime is not very satisfactory.
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