I tried liquid evaporation under vacuum, at 50, 60 and 70 degrees C and respective vacuum pressures 165 mbar, 250 mbar and 395 mbar respectively.
But I found water evaporate at faster rate in case of 60 deg. C at 250 mbar (12 min), while (18 min) for 50 deg C at 65 mbar and (21 min) for 70 deg at 395 mbar.
I need your help to explain why it is so?
I repeatedly did my experiments and found the same results.
I need some scientific reason with reference please.?
Thanks in advance
Tuseef.
The reported vacuum pressure (Pvac) data seems reasonable for the reported temperatures (50, 60, 70 ºC), being linearly (well) correlated to the vapour pressure of pure water (Pw). I have found (Pvac / torr) = 1.23·(Pw / torr) + 7.94 for such a correlation. As for the reported evaporation/drying time, it seems that it may possibly have been somewhat inadequately or ambiguously defined/reported, since, in principle, a shorter drying time could be generally expected for higher temperature.
Please notice that, after drying, the humidity/moisture content of the samples, is possibly, not the same. So, the drying time must be defined considering that final humidity content, which must be accessed, even supposing that the initial humidity content was (I suppose) the same.
Moreover, it is also not unambiguously clear how the reported temperatures were measured ― the actual sample temperature tends to be initially somewhat lower than that of the drying atmosphere, to which contributes, with, at least, water vapour. Typically, for relatively high moisture contents, the initial sample temperature closely matches the adiabatic saturation temperature of the drying atmosphere. Both temperatures ― of the sample and that of the drying atmosphere ― tend to match by the final stage of drying. In practice, it is often the temperature of the drying atmosphere that is actually (indirectly) monitored and controlled ― perhaps after a temperature sensor located at the inner surface of the drying chamber. You may want to monitor the weight of the sample while drying samples at similar conditions ― by either thermobalance or TGA analysis.
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