Drying with an Air Blower A Fermi Problem

Illustration 1.7 Drying with an Air Blower A Fermi Problem 

Readers are familiar with the use of warm-air blowers for fhe purpose of drying their hands. What we wish to do here is to eshmate the associated mass transfer coefficient kc in units of m/s. To do fhis, the following approximate estimates will be needed 1. the amount of moisture to be evaporated, 2. the drying time, and 3. temperature and corresponding vapor pressure of the adhering moisture. 

Amount of Moisture. Let us assume the thickness L of fhe moisture to be 0.1 mm. This leads to a rate of evaporation of 

Drying Time. A survey of various individuals who had made use of the device led to an agreed average value of f = 100 s. We then obtain from Equation 1.26a 

This is in line with the order-of-magnitude estimates given in Illustration 1.5. Comments  

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