A 3 centimeter diameter tube is used to measure the binary diusion coefcient of

Question

A 3 centimeter diameter tube is used to measure the binary diusion coefcient of water vapor in air at 20 oC. The tube is partially lled with water and the distance from the water surface to the open end of the tube is 40 cm. Air is blown over the open end of the tube so that the water vapor rising to the top of the tube is removed immediately and the concentration of the water vapor at the top of the tube is zero. After 15 days, the amount of water evaporated was measured to be 1.23 grams. Determine the diusion coecient of water vapor in air. The atmospheric pressure can be taken as 101.33 kilopascals.

Explanation / Answer

diffusion coefficient which is defined by the formula

D = RT/M , [m2 .s -1]

where R is the universal gas constant [8.314 J mol-1K-1], T is the absolute temperature [K] and M is the molar mass of water [0.018 kg mol-1].

The water vapor diffusion permeability is calculated from the equation

= m d / S P [s],

where m is the amount of water vapour diffused through the sample [kg], d is the sample thickness [m], S is the surface of the sample [m2 ], is the period of time corresponding to the mass transport of water vapour m [s] and p is the difference between the partial vapor pressure in air over and under the specific surface of the sample [Pa]. difference between the partial vapor pressure in air over and under the specific surface of the sample [Pa].

By using above equation you can calculate the diusion coecient of water vapor in air

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.