Question
q2 please
Estimate the time taken (in hours) for the cylinder pressure to 10 atm, by assuming the system is ideal and isothermal at 293 K, and that diffusion through the balloon obeys Fick's Law with a linear concentration gradient. The diffusivity of helium through the balloon wall is 5 times 10^-10 m^2/s Water at 20 degree C is flowing in a covered irrigation ditch below ground. Every 50 m there is a vertical vent line of 25mm internal diameter and 300 mm long to the outside atmosphere. Assume the outside air is dry and at 20 degree C, and that the partial pressure of water at the water surface is equal to the vapour pressure of 2.3 kPa. Given that the diffusivity of air-water is 2.5 times 10^-5 m^2/s, calculate the mass of water lost per 1 km of the ditch each day. Hydrogen Cyanide gas is to be absorbed into an aqueous sulphuric acid solution at 2 bar. The overall gas-side mass transfer coefficient is 0.7 mol middot m^-2 s^-1 and the liquid film mass transfer coefficient is 0.1 mol middot m^-2 s^-1. The Henry's law constant for this system is 40 Pa.m^3 middot kmol^-1. If the molar volume of the liquid is 1.8 times 10^-2 m^1 middot kmol^-1, find the gas film mass transfer coefficient and comment on the controlling mass transfer resistance, and determine the overall liquid
Explanation / Answer
diffusity of water vapor = 2.5e-5 m2/s
outside air is completely dry hence we take outside concentration as 0
concetration of water vapor in the tube = 2.3 kPa
length of the tube = 300 mm
flow rate = 2.5e-5 /300e-3 = 8.33e-5 m/s
area of the tube = 3.14*(12.5e-3)2 = 4.90e-4 sq.m
flow of water vapor = 8.33e-5 *4.90e-4 cu.m /s
flow in one day = 8.33e-5 *4.90e-4 *24*3600
= 3.53e-3 cu.m /day
vapor pressure P = 2.3 kPa
volume V = 3.53e-3 cu.m
PV = nRT , T = 293 K
number of moles in the water vapor diffused
n = PV/RT , molecular weight of water = 18 gms
mass of water diffused per day = n*18 = 2.73e+3*3.53e-3/(8.3*293) *18 gms
= 7.13e-2 gms from 1 vent
in 1 Km length of the pipe there are 1000/50 = 200 vents
total water diffused = 200*7.13e-2 = 14.26 gms
