You are inside a small (125 m3) laboratory, using liquid nitrogen at rate of 3 l/min from a large, insulated container. the liquid nitrogen expands as it evaporates, mixing with the air in the room (there is a fan that ensures that it is well-mixed), and all gases behave ideally. air leaves the room through a small crack in the door, such that the volume, pressure and temperature of the gas in the room all remain constant at 125 m3, 1 atm and 24°c, respectively. therefore, the mole fractions of nitrogen and oxygen are both time dependent. using the knowledge that the composition of normal air is 79% n2/21% o2, and that oxygen deprivation becomes a threat below 18% o2, calculate the maximum time (in minutes) that you can safely remain in the laboratory after starting the flow of nitrogen.

On a average work day more than work place firs are reorted

Agas mixture consists of 8 kmol of h2 and 2 kmol of n2. determine the mass of each gas and the apparent gas constant of the mixture.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?