It is August in West Philly. It is hot $(90$F$)$ and humid $(75\%$ RH$)$ and there is no breeze. Water in the air is

diffusing to the coils of a window $\frac{A}{C}$ unit. When it reaches the coils, which are still cooler than the air

outside, the water condenses into a film, which continually drips onto the sidewalk $($or your head$).$

a$.$ Draw a picture of the problem. List the control volume $($domain$),$ the species to be modeled,

and the sources and sinks of each species.

b$.$ List the variables and assumptions about mass transfer that will affect your model.

c$.$ Write the continuity equation in terms of the molar flux. Cross out any terms that are zero.

d$.$ Write the flux equation for this system.

e$.$ Write the initial and boundary conditions.

f$.$ Should the concentration gradient and flux be positive or negative? Explain why this would be a

very challenging problem to solve.