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 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.